U.S. patent application number 12/499049 was filed with the patent office on 2009-10-29 for particle counter with laser diode.
This patent application is currently assigned to PARTICLE MEASURING SYSTEMS, INC.. Invention is credited to Gregg A. Wagner.
Application Number | 20090268202 12/499049 |
Document ID | / |
Family ID | 35909304 |
Filed Date | 2009-10-29 |
United States Patent
Application |
20090268202 |
Kind Code |
A1 |
Wagner; Gregg A. |
October 29, 2009 |
Particle Counter with Laser Diode
Abstract
A liquid particle counter for optically detecting an
unconstrained particle suspended in a flowing liquid includes a
sample chamber having a liquid inlet and a liquid outlet; a laser
diode module producing a symmetrically collimated laser beam; a
beam shaping optical system directing the laser beam at the sample
chamber; and an optical detector located to detect light scattered
by the particle in the sample chamber, the detector producing an
electric signal characteristic of a parameter of the particle. The
laser beam has an energy of a watt or more and passed through an
aperture in a black glass aperture element in the sample chamber.
The black glass aperture element removes diffracted and stray light
from the beam without damage to the sample chamber.
Inventors: |
Wagner; Gregg A.; (Boulder,
CO) |
Correspondence
Address: |
GREENLEE WINNER AND SULLIVAN P C
4875 PEARL EAST CIRCLE, SUITE 200
BOULDER
CO
80301
US
|
Assignee: |
PARTICLE MEASURING SYSTEMS,
INC.
Boulder
CO
|
Family ID: |
35909304 |
Appl. No.: |
12/499049 |
Filed: |
July 7, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10923339 |
Aug 20, 2004 |
7576857 |
|
|
12499049 |
|
|
|
|
10228577 |
Aug 27, 2002 |
6859277 |
|
|
10923339 |
|
|
|
|
Current U.S.
Class: |
356/338 ;
204/157.41 |
Current CPC
Class: |
G01N 2201/0642 20130101;
G01N 15/0205 20130101; G01N 2201/0612 20130101; G01N 21/05
20130101; G01N 2201/0633 20130101; G01N 2021/0346 20130101; G01N
21/51 20130101 |
Class at
Publication: |
356/338 ;
204/157.41 |
International
Class: |
G01N 21/49 20060101
G01N021/49; B01J 19/12 20060101 B01J019/12 |
Claims
1. A device for optically detecting an unconstrained single
particle suspended in a flowing liquid, said device comprising: a
sample chamber having a liquid inlet and a liquid outlet, said
sample chamber adapted to permit said single particle to flow
essentially without constraint between said inlet and outlet; a
laser diode module producing a symmetrically collimated laser beam;
a beam shaping optical system directing said laser beam at said
sample chamber; and an optical detector located to detect light
scattered by said particle in said sample chamber, said detector
producing an electric signal characteristic of a parameter of said
particle.
2. A device as in claim 1 wherein said device is a non-in-situ
particle counter.
3. A device as in claim 2 wherein said device is a volumetric
particle counter.
4. A device as in claim 1 wherein said device is an in-situ
particle counter.
5. A device as in claim 1 wherein said sample chamber includes a
glass or crystalline aperture element having an aperture and said
beam shaping system directs said laser beam through said
aperture.
6. A device as in claim 5 wherein said glass or crystalline
aperture element is made of light-absorbing glass or
light-absorbing crystalline material.
7. A device as in claim 6 wherein said glass or crystalline
aperture element is made of NG1 black glass or black diamond.
8. A device as in claim 5 wherein said device includes a light
baffle chamber, and said glass aperture element is located between
said light baffle chamber and said sample chamber.
9. A device as in claim 5 wherein said light baffle chamber is
fluidly connected to said inlet and outlet to permit said liquid to
flow through it.
10. A device as in claim 1 wherein said laser diode module a unique
m.o.d.e..TM. laser diode module.
11. A device as in claim 1 wherein said beam shaping optics
includes an aperture system blocking a third or more of the power
of said laser beam.
12. A particle counter for optically detecting an unconstrained
single particle suspended in a flowing liquid, said particle
counter comprising: a sample chamber having a liquid inlet and a
liquid outlet, said sample chamber having a plastic wall and
adapted to permit said single particle to flow essentially without
constraint between said inlet and said outlet; a glass or
crystalline aperture element having an aperture and located in said
plastic sample chamber wall; a laser diode module producing a laser
beam; a beam shaping optical system directing said laser beam
through said aperture into said sample chamber; and an optical
detector located to detect light scattered by said particle in said
sample chamber, said detector producing an electric signal
characteristic of a parameter of said particle.
13. A device as in claim 12 wherein said glass or crystalline
aperture element is made of black glass or black crystal.
14. A method of manufacturing a liquid particle counter, said
method comprising: providing a plastic sample chamber having a
black glass or black crystalline aperture element having an
aperture; flowing a liquid containing an unconstrained particle
through said sample chamber; providing a laser beam; directing said
laser beam through said aperture; collecting light scattered by
said particle in said liquid; and providing an output based on said
collected light scattered by said particle detected in said flowing
liquid.
15. A method as in claim 14 and further comprising cooling said
black glass or black crystalline aperture element with said fluid
flow.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 10/923,339 filed on Aug. 20, 2004, which is a continuation in
part of U.S. application Ser. No. 10/228,577, filed on Aug. 27,
2002, now U.S. Pat. No. 6,859,277, all of which are hereby
incorporated by reference in their entireties.
FIELD OF THE INVENTION
[0002] The invention in general relates to systems which utilize
light scattering principles to detect and count undesirable single
particles in fluids, referred to in the art as light scattering
particle counters, and more particular to such a particle counter
that utilizes a laser diode light source.
STATEMENT OF THE PROBLEM
[0003] Particle counters are used to detect and measure the size of
individual particles suspended in a fluid. Each particle that is
detected is counted, and an indication of the number of particle
counts within a channel, with each channel corresponding to a
particular size range, is provided. For particle counters to
operate effectively, the density of particles in the fluid must be
very small--indeed, the particles are generally considered to be
contaminants. It is important to distinguish the science of
particle counting from other scientific fields, such as photometry
and cytometry, which also utilize scattered light, but in which the
density of the particles in the fluid is relatively large; often it
is the particles of the fluid itself that are detected and
analyzed. These latter systems rely on collecting scattered light
from thousands, millions, and even billions of particles;
therefore, their principles of operation are very different from
the principles used in particle counters.
[0004] Particle counters are generally used to detect contaminants
in extremely pure fluids, such as those used in high tech
electronics and the pharmaceutical industry. Generally, small
samples of the fluids used in the manufacturing processes are
diverted to the particle counters, which sound an alarm if the
number and/or size of the particles detected is above a
predetermined threshold. Since a small sample of the manufacturing
fluid is generally not completely representative of the entire
volume of the manufacturing fluid, statistics is used to
extrapolate the state of the manufacturing fluid from the sample.
The larger the sample, the more representative it is, and the more
quickly an accurate determination of the number and size of
particles in the manufacturing fluid can be made. It is desirable
for a particle counter to detect particles as small as possible, as
fast as possible, in as large a sample as possible.
[0005] Physical constraints require tradeoffs between the above
goals. For example, sample volume and speed usually must be
sacrificed to detect smaller particles. This is a direct result of
the fact that, for particles to be detected in a particular fluid,
the fluid must be constrained to flow through the monitoring region
of a particle counter. Physical objects, such as nozzles and flow
tubes, must be used to direct the fluid flow to the particle
counter monitoring region. If it is desired to detect the particles
in the entire sample flow, then scattered light from the entire
sample flow must be collected. This generally results in light
scattered from the physical constraining objects, such as a nozzle
or flow tube, also being collected, which light creates noise in
the output. The noise prevents detection of extremely small
particles. This noise can be avoided by detecting particles in only
a small portion of the sample flow. Particle counters that attempt
to count all the particles in a fluid sample are generally referred
to as volumetric particle counters, and particle counters that
detect particles in only a small portion of the fluid flow are
generally referred to as in-situ particle counters.
[0006] The word in-situ in Latin literally means in the natural
state. That is, ideally, it refers to measurements unaffected by
the measurement instrumentation. In an in-situ system, to be
unaffected from the constraining elements, the detected particles
must be far from the constraining elements, and only particles in a
small fraction of the sample fluid flow are detected. In-situ
systems commonly process 5% or less of the sampled fluid. As a
result of measuring only a selected fraction of fluid flow,
however, in-situ systems take more time to achieve a statistically
significant determination of the fluid cleanliness level or fluid
quality. When measuring particle contamination levels in a clean
room environment, this extended measurement time generally incurs
the risk that an unacceptably high level of airborne or liquid
particle concentration could go undetected for substantial time
periods, thereby allowing a large number of manufactured parts to
be produced under unacceptably "dirty" conditions. This situation
can lead to substantial economic loss owing to the waste of time
and production materials in the affected facility.
[0007] Since it is practically impossible to actually measure 100%
of the particles carried by flowing fluid, herein the term
"volumetric" generally corresponds to systems which measure 90% or
more of the particles flowing through a measurement device.
Volumetric particle measurement systems generally provide the
advantage of measuring a greater volume of fluid, whether liquid or
gas, within a fixed time period, thereby enabling a more rapid
determination of a statistically significant measure of fluid
quality. In the case where the particle concentration exceeds a
predetermined permissible limit, this more rapid fluid processing
generally enables a defective manufacturing process to be halted
more quickly and more economically than would be possible employing
in-situ measurement systems. However, as indicated above,
volumetric measurement systems generally experience more noise than
do in-situ systems because the efforts expended to control the
location and flow characteristics of the fluid being analyzed
generally perturbs the characteristics being measured to a greater
extent than does in-situ measurement.
[0008] In various circumstances, there may be measurement processes
having characteristics which are intermediate between in-situ and
volumetric processes. Thus, where in-situ measurement generally
corresponds to particle measurement within 5% or less of fluid
transported through a measurement device, and volumetric
measurement generally corresponds to analysis of 90% or more of
such fluid, it will be recognized that measurement processes may be
configured to process 10%, 30%, 50%, or other percentages in
between the levels associated with in-situ and volumetric
operation. Accordingly, herein, the term "non-in-situ" measurement
generally corresponds to measurement of a proportion of fluid equal
to more than 5% of total fluid flow.
[0009] In the field of particle counting, the use of high power
illumination generally enhances particle detection. Specifically,
higher power levels generally enable the detection of smaller
particles than lower power systems. Higher power levels also
generally permit particles of a given size to be detected more
quickly. Thus, high power lasers are generally used as the light
source in particle counters.
[0010] Diode lasers have recently been incorporated into particle
counters because of their relatively small size, economy and
reliability. However diode particle counters have an inherent
limitation for use in particle counters that limits their power.
The power of diode lasers increases with the size of radiating
surface. However, as the size of the radiating surface increases
transverse radiation modes increase. FIG. 1 shows the radiation
patterns, looking into the laser, for various transfers modes. As
can be seen, the radiation in the fundamental transverse
electromagnetic mode, designated as TEM.sub.00, is compact and
concentrated in the center. In the other modes a significant
portion of the light is contained in zones separated from and some
distance from the center of the beam. In certain applications, such
as fiber optics, these features of the non TEM.sub.00 modes are not
a problem because multiple reflections from the sides of the fiber
contains the radiation in a compact space. However, in particle
counters, these modes scatter and reflect from the parts of the
system constraining the fluid flow and create noise which
interferes with the detection of particles and places a lower limit
on the size of the particles that can be detected. Thus, particle
counters that use laser diodes generally limit the mode to the
TEM.sub.00 mode, which however limits the amount of power of the
diode, because, as indicted above, higher power requires a larger
radiating surface, which inherently creates non TEM.sub.00 modes.
The problems with using high power diodes are particularly acute in
particle counters that detect single particles in liquids, referred
to herein as "liquid particle counters". While gases will remain
collimated in constraint-free jets for at least a distance
necessary to pass the jets through a laser beam, liquids resist
such collimation. Thus, in particle counters, liquids must be
constrained by the physical walls of flow cells, and the laser beam
must thus pass through the flow cell. The non TEM.sub.00 transverse
modes scatter and reflect from the flow cell walls creating noise.
In addition, bubbles in the fluid, which are often present-at
start-up, diffract the light from all the modes. If lasers having a
power of one watt or greater are used in a liquid particle counter,
the heat from the combination of the non TEM.sub.00 mode scattering
and the diffraction from a bubble will damage the flow cell. Thus,
all known commercial liquid particle counters that utilize laser
diodes to detect and measure single particles in fluids have, up
until now, been limited to single mode systems, typically the
TEM.sub.00 mode, and thus limited to less than 1 watt in power.
[0011] Accordingly, there is a need in the art for a particle
counter system and method, particularly a liquid particle counter
system and method, which provides high power illumination in a low
noise environment and which produces a scattered light energy
spectrum which is readily convertible into particle measurement
data. Further, to accomplish this in a non-in-situ system would be
highly advantageous.
SUMMARY OF THE INVENTION
[0012] The present invention advances the art and helps to overcome
the aforementioned problems by providing a liquid particle counter
utilizing a laser diode which provides a high power beam in a low
noise system for rapid detection and measurement of small
particles. Preferably, the beam is symmetrically collimated and has
a power of a watt or more. Preferably the beam is passed through
apertures that remove most of the diffracted and stray light
inherent in high power symetrized laser beams. One aspect of the
invention provides a glass or crystalline aperture element in the
sample chamber wall which blocks diffracted and stray light without
being damaged by the high power laser beam.
[0013] The invention provides a device for optically detecting an
unconstrained particle suspended in a flowing liquid, the device
comprising: a sample chamber having a liquid inlet and a liquid
outlet; a laser diode module producing a symmetrically collimated
laser beam; a beam shaping optical system directing the laser beam
at the sample chamber; and an optical detector located to detect
light scattered by the particle in the sample chamber, the detector
producing an electric signal characteristic of a parameter of the
particle. Preferably, the device is a non-in-situ particle counter.
Preferably, the device is a volumetric particle counter.
Preferably, the device is an in-situ particle counter. Preferably,
the sample chamber includes a glass or crystalline aperture element
having an aperture and the beam shaping system directs the laser
beam through the aperture. Preferably, the glass or crystalline
aperture element is made of black glass or light-absorbing
crystalline material. Preferably, the glass or light-absorbing
crystalline aperture element is made of NG1 glass or black diamond.
Preferably, the device includes a light baffle chamber, and the
glass aperture element is located between the light baffle chamber
and the sample chamber. Preferably, the light baffle chamber is
fluidly connected to the inlet and outlet to permit the liquid to
flow through it. Preferably, the laser beam has an energy of one
watt or greater. Preferably, the laser diode module a unique
m.o.d.e..TM. laser diode module. Preferably, the beam shaping
optics includes an aperture system blocking a third or more of the
power of the laser beam.
[0014] In another aspect, the invention provides a particle counter
for optically detecting an unconstrained particle suspended in a
flowing liquid, the particle counter comprising: a sample chamber
having a liquid inlet and a liquid outlet, the sample chamber
having a plastic wall; a glass or crystalline aperture element
having an aperture and located in the plastic sample chamber wall;
a laser diode module producing a laser beam; a beam shaping optical
system directing the laser beam through the aperture into the
sample chamber; and an optical detector located to detect light
scattered by the particle in the sample chamber, the detector
producing an electric signal characteristic of a parameter of the
particle. Preferably, the glass or crystalline aperture element is
made of black glass or black crystal.
[0015] In a further aspect, the invention provides a device for
optically detecting an unconstrained particle suspended in a
flowing liquid, the device comprising: a sample chamber having a
liquid inlet and a liquid outlet; a laser diode module producing a
laser beam having an energy of one watt or greater; a beam shaping
optical system directing the laser beam at the sample chamber; and
an optical detector located to detect light scattered by the
particle in the sample chamber, the detector producing an electric
signal characteristic of a parameter of the particle.
[0016] The invention also provides a method of detecting an
unconstrained particle in a flowing liquid, the method comprising:
flowing the liquid containing the unconstrained particle; providing
a laser diode module producing a symmetrically collimated laser
beam; directing the laser beam at the liquid flow; collecting light
scattered by the particle in the liquid; and providing an output
based on the collected light scattered by the particle detected in
the flowing liquid. Preferably, the flowing comprises flowing the
liquid through a sample chamber having a glass or crystalline
aperture element having an aperture; and the directing comprises
directing the laser beam through the aperture. Preferably, the
method further comprises cooling the glass or crystalline aperture
element with the fluid flow.
[0017] In an additional aspect, the invention provides a method of
detecting an unconstrained particle in a flowing liquid, the method
comprising: flowing the liquid containing the unconstrained
particle; providing a laser diode producing a laser beam of one
watt or more; directing the laser beam at the liquid flow;
collecting light scattered by the particle in the liquid; and
providing an output based on the collected light scattered by the
particle detected in the flowing liquid. Preferably, the flowing
comprises flowing the liquid through a sample chamber having a
glass or crystalline aperture element having an aperture; and the
directing comprises directing the laser beam through the aperture.
Preferably, the method further comprises cooling the glass or
crystalline aperture element with the fluid flow.
[0018] In yet another aspect, the invention provides a method of
manufacturing a liquid particle counter, the method comprising:
providing a plastic sample chamber having a black glass or black
crystalline aperture element having an aperture; flowing a liquid
containing an unconstrained particle through the sample chamber;
providing a laser beam; directing the laser beam through the
aperture; collecting light scattered by the particle in the liquid;
and providing an output based on the collected light scattered by
the particle detected in the flowing liquid. Preferably, the method
further comprises cooling the glass or crystalline aperture element
with the fluid flow.
[0019] In still another aspect, the invention provides a device for
optically detecting an unconstrained particle suspended in a
flowing fluid, the device comprising: a fluid inlet for producing a
fluid flow; a laser diode module producing a symmetrically
collimated laser beam; a beam shaping optical system directing the
laser beam at the fluid flow; and an optical detector located to
detect light scattered by the particle in the fluid flow, the
detector producing an electric signal characteristic of a parameter
of the particle.
[0020] The invention also provides a method for optically detecting
an unconstrained particle suspended in a fluid, the method
comprising: flowing the fluid containing the unconstrained
particle; providing a laser diode module producing a symmetrically
collimated laser beam; directing the laser beam at the fluid flow;
collecting light scattered by the particle in the fluid; and
providing an output based on the collected light scattered by the
particle detected in the flowing fluid.
[0021] The invention enables much larger, and therefore more
powerful, laser diodes to be used effectively in a particle
counter, particularly a liquid particle counter. As will be seen in
more detail below, the invention teaches how to control block
diffracted and stray light created in symetrizing the beam while
examining a large portion of the fluid flow. While the system
permits high-powered, low noise, volumetric liquid particle
counters that were not previously possible, it should be understood
that the invention is not limited to volumetric systems. The
invention can be used to advantage in any liquid particle counter,
including non-in-situ and in-situ systems. In some aspects the
invention can be incorporated into any fluid particle counter. The
above and other advantages of the present invention may be better
understood from a reading of the following description of the
preferred exemplary embodiments of the invention taken in
conjunction with the drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 shows the radiation pattern for twelve different
modes of a high power diode laser;
[0023] FIG. 2 is a depiction of a photograph of a laser beam
passing through the flow cell of the particle counter according to
the invention without the black glass aperture element;
[0024] FIG. 3 is a depiction of a photograph of a laser beam
passing through the flow cell of the particle counter according to
the invention with the black glass aperture element;
[0025] FIG. 4 is a top view of a particle counter according to a
preferred embodiment of the present invention;
[0026] FIG. 5 is a partially plan and partially cross-sectional
view of the particle counter of FIG. 4 taken through the line 5-5
of FIG. 4;
[0027] FIG. 6 is a cross-sectional view of the particle counter of
FIG. 4 taken through the line 6-6 of FIG. 4;
[0028] FIG. 7 is a perspective view of the entrance aperture
element and negative lens retainer of the particle counter of FIG.
4;
[0029] FIG. 8 is a cross-sectional view of the beam expander
entrance aperture element and negative lens retainer of FIG. 7
taken through the line 8-8 of FIG. 7;
[0030] FIG. 9 is an end view of the beam expander exit aperture
element and positive lens retainer of the particle counter of FIG.
4;
[0031] FIG. 10 is a cross-sectional view of the beam expander exit
aperture element and negative lens retainer of FIG. 9 taken through
the line 10-10 of FIG. 9;
[0032] FIG. 11 is a cross-sectional view of the flow cell aperture
element of the particle counter of FIG. 4; and
[0033] FIG. 12 is a side view of the flow cell aperture element of
FIG. 11.
DETAILED DESCRIPTION OF THE PREFERRED INVENTION
[0034] In this disclosure, the term light is not limited to visible
radiation but is used in a broad sense meaning any electromagnetic
radiation. Stray light includes any light that is not wanted; i.e.,
light that is not light scattered from particles but which can get
into the collection optics. Multiply reflected light is a
significant source of stray light in a particle counter. That is,
light that is reflected once, scattered from a scattering source,
or diffracted by a lens or aperture can usually be blocked out by
other apertures or absorbing black walls because the source of the
unwanted light is. However, multiple reflections make it difficult
to determine the direction of the light, and thus often cannot be
apertured or otherwise blocked out. The terms in-situ and
volumetric are used as described in the Background of the Invention
above. It is also noted that this disclosure is limited to fluid
particle counters, which is a term of art. There are particle
counters that detect particle counters in a vacuum. Because there
is no fluid present, or rather any fluid present is rarified as
compared to normal fluids, problems associated with fluid flow,
light scattering from the fluid and the apparatus used to control
the fluid flow are absent and the physics of such particle counters
is significantly different than that of fluid particle counters.
Further, it should be noted that particle counters as disclosed
herein are designed to be able to detect single particles which are
unconstrained in a flowing fluid as distinguished from other
systems that detect and analyze the particles of the fluid itself,
clouds of particles suspended in a fluid, or particles which are
constrained in the fluid, such as constrained to flow in a single
line past a light beam. Those skilled in the art recognize that it
is a much more difficult task to detect and size single particles
flowing unconstrained in a fluid; therefore, the art of particle
counting involves different technology than these other particle
detection and analysis systems.
[0035] FIG. 4 is a top view of a particle counter 100 according to
the invention, FIG. 5 is a partially plan and partially
cross-sectional side view taken through the line 5-5 of FIG. 4, and
FIG. 6 is a cross-sectional view taken through the line 6-6 of FIG.
4. Particle counter 100 is shown with a break in FIGS. 4 and 5 so
as to better fit in on the drawing without altering the scale
significantly, except as mentioned below. Particle counter 100
includes a laser assembly 102 and a flow cell and detection optics
assembly 104. Laser assembly 102 includes laser module 105 and a
beam shaping optics system 114 including polarization rotation unit
106, beam expander 110, and focusing optics 111, all within a
housing 107. Laser assembly 102 also includes timer 142, laser base
plate 140 and heat sink 146. Timer 142 is mounted on a bracket 143
and includes an electrical connector 144 for connecting it to the
particle counter system electronics. Laser assembly module 105
includes strip diode laser 108 and electronics connector pins 109.
Polarization rotator 106 includes half-wave plate 117 and half-wave
plate support 113. Beam expander 110 includes entrance aperture
element and lens retainer 115, negative lens 116, positive lens
118, lens retainer and exit aperture element 119, focusing lens
122, and lens retainer and aperture element 124, all of which are
supported and held in place by optics support 126. Suitable
adjusting mechanisms 128 are provided as known in the art to align
and adjust the various optics elements.
[0036] Flow cell and detection optics assembly 104 includes flow
cell 150, inlet assembly 164, outlet assembly 166, collection
optics assembly 180, and detector 190. Flow cell 150 includes flow
enclosure 151 having a wall portion 152 and a light baffle portion
156, entrance window 153, exit window 154, window retainers 157 and
158, window retainer fasteners 159, main flow volume entrance
aperture element 160 and main flow volume exit aperture element
161. Inlet assembly 164 includes inlet connector 167 having an
inlet passage 168 and auxiliary outlet channel 175, and outlet
assembly 166 includes outlet connector 169 having an outlet passage
170 and an auxiliary outlet channel 174. O-ring 171 seals the
interface between inlet connector 167 and flow cell enclosure 151,
and O-ring 172 seals the interface between inlet connector 169 and
flow cell enclosure 151. Baffle 156 separates the flow volume 177
into an auxiliary flow volume 173 in light baffle chamber 176 and
an inner main flow channel volume 178. Aperture elements 160 and
161 fit into cup-shaped openings in baffle 156, and are held in
place with an epoxy cement. Auxiliary inlet channel 175 is in fluid
communication with baffle chamber 176 which is in fluid
communication with auxiliary outlet channel 174. As shown in FIG.
6, main flow volume 178 narrows to a capillary sample chamber 202
in the center of the flow cell, in which capillary sample chamber
202 the laser beam 130 (FIG. 5) intersects the fluid flow and
particles in the liquid scatter light which is collected by lenses,
of which only the first lens 204 is visible in FIG. 5, and particle
measurement and counting occurs.
[0037] Collection optics 180 (FIG. 6) includes lenses 204, 206, and
208, lens housing 210, lens retainer ring 214 and seals, such as
217.
[0038] A perspective view of the preferred embodiment of beam
expander entrance aperture and lens retainer element 115 is shown
in FIG. 7, and a cross-sectional view taken through the line 8-8 is
shown in FIG. 8. Aperture and lens retainer element 115 preferably
comprises a cylinder 230 having a cylindrical bore 234. At the left
end in FIG. 8, the bore 234 is slightly smaller to form entrance
aperture element 240, and at the right end in FIG. 8 the bore 234
is enlarged to form a lens cup 232. Holes 237 receive screws to
hold the aperture and lens retainer element 115 to support 126.
Preferably, cylinder 230 is 0.220 inches long (the horizontal
direction in FIG. 8) and 0.400 inches in diameter, aperture element
240 is 0.067 inches in diameter and 0.02 inches deep, central
portion 233 of bore 234 is 0.109 inches in diameter, and lens cup
232 is 0.228 inches in diameter and 0.030 inches deep. Both ends of
cylinder 230 are chamfered, as at 235. An end view of beam expander
exit aperture and lens retainer element 119 is shown in FIG. 9, and
a cross-section taken through lines 10-10 of FIG. 9 is shown in
FIG. 10. Expander exit aperture and lens retainer element 119 is
preferably a cylinder 250 having a bore 251 shaped like a frustum
of a cone with a smaller diameter 254 at its end toward laser 105
and a larger diameter 252 at its other end. It also includes screw
holes 258 and its ends, such as 256 are chamfered. Preferably,
cylinder 250 is 1.750 inches in diameter and 0.150 inches thick
(the horizontal direction in FIG. 10). Preferably, small diameter
254 is 0.354 inches in diameter, and large diameter 252 is 0.460
inches in diameter. Lens retainer and aperture element 124 is
preferably identical to lens retainer and aperture element 119.
[0039] Flow cell entrance aperture element 160 and flow cell exit
aperture element 161 are preferably identical and are shown in
perspective in FIG. 11 and in a side view in FIG. 12. Aperture
element 160 preferably includes a cylindrical portion 270 and a
portion 276 shaped like a frustum of a cone and having a
cylindrical aperture 274. Preferably, the length of aperture
element 160 in the horizontal direction in FIG. 12 is 2.08 mm and
its aperture 274 is 1.4 mm in diameter. Preferably, cylindrical
portion 270 is 3.18 mm in diameter and 0.81 mm thick. Preferably,
the outside diameter of the small end 278 of conical portion 276 is
preferably 1.98 mm. Flow cell aperture elements 160 and 161 are
preferably made of NG1 black glass, with the outer surfaces ground
fine and the inner and end surfaces polished, though other
materials may be used. For example, any light-absorbing and heat
resistant flow cell material commonly used in the liquid particle
counter art such as quartz, diamond, sapphire, or other
light-absorbing, durable and heat resistant crystalline material
may be used. Preferably, aperture and lens retainer elements 115,
119, and 124 are made of black anodized aluminum, though other
nonreflective solid materials may be used. Flow enclosure 151 and
window retainers 157 and 158 are preferably made of black Kel-F
plastic. Windows 153 and 154 are preferably made of clear fused
silica or sapphire, though any other essentially transparent
material may be used. Preferably, laser module 105 is a model
UM4200/M20/CBITEC laser package made by unique m.o.d.e. AG, Jena,
Germany, though any diode laser having a power of one watt or
greater may be used. The unique m.o.d.e. laser is described in U.S.
Pat. No. 6,680,800 issued Jan. 20, 2004 on an invention of Peter
Schreiber and Thilo von Freyhold and is discussed in Thilo von
Freyhold and Thomas Wittschirk, "Powerful Laser Diodes Become
High-Brightness Laser Tools", Photonics Showcase, pp. 5-6, November
2002, both of which references are hereby incorporated by reference
to the same extent as though fully disclosed herein. As known in
the art, beam expander 110 includes a negative lens 116 and a
positive lens 118. Negative lens 116 is preferably a F? lens while
positive lens 118 is a 40 mm F4.7 lens. Focusing lens 122 is
preferably also a 40 mm F4.7 lens and is? cm thick. Preferably,
aperture element 115 is preferably located ? cm from the beam exit
of laser module 105, the concave surface of negative lens 116 and
the convex surface of positive lens 118 are spaced ? cm apart, and
the convex surfaces of lenses 118 and 122 are ? cm apart. The
center 184 of flow cell 150 is placed at the waist of the expanded
and focused laser beam. As known in the art, the precise positions
of the optical elements are preferably adjusted to maximize the
accuracy of the particle count.
[0040] The other elements of particle counter 100 for which details
of dimensions, materials and/or manufacturer and part numbers are
not given above or below are known in the art and thus will not be
discussed in detail herein.
[0041] The invention operates as follows. A source of liquid, such
as de-ionized water from a semiconducting manufacturing operation,
is connected to inlet 167 and the outlet is connected back into the
manufacturing liquid loop or to a waste line. A small portion of
the liquid passes from inlet, through auxiliary inlet channel 175
to light baffle chamber 176 and then to auxiliary outlet channel
174 to outlet 174. Just enough liquid flows in the auxiliary route
to keep any particles from settling in the light baffle chamber
176. Most of the liquid flows into main flow volume 178 and through
capillary 202. Because the pressure difference between the baffle
chamber 176 and the sample chamber 202 is relatively small, and
especially because aperture 274 is very small compared to the size
of the baffle chamber 176 and the main sample chamber 202,
negligible fluid flows through aperture 274 of aperture elements
160 and 161. Laser beam 130 is generated at the exit window of
laser package 105. The beam as generated has the S electromagnetic
vector in the vertical direction in FIG. 5 and the polarization (P)
vector out of the paper in FIG. 5. Half-wave plate rotates the beam
so that the polarization is in the vertical direction in FIG. 5 and
the S vector is into the paper. The beam shaping optics system 114
comprising half-wave place 117 and lenses 116, 118, and 122 is
placed so that the focal plane of the system is located on the exit
window 121 of laser module 105. As described in the references
cited above, the optics of the preferred unique m.o.d.e. transforms
the laser diode emitter into a square virtual emitter. The beam of
the preferred unique m.o.d.e. laser is symmetrically divergent and
preferably has an essentially square focus and an essentially
square far field, with equal quality in the fast and slow axes. The
divergence angle of the unique m.o.d.e. laser is approximately 8
milliradians, which corresponds to a beam quality of
M.sub.x.sup.2.apprxeq.M.sub.y.sup.2.ltoreq.20. However, the optics
also creates a large amount of diffracted radiation at the edges of
the beam. Entrance aperture element 115 removes most of this
diffracted radiation and leaves just the essentially uniform beam
center. Diffractions and stray light due to entrance aperture
element 115 and beam expander optics 110 are removed by aperture
element 119, while diffractions and stray light from aperture
element 119 and focusing lens 122 are removed by aperture element
124. Recessed window opening 129 further removes diffractions and
stray light from the earlier structures. Diffractions and stray
light from windows 153 and 154 and other parts of the flow cell are
trapped and absorbed in light baffle chamber 176. Glass aperture
elements 160 and 161 block and absorb diffractions and stray light
from laser beam 130 and from other sources in the particle counter
system. Laser beam 130 passes through aperture 274 in aperture
elements 160 and 161. Particles in liquid passing through the
capillary 202 scatter the light from the laser beam 130, a portion
of which scattered light is collected by collection optics 180 and
directed to detector 190. As known in the art, detector 190 is
preferably a photo detector which produces an output data signal on
output 192, which output signal is representative of the number and
size of particles detected by the particle counter 100. The data
signal may be processed by electronics that form part of the
particle counter 100, but more often is processed by a computer
system (not shown) which stores and presents the data in forms
desired by the user.
[0042] A key aspect of the invention is that laser 105 is a strip
laser diode which produces much more power than any laser diode
used in prior art liquid particle counters. In FIG. 4, laser diode
108 is being viewed from the long "strip" side and its size is
exaggerated; otherwise, it would be difficult to show clearly.
Preferably, the length of strip laser diode 108 in the vertical
direction in FIG. 2 is 100 microns or more, while the width
extending into and out of the paper is 1 micron (the vertical
direction in FIG. 5), though the invention contemplates that other
sizes of strip laser diodes may be used. To develop significant
power, at least one dimension of the laser diode should be 10
microns or greater, and more preferably 50 microns or greater. Most
preferably, it is 100 microns or greater. The strip laser diode
according to the invention has a power of 1 watt or greater, and
more preferably 2 watts or greater. As indicted above, the
preferred laser is the unique m.o.d.e. symmetrically collimated
laser. This laser has a center wavelength of 808 nanometers, though
other wavelengths may be used. Preferably, a laser of from 1 watt
to 5 watts of power is used in particle counter 100 according to
the invention.
[0043] An important aspect of the invention is the black glass
aperture elements 20 160 and 161. FIG. 2 is a depiction of a
photograph of the laser beam 130 passing through capillary 202
without the aperture elements 160 and 161. As can be seen, there is
a large amount of scattered light 281 and 282 generated at the
fluid/glass interfaces, as well as a large amount of stray light
284, that probably originates at the interfaces. FIG. 3 is a
depiction of a photograph of the laser beam 130 passing through the
capillary 202 with the aperture elements 160 and 161 in place. As
can be seen, the scattered light 286 and 287 at the interfaces as
well as the stray light 288 is much less. The important aspect to
compare is the apparent intensity of the laser beam at 285 and 289.
The laser beam 289 is much brighter, with the laser beam 285 nearly
washed out by the stray light 284. It is important to keep in mind
that FIGS. 2 and 3 only show the relative intensities of the
scattered light and stray light to the laser beam in the same
picture (comparing 281, 282, and 284 to 285 and comparing 286, 287
and 288 to 289). That is, the camera taking the picture adjusts its
aperture to the high intensity of the scattered light in FIG. 2,
which washes out the less intense laser beam, while in FIG. 3 the
scattered light is of less intensity than the laser beam so the
laser beam is not washed out. One skilled in the art will recognize
that in FIG. 2 the scattered and stray light will wash out the
scattering from particles to even a greater extent, since the
intensity of scattered light from the particles is much less than
the intensity of the laser beam, so that the particle counter of
FIG. 2 would be essentially useless, while the particle counter of
FIG. 3 is able to detect particles as small as 0.05 microns at flow
rates of 1000 ml/minute.
[0044] Another important advantage of the glass aperture elements
160 and 161 is their ability to withstand significant heating.
Without the glass aperture elements, the heating due to the large
amount of diffracted radiation in the symmetrically collimated beam
130 is sufficient to melt the Kel-F plastic. This is particularly
true if a bubble becomes trapped in capillary 202. Such a bubble
diffracts the laser light causes it to heat the flow cell even more
than normal. Users are generally warned not to turn the laser on in
particle counters until the liquid flow has started, to prevent
damage to the flow cell, but this cannot always be counted on
because particle counters are often used in high-pressure
emergencies and/or by lesser skilled persons. Because of its
resistance to damage from de-ionized water and other chemicals,
Kel-F plastic has become the state-of-the-art in liquid particle
counter flow cells. Thus, conventional liquid flow cell
construction techniques are not suitable for use with high-powered
lasers. Glass aperture elements 160 and 162 overcome these
problems.
[0045] A related feature of the invention is the use of the glass
aperture elements 160, 161 in combination with the flow cell baffle
156, and the associated outer flow channel with auxiliary volume
173 which contacts the exterior side of the glass aperture
elements. This flow of fluid over the glass aperture element cools
the aperture element, and further reduces the heating problems do
to the high power of the laser and the diffractions associated with
symmetrical collimation. The fluid in the sample chamber 202 also
contacts the glass and cools it.
[0046] As suggested by the baffles 156 that separate the flow as
shown in FIG. 5 and the small diameter of the aperture 274 in the
glass aperture element 160, the particle counter 100 describe
herein is an in-situ particle counter. It samples approximately
0.375 percent of the flow volume. However, the invention can also
be used in non-in-situ particle counters, including volumetric
particle counters. Another important aspect of the invention is the
use of a symmetrically collimated strip diode laser. As indicated
above, the symmetrical collimation results in extensive
diffraction. Up until the invention, this diffraction has resulted
in such a high level of stray light, as shown in FIG. 2, that the
symmetrically collimated lasers were not seen to be useful in
particle counting.
[0047] The aperturing of the unique m.o.d.e. laser is another
important feature of the invention. The optics 114 takes the 1.1
mm.times.1.1 mm cross-section of the unique m.o.d.e. laser and
focuses it to a 96 micron x 96 micron cross-sectional beam, i.e., a
96 .mu.m.sup.2 spot size. The aperturing system 112 described above
creates a beam with a 43 .mu.m.sup.2 spot size. Preferably,
aperturing system 112 blocks a third or more of the power of the
laser beam, including nearly all of the original diffracted light
in the beam.
[0048] Having solved the problem of employing a high-powered laser
in a particle counter, numerous other advantages of the particle
counter 100 have been found. To explain these advantages, we shall
compare the system according to the invention to the
state-of-the-art prior art particle counter using a double
frequency Nd-YAG 532 nm laser. To get a comparable signal-to-noise
ratio as the prior art system, it is necessary to run the unique
m.o.d.e laser at 1.6 watts output. The double frequency Nd-YAG
laser has a rated mean time to failure (MTTF) of 15,000 hours. This
is less than two years of constant run time in most particle
counter applications. The MTTF of the semiconductor laser according
to the invention is 16,000 hours running at full optical output
power and at 25.degree. C. This is better than the Nd-YAG laser,
but only a little. However, as indicated above, the semiconductor
laser can be run at 1.6 watts for a comparable performance to the
Nd-YAG laser system. The full power of the preferred semiconductor
laser is 4.2 watts. This gives a power factor advantage of
Operation Power/Maximum power equal to 13.4. Thus, the MTTF of the
laser in the system according to the invention is 13.4.times.16,000
hours=24.7 years!
[0049] Another advantage is the power consumption of the system 100
according to the invention. Power consumption of the Nd-YAG laser
mentioned above is typically 40 watts (W), but can be as high as
150 watts in maximum delta temperature conditions. The laser
deliver 80 mW of power. Thus, it takes 40 W to deliver 80 mW of
laser power. In comparison, at the 1.6 W of optical power required
for a comparable result, the preferred laser consumes 6 W of power.
If a thermoelectric cooler is used to cool the laser to a
20.degree. C. delta temperature, this will consume another 7 W.
Thus, it requires 13 W to deliver 1.6 W of laser power, which is
much more efficient than the prior art system.
[0050] The liquid particle counter 100 according to the invention
has been found to have many other advantages over the prior art
liquid particle counters. It is relatively maintenance free; its
power remains constant over longer periods, that is, it maintains
calibration; it is easier to manufacture and calibrate; it is more
reliable, enabling longer warranty periods; it is less costly to
manufacture and operate; beam waist movement, and thus image
movement, is greatly reduced because the solid state lasers are
thermally controlled; optics design is simplified; and no frequency
locking is required for solid state lasers in contrast to Nd-YAG
lasers.
[0051] Another advantage of the preferred symmetrically collimated
laser according to the invention is that the energy distribution
across the laser beam is more uniform. In prior art cavity-type
lasers, the energy distribution was essentially Gaussian, wherein
in the symmetrically collimated laser the distribution is much more
of a flat-topped curve with steep sides, almost a square-wave
shape. The square shape results in better resolution of particle
size. Also, with the prior art Gaussian energy distributions, less
than 100% of particles less than about 0.117 .mu.m in size were
counted, but for particles greater than 0.117 .mu.m in size the
percentage counted was greater than 100%. That is, for larger
particles, there were significant false counts. In the particle
counter of the present invention, the percentage detected versus
size curve is much flatter, resulting in a lower number of false
counts.
[0052] There has been described a novel particle counter system
that utilizes a symmetrically collimated laser diode and which
permits the use of lasers of one watt or greater power in a liquid
particle counter. It should be understood that the particular
embodiments shown in the drawings and described within this
specification are for purposes of example and should not be
construed to limit the invention, which will be described in the
claims below. Further, it is evident that those skilled in the art
may now make numerous uses and modifications of the specific
embodiments described, without departing from the inventive
concepts. For example, a wide variety of beam shaping optics 114
may be used. Mirrors may be used in place of lenses. Or, the entire
flow cell 150, or at least a larger portion of it than aperture
elements 160 and 161, may be made of black glass or similar
material. As another example, the light collector 180 and detector
190 may be replaced with a wide variety of other collection and
detection systems, ranging from a single photodetector to very
complex systems using a large number of lenses and/or mirrors
and/or multiple detectors and/or detector arrays. Light collection
is shown as collecting scattered light in directions about a
perpendicular to the laser beam 130, but, as know in the art, the
light collection may also be about a direction parallel to the
beam, or entirely around the scattering particle, or in any other
direction. It is also evident that the methods recited may in many
instances be performed in a different order; or equivalent
structures and processes may be substituted for the various
structures and processes described. Consequently, the invention is
to be construed as embracing each and every novel feature and novel
combination of features present in and/or possessed by the
invention herein described.
* * * * *