U.S. patent application number 15/342372 was filed with the patent office on 2018-05-03 for control system using a phase modulation capable acousto-optic modulator for diverting laser output intensity noise to a first order laser light beam and related methods.
The applicant listed for this patent is Harris Corporation. Invention is credited to Pat O. Bentley, Lee M. Burberry, Michael R. Lange, Catheryn D. Logan, RANDALL K. MORSE, Peter A. Wasilousky.
Application Number | 20180120600 15/342372 |
Document ID | / |
Family ID | 60190526 |
Filed Date | 2018-05-03 |
United States Patent
Application |
20180120600 |
Kind Code |
A1 |
MORSE; RANDALL K. ; et
al. |
May 3, 2018 |
CONTROL SYSTEM USING A PHASE MODULATION CAPABLE ACOUSTO-OPTIC
MODULATOR FOR DIVERTING LASER OUTPUT INTENSITY NOISE TO A FIRST
ORDER LASER LIGHT BEAM AND RELATED METHODS
Abstract
A laser system may include a laser source configured to generate
a laser light beam and an acousto-optic modulator (AOM). The AOM
may include an acousto-optic medium configured to receive the laser
light beam, and a phased array transducer comprising a plurality of
electrodes coupled to the acousto-optic medium and configured to
cause the acousto-optic medium to output a zero order laser light
beam and a first order diffracted laser light beam. The system may
further include a beamsplitter downstream from the AOM and
configured to split a sampled laser light beam from the zero order
laser light beam, a photodetector configured to receive the sampled
laser light beam and generate a feedback signal associated
therewith, and a radio frequency (RF) driver configured to generate
an RF drive signal to the phased array transducer electrodes so
that noise is diverted to the first order diffracted laser light
beam based upon the feedback signal.
Inventors: |
MORSE; RANDALL K.; (Palm
Bay, FL) ; Wasilousky; Peter A.; (Indialantic,
FL) ; Burberry; Lee M.; (West Melbourne, FL) ;
Lange; Michael R.; (Melbourne, FL) ; Logan; Catheryn
D.; (Melbourne, FL) ; Bentley; Pat O.; (West
Melbourne, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Harris Corporation |
Melbourne |
FL |
US |
|
|
Family ID: |
60190526 |
Appl. No.: |
15/342372 |
Filed: |
November 3, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 1/113 20130101;
H01L 21/268 20130101; G02F 2201/122 20130101; H01L 21/67115
20130101; G21K 1/00 20130101; H01L 21/0273 20130101; G02F 2203/21
20130101; H01S 3/0085 20130101; B23K 26/067 20130101; G02F 1/332
20130101; H01S 3/005 20130101; H01S 2301/02 20130101; H01S 3/1306
20130101; B23K 26/362 20130101; G02B 27/10 20130101; B23K 26/361
20151001 |
International
Class: |
G02F 1/11 20060101
G02F001/11; H01S 3/00 20060101 H01S003/00; G02B 27/10 20060101
G02B027/10; G21K 1/00 20060101 G21K001/00; H01L 21/67 20060101
H01L021/67; H01L 21/027 20060101 H01L021/027; H01L 21/268 20060101
H01L021/268; B23K 26/362 20060101 B23K026/362; B23K 26/067 20060101
B23K026/067 |
Claims
1. A laser system comprising: a laser source configured to generate
a laser light beam; an acousto-optic modulator (AOM) comprising an
acousto-optic medium configured to receive the laser light beam,
and a phased array transducer comprising a plurality of electrodes
coupled to the acousto-optic medium and configured to cause the
acousto-optic medium to output a zero order laser light beam and a
first order diffracted laser light beam; a beamsplitter downstream
from the AOM and configured to split a sampled laser light beam
from the zero order laser light beam; a photodetector configured to
receive the sampled laser light beam and generate a feedback signal
associated therewith; and a radio frequency (RF) driver configured
to generate an RF drive signal to the phased array transducer
electrodes so that noise is diverted to the first order diffracted
laser light beam based upon the feedback signal.
2. The laser system of claim 1 wherein the RF driver is configured
to drive alternating electrodes of the phased array transducer
electrodes with different phases.
3. The laser system of claim 2 wherein the RF driver is configured
to drive the alternating electrodes with different phases within a
range of 0.degree. to 180.degree..
4. The laser system of claim 1 wherein an RF power level associated
with the RF drive signal has a constant power.
5. The laser system of claim 1 wherein the sampled laser light beam
utilizes .ltoreq.3% of the light of the zero order laser light
beam.
6. The laser system of claim 1 wherein the first order diffracted
laser light beam has .ltoreq.3% of the light from the laser
source.
7. The laser system of claim 1 further comprising an ion trap, and
wherein the beamsplitter is configured to direct the zero order
laser light beam from the AOM to the ion trap.
8. The laser system of claim 1 further comprising a semiconductor
workpiece having a photoresist layer, and wherein the beamsplitter
is configured to direct the zero order laser light beam from the
AOM to the photoresist layer.
9. The laser system of claim 1 further comprising a micromachining
workpiece, and wherein the beamsplitter is configured to direct the
zero order laser light beam from the AOM to the micromachining
workpiece.
10. A laser system comprising: a laser source configured to
generate a laser light beam; an acousto-optic modulator (AOM)
comprising an acousto-optic medium configured to receive the laser
light beam, and a phased array transducer comprising a plurality of
electrodes coupled to the acousto-optic medium and configured to
cause the acousto-optic medium to output a zero order laser light
beam and a first order diffracted laser light beam; a beamsplitter
downstream from the AOM and configured to split a sampled laser
light beam from the zero order laser light beam; a photodetector
configured to receive the sampled laser light beam and generate a
feedback signal associated therewith; and a radio frequency (RF)
driver configured to generate an RF drive signal to the phased
array transducer electrodes so that noise is diverted to the first
order diffracted laser light beam based upon the feedback signal,
the RF driver driving alternating electrodes of the phased array
transducer electrodes with different phases, and an RF power level
associated with the RF drive signal having a constant power.
11. The laser system of claim 10 wherein the RF driver is
configured to drive the alternating electrodes with different
phases within a range of 0.degree. to 180.degree..
12. The laser system of claim 10 wherein the sampled laser light
beam utilizes .ltoreq.3% of the light of the zero order laser light
beam.
13. The laser system of claim 10 wherein the first order diffracted
laser light beam has .ltoreq.3% of the light from the laser
source.
14. The laser system of claim 10 further comprising an ion trap,
and wherein the beamsplitter is configured to direct the zero order
laser light beam from the AOM to the ion trap.
15. The laser system of claim 10 further comprising a semiconductor
workpiece having a photoresist layer, and wherein the beamsplitter
is configured to direct the zero order laser light beam from the
AOM to the photoresist layer.
16. The laser system of claim 10 further comprising a
micromachining workpiece, and wherein the beamsplitter is
configured to direct the zero order laser light beam from the AOM
to the micromachining workpiece.
17. A method comprising: generating a laser light beam using a
laser source directed at an acousto-optic medium; causing the
acousto-optic medium to output a zero order laser light beam and a
first order diffracted laser light beam using a phased array
transducer comprising a plurality of electrodes coupled to the
acousto-optic medium; splitting a sampled laser light beam from the
zero order laser light beam using a beamsplitter downstream from
the acousto-optic medium; generating a feedback signal associated
with the sampled laser light beam; and generating a radio frequency
(RF) drive signal to the phased array transducer electrodes with an
RF driver so that noise is diverted to the first order diffracted
laser light beam based upon the feedback signal.
18. The method of claim 17 wherein generating the RF drive signal
comprises generating the RF drive signal to drive alternating
electrodes of the phased array transducer electrodes with different
phases.
19. The method of claim 17 wherein an RF power level associated
with the RF drive signal has a constant power.
20. The method of claim 17 wherein the sampled laser light beam
utilizes .ltoreq.3% of the light of the zero order laser light
beam.
21. The method of claim 17 wherein the first order diffracted laser
light beam has .ltoreq.3% of the light from the laser source.
22. The method of claim 17 wherein splitting the beam further
comprises directing the zero order laser light beam to an ion
trap.
23. The method of claim 17 wherein splitting the beam further
comprises directing the zero order laser light beam to a
photoresist layer on a semiconductor workpiece.
24. The method of claim 17 wherein splitting the beam further
comprises directing the zero order laser light beam to a
micromachining workpiece.
Description
TECHNICAL FIELD
[0001] The present invention relates to the field of optical
devices, and, more particularly, to acousto-optic modulators for
lasers and related methods.
BACKGROUND
[0002] Acousto-optic modulators, sometimes referred to as Bragg
cells, diffract and shift light using sound waves at radio
frequency. These devices are often used for Q-switching, signal
modulation in telecommunications systems, laser scanning and beam
intensity control, frequency shifting, and wavelength filtering in
spectroscopy systems. Many other applications lend themselves to
using acousto-optic devices.
[0003] In such acousto-optic devices, a piezoelectric transducer,
sometimes also referred to as an RF transducer, is secured to an
acousto-optic bulk medium as a transparent optical material, for
example, fused silica, quartz or similar glass material. An
electric RF signal oscillates and drives the transducer to vibrate
and create sound waves within the transparent medium which effect
the properties of an optical field in the medium via the photo
elastic effect, in which a modulating strain field of an ultrasonic
wave is coupled to an index of refraction for the acousto-optic
bulk medium. As a result, the refractive index change in amplitude
is proportional to that of sound.
[0004] The index of refraction is changed by moving periodic planes
of expansion and compression in the acousto-optic bulk material.
Incoming light scatters because of the resulting periodic index
modulation and interference, similar to Bragg diffraction.
[0005] Acousto-optic modulators are preferred in many applications
because they are faster than tiltable mirrors and other mechanical
devices. The time it takes for the acousto-optic modulator to shift
an exiting optical beam is limited to the transit time of the sound
wave. The acousto-optic modulators are often used in Q-switches
where a laser produces a pulsed output beam at high peak power,
typically in the Kilowatt range. This output could be higher than
lasers operating a continuous wave (CW) or constant output
mode.
[0006] Examples of acousto-optic modulator devices and similar
acousto-optic systems are disclosed in commonly assigned U.S. Pat.
Nos. 4,256,362; 5,923,460; 6,320,989; 6,487,324; 6,538,690;
6,765,709; and 6,870,658, the disclosures of which are hereby
incorporated by reference in their entireties.
[0007] Some applications using acousto-optic devices modulate the
intensity of an optical beam. This modulation may create small
deviations in the output angle of the diffracted beam because of
the local thermal transients introduced when the RF modulation
waveform to the device is turned ON and OFF. These thermal
transients may negatively impact the resolution and location of the
focused spot, which may be produced. One advantageous approach
which may be used to help enhance the resolution of acousto-optic
devices is set forth in U.S. Pat. No. 7,538,929 to Wasilousky,
which is assigned to the present Applicant and is hereby
incorporated herein in its entirety by reference. Wasilousky
discloses an acousto-optic modulator which includes an
acousto-optic bulk medium and transducer attached to the
acousto-optic bulk medium and formed as a linear array of
electrodes. A transducer driver is connected to each electrode and
is coherently phase driven to alter the angular momentum
distribution of an acoustic field and alternately allow and inhibit
phase matching between the optical and acoustic field and produce a
desired intensity modulation of an optical wavefront.
[0008] Despite the existence of such configurations, further
advancements in laser systems using acousto-optic modulators may be
desirable in certain applications.
SUMMARY
[0009] A laser system may include a laser source configured to
generate a laser light beam and an acousto-optic modulator (AOM).
The AOM may include an acousto-optic medium configured to receive
the laser light beam, and a phased array transducer comprising a
plurality of electrodes coupled to the acousto-optic medium and
configured to cause the acousto-optic medium to output a zero order
laser light beam and a first order diffracted laser light beam. The
system may further include a beamsplitter downstream from the AOM
and configured to split a sampled laser light beam from the zero
order laser light beam, a photodetector configured to receive the
sampled laser light beam and generate a feedback signal associated
therewith, and a radio frequency (RF) driver configured to generate
an RF drive signal to the phased array transducer electrodes so
that noise is diverted to the first order diffracted laser light
beam based upon the feedback signal.
[0010] More particularly, the RF driver may be configured to drive
alternating electrodes of the phased array transducer electrodes
with different phases. By way of example, the RF driver may be
configured to drive the alternating electrodes with different
phases within a range of 0.degree. to 180.degree.. Furthermore, the
RF power level associated with the drive signal may have a constant
power.
[0011] The sampled laser light beam may utilize .ltoreq.3% of the
light of the zero order laser light beam, for example. Also by way
of example, at the set point the first order diffracted light beam
may also utilize a similarly small percentage of the laser light
from the laser source. For example, the first order diffracted
laser light beam have .ltoreq.3% of the light from the laser
source.
[0012] In one example embodiment, the laser system may further
include an ion trap, and the beamsplitter may be configured to
direct the zero order laser light beam from the AOM to the ion
trap. In accordance with another example, the laser system may
further include a semiconductor workpiece having a photoresist
layer, and the beamsplitter may be configured to direct the zero
order laser light beam from the AOM to the photoresist layer. In
still another example, the laser system may further include a
micromachining workpiece, and the beamsplitter may be configured to
direct the zero order laser light beam from the AOM to the
micromachining workpiece.
[0013] A related method may include generating a laser light beam
using a laser source and directed at an acousto-optic medium,
causing the acousto-optic medium to output a zero order laser light
beam and a first order diffracted laser light beam using a phased
array comprising a plurality of electrodes coupled to the
acousto-optic medium, and splitting a sampled laser light beam from
the zero order laser light beam using a beamsplitter downstream
from the acousto-optic medium. The method may further include
generating a feedback signal associated with the sampled laser
light beam using a photodetector, and generating an RF drive signal
to the phased array transducer electrodes with an RF driver so that
noise is diverted to the first order diffracted laser light beam
based upon the feedback signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic block diagram of a laser system
including a phase-capable acousto-optic modulator (AOM) in
accordance with an example embodiment.
[0015] FIGS. 2 and 3 are schematic circuit diagrams illustrating
different electrode connection configurations and associated
driving signals therefor which may be used with the systems of
FIGS. 1-3.
[0016] FIG. 4 is a flow diagram illustrating method aspects
associated with the system of FIG. 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] The present description is made with reference to the
accompanying drawings, in which exemplary embodiments are shown.
However, many different embodiments may be used, and thus the
description should not be construed as limited to the particular
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete.
Like numbers refer to like elements throughout.
[0018] By way of background, excessive noise levels from laser
sources in optical illumination systems generate instabilities and
errors. In particular, systems that manipulate the quantum states
of particles, atoms and electrons, typically require extreme
stability. Beam pointing errors correlate to noise in quantum state
manipulation systems. Moreover, beam pointing stability due to
thermal transients in the bulk material of active acousto-optic
devices in an optical illumination system affect many applications,
but especially those designed for quantum state illumination.
[0019] Referring initially to FIGS. 1 and 4, a laser system 30 and
associated method aspects which may provide enhanced stability and
noise reduction are first described. Beginning at Block 61 of the
flow diagram 60, the laser system 30 illustratively includes a
laser source 31 configured to generate a laser light beam, at Block
62. In accordance with one example embodiment, a Paladin Advanced
355 nm mode locked UV laser source from Coherent, Inc. of Santa
Clara, Calif. may be used, although other suitable laser sources
may also be used in different embodiments. The system 30 further
illustratively includes an acousto-optic modulator (AOM) 32. The
AOM illustratively includes an acousto-optic medium 33 configured
to receive the laser light beam from the laser source 31, and a
phased array of electrodes 34 coupled to the acousto-optic medium.
The acousto-optic medium 33 may include a piezoelectric transducer
and bulk acousto-optic medium (e.g., silica, quartz, glass, etc.),
as discussed above. The phased array of electrodes 34 are
configured to cause the acousto-optic medium 33 to output a zero
order laser light beam to an optical target 38, and a first order
diffracted laser light beam, at Block 63, as will be discussed
further below.
[0020] The system further illustratively includes a beamsplitter 35
downstream from the AOM 32 which is configured to split a sampled
laser light beam from the zero order laser light beam, at Block 64.
The beamsplitter 35 need only divert a small portion of light from
the zero order laser light beam into the sampled laser light beam
(e.g., .ltoreq.3%) to provide adequate feedback to a radio
frequency (RF) driver 36 for driving the phase array of electrodes
34. More particularly, a photodetector 37 is configured to receive
the sampled laser light beam and generate an electrical feedback
signal for the RF driver 36 based upon the sampled laser light
beam. As such, the RF driver 36 is able to generate one or more RF
drive signals to the phased array of electrodes 34 to generate the
zero order beam and the first order diffracted beam accordingly,
which illustratively concludes the method of FIG. 4 (Block 67).
[0021] In particular, the RF driver 36 drives the phased array of
electrodes 34 such that noise measured from the feedback signal is
diverted to the first order diffracted laser light beam, which may
be directed to a beam dump 39 (or simply away from the optical
target 38). This advantageously provides noise cancelation by
diffracting a relatively small amount of light from the zero order
beam (e.g., .ltoreq.3%) into the first order diffracted beam by
changing the phase of the RF drive signal to alternating electrode
elements of the phased array of electrodes 34. In particular, the
feedback signal is inverted and sent to the phase modulation
capable AOM 32 to subtract and correct for the inherent noise in
the laser.
[0022] This may be done while the RF power applied to the
acousto-optic medium 33 remains essentially constant which helps to
eliminate beam pointing errors which may otherwise be associated
with varying thermal transients due to changing RF power levels, as
may be experienced with typical amplitude modulation AOMs, for
example. Stated alternatively, by only effecting the phase of the
RF drive signal to the N element phased array electrode pattern on
the AOM and leaving the RF power level essentially constant, this
advantageously reduces the laser intensity noise appearing on the
zero order beam while still retaining a positionally stable
beam.
[0023] More particularly, referring additionally to FIGS. 2 and 3,
two example configurations for driving alternating electrodes 40 of
the phased array of electrodes 34 with different phases to provide
the zero and first order beam configuration described above are now
described. In the first configuration (FIG. 2), the first and third
driving signals (shown on the right hand side of FIG. 2) provided
to corresponding odd numbered electrodes are 180.degree. out of
phase with the second and fourth driving signals provided to
corresponding even numbered electrodes. In the second configuration
(FIG. 3), first and second drive signals are respectively connected
to odd and even electrodes in an interdigitated fashion as shown,
and as before these drive signals are 180.degree. out of phase to
one another. In this way, directly adjacent electrodes are driven
at opposite phases to one another. However, it should be noted that
the RF drive signals need not always be 180.degree. out of phase,
i.e., they may be somewhere between 0.degree. and 180.degree. to
vary the level of phase matching occurring in the AO diffraction
process, thereby selectively altering the amount of light directed
from the zero order beam into the first order beam.
[0024] The system 30 accordingly combines intensity modulation via
RF-phase variation on a phased array transducer with active optical
feedback to accomplish noise cancelation in an optical illumination
system. Moreover, performing phase modulation by flipping the phase
of alternating elements of a multi-element phased array has
inherently better pointing stability because the RF power applied
to the device remains essentially constant, as noted above.
Further, applying this to the zero order beam allows the RF power
to remain low, reducing the potential of thermal gradients and
thermal transients.
[0025] The system 30 may accordingly provide advantages with
respect to numerous different types of optical targets. By way of
example, in one configuration the optical target 38 may be an ion
trap, such as in a quantum computing device. In accordance with
another example, the optical target 38 may be a semiconductor
workpiece to perform photolithographic patterning of a photoresist
layer, for example. In still another example, the optical target 38
may be a micromachining workpiece. It should be noted that the
laser system 30 may be used with other optical targets in different
embodiments as well.
[0026] Other example systems in which the above-described stability
and noise reduction techniques may be used are set forth in the
following co-pending applications: attorney docket no. GCSD-2899
(62084) entitled MULTI-CHANNEL LASER SYSTEM INCLUDING AN
ACOUSTO-OPTIC MODULATOR (AOM) AND RELATED METHODS; and attorney
docket no. GCSD-2900 (62087) entitled MULTI-CHANNEL ACOUSTO-OPTIC
MODULATOR (AOM) AND RELATED METHODS. Both of these applications are
assigned to the present Applicant Harris Corporation and are hereby
incorporated herein in their entireties by reference.
[0027] Many modifications and other embodiments will come to the
mind of one skilled in the art having the benefit of the teachings
presented in the foregoing descriptions and the associated
drawings. Therefore, it is understood that the disclosure is not to
be limited to the specific embodiments disclosed, and that
modifications and embodiments are intended to be included within
the scope of the appended claims.
* * * * *