U.S. patent application number 15/868164 was filed with the patent office on 2018-07-19 for terahertz wave generator.
The applicant listed for this patent is SHIBUYA CORPORATION. Invention is credited to Toshiaki NAKA, Motoi SASAKI, Akito TSUCHIYA.
Application Number | 20180203327 15/868164 |
Document ID | / |
Family ID | 60953733 |
Filed Date | 2018-07-19 |
United States Patent
Application |
20180203327 |
Kind Code |
A1 |
NAKA; Toshiaki ; et
al. |
July 19, 2018 |
TERAHERTZ WAVE GENERATOR
Abstract
A pumping beam L1 enters from a pumping beam projector 3 into
one end surface 2a of a nonlinear crystal 2, the pumping beam L1
and idler wave L2 are generated from another end surface 2b of the
nonlinear crystal 2. The pumping beam L1 emitted from the other end
surface 2b of the nonlinear crystal 2 is reflected and re-enters as
a pumping beam L' into the other end surface 2b and the idler wave
L2 generated from the other end surface 2b of the nonlinear crystal
is reflected by the reflection optical system 6 and re-enters as a
seed beam L2' into the other end surface 2b. The idler wave L2
enters as the seed beam L2' together with the pumping beam L1' into
the nonlinear crystal and thus a terahertz wave with a large output
and including a plurality of wavelengths can be generated.
Inventors: |
NAKA; Toshiaki;
(Kanazawa-shi, JP) ; SASAKI; Motoi; (Kanazawa-shi,
JP) ; TSUCHIYA; Akito; (Kanazawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHIBUYA CORPORATION |
Kanazawa-shi |
|
JP |
|
|
Family ID: |
60953733 |
Appl. No.: |
15/868164 |
Filed: |
January 11, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 1/3501 20130101;
G02F 2203/13 20130101; G02F 2203/055 20130101; G02F 2001/3503
20130101; G02F 1/39 20130101 |
International
Class: |
G02F 1/39 20060101
G02F001/39; G02F 1/35 20060101 G02F001/35 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 17, 2017 |
JP |
2017-006110 |
Claims
1. A terahertz wave generator including a nonlinear crystal for
generating a terahertz wave by a parametric effect when a seed beam
and a pumping beam enter therein, characterized in that the
terahertz wave generator comprises: pumping beam projecting means
for allowing the pumping beam to enter one end surface of the
nonlinear crystal and emit the pumping beam from another end
surface of the nonlinear crystal, and for generating an idler wave;
and a reflection optical system for reflecting the pumping beam
emitted from the other end surface of the nonlinear crystal to
re-enter the other end surface, and for reflecting the idler wave
generated from the other end surface of the nonlinear crystal as
the seed beam to enter the other end surface of the nonlinear
crystal so as to generate the terahertz wave.
2. The terahertz wave generator according to claim 1, characterized
in that the reflection optical system includes a reflection mirror
having a flat-plate shaped reflection surface facing the other end
surface of the nonlinear crystal and a convex lens disposed between
the reflection mirror and the other end surface of the nonlinear
crystal, and the convex lens is separated from the other end
surface of the nonlinear crystal only by a focal distance of the
convex lens.
3. The terahertz wave generator according to claim 1, characterized
in that the reflection optical system includes a reflection mirror
having a spherical-shaped reflection surface facing the other end
surface of the nonlinear crystal, and the reflection mirror
reflects the idler wave generated from the other end surface of the
nonlinear crystal as the seed beam toward the other end surface of
the nonlinear crystal.
4. The terahertz wave generator according to claim 2, characterized
in that between the other end surface of the nonlinear crystal and
the reflection mirror, a wavelength selecting means is provided
having a passing portion for passing the pumping beam and a passing
portion for passing only the idler wave having a specific
wavelength in the idler wave generated from the other end surface
of the nonlinear crystal.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a terahertz wave generator
and more particularly to a terahertz wave generator constituted to
generate a terahertz wave by a parametric effect of a nonlinear
crystal.
Description of the Related Art
[0002] Conventionally, as a terahertz wave generator, those
including laser beam generating means for generating a pumping beam
and a seed beam and a nonlinear crystal for generating a terahertz
wave by a parametric effect when the pumping beam and the seed beam
enter (Japanese Patent Laid-Open No. 2002-72269) are known.
[0003] In the aforementioned terahertz wave generator, by allowing
the pumping beam and the seed beam to enter the nonlinear crystal,
the terahertz wave can be generated with a pulse having a large
peak output with a narrowed spectral width from the nonlinear
crystal.
[0004] In the aforementioned Japanese Patent Laid-Open No.
2002-72269, a laser beam with a single wavelength is used for the
pumping beam and the seed beam, respectively, and as a result, the
terahertz wave is generated with a narrowed spectral width. In
other words, the terahertz wave could not be generated with a wide
wavelength band.
[0005] In view of such circumstances, the present invention
provides a terahertz wave generator which can generate a terahertz
wave with a large output in a wide wavelength band.
SUMMARY OF THE INVENTION
[0006] An invention (1) is a terahertz wave generator including a
nonlinear crystal for generating a terahertz wave by a parametric
effect when a seed beam and a pumping beam enter, characterized in
that
[0007] the terahertz wave generator includes:
[0008] pumping beam projecting means for allowing the pumping beam
to enter from one end surface of the nonlinear crystal and emitting
the pumping beam from the other end surface of the nonlinear
crystal, and for generating an idler wave; and
[0009] a reflection optical system for allowing the pumping beam
emitted from the other end surface of the nonlinear crystal to be
reflected and to re-enter the other end surface, and for allowing
the idler wave generated from the other end surface of the
nonlinear crystal to be reflected and allowing the idler wave as
the seed beam to enter from the other end surface of the nonlinear
crystal so as to generate terahertz wave.
[0010] An invention (2) is, in invention (1), characterized in that
the reflection optical system includes a reflection mirror having a
flat-plate shaped reflection surface facing the other end surface
of the nonlinear crystal and a convex lens disposed between the
reflection mirror and the other end surface of the nonlinear
crystal, and the convex lens is disposed by being separated from
the other end surface of the nonlinear crystal only by a focal
distance of the convex lens.
[0011] An invention (3) is, in invention (1), characterized in that
the reflection optical system includes a reflection mirror having a
spherical-shaped reflection surface facing the other end surface of
the nonlinear crystal, and the reflection mirror reflects the idler
wave generated from the other end surface of the nonlinear crystal
as the seed beam toward the other end surface of the nonlinear
crystal.
[0012] An invention (4) is, in invention (2) or (3), characterized
in that, between the other end surface of the nonlinear crystal and
the reflection mirror, wavelength selecting means having a passing
portion for passing the pumping beam and a passing portion for
passing only the idler wave having a specific wavelength in the
idler wave generated from the other end surface of the nonlinear
crystal is provided.
[0013] According to invention (1), by allowing the pumping beam
from the pumping beam projecting means to enter from the one end
surface of the nonlinear crystal, the idler wave including a
plurality of wavelengths can be generated from the other end
surface of the nonlinear crystal and by allowing the pumping beam
emitted from the other end surface of the nonlinear crystal to be
reflected and to re-enter the other end surface and by allowing the
idler wave including the plurality of wavelengths to be reflected
and by allowing the idler wave to enter as the seed beam from the
other end surface of the nonlinear crystal by the reflection
optical system, a terahertz wave having a large output and
including a plurality of wavelengths can be generated from the
nonlinear crystal.
[0014] Therefore, in a case where the terahertz wave is passed
through or reflected by a test object so as to test components and
the like of the test object, for example, since the terahertz wave
has a wide wavelength band, the components and the like of the test
object can be tested at one time as compared with the case of
projecting the terahertz wave with individual wavelengths to the
test object.
[0015] Moreover, since the terahertz wave generated from the
nonlinear crystal is emitted at an angle different for each of the
wavelengths, spectral analysis is facilitated. That is, when a test
is conducted with terahertz wave with a plurality of mixed
wavelengths, the terahertz wave needs to be separated for each
wavelength on a receiving side, but according to the present
invention, such an operation can be omitted.
[0016] Moreover, according to invention (4), since only the idler
wave with the specific wavelength in the idler wave including the
plurality of wavelengths generated from the nonlinear crystal can
be passed by the passing portion of the wavelength selecting means,
without changing the wavelength of the idler wave itself generated
from the nonlinear crystal, the terahertz wave with the specific
wavelength can be generated by selecting/using only the idler wave
with the specific wavelength by the wavelength selecting means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a layout view illustrating a first embodiment of
the present invention;
[0018] FIG. 2 is a layout view illustrating a second embodiment of
the present invention;
[0019] FIG. 3 is a front view illustrating another embodiment of
wavelength selecting means 11 illustrated in FIG. 2; and
[0020] FIG. 4 is a front view illustrating still another embodiment
of the wavelength selecting means 11 illustrated in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The present invention will be described by referring to
embodiments illustrated below, and in FIG. 1, a terahertz wave
generator 1 includes a nonlinear crystal 2 for generating a
terahertz wave by a parametric effect when a seed beam and a
pumping beam enter. The nonlinear crystal 2 is formed having a
cuboid shape.
[0022] Pump beam projecting means 3 for allowing a pumping beam L1
to enter the nonlinear crystal 2 is disposed on an optical axis of
the nonlinear crystal 2 in the illustrated embodiment. For the
pumping beam projecting means 3, a semiconductor laser oscillating
a pulse laser can be used, and the pulse laser as the pumping beam
L1 oscillated from the pumping beam projecting means 3 enters the
nonlinear crystal 2 from one end surface 2a thereof, passes through
the nonlinear crystal 2 and is emitted from the other end surface
2b.
[0023] As the wavelength of the pumping beam L1, a wavelength of
1064.4 nm, for example, can be used.
[0024] When the pumping beam L1 enters the nonlinear crystal 2 from
on an optical axis thereof, the pumping beam L1 is emitted from the
other end surface 2b of the nonlinear crystal 2 to on the optical
axis, and two idler wave L2, L2 are generated from the other end
surface 2b symmetrically by sandwiching the optical axis.
[0025] A sectional shape of the idler wave L2, L2 generated from
the nonlinear crystal 2 is a substantially elliptic shape which is
laterally longer in a direction perpendicular to the paper surface
of FIG. 1. The idler wave L2, L2 have a spectral width with a wide
wavelength band of 1069 to 1077 nm, for example, and are spatially
separated for each wavelength, but the output is weak.
[0026] The pumping beam L1 transmitted through the nonlinear
crystal 2 and one of the idler wave L2 generated in the nonlinear
crystal 2 are reflected in the reflection optical system 6,
respectively, and the reflected pumping beam L1 as a pumping beam
L1' and the idler wave L2 as a seed beam L2' are constituted to
enter the nonlinear crystal 2, respectively, at the same angle as
the respective emission angles. Moreover, the other idler wave L2
is constituted to be absorbed by a damper portion 11c of wavelength
selecting means 11 which will be described later in detail.
[0027] As described above, the pumping beam L1' and the seed beam
L2' reflected by a reflection mirror 12 are constituted to enter
the nonlinear crystal 2 at the same angle as the respective
emission angles and thus, they automatically enter the nonlinear
crystal 2 in a state satisfying a phase matching condition for the
nonlinear crystal 2.
[0028] Moreover, by allowing the pumping beam L1' and the seed beam
L2' to enter the nonlinear crystal 2, a light-injection type
terahertz parametric generator (Is-TPG) for generating terahertz
wave TH is constituted.
[0029] Since the idler wave L2 has a wide wavelength band, the seed
beam L2' incident to the nonlinear crystal 2 also has a wide
wavelength band and thus, since the pumping beam L1' enters the
nonlinear crystal 2 together with the seed beam L2' with a wide
wavelength band, the nonlinear crystal 2 generates the terahertz
wave TH with a large output and a wide wavelength band or a
wavelength band of 1 to 3 THz, for example.
[0030] At this time, in order to prevent the pumping beam L1'
having been transmitted through the nonlinear crystal 2 from
returning to the pumping beam projecting means 3, an isolator 7 is
provided on the optical axis between the one end surface 2a of the
nonlinear crystal 2 and the pumping beam projecting means 3. That
is, the isolator 7 allows transmission of the pumping beam L1 but
prevents transmission of the pumping beam L1' in an opposite
direction.
[0031] In FIG. 1, reference numeral 8 denotes a prism for taking
out the terahertz wave TH from the nonlinear crystal 2.
[0032] The reflection optical system 6 has a reflection mirror 12
having a flat-plate shaped reflection surface disposed by facing
the other end surface 2b of the nonlinear crystal 2 so as to be
perpendicular to its optical axis and a convex lens 13 disposed
between the reflection mirror 12 and the other end surface 2b of
the nonlinear crystal 2, and the convex lens 13 is disposed at a
position separated away from the other end surface 2b of the
nonlinear crystal 2 only by a focal distance f of the convex lens
13.
[0033] Therefore, the pumping beam L1 emitted on the optical axis
thereof from the other end surface 2b of the nonlinear crystal 2 is
transmitted on the optical axis of the convex lens 13 and is
reflected by the reflection mirror 12, transmitted on the optical
axis of the convex lens 13 again and enters as the pumping beam L1'
into the other end surface 2b of the nonlinear crystal 2 from on
the optical axis.
[0034] On the other hand, regarding the idler wave L2 emitted from
the other end surface 2b of the nonlinear crystal 2, since the
convex lens 13 is disposed at a position separated away from the
other end surface 2b of the nonlinear crystal 2 only by the focal
distance f of the convex lens 13, it is refracted so as to be in
parallel with the optical axis of the nonlinear crystal 2 when it
is transmitted through the convex lens 13 and is reflected by the
reflection mirror 12 on the same optical axis.
[0035] Then, the idler wave L2 reflected on the same optical axis
is refracted again when it is transmitted through the convex lens
13 and enters as the seed beam L2' into the other end surface 2b of
the nonlinear crystal 2 at the same angle as that of the idler wave
L2 emitted from the other end surface 2b of the nonlinear crystal
2.
[0036] As a result, the terahertz wave TH generated in the
nonlinear crystal 2 has a large output and a wide wavelength band
as described above.
[0037] By allowing the terahertz wave TH output from the nonlinear
crystal 2 transmitted through or reflected by a test object such as
a container, an envelope or a biological sample, not shown, and by
applying spectral analysis to a wavelength component absorbed by
the test object from a test beam obtained by that, the components,
characteristics and the like of the test object can be tested. At
that time, since the terahertz TH has a wide wavelength band, the
test beam also has a wide wavelength band and thus, the components
and the like of the test object can be tested at one time by the
terahertz wave TH with a wide wavelength band.
[0038] The terahertz TH output from the nonlinear crystal 2 has a
wide wavelength band, but in the illustrated embodiment, it is
constituted such that a terahertz wave TH1 with a narrow wavelength
band can be selectively generated.
[0039] That is, in the illustrated embodiment, by providing the
wavelength selecting means 11 for preventing the passing of a part
of the beam between the reflection mirror 12 and the convex lens 13
and by providing a passing portion 11a such as a slit in a
shielding plate of a rectangular thin plate shape constituting a
body portion of the wavelength selecting means 11, it is
constituted that transmission of only the idler wave L2 with the
specific wavelength can be selected from the idler wave L2 having a
wide wavelength band having passed through the convex lens 13.
[0040] The passing portion 11a has a laterally long shape elongated
in a direction perpendicular to the paper surface of FIG. 1 so that
substantially one wavelength can be selected, whereby passage of
only the specific wavelength through the passing portion 11a is
allowed from the idler wave L2 having a wide wavelength band, while
passage of the other wavelengths can be shut off by the wavelength
selecting means 11. The passing portion 11a has a laterally long
shape elongated in the direction perpendicular to the paper surface
of FIG. 1 because a sectional shape of the idler wave L2 is a
substantially elliptic shape which is laterally long in the
direction perpendicular to the paper surface of FIG. 1 as described
above.
[0041] Furthermore, in the wavelength selecting means 11, a passing
portion 11b allowing the transmission of the pumping beams L1, L1'
is provided, and a damper portion 11c for absorbing the other idler
wave L2 described above in the two idler wave L2, L2 generated from
the other end surface 2b of the nonlinear crystal 2 is provided as
described above.
[0042] As described above, by providing the passing portion 11a in
the wavelength selecting means 11 so as to allow the passage of the
idler wave L2 only with the specific wavelength, the seed beam L2'
only with the specific wavelength can be allowed to enter the
nonlinear crystal 2. As a result, the terahertz wave TH generated
by the nonlinear crystal 2 also becomes the terahertz wave TH only
with the specific wavelength depending on the seed beam L2' only
with the specific wavelength.
[0043] When the wavelength of the terahertz wave TH is to be
changed, it is only necessary to prepare a plurality of wavelength
selecting means 11 with only the position of the passing portion
11a made different and to switch them, whereby the wavelength of
the terahertz wave TH can be easily changed.
[0044] FIG. 2 illustrates a second embodiment of the present
invention, and in a reflection optical system 16 in this
embodiment, instead of the reflection mirror 12 and the convex lens
13 in the reflection optical system 6 in the first embodiment, a
reflection mirror 17 having a spherical-shaped reflection surface
facing the other end surface 2b of the nonlinear crystal 2 is
provided.
[0045] The reflection mirror 17 has a spherical-shaped reflection
surface which can reflect the idler wave L2 generated from the
other end surface 2b of the nonlinear crystal 2 toward the other
end surface 2b of the nonlinear crystal 2 as the seed beam L2'.
[0046] Moreover, the reflection mirror 17 is constituted such that
the pumping beam L1 emitted from the other end surface 2b of the
nonlinear crystal 2 on the optical axis thereof is reflected and
passed on the optical axis again so that it can enter as the
pumping beam L1' into the other end surface 2b of the nonlinear
crystal 2 from on the optical axis.
[0047] The spherical-shaped reflection mirror 17 is disposed,
assuming that it has a curvature R of its reflection surface, a
center point of the curvature is disposed at a distance L which
corresponds to the other end surface 2b of the nonlinear crystal
2.
[0048] The other constitutions are similar to the constitution of
the first embodiment, and the same reference numerals as those in
FIG. 1 are given in illustration to the same or corresponding
portions.
[0049] In the second embodiment with the aforementioned
constitution, too, by means of the passing portion 11a provided in
the wavelength selecting means 11, transmission of only the idler
wave L2 with the specific wavelength can be selected from the idler
wave L2 having a wide wavelength band and thus, the seed beam L2'
only with the specific wavelength can be allowed to enter the
nonlinear crystal 2. As a result, the terahertz wave TH generated
by the nonlinear crystal 2 also becomes the terahertz wave TH only
with the specific wavelength depending on the seed beam L2' only
with the specific wavelength.
[0050] On the other hand, by leaving the damper portion 11c of the
wavelength selecting means 11 and by omitting the other portions,
the seed beam L2' having a wide wavelength band can be allowed to
enter the nonlinear crystal 2 together with the pumping beam L1'
and thus, the terahertz wave TH with a large output and having a
wide wavelength band can be generated by the nonlinear crystal
2.
[0051] FIG. 3 is another embodiment of the aforementioned
wavelength selecting means 11, and in wavelength selecting means 21
in this embodiment, two passing portions 21a, 21b such as slits
through which two different wavelengths are passed are
provided.
[0052] Each of the passing portions 21a, 21b is formed having a
laterally long shape elongated in the direction perpendicular to
the paper surface of FIG. 1 similarly to the passing portion 11a in
the first embodiment.
[0053] In this embodiment, too, the passing portion 21c allowing
transmission of the pumping beams L1, L1' is provided, and a damper
portion 21d is provided.
[0054] According to this embodiment, a terahertz wave TH with a
large output and having two different wavelengths can be generated
from the nonlinear crystal 2.
[0055] In this embodiment, the passing portions 21a, 21b may be
provided in three or more.
[0056] FIG. 4 is still another embodiment of the aforementioned
wavelength selecting means 11, 21, and in the wavelength selecting
means 11, 21 in each of the aforementioned embodiments, when a
different wavelength is to be selected, the wavelength selecting
means 11, 21 need to be replaced with a wavelength selecting means
having a passing portion allowing transmission of a required
wavelength, but in this embodiment, the passing portion can be
moved to a different wavelength direction so that the required
wavelength can be selected without replacing the wavelength
selecting means.
[0057] That is, the wavelength selecting means 31 of this
embodiment is configured so that four different wavelengths can be
selected and for that purpose, the wavelength selecting means 31
includes a first shielding plate 32 and a second shielding plate 33
overlapping it. One of them, that is, the first shielding plate 32
is provided movably by a member, not shown, to a right-left
direction on the paper surface indicated by an arrow in FIG. 4 with
respect to the reflection optical system 6 or 16, that is, in the
direction perpendicular to the paper surface of FIG. 1, and two
parallel optical passing portions 32a, 32b such as slits are formed
in the first shielding plate 32 diagonally to the direction
perpendicular to the paper surface of FIG. 1.
[0058] Moreover, in the first shielding plate 32, the passing
portion 32c for the pumping beams L1, L1' and the damper portion
32d for the idler wave L2 are provided.
[0059] On the other hand, the other second shielding plate 33 is
fixed to the first shielding plate 32 or the reflection optical
system 6 or 16 by a member, not shown, and the second shielding
plate 33, two parallel passing portions 33a, 33b such as slits are
formed in a vertical direction of the paper surface of FIG. 4 (FIG.
1).
[0060] Moreover, the second shielding plate 33 is formed having an
elongated rectangular shape as compared with the first shielding
plate 32 so that it does not cover the passing portion 32c for the
pumping beams L1, L1' formed in the first shielding plate 32.
[0061] By overlapping each of the passing portions 32a, 32b, 33a,
and 33b, transmission of the idler wave L2 and the seed beam L2' is
allowed only at the intersection of each of the passing
portions.
[0062] According to this embodiment, the terahertz wave TH having
four different wavelengths can be generated by four intersections
of each of the passing portions 32a, 32b, 33a, and 33b.
[0063] When the wavelength to be selected is to be made different,
it is only necessary to move the first shielding plate 32 to the
arrow direction with respect to the second shielding plate 33,
whereby positions of the intersections of each of the passing
portions 32a, 32b, 33a, and 33b can be moved, and the wavelength to
be selected can be made different.
[0064] In this embodiment, the number of the passing portions 32a
and 32b provided in the first shielding plate 32 and the number of
passing portions 33a and 33b provided on the second shielding plate
33 only need to be one or more, respectively.
REFERENCE SIGNS LIST
[0065] 1 terahertz wave generator [0066] 2 nonlinear crystal [0067]
2a one end surface [0068] 2b the other end surface [0069] 3 pumping
beam projecting means [0070] 6, 16 reflection optical system [0071]
11, 21, 31 wavelength selecting means [0072] 11b, 21c, 32c passing
portion [0073] 11a, 21a, 21b, 32a, 32b passing portion [0074] 11c,
21d, 32d damper portion [0075] 12, 17 reflection mirror [0076] 13
convex lens [0077] L1, L1' pumping beam [0078] L2 idler wave [0079]
L2' seed beam [0080] TH terahertz wave
* * * * *