GB1587992A - Shifting of co2 laser radiation using rotational raman resonances in h2 and d2 - Google Patents
Shifting of co2 laser radiation using rotational raman resonances in h2 and d2 Download PDFInfo
- Publication number
- GB1587992A GB1587992A GB1727578A GB1727578A GB1587992A GB 1587992 A GB1587992 A GB 1587992A GB 1727578 A GB1727578 A GB 1727578A GB 1727578 A GB1727578 A GB 1727578A GB 1587992 A GB1587992 A GB 1587992A
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- GB
- United Kingdom
- Prior art keywords
- capillary
- infrared radiation
- molecular gas
- raman
- laser
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
- H01S3/305—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects in a gas
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optics & Photonics (AREA)
- Lasers (AREA)
- Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Description
(54) SHIFTING OF CO2 LASER RADIATION USING ROTATIONAL RAMAN
RESONANCES IN H2 AND D2 (71) We. UNITED STATES
DEPARTMENT OF ENERGY, Washington, District of Columbia 20545. United
States of America. a duly constituted department of the Government of the
United States of America. established by the
Department of Energy Organization Act of
1977 (Public Law 95-91). do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed. to be particularly described in and by the following statement:
The present invention pertains generally to infrared lasers and more particularly to stimulated Raman scattering utilizing rotational transitions in a diatomic molecular gas.
Various methods have been disclosed for shifting frequencies of conventional laser outputs in the IR spectrum. These methods have included four-wave mixing as disclosed in U.S. Patent No. 4.095.121 and Raman scattering as disclosed in U.S. Patent No.
4.061.921 of which the present invention comprises an improvement.
In each of these systems and other previous systems for IR frequency shifting to a broad range of frequencies. simplicity and overall efficiency are important factors for economic utilization of the device. By minimizing the steps required for frequency shifting. such as the elimination of the
Raman spin flip laser as set forth in the above
disclosed U.S. Patent No. 4.061.921. the
device can be simplified to reduce problems
inherent in more complex systems.
Since the stimulated Raman effect can be
produced in a single step with high conver
sion efficiencies. Raman shifting of a CO2
laser output provides high overall efficien
cies because of the high efficiencies and well developed technology of CO2 lasers. However. Raman gain in gaseous media such as
H2 or D2 in the infrared requires threshold powers for stimulated Raman scattering which are near the breakdown threshold of the diatomic molecular gas for single pass focused geometry, such as suggested by
Robert L. Byer. in an article entitled "A 16 ,tzm Source for Laser Isotope Enrichment" published in IEEE J. of Quantum Electron ices, Vol. QE 12-732-733, November 1976.
It is an object of the present invention to provide a device for shifting infrared radiation using rotational Raman resonances in a diatomic molecular gas. which device at least minimizes the disadvantages and limitations of the prior art.
Throughout the specification and claims.
the term "restrahl" is intended to mean the nearly monochromatic radiation resulting from several reflections of light or other radiation from polished surfaces of certain substances due to high reflectivity of these substances in certain bands of wavelengths.
According to the present invention there is provided a Raman laser for frequency shifting infrared radiation from an infrared radiation source comprising: an interaction cell containing a diatomic molecular gas; a capillary waveguide disposed within said interaction cell; dichroic means disposed at each end of said interaction cell for primarily reflecting frequency shifted radiation and primarily transmitting said infrared radiation from said infrared radiation source; whereby said capillary waveguide increases focal interaction length between said infrared radiation from said infrared radiation source and said diatomic molecular gas to overcome losses and produce stimulated Raman scat tered frequency shifted radiation from rotational transitions in said diatomic molecular gas.
Also in accordance with the present invention there is provided a device for producing stimulated Raman scattering from rotational transitions in a diatomic molecular gas to frequency shift infrared radiation produced by an infrared laser source comprising; and interaction cell containing said diatomic molecular gas; capillary waveguide means disposed within said interaction cell to increase focal interaction length; means for circularly polarizing said infrared radiation to increase Raman gain and reduce anti
Stokes generation within said capillary waveguide; whereby said focal interaction length is increased sufficiently within said capillary waveguide to overcome losses and produce stimulated Raman scattered frequency shifted radiation from rotational transitions in said molecular gas in a single pass of said infrared radiation through said capillary waveguide.
The present invention will be further illustrated, by way of example, with reference to the accompanying drawings, in which:
Figure 1 discloses the Raman laser of the preferred embodiment of the invention;
Figure 2 discloses a variation of the preferred embodiment of Figure 1; and
Figure 3 discloses an alternative embodiment.
Figure 1 discloses the Raman laser which comprises the preferred embodiment of the invention. CO2 input radiation 10 is applied to spatial filter 12 to eliminate "hot spots" from the spatial intensity of the beam which prevents possible demage to various mirrors and windows of the Raman oscillator. The spatially filtered beam is reflected by mirror 14 and focused by lens 16 through dichroic mirror 18 into the interaction cell 20. Dichroic mirrors 18 and 30 function to transmit the 10 ijm infrared radiation produced by the CO2 radiation source and reflect nearly all of the frequency shifted radiation generated within the interaction cell 20 produced by stimulated Ram an scattering from rotational transitions of a diatomic molecular gas such as H2 or D2.A capillary waveguide 22 is positioned within the interaction cell 20 such that the diatomic molecular gas flowing through the interaction cell 20 via gas inlet 26 and gas outlet 28 is contained within the capillary waveguide 22. A liquid nitrogen jacket 24 surrounds the primary length of the capillary waveguide 22 and functions to cryogenically cool the diatomic molecular gas to maintain ground state population. The capillary waveguide 22 is tapered at one end to minimize ablation or sputtering of the waveguide material upon the application of infrared radiation from the infrared CO2 radiation source. The capillary 22 can be constructed of "Pyrex" (Registered Trade
Mark), or quartz or of either MgO or Al203 to reduce losses as a result of restrahl reflectivity of these materials at desired IR frequencies.A LiF restrahl filter 32 reflects the frequency shifted radiation which is focused bylens34upona 14,umto 17Ccm filter36. A HgCdTe or other infrared type detector 38 is utilized to detect the presence of desired spectral lines.
In operation, the device of Fig. 1 functions as a Raman oscillator in which the capillary waveguide 22 increases the focal interaction length (L) by the length of the capillary 22.
Stimulated Raman scattering is initiated by rotational transitions of the diatomic molecular gas. Frequency shifted radiation produced by Raman scattering oscillates within the optical cavity of the Raman laser defined by dichroic mirrors 18 and 30, and a portion of this energy is emitted from the oscillating cavity via partially reflective dichroic mirror 30. The focal interaction length is therefore increased by the number of times the frequency shifted radiation traverses the length of the capillary waveguide. This large increase in the focal interaction length (L) increases the exponential gain factor (egL) by an amount sufficient to overcome losses and produce a frequency shifted output signal.
Diatomic molecular gases suitable for operation in such a device comprise both D2 and H2. Stimulated Raman scattering from rotation transitions of H2 give coverage throughout the range 13.5 to 18 1Lm using the 354 cm - ' Soo(0) transition and from 20 to 30 im using the 587 cell Soo(l) transition.
Rotational transitions of D2 give coverage from 11 ,um to 14 ,um using the 179 cell Soo(0) transition, 12.6 ,um to 16.9 ,am using the 298 cm-' Soo(l) transition. and 14.7 ,um to 21 ,u m using the 415 cm-' ' Soo(2) transition. With a tunable high pressure CO2 laser utilizing either D2 or H2, any wavelength in the range 11 m to 30 m can be generated by Raman lasing in the device of the preferred embodiment.
Figure 2 discloses a variation of the preferred embodiment of Fig. 1 in which a
Fresnel rhomb A/4 plate 44 is introduced between the spatial filter 12 and focusing optics 16. The fresnel rhomb A/4 plate 44 functions to circularly polarize the infrared radiation 10 from the infrared CO2 radiation source. When circularly polarized radiation is applied to the interaction cell 20. it increases Raman gain and reduces anti
Stokes generation in the diatomic molecular gas.
Figure 3 discloses an alternative embodiment in which CO2 IR radiation 46 is circularly polarized by Fresnel rhomb A/4 plate 52 and applied to a single pass interaction cell 72. The single pass interaction cell comprises a several meter long capillary 64 positioned within the interaction cell 72 which contains the desired diatomic molecular gas D2 or H2. The capillary is cooled by a liquid nitrogen cooling jacket or trough 68 to maintain ground state population in the diatomic molecular gas. A flat window 60 is utilized rather than a Brewster angle window because of the circular polarization of the IR radiation. The use of circularly polarized light in the embodiment of Fig. 3 is especially necessary to reduce competition from anti
Stokes generation.In the embodiment of
Fig. 3, interaction length is provided by extending the length of the capillary 64 rather than by multiple passes in the Ram an oscillator as accomplished in the devices of
Figs. land 2.
The present invention therefore provides a means for, increasing the exponential gain factor (ego) sufficiently to overcome losses in the molecular gas and produce stimulated
Raman scattered frequency shifted radiation from rotational transitions. The embodiments of the present invention have the advantage of simplicity and single step operation for generating a wide range of frequencies in the infrared spectral region.
Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than is described.
WHAT WE CLAIM IS:
1. A Raman laser for frequency shifting infrared radiation from an infrared radiation source comprising: a interaction cell containing a diatomic molecular gas; a capillary waveguide disposed within said interaction cell; dichroic means disposed at each end of said interaction cell for primarily reflecting frequency shifted radiation and primarily transmitting said infrared radiation from said infrared radiation source; whereby said capillary waveguide increases focal interaction length between said infrared radiation from said infrared radiation source and said diatomic molecular gas to overcome losses and produce stimulated Raman scattered frequency shifted radiation from rotational transitions in said diatomic molecular gas.
2. A Raman laser as claimed in claim 1, further comprising: a spatial filter aligned with said infrared radiation source; and means for focusing said infrared radiation from said infrared radiation source, said means for focusing having a short focal length to maximize radiation intensity within said capillary waveguide without causing window damage to said dichroic means.
3. A Raman laser as claimed in claim 1 or 2 wherein said capillary comprises a MgO capillary having restrahl reflectivity to reduce losses.
4. A Raman laser as claimed in claim 1 or 2 wherein said capillary comprises an Al203 capillary having restrahl reflectivity to reduce losses.
5. A Raman laser as claimed in claim 1 or 2 wherein said capillary is cryogenically cooled to maintain ground state population of said diatomic molecular gas.
6. A Raman laser as claimed in claim 1 or 2 wherein said infrared radiation source is a variable frequency CO2 laser.
7. A Raman laser as claimed in any preceding claim wherein said diatomic molecule comprises H2.
8. A Raman laser as claimed in any one of claims 1 to 6, wherein said diatomic molecule comprises D 2.
9. A Raman laser as claimed in any preceding claim, further comprising means for circularly polarizing said infrared radiation to increase Raman gain and reduce anti-Stokes generation within said capillary waveguide.
10. A Raman laser, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
11. A device for producing stimulated
Raman scattering from rotational transitions in a diatomic molecular gas to frequency shift infrared radiation produced by an infrared laser source comprising; an interaction cell containing said diatomic molecular gas; capillary waveguide means disposed within said interaction cell to increase focal interaction length; means for circularly polarizing said infrared radiation to increase
Raman gain and reduce anti-Stokes generation within said capillary waveguide; whereby said focal interaction length is increased sufficiently within said capillary waveguide to overcome losses and produce stimulated Raman scattered frequency shifted radiation from rotational transitions in said molecular gas in a single pass of said infrared radiation through said capillary waveguide.
12. A device as claimed in claim 11, further comprising means for focusing said infrared radiation at one end of said capillary waveguide at an intensity sufficient to produce frequency shifted infrared radiation.
13. A device as claimed in claim 11 or 12 further comprising means for cryogenically cooling said capillary waveguide means to maintain ground state population in said diatomic molecular gas.
14. A device as claimed in claims 11, 12 or 13. wherein said capillary waveguide means comprises a MgO capillary having restrahl reflectivity to reduce losses.
15. A device as claimed in claim 11, 12 or 13, wherein said capillary waveguide
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (20)
1. A Raman laser for frequency shifting infrared radiation from an infrared radiation source comprising: a interaction cell containing a diatomic molecular gas; a capillary waveguide disposed within said interaction cell; dichroic means disposed at each end of said interaction cell for primarily reflecting frequency shifted radiation and primarily transmitting said infrared radiation from said infrared radiation source; whereby said capillary waveguide increases focal interaction length between said infrared radiation from said infrared radiation source and said diatomic molecular gas to overcome losses and produce stimulated Raman scattered frequency shifted radiation from rotational transitions in said diatomic molecular gas.
2. A Raman laser as claimed in claim 1, further comprising: a spatial filter aligned with said infrared radiation source; and means for focusing said infrared radiation from said infrared radiation source, said means for focusing having a short focal length to maximize radiation intensity within said capillary waveguide without causing window damage to said dichroic means.
3. A Raman laser as claimed in claim 1 or 2 wherein said capillary comprises a MgO capillary having restrahl reflectivity to reduce losses.
4. A Raman laser as claimed in claim 1 or 2 wherein said capillary comprises an Al203 capillary having restrahl reflectivity to reduce losses.
5. A Raman laser as claimed in claim 1 or 2 wherein said capillary is cryogenically cooled to maintain ground state population of said diatomic molecular gas.
6. A Raman laser as claimed in claim 1 or 2 wherein said infrared radiation source is a variable frequency CO2 laser.
7. A Raman laser as claimed in any preceding claim wherein said diatomic molecule comprises H2.
8. A Raman laser as claimed in any one of claims 1 to 6, wherein said diatomic molecule comprises D 2.
9. A Raman laser as claimed in any preceding claim, further comprising means for circularly polarizing said infrared radiation to increase Raman gain and reduce anti-Stokes generation within said capillary waveguide.
10. A Raman laser, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
11. A device for producing stimulated
Raman scattering from rotational transitions in a diatomic molecular gas to frequency shift infrared radiation produced by an infrared laser source comprising; an interaction cell containing said diatomic molecular gas; capillary waveguide means disposed within said interaction cell to increase focal interaction length; means for circularly polarizing said infrared radiation to increase
Raman gain and reduce anti-Stokes generation within said capillary waveguide; whereby said focal interaction length is increased sufficiently within said capillary waveguide to overcome losses and produce stimulated Raman scattered frequency shifted radiation from rotational transitions in said molecular gas in a single pass of said infrared radiation through said capillary waveguide.
12. A device as claimed in claim 11, further comprising means for focusing said infrared radiation at one end of said capillary waveguide at an intensity sufficient to produce frequency shifted infrared radiation.
13. A device as claimed in claim 11 or 12 further comprising means for cryogenically cooling said capillary waveguide means to maintain ground state population in said diatomic molecular gas.
14. A device as claimed in claims 11, 12 or 13. wherein said capillary waveguide means comprises a MgO capillary having restrahl reflectivity to reduce losses.
15. A device as claimed in claim 11, 12 or 13, wherein said capillary waveguide
means comprises an A1203 capillary having restrahl reflectivity to reduce losses.
16. A device as claimed in any one of claims 1 I to 15, further comprising spatial filter means for eliminating hotspots in the spatial intensity of said infrared radiation,
17. A device as claimed in any one of claims 11 to 16, wherein said diatomic molecular gas comprises H2.
18. A device as claimed in any one of claims 11 to 16, wherein said molecular gas comprises D2.
19. A device as claimed in any one of claims 11 to 18 wherein said infrared laser source comprises a tunable CO2 laser.
20. A device for producing stimulated
Raman scattering from rotational transitions in a diatomic molecular gas to frequency shift infrared radiation produced by an infrared laser source, substantially as hereinbefore described with reference to and as illustrated in the accompany drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80240077A | 1977-06-01 | 1977-06-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1587992A true GB1587992A (en) | 1981-04-15 |
Family
ID=25183597
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1727578A Expired GB1587992A (en) | 1977-06-01 | 1978-05-02 | Shifting of co2 laser radiation using rotational raman resonances in h2 and d2 |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS54994A (en) |
| CA (1) | CA1089066A (en) |
| DE (1) | DE2824087A1 (en) |
| FR (1) | FR2401538A1 (en) |
| GB (1) | GB1587992A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2118768A (en) * | 1982-04-21 | 1983-11-02 | Chevron Res | Frequency shifted cavity for electromagnetic radiation |
| US4586184A (en) * | 1983-10-21 | 1986-04-29 | Chevron Research Company | Acoustically controlled frequency shifted cavity for electromagnetic radiation |
| CN113916864A (en) * | 2021-10-09 | 2022-01-11 | 中国工程物理研究院激光聚变研究中心 | ICF target internal D2Method for Raman spectrum quantitative analysis of fuel gas |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4222011A (en) * | 1978-10-03 | 1980-09-09 | The United States Of America As Represented By The United States Department Of Energy | Stokes injected Raman capillary waveguide amplifier |
| JPH02260589A (en) * | 1989-03-31 | 1990-10-23 | Power Reactor & Nuclear Fuel Dev Corp | Optical waveguide type infrared raman laser |
| JPH0330868A (en) * | 1989-06-27 | 1991-02-08 | Fuji Xerox Co Ltd | Coating material circulating apparatus for immersion coating |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3655993A (en) * | 1970-07-10 | 1972-04-11 | Bell Telephone Labor Inc | Optically rotatory dielectric-guided parametric oscillators |
| US4061921A (en) * | 1974-05-02 | 1977-12-06 | The United States Of America As Represented By The United States Energy Research & Development Administration | Infrared laser system |
-
1978
- 1978-05-02 GB GB1727578A patent/GB1587992A/en not_active Expired
- 1978-05-02 CA CA302,478A patent/CA1089066A/en not_active Expired
- 1978-05-30 FR FR7816131A patent/FR2401538A1/en not_active Withdrawn
- 1978-06-01 DE DE19782824087 patent/DE2824087A1/en not_active Withdrawn
- 1978-06-01 JP JP6628078A patent/JPS54994A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2118768A (en) * | 1982-04-21 | 1983-11-02 | Chevron Res | Frequency shifted cavity for electromagnetic radiation |
| US4697888A (en) * | 1982-04-21 | 1987-10-06 | Chevron Research Company | Frequency shifted cavity for electromagnetic radiation |
| US4586184A (en) * | 1983-10-21 | 1986-04-29 | Chevron Research Company | Acoustically controlled frequency shifted cavity for electromagnetic radiation |
| CN113916864A (en) * | 2021-10-09 | 2022-01-11 | 中国工程物理研究院激光聚变研究中心 | ICF target internal D2Method for Raman spectrum quantitative analysis of fuel gas |
| CN113916864B (en) * | 2021-10-09 | 2024-04-19 | 中国工程物理研究院激光聚变研究中心 | ICF target D2Method for quantitative analysis of Raman spectrum of fuel gas |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS54994A (en) | 1979-01-06 |
| CA1089066A (en) | 1980-11-04 |
| DE2824087A1 (en) | 1978-12-14 |
| FR2401538A1 (en) | 1979-03-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| 746 | Register noted 'licences of right' (sect. 46/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |