Abstract
The invention is related to a parametric light generation method and its application and belongs to the technical field of laser and nonlinear optics. The generation method comprises steps as follows: a nonlinear optical material that meets the sum-frequency phase-matched conditions, namely it shall satisfy the energy conservation condition ω.sub.p+ω.sub.i=ω.sub.s and the momentum conservation condition n.sub.pω.sub.p+n.sub.iω.sub.i=n.sub.sω.sub.s simultaneously, is provided; laser light with a wavelength of λ.sub.p is injected into the said nonlinear optical material as pump light; then, the material will output signal light with a wavelength of λ.sub.s, namely the tunable sum-frequency parametric light. With sum-frequency as the basic principle, the invention can realize frequency up-conversion and obtain visible and UV light sources through simple infrared light sources easily.
Claims
1. A parametric light generation method, which comprises steps as follows: a nonlinear optical material that meets the sum-frequency phase-matched conditions is provided, that is, it shall satisfy the energy conservation condition ω.sub.p+ω.sub.i=ω.sub.s and the momentum conservation condition n.sub.pω.sub.p=n.sub.iω.sub.i+n.sub.sω.sub.s simultaneously, where s denotes signal light, p denotes pump light, and i denotes idle frequency light; laser light with a wavelength of λ.sub.p is injected into the said nonlinear optical material as pump light. Then, the material will output signal light with a wavelength of λ.sub.s, namely the tunable sum-frequency parametric light.
2. The said parametric light generation method according to claim 1, characterized in that the sum-frequency phase-matching conditions can be changed continuously by adjusting the space direction, temperature, voltage, or microstructure parameters of the nonlinear optical material to realize the continuous change of λ.sub.s and the output of the tunable sum-frequency parametric light.
3. The said parametric light generation method according to claim 1, characterized in that light waves with wavelengths of λ.sub.i and λ.sub.s are generated and amplified spontaneously by the nonlinear optical material through parametric scattering or parametric fluorescence; or, light waves with wavelengths of λ.sub.i and λ.sub.s are generated and amplified spontaneously by the nonlinear optical material through parametric scattering or parametric fluorescence, and, in the resonant cavity formed by adding cavity mirrors at both ends of the nonlinear optical material, the signal light will make multiple round trips to gain significantly enhanced output; or, signal light λ.sub.s, λ.sub.p, and λ.sub.s with lower energy are provided at the input end, and they will interact with each other on the premises of satisfying the sum-frequency phase-matching conditions to amplify the signal light significantly at the output end at the cost of consuming the pump light.
4. The said parametric light generation method according to claim 1, characterized in that the said nonlinear optical material is a bulk crystal with a single structure, a crystal with a periodic structure that can realize quasi-phase matching, an ordinary optical fiber, or a photonic crystal fiber.
5. The said parametric light generation method according to claim 4, characterized in that the said bulk crystal is GdCOB, YCOB, KDP, or BBO.
6. The said parametric light generation method according to claim 1, characterized in that the pulse laser is to be used as the pump light.
7. The said parametric light generation method according to claim 1, characterized in that the pump light is to be focalized or reduced in beams for space shaping to boost its power density and improve the output energy and conversion efficiency of the signal light.
8. The said parametric light generation method according to claim 1, characterized in that the 1540 nm femtosecond laser is to be used as the pump light: when the nonlinear optical material is a GdCOB crystal processed along (θ=146°, ϕ=0°), the tunable laser output at the visible waveband of 485-770 nm can be obtained by rotating the crystal to adjust the sum-frequency phase-matching conditions; when the nonlinear optical material is a YCOB crystal processed along (θ=140°, ϕ=0°), the tunable laser output at the visible waveband of 450-770 nm can be obtained by rotating the crystal to adjust the sum-frequency phase-matching conditions.
9. The said parametric light generation method according to claim 1, characterized in that the 1056 nm femtosecond laser is used as the pump light, and when the nonlinear optical material is a YCOB crystal processed along (θ=149°, ϕ=0°), the tunable laser output at the visible waveband of 425-528 nm can be obtained by rotating the crystal to adjust the sum-frequency phase-matching conditions; or, the 1056 nm femtosecond laser is used as the pump light, and when the nonlinear optical material is a KDP crystal processed along (θ=41°, ϕ=45°), the tunable laser output at the visible waveband of 390-670 nm can be obtained by rotating the crystal to adjust the sum-frequency phase-matching conditions; or, the 1053 nm femtosecond laser is used as the pump light, and when the nonlinear optical material is a β-BBO crystal processed along (θ=23°, ϕ=30°), the tunable laser output at the visible waveband of 185-526.5 nm can be obtained by rotating the crystal to adjust the sum-frequency phase-matching conditions.
10. Any of the following applications of the said parametric light generation method according to claim 1: the sum-frequency parametric light generation of the lithography machine (193 nm) and the medical diagnosis and radiation treatment (325 nm); the dual-wavelength sum-frequency parametric light generation of the ultraviolet differential absorption laser radar; the dual-wavelength sum-frequency parametric light generation of the hemoglobin detection in carbon monoxide poisoning; the dual-wavelength sum-frequency parametric light generation for the treatment of intractable port-wine stains; the sum-frequency parametric light generation of the white light laser.
11. A parametric light generator which comprises a pump light source and a nonlinear optical medium sequentially arranged along the optical path; the nonlinear optical medium satisfies the energy conservation condition ω.sub.p+ω.sub.i=ω.sub.s and the momentum conservation condition n.sub.pω.sub.p+n.sub.iω.sub.i=n.sub.sω.sub.s simultaneously, where s denotes signal light, p denotes pump light, and i denotes idle frequency light.
12. The said parametric light generating device according to claim 11, characterized in that a focusing lens is also provided between the pump light source and the nonlinear optical medium.
13. The said parametric light generating device according to claim 12, characterized in that a color filter is also arranged behind the nonlinear optical medium along the light path; preferably, an input mirror of optical parametric oscillation is provided between the focusing lens and the nonlinear optical medium along the light path, and an output mirror of optical parametric oscillation is provided behind the nonlinear optical medium.
14. The said parametric light generating device according to claim 12, characterized in that a signal light source, a signal light reflecting mirror, and a beam combiner for the pump light and the signal light are also provided to enable the signal light generated by the signal light source to enter the focusing lens together with the pump light generated by the pump light source upon the reflecting of the signal light reflecting mirror and the combining of the beam combiner for the pump light and the signal light.
15. The said parametric light generating device according to claim 12, characterized in that behind the nonlinear optical medium is provided the second nonlinear optical medium along the optical path, between the pump light source and the nonlinear optical medium are provided the front mirror and the rear mirror of the beam reduction system, and a color filter is arranged behind the second nonlinear optical medium.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0050] FIG. 1 is the mechanism diagram of the sum-frequency parametric light generation in the invention: the cascade transition process of the one-photon absorption, relaxation, and sum-frequency; the cascade transition process of the two-photon absorption, relaxation, and sum-frequency; the cascade transition process of the three-photon absorption, relaxation, and sum-frequency; and another cascade transition process of the three-photon absorption, relaxation, and sum-frequency.
[0051] FIG. 2 shows the diagram of the installation for the “sum-frequency optical parametric generation” solution as described in Embodiments 1, 3, 4, 5, 6, and 7 of the invention.
[0052] FIG. 3 shows the diagram of the installation for the “sum-frequency optical parametric oscillation” solution described in the invention.
[0053] FIG. 4 shows the diagram of the installation for the “sum-frequency optical parametric amplification” solution described in the invention.
[0054] FIG. 5 shows the spectrogram obtained via the “sum-frequency optical parametric generation” solution based on 1540 nm pump light and a GdCOB crystal as described in Embodiment 1 of the invention.
[0055] FIG. 6 shows the theoretical and experimental data obtained via the “sum-frequency optical parametric generation” solution based on 1540 nm pump light and a GdCOB crystal as described in Embodiment 1 of the invention.
[0056] FIG. 7 shows the diagram of the installation for the “sum-frequency optical parametric generation” solution based on 1540 nm pump light and a GdCOB crystal as described in Embodiment 2 of the invention.
[0057] FIG. 8 shows the spectrogram obtained via the “sum-frequency optical parametric generation” solution based on 1540 nm pump light and a GdCOB crystal as described in Embodiment 2 of the invention.
[0058] FIG. 9 shows the spot contrast diagram obtained via the “sum-frequency optical parametric generation” solution based on 1540 nm pump light and a GdCOB crystal as described in Embodiment 1 and Embodiment 2 of the invention.
[0059] FIG. 10 shows the spectrogram obtained via the “sum-frequency optical parametric generation” solution based on 1540 nm pump light and a YCOB crystal as described in Embodiment 3 of the invention.
[0060] FIG. 11 shows the theoretical and experimental data obtained via the “sum-frequency optical parametric generation” solution based on 1540 nm pump light and a YCOB crystal as described in Embodiment 3 of the invention.
[0061] FIG. 12 shows the spectrogram obtained via the “sum-frequency optical parametric generation” solution based on 1056 nm pump light and a YCOB crystal as described in Embodiment 4 of the invention.
[0062] FIG. 13 shows the theoretical and experimental data obtained via the “sum-frequency optical parametric generation” solution based on 1056 nm pump light and a YCOB crystal as described in Embodiment 4 of the invention.
[0063] FIG. 14 shows the spectrogram obtained via the “sum-frequency optical parametric generation” solution based on 1056 nm pump light and a KDP crystal as described in Embodiment 5 of the invention.
[0064] FIG. 15 shows the theoretical and experimental data obtained via the “sum-frequency optical parametric generation” solution based on 1056 nm pump light and a KDP crystal as described in Embodiment 5 of the invention.
[0065] FIG. 16 shows the diagram of the installation for the “sum-frequency optical parametric generation” solution capable of outputting dual-wavelength signal light as described in Embodiments 8, 9, and 10 of the invention.
[0066] Where 1. Pump light source, 2. Pump light with a wavelength of λ.sub.p, 3. Focusing lens, 4. Non-linear optical medium, 5. Color filter, 6. Signal light with a wavelength of λ.sub.s, 7. Input mirror of optical parametric oscillation, 8. Output mirror of optical parametric oscillation, 9. Signal light source, 10. Signal light reflecting mirror, 11. Beam combiner of the pump light and the signal light, 12. Front mirror of the beam reduction system, 13. Rear mirror of the beam reduction system, 14. The first non-linear optical medium, 15. The second non-linear optical medium.
Detailed Embodiments
[0067] The invention is further described in combination with the attached figures and embodiments as follows, but the protection scope of the present invention is not limited to this.
[0068] The invention presents a parametric light generation method, which comprises steps as follows: A nonlinear optical material that meets the sum-frequency phase-matched conditions is provided. That is it shall satisfy the energy conservation condition ω.sub.p+ω.sub.i=ω.sub.s (namely 1/λ.sub.p+1/λ.sub.i=1/λ.sub.s) and the momentum conservation condition n.sub.pω.sub.p+n.sub.iω.sub.i=n.sub.sω.sub.s simultaneously. Laser light with a wavelength of λ.sub.p is injected into the said nonlinear optical material as pump light. Then, the material will output signal light with a wavelength of λ.sub.s. The sum-frequency phase-matching conditions can be changed continuously by adjusting the space direction, temperature, voltage, or microstructure parameters of the nonlinear optical material to realize the continuous change of λ.sub.s and output the tunable sum-frequency parametric light. On this basis, different technical routes can be selected depending on the needs, and the corresponding installations also vary. [0069] (1) As shown in FIG. 2, the pump light source 1 and the focusing lens 3 are both arranged along the optical path. Among them, the pump light source 1 is used to generate the pump light with a wavelength of λ.sub.p, and the focusing lens 3 plays a focusing role to improve the power density of the pump light 2. For the non-linear optical medium 4, only the pump light is input from outside, and the light waves with wavelengths of λ.sub.i and λ.sub.s are generated and amplified spontaneously by the nonlinear optical material through parametric scattering or parametric fluorescence. At the end of the non-linear optical medium 4, the color filter 5 will filter out the residual pump light λ.sub.p and the idle frequency light λ.sub.i to obtain the pure signal light 6 with a wavelength of λ.sub.s. The invention refers to this solution as “sum-frequency optical parametric generation”. [0070] (2) As shown in FIG. 3, the pump light source 1 and the focusing lens 3 are both arranged along the optical path. Among them, the pump light source 1 is used to generate the pump light with a wavelength of λ.sub.p, and the focusing lens 3 plays a focusing role to improve the power density of the pump light 2. For the non-linear optical medium 4, only the pump light is input from outside, and the light waves with wavelengths of λ.sub.i and λ.sub.s are generated and amplified spontaneously by the nonlinear optical material through parametric scattering or parametric fluorescence. In the resonant cavity formed by adding cavity mirrors at both ends of the nonlinear optical material, the signal light will make multiple round trips to gain significantly enhanced output. The input mirror of the optical parametric oscillation 7 presents a high transmittance for the pump light and high reflectivity in the waveband of the signal light, and the output mirror of the optical parametric oscillation 8 presents a high reflectivity for the pump light and allows only part of the signal light to pass through, so the signal light 6 with a wavelength of λ.sub.s can be output. The invention refers to this solution as “sum-frequency optical parametric oscillation”. [0071] (3) As shown in FIG. 4, arranged along the optical path, the pump light source 1 generates the high-intensity pump light 2 with a wavelength of λ.sub.p, and the signal light source 9 generates the low-intensity signal light 6 with a wavelength of λ.sub.s. Upon going through the signal light reflecting mirror 10 and the beam combiner of the pump light and the signal light 11, the signal light will be combined with the pump light 2 with a wavelength of λ.sub.p (the signal light reflecting mirror 10 presents a high reflectivity for the signal light, and the beam combiner for the pump light and the signal light 11 presents a high reflectivity for the signal light and high transmittance for the pump light). The combined light then is focalized into the non-linear optical medium 4 by the focusing lens 3. λ.sub.p and λ will interact with each other on the premises of satisfying the sum-frequency phase-matching conditions to amplify the signal light significantly at the output end at the cost of consuming the pump light. The color filter 5 will filter out the residual pump light λ.sub.p and the newly generated idle frequency light λ to obtain the pure and high-energy signal light 6 with a wavelength of λ.sub.s. If the signal light source 9 is tunable in wavelengths, the signal light with high energy and tunable wavelengths can be obtained at the output end, by adjusting the sum-frequency phase-matching conditions of the non-linear optical medium 4 according to the wavelengths of the signal light source 9. The invention refers to the solution as “sum-frequency optical parametric amplification”.
[0072] The focusing lens 3 in the above three solutions can be replaced by an optical beam reduction system formed by two convex lenses with different focal lengths to improve the beam quality of the output light and reduce divergence.
[0073] Based on the three representative technical solutions above, a low-cost, miniaturized, wide-band tunable, precise, reliable, simple and effective frequency up-conversion laser device can be produced. Its signal light can meet the needs for tunable laser light in many fields. All sum-frequency parametric light generation methods based on the sum-frequency optical parametric generation mechanism as described in the invention and derived from the above solutions, as well as the related applications thereof, are within the scope of protection of the invention.
Embodiment 1
[0074] A “sum-frequency optical parametric generation” solution with a GdCOB crystal pumped by a 1540 nm laser as the non-linear optical medium, which follows the mechanism as shown in B and C of FIG. 1. The installation is as shown in FIG. 2, with all parts arranged along the optical path. Among them, the pump light source 1 is an ultrafast laser with a wavelength of 1540 nm, a pulse width of 160 fs, and a repeated frequency of 100 kHz, the focusing lens 3 is with a 200 mm focal length, the non-linear optical medium 4 is a GdCOB crystal with the size of 6×6×10 mm.sup.3 and processed along (θ=146°, ϕ=0°), and the color filter 5 presents a high reflectivity for the wavelength 1540 nm and high transmittance for the waveband 300-800 nm. The test result of the solution is shown in FIG. 5 and FIG. 6.
[0075] FIG. 5 shows the signal light spectra obtained in different positions when the GdCOB crystal is rotated, where Figure A is the spectrum of the pump light (λ.sub.p=1540 nm), and Figure B is the spectrum of the frequency doubling output (λ.sub.p=770 nm) realized during the normal incidence of the crystal. The light path of the pump light in the crystal can be continuously changed by rotating the GdCOB crystal to satisfy the different sum-frequency phase-matching conditions, thereby realizing the continuous change of the wavelength λ.sub.s of the signal light and the output of the tunable sum-frequency parametric light. Based on the refraction law, the direction of light propagation within the crystal can be calculated from the external rotation angle of the crystal. Figures C through to H show the spectra of the signal light obtained in several representative directions, namely θ=149.4°, 151.1°, 153.3°, 156.0°, 157.8°, and 161.5°. The ϕ is fixed as 0°, namely the crystal is rotated in its XZ principal plane only. The test results show that the installation can generate sum-frequency parametric light of 485-770 nm.
[0076] FIG. 6 (A) shows the sum-frequency phase-matching curve (1/λ.sub.p+1/λ.sub.i=1/λ.sub.s, where: λ.sub.v=1540 nm, λ.sub.s denotes the bottom X-coordinate, the corresponding λ.sub.i denotes the top X-coordinate, and the Y-coordinate is the phase-matching angle θ) calculated for Embodiment 1, as well as the corresponding experimental points. As can be seen from Figure A, the theoretical results agree well with the measured values, thus confirming that this effect is a sum-frequency process. In addition, as the pump light polarizations are observed to be mutually perpendicular to the signal light polarizations, this phase matching turns out to be type-I. Figure B shows the relationship between the effective nonlinear optical coefficient d.sub.eff and the wavelength λ.sub.s of the signal light. As can be seen from Figure B, the d.sub.eff increases along with the λ.sub.s. Such a calculated law agrees with the experimental law obtained in Figure C, namely the output power and conversion efficiency of the signal light increases with the increase of the λ.sub.s and, at the same time, the pump threshold reduces. Figure D shows the change relationship between the output power of the signal light and that of the pump light when λ.sub.s=622 nm: the pump threshold is 86 mW, and the corresponding pump power density is 826 MW/cm.sup.2; under the 124 mW pump power, the signal light output is 3.7 mW, and the optical conversion efficiency is 3.0%. If the pump light source and the non-linear optical medium are kept unchanged, the “sum-frequency optical parametric oscillation” solution in FIG. 3 can reduce the pump threshold and further improve the output power and conversion efficiency.
Embodiment 2
[0077] A “sum-frequency optical parametric generation” solution with a GdCOB crystal pumped by a 1540 nm laser as the non-linear optical medium, which follows the mechanism as shown in B and C of FIG. 1. The installation is as shown in FIG. 7, with all parts arranged along the optical path. Distinguished from that in FIG. 2, this installation uses an optical beam reduction system formed by two convex lenses with different focal lengths to replace the focusing lens 3. The pump light beam reduction system comprises the front mirror 12 and the rear mirror 13 in replacement of the focusing lens 3 as shown in FIG. 2. Therefore, the incident pump light beam of the crystal has better parallelism.
[0078] Among them, the pump light source 1 is an ultrafast laser with a wavelength of 1540 nm, a pulse width of 160 fs, and a repeated frequency of 100 kHz; the focal lengths of the front mirror 12 and the rear mirror 13 of the beam reduction system are 300 mm and 100 mm respectively, so the beam reduction ratio is 3:1; the non-linear optical medium 4 is a GdCOB crystal with the size of 6×6×10 mm.sup.3 processed along (θ=146°, ϕ=0°); and, the color filter 5 presents a high reflectivity for the wavelength 1540 nm and high transmittance for the waveband 300-800 nm.
[0079] The test result of the solution is shown in FIG. 8. It shows the signal light spectra obtained in different positions when the GdCOB crystal is rotated. The light path of the pump light in the crystal can be continuously changed by rotating the GdCOB crystal to satisfy the different sum-frequency phase-matching conditions, thereby realizing the continuous change of the wavelength λ of the signal light and the output of the tunable sum-frequency parametric light. The test results show that the installation can be used to generate sum-frequency parametric light of 490-770 nm. As the crystal sample used in the test has good parallelism at the two end faces and can form partial resonant cavity under uncoated conditions, which is conducive to the output of frequency-doubled light in the tangential direction (namely in the frequency doubling direction of 1540 nm), frequency doubling signals with a wavelength of 770 nm are detected, more or less, in each spectrum. If frequency-doubled light is undesirable, the frequency-doubled signals in the tunable output may be eliminated through such technological means as reducing the parallelism of the end faces of the crystal, coating the two end faces with fundamental-frequency antireflective (AR) film, and coating the output end with the frequency-doubled high-reflective (HR) film.
[0080] FIG. 9 shows the light spot images of the installation in FIG. 2 and that in FIG. 7, among which Figure A shows the light spot of the signal light (λ.sub.s=497 nm) obtained by the installation in FIG. 2, and Figure B shows the light spot of the signal light (λ.sub.s=490 nm) obtained by the installation in FIG. 7. The comparison shows that the pump light beam reduction solution is more beneficial to obtaining light spots with higher beam quality.
Embodiment 3
[0081] A “sum-frequency optical parametric generation” solution with a YCOB crystal pumped by a 1540 nm laser as the non-linear optical medium, which follows the mechanism as shown in B of FIG. 1. The installation is as shown in FIG. 2, with all parts arranged along the optical path. Among them, the pump light source 1 is an ultrafast laser with a wavelength of 1056 nm, a pulse width of 160 fs, and a repeated frequency of 100 kHz, the focusing lens 3 is with a 200 mm focal length, the non-linear optical medium 4 is a YCOB crystal with the size of 4×4×10 mm.sup.3 and processed along (θ=149°, ϕ=0°), and the color filter 5 presents a high reflectivity for the wavelength 1064 nm and high transmittance for the waveband 300-800 nm. The test results of the solution are shown in FIG. 10 and FIG. 11.
[0082] FIG. 10 shows the signal light spectra obtained in different positions when the YCOB crystal is rotated, where Figure A is the spectrum of the pump light (λ.sub.p=1540 nm), and Figure B is the spectrum of the frequency doubling output (λ.sub.s=770 nm) realized during the normal incidence of the crystal. The light path of the pump light in the crystal can be continuously changed by rotating the YCOB crystal to satisfy the different sum-frequency phase-matching conditions, thereby realizing the continuous change of the wavelength λ.sub.s of the signal light and the output of the tunable sum-frequency parametric light. Based on the refraction law, the direction of light propagation within the crystal can be calculated from the external rotation angle of the crystal. Figures C through to H show the spectrums of the signal light obtained in several representative directions, namely θ=142.8°, 144.6°, 147.0°, and 149.8°. The ϕ is fixed as 0°, namely the crystal is rotated in its XZ principal plane only. The test results show that the installation can generate sum-frequency parametric light of 450-770 nm.
[0083] FIG. 11 shows the sum-frequency phase-matching curve (1/λ.sub.p+1/λ.sub.i=1/λ.sub.s, where: λ.sub.p=1540 nm, λ.sub.s denotes the bottom X-coordinate, the corresponding λ.sub.i denotes the top X-coordinate, and the Y-coordinate is the phase-matching angle θ) calculated for Embodiment 3, as well as the corresponding experimental points. As can be seen from FIG. 11, the theoretical results agree well with the measured values, thus confirming that this effect is a sum-frequency process. In addition, as the pump light polarizations are observed to be mutually perpendicular to the signal light polarizations, this phase matching turns out to be type-I. If the pump light source and the non-linear optical medium are kept unchanged, the “sum-frequency optical parametric oscillation” solution in FIG. 3 can reduce the pump threshold and further improve the output power and conversion efficiency.
Embodiment 4
[0084] A “sum-frequency optical parametric generation” solution with a YCOB crystal pumped by a 1056 nm laser as the non-linear optical medium, which follows the mechanism as shown in B and C of FIG. 1. The installation used is similar to that shown in FIG. 2, with all parts arranged along the optical path. Among them, the pump light source 1 is an ultrafast laser with a wavelength of 1540 nm, a pulse width of 160 fs, and a repeated frequency of 100 kHz, the focusing lens 3 is with a 200 mm focal length, and the non-linear optical medium 4 is a YCOB crystal with the size of 6×6×10 mm.sup.3 and processed along (θ=140°, ϕ=0°). As there is no suitable color filter, the solution uses no color filter 5. The test result of the solution is shown in FIG. 12 and FIG. 13.
[0085] FIG. 12 shows the signal light spectra obtained in different positions when the YCOB crystal is rotated, where Figure A is the spectrum of the pump light (λ.sub.p=1056 nm), and Figure B is the spectrum of the frequency doubling output (λ.sub.s=528 nm) realized during the normal incidence of the crystal. The light path of the pump light in the crystal can be continuously changed by rotating the YCOB crystal to satisfy the different sum-frequency phase-matching conditions, thereby realizing the continuous change of the wavelength λ.sub.s of the signal light and the output of the tunable sum-frequency parametric light. Based on the refraction law, the direction of light propagation within the crystal can be calculated from the external rotation angle of the crystal. Figures C through to F show the spectra of the signal light obtained in several representative directions, namely θ=150.6°, 152.5°, 154.9°, and 157.3°. The ϕ is fixed as 0°, namely the crystal is rotated in its XZ principal plane only. The test results show that the installation can generate sum-frequency parametric light of 425-528 nm.
[0086] FIG. 13 shows the sum-frequency phase-matching curve (1/λ.sub.p+1/λ.sub.i=1/λ.sub.s, where: λ.sub.p=1056 nm, λ.sub.s denotes the bottom X-coordinate, the corresponding λ.sub.i denotes the top X-coordinate, and the Y-coordinate is the phase-matching angle θ) calculated for Embodiment 4, as well as the corresponding experimental points. As can be seen from FIG. 13, the theoretical results agree well with the measured values, thus confirming that this effect is a sum-frequency process. In addition, as the pump light polarizations are observed to be mutually perpendicular to the signal light polarizations, this phase matching turns out to be type-I. If the pump light source and the non-linear optical medium are kept unchanged, the “sum-frequency optical parametric oscillation” solution in FIG. 3 can reduce the pump threshold and further improve the output power and conversion efficiency.
Embodiment 5
[0087] A “sum-frequency optical parametric generation” solution with a KDP crystal pumped by a 1056 nm laser as the non-linear optical medium, which follows the mechanism as shown in A, B, and D of FIG. 1. The installation used is similar to that shown in FIG. 2, with all parts arranged along the optical path. Among them, the pump light source 1 is an ultrafast laser with a wavelength of 1056 nm, a pulse width of 160 fs, and a repeated frequency of 100 kHz, the focusing lens 3 is with a 200 mm focal length, and the non-linear optical medium 4 is a KDP crystal with the size of 50×30×13 mm.sup.3 and processed along (θ=41°, ϕ=45°). As there is no suitable color filter, the solution uses no color filter 5. The test results of the solution are shown in FIG. 14 and FIG. 15.
[0088] FIG. 14 shows the signal light spectra obtained in different positions when the YCOB crystal is rotated, where Figure A is the spectrum of the pump light (λ.sub.p=1056 nm), and Figure B is the spectrum of the frequency doubling output (λ.sub.s=528 nm) realized during the normal incidence of the crystal. The light path of the pump light in the crystal can be continuously changed by rotating the KDP crystal to satisfy the different sum-frequency phase-matching conditions, thereby realizing the continuous change of the wavelength λ.sub.s of the signal light and the output of the tunable sum-frequency parametric light. Based on the refraction law, the direction of light propagation within the crystal can be calculated from the external rotation angle of the crystal. Figures C through to E show the spectra of the signal light obtained in several representative directions, namely θ=42.6°, 43.7°, and 44.4°. The ϕ is fixed as 45°. The test results show that the installation can generate sum-frequency parametric light with λ.sub.s of 390-670 nm.
[0089] FIG. 15 shows the sum-frequency phase-matching curve (1/λ.sub.p+1/χ.sub.i=1/χ.sub.s, where: λ.sub.p=1056 nm, λ denotes the bottom X-coordinate, the corresponding χ.sub.i denotes the top X-coordinate, and the Y-coordinate is the phase-matching angle θ) calculated for Embodiment 5, as well as the corresponding experimental points. The two refractive index dispersion equations from the literature “F. Zernike, J. Opt. Soc. Am. 54, 1215-1220, 1964” and “D. Eimerl, Ferroelectrics. 72, 95-139, 1987” are used as the basis for calculation, and the calculated results are presented by the solid line and the dotted line respectively. As can be seen from the figure, the theoretical results agree well with the measured values, on the whole, thus confirming that this effect is a sum-frequency process. Based on the recorded output light spectra, more experimental points can be obtained. As shown in Figure B, the sum-frequency theoretical calculations also agree well with the experimental value, which further confirms that this effect is a sum-frequency process. Additionally, another signal light λ.sub.s′ is also found in the experiment, and its generation mechanism corresponds to the Figure D in FIG. 1, namely 1/λ.sub.i1′+1/λ.sub.i2′=1/λ.sub.s′. As shown in Figures C and D, when λ.sub.s changes from 397 nm to 484 nm, λ.sub.s′ changes from 447 nm to 518 nm; the corresponding λ.sub.i1′ varies within 536-803 nm, and the λ.sub.i2′ within 2681-1458 nm. If the pumping source and the non-linear optical medium are kept unchanged, the “sum-frequency optical parametric oscillation” solution in FIG. 3 can reduce the pump threshold and further improve the output power and conversion efficiency.
Embodiment 6
[0090] A “sum-frequency optical parametric generation” solution with a BBO crystal pumped by a 1053 nm laser as the non-linear optical medium. The installation used is similar to that shown in FIG. 2, with all parts arranged along the optical path. Among them, the pump light source 1 is a Yb.sup.3+ ultrafast laser with a wavelength of 1053 nm, the focusing lens 3 is with a 300 mm focal length, and the non-linear optical medium 4 is a BBO crystal with the size of 10×10×10 mm.sup.3 and processed along (θ=45.8°, ϕ=30°), a direction in which the wavelength of the sum-frequency signal light is 236 nm. When the crystal is rotated in the plane of ϕ=30°, with the exterior angle changing from +30° to −30° around the normal incidence direction, the sum-frequency phase-matching angle in the crystal also changes from 62.9° to 28.7°, and the corresponding tunable range of λ is 185-395 nm, covering the entire UV band that can propagate in the air. Such a tunable light source can meet the various demands for ultraviolet coherent light. For example, the 193 nm light can be used as the ultraviolet light source in the lithography, and the 325 nm light can replace the large-volume and high-noise He—Cd ion laser for medical diagnosis and irradiating treatment, such as checking the five sense organs for cancer and acupoint radiation to treat hypertension and chronic hepatitis, etc.
Embodiment 7
[0091] A “sum-frequency optical parametric generation” solution used for the tunable frequency conversion of ultrafast and ultra-intense lasers. The installation used is similar to that shown in FIG. 2, with all parts arranged along the optical path. Among them, the pump light source 1 is an ultrafast and ultra-intense laser with a wavelength of 1053 nm and a peak power between TW and EW. As the pumping source has a high power density already, it needs no focusing. Therefore, the focusing lens 3 is omitted. The non-linear optical medium 4 is a KDP crystal with a thickness of 10 mm. Its sectional area depends on the diameter of the installation and varies between 100×100 mm.sup.2 and 500×500 mm.sup.2. Its tangent angle is (θ=46.2°, ϕ=45°), a direction in which the wavelength of the sum-frequency signal light is 660 nm and 370 nm. When the crystal is rotated in the plane of ϕ=45°, with the exterior angle changing from +7.5° to −7.5° around the normal incidence direction, the sum-frequency phase-matching angle in the crystal also changes from 51.2° to 41.2°, and the corresponding tunable range of λ.sub.s is 318-710 nm, covering the entire visible waveband. Such an installation can be used for laser fusion, studies of ultrarelativistic phenomena, and laboratory astrophysics.
Embodiment 8
[0092] A dual-wavelength sum-frequency optical parametric generator used for ultraviolet differential absorption laser radars. Its construction is as shown in FIG. 16, with all parts arranged along the optical path. Among them, the pump light source 1 is a Yb.sup.3+ ultrafast laser with a wavelength of 1053 nm, and the focal lengths of the front mirror 12 and the rear mirror 13 of the beam reduction system are 300 mm and 100 mm respectively. The first non-linear optical medium 14 is a BBO crystal with a size of 10×10×10 mm.sup.3 and a tangent angle of (θ=43°, ϕ=30°), a direction in which the wavelength of the sum-frequency signal light is 250 nm, while the second non-linear optical medium 15 is a BBO crystal with a size of 10×10×10 mm.sup.3 and a cutting angle of (θ=30°, ϕ=30°), a direction in which the wavelength of the sum-frequency signal light is 370 nm. Since the wavelengths 250 nm and 370 nm correspond to the absorption peak and valley of ozone respectively, this dual-wavelength light source can be used in UV differential absorption laser radars to accurately measure the ozone concentration in the stratosphere. In addition, by adjusting the directions or temperatures of the two crystals, the output wavelengths can be tuned to conduct UV differential absorption measurement for other gases conveniently and flexibly.
Embodiment 9
[0093] A dual-wavelength sum-frequency optical parametric generator used for hemoglobin detection of carbon monoxide poisoning. Its construction is as shown in FIG. 16, with all parts arranged along the optical path. Among them, the pump light source 1 is an ultrafast laser with a wavelength of 1550 nm, and the focal lengths of the front mirror 12 and the rear mirror 13 of the beam reduction system are 300 mm and 100 mm respectively. The first non-linear optical medium 14 is a GdCOB crystal with a size of 10×10×10 mm.sup.3 and a tangent angle of (θ=156°, ϕ=0°), a direction in which the wavelength of the sum-frequency signal light is 555 nm, while the second non-linear optical medium 15 is a YCOB crystal with a size of 10×10×10 mm.sup.3 and a tangent angle of (θ=147°, ϕ=0°), a direction in which the wavelength of the sum-frequency signal light is 540 nm. Since the wavelengths 555 nm and 540 nm basically correspond to the absorption peak and valley of carbonyl hemoglobin respectively, this dual-wavelength light source can be used to detect carbonyl hemoglobin, thus determining the extent of carbon monoxide poisoning. In addition, by adjusting the directions or temperatures of the two crystals, the output wavelengths can be tuned to measure the blood content of alcohol and other substances conveniently and flexibly.
Embodiment 10
[0094] A dual-wavelength sum-frequency optical parametric generator used to treat intractable port-wine stains. Its construction is similar to that in FIG. 7, with all parts arranged along the optical path. Among them, the pump light source 1 is a Yb.sup.3+ ultrafast laser with a wavelength of 1053 nm, and the focal lengths of the front mirror 12 and the rear mirror 13 of the beam reduction system are 300 mm and 100 mm respectively. The non-linear optical medium 4 is a KDP crystal with a size of 10×10×10 mm.sup.3 and a tangent angle of (θ=42.5°, ϕ=45°), a direction in which the wavelength of the sum-frequency signal light is 595 nm. The color filter 5 is omitted here, so the remaining pump light is output together with the signal light to form a 1053 nm and 595 nm dual-wavelength laser. The 595 nm light can be specifically absorbed by the oxyhemoglobin in blood vessels to form methemoglobin instantly The methemoglobin can hardly absorb the 595 nm light, but can absorbed the 1053 nm light. Such a synergistic thermal effect can greatly improve the therapeutic effect of the intractable port-wine stains and reduce adverse reactions. In addition, by adjusting the direction or temperature of the KDP crystal, the wavelengths of the signal light can be tuned to treat other skin complaints conveniently and flexibly.
Embodiment 11
[0095] A sum-frequency optical parametric generator capable of outputting white light. Its construction is as shown in FIG. 16, with all parts arranged along the optical path. Among them, the pump light source 1 is an ultrafast laser with a wavelength of 1550 nm, and the focal lengths of the front mirror 12 and the rear mirror 13 of the beam reduction system are 300 mm and 100 mm respectively. The first non-linear optical medium 14 is a BBO crystal with a size of 10×10×10 mm.sup.3 and a tangent angle of (θ=24.4°, ϕ=30°), a direction in which the wavelength of the sum-frequency signal light is 445 nm, while the second non-linear optical medium 15 is a BBO crystal with a size of 10×10×10 mm.sup.3 and a tangent angle of (θ=21.3°, ϕ=30°), a direction in which the wavelength of the sum-frequency signal light is 580 nm. The wavelengths 445 nm and 580 nm can realize white light output by superimposing with each other. In addition, by adjusting the directions or temperatures of the two crystals, the output wavelengths can be tuned to adjust the color temperature of the white light conveniently and flexibly.
