A method for generating ultraviolet band tunable laser

Abstract

The present invention discloses a method for generating tunable ultraviolet laser, comprising: providing a near-infrared ultrafast laser with a central wavelength of λ p as a pump light source, wherein the pump light intensity of the pump light source exceeds the self-phase modulation threshold; focusing the pump light and then injecting it into a nonlinear optical crystal, and the pump light generates self-phase modulation light λ s through the self-phase modulation effect; the nonlinear optical crystal is non-centrosymmetric; the self-phase modulation light λ s and the pump light λ p perform five-wave mixing according to the phase matching condition to generate an ultraviolet laser with an output frequency of ω o , corresponding to a wavelength of λ o ; adjusting the spatial direction of the nonlinear optical crystal to change the phase matching condition of the five-wave mixing, thereby realizing continuous tuning of the output light frequency ω o . This method has significant advantages of short wavelength, high intensity and narrow linewidth, improves the overall performance of deep ultraviolet laser output, can meet the special application requirements of many short-wavelength ultraviolet lasers, and makes up for the defects of previous technologies.

Description

Technical Field

[0001] The invention relates to the field of laser and nonlinear optics, and in particular to a method for generating ultraviolet band tunable laser. Background Art

[0002] Before the advent of lasers, people's understanding of optics was mainly limited to linear optics, that is, light beams propagating in a medium do not interfere with each other, propagate independently and are not disturbed by other light beams, and the optical parameters of the medium are independent of the intensity of the incident light. In 1960, Maiman invented the first ruby ​​laser, and laser technology developed rapidly afterwards. In 1961, Franken et al. discovered that ruby ​​lasers acted on quartz crystals to produce frequency doubling, a phenomenon that could not be explained by linear optics. In 1962, Bloembergen et al. explained this phenomenon by considering the quadratic nonlinear term in Maxwell's equations, laying the theoretical foundation for nonlinear optics. Giordmaine, Maker et al. proposed phase matching technology, which improved the efficiency of laser frequency conversion and made nonlinear optics practical.

[0003] Phase matching means that in the process of nonlinear optical frequency conversion, when the propagation speed of the incident light wave is equal to the propagation speed of the harmonic, the harmonics generated at each position are in phase and can reinforce each other, thus achieving the most effective harmonic output. On the contrary, if the phase is inconsistent, the harmonics will cancel each other out, resulting in a weakened output intensity, or even no harmonic output can be observed at all.

[0004] Patent document CN114185223A A method for generating parametric light and its application, providing a nonlinear optical material, which satisfies the sum frequency phase matching condition, that is, satisfies ω at the same time p +ω i =ω s The energy conservation condition and n p ω p +n i ω i =n s ω s The momentum conservation condition. Let the wavelength be λ p The laser is incident as pump light into the nonlinear optical material, and the material will output a wavelength of λ s The signal light is tunable and frequency parametric light. The physical basis of this technology is three-wave mixing, which is a second-order nonlinear optical effect. Patent document application number 202411245661.0 discloses a method for generating tunable lasers in the visible to deep ultraviolet band by using the composite effect of self-phase modulation and four-wave mixing. The physical basis of this technology is four-wave mixing, which is a third-order nonlinear optical effect.

[0005] Although both of the above technologies can generate ultraviolet tunable lasers, they still have the defects of low output light intensity and wide spectrum lines, and cannot meet the requirements of many high-precision applications. In order to solve the above problems, the present invention is proposed. Summary of the invention

[0006] In view of this, the present invention provides a method for generating ultraviolet tunable laser, which makes up for the shortcomings of the prior art and solves the problems of low output light intensity and wide spectrum lines in the current process of generating ultraviolet tunable laser.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] The present invention provides a method for generating ultraviolet band tunable laser, which uses an optical frequency conversion device to simultaneously realize self-phase modulation and five-wave mixing cascade effect in a single nonlinear optical crystal, thereby obtaining a tunable laser output with a frequency in the ultraviolet band, and specifically comprises the following steps: the optical frequency conversion device comprises: a pump light source, a focusing lens, a nonlinear optical crystal and a color filter arranged in sequence along an optical path; the specific method comprises:

[0009] a) Provide a central wavelength of λ p A near-infrared ultrafast laser is used as a pump light source, and the pump light intensity of the pump light source exceeds a self-phase modulation threshold;

[0010] b) focusing the pump light and injecting it into a nonlinear optical crystal, and generating a self-phase modulated light λ through a self-phase modulation effect s ; The nonlinear optical crystal is non-centrosymmetric;

[0011] c) Self-phase modulated light λ s With pump light λ p Five-wave mixing occurs according to the phase matching condition, generating an output frequency of ω o , the corresponding wavelength is λ o UV laser;

[0012] d) Adjust the spatial direction of the nonlinear optical crystal to change the phase matching condition of five-wave mixing, thereby achieving the output optical frequency ω o Continuous tuning.

[0013] Furthermore, the phase matching condition of the five-wave mixing satisfies at least one of the following energy conservation and momentum conservation conditions:

[0014] (1)ω s +ω s +ω s +ω s =ω o The energy conservation condition and n s ω s+n s ω s +n s ω s +n s ω s =n o ω o The momentum conservation condition of

[0015] (2)ω p +ω s +ω s +ω s =ω o The energy conservation condition and n p ω p +n s ω s +n s ω s +n s ω s =n o ω o The momentum conservation condition of

[0016] (3)ω p +ω p +ω s +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n s ω s +n s ω s =n o ω o The momentum conservation condition of

[0017] (4)ω p +ω p +ω p +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n p ω p +n s ω s =n o ω o The momentum conservation condition of

[0018] Among them, ω p represents the frequency of the pump light, ω s represents the frequency of the self-phase modulated light, ωo Indicates the frequency of the output light; n p represents the refractive index of the pump light in the nonlinear optical crystal, n s represents the refractive index of the self-phase modulated light in the nonlinear optical crystal, n o Represents the refractive index of the output light in the nonlinear optical crystal.

[0019] Furthermore, the step d) specifically comprises:

[0020] By continuously adjusting the spatial orientation of the nonlinear optical crystal, the refractive index of the crystal is continuously changed, and then the five-wave mixing phase matching condition satisfied by the ultrafast laser propagation in the crystal is continuously changed, so that the output light frequency ω o Continuously changing, the output is tunable laser in the visible deep ultraviolet band.

[0021] Furthermore, the pump light source is any one of the following:

[0022] Ti:sapphire femtosecond laser with a central wavelength of 800nm;

[0023] Yb with a central wavelength of 1030nm 3+ Femtosecond lasers;

[0024] Or Er with a central wavelength of 1550nm 3+ Femtosecond laser.

[0025] Furthermore, the nonlinear optical crystal satisfies the following characteristics: five-wave mixing phase matching capability, good transmission performance, and high light damage resistance threshold in the ultraviolet to near-infrared band;

[0026] The nonlinear optical crystal is made of any of the following materials:

[0027] β-BBO, CLBO and KBBF.

[0028] Furthermore, when the nonlinear optical crystal is β-BBO, when the Yb 3+ When a femtosecond laser is used as a pump source and the tangential angle of the β-BBO crystal is θ=60.8° and φ=30°, the step d) comprises: adjusting the five-wave mixing phase matching condition by rotating the β-BBO crystal, and obtaining a tunable laser output in the ultraviolet band with a wavelength range of 330-227 nm when the crystal rotates clockwise or counterclockwise in a φ=30° plane and the internal angle θ of the crystal rotates from 42.8° to 78.8°;

[0029] When the outer angle of the crystal rotates 1°, the inner angle rotates 0.6° accordingly. The light propagates in the direction of θ=60.2° in the crystal. At this time, the output light wavelength is 254nm.

[0030] Further, when the nonlinear optical crystal is β-BBO, when a titanium sapphire femtosecond laser with a central wavelength of 800 nm is used as a pump source, and the tangential angle of the β-BBO crystal is θ=58.4° and φ=30°, the step d) includes: adjusting the five-wave mixing phase matching condition by rotating the β-BBO crystal, and when the crystal rotates clockwise or counterclockwise in the φ=30° plane, and the internal angle θ of the crystal rotates from 42.5° to 74.3°, a tunable laser output in the ultraviolet band with a wavelength range of 330-230 nm is obtained;

[0031] When the outer angle of the crystal rotates 4.3°, the inner angle rotates 2.6° accordingly. The light propagates in the crystal along the direction of θ=55.8°. At this time, the output light wavelength is 266nm.

[0032] Further, when the nonlinear optical crystal is KBBF, when a Yb3+ femtosecond laser with a central wavelength of 1030 nm is used as a pump source, and the tangential angle of the KBBF crystal is θ=56.2°, φ=0°, the step d) includes: adjusting the five-wave mixing phase matching condition by rotating the KBBF crystal, and when the crystal rotates clockwise or counterclockwise in the φ=0° plane, and the internal angle θ of the crystal rotates from 36° to 76.4°, a tunable laser output in the ultraviolet band with a wavelength range of 330-180 nm is obtained;

[0033] When the external angle of the crystal rotates 14.3°, the internal angle rotates 9.5° accordingly. The light propagates in the crystal along the direction of θ=65.7°. At this time, the output light wavelength is 193nm.

[0034] Further, when the nonlinear optical crystal is KBBF, when a titanium sapphire femtosecond laser with a central wavelength of 800 nm is used as a pump source, and the tangential angle of the KBBF crystal is θ=56.4° and φ=0°, the step d) includes: adjusting the five-wave mixing phase matching condition by rotating the KBBF crystal, and when the crystal rotates clockwise or counterclockwise in the φ=0° plane, and the internal angle θ of the crystal rotates from 36° to 76.8°, a tunable laser output in the ultraviolet band with a wavelength range of 330-180 nm is obtained;

[0035] When the external angle of the crystal rotates 4.1°, the internal angle rotates 2.7° accordingly. The light propagates in the crystal along the direction of θ=59.1°. At this time, the output light wavelength is 206nm.

[0036] Furthermore, when the nonlinear optical crystal is CLBO, when the Yb 3+When a femtosecond laser is used as a pump source and the tangential angle of the CLBO crystal is θ=66.4° and φ=45°, the step d) comprises: adjusting the five-wave mixing phase matching condition by rotating the CLBO crystal, and when the crystal rotates clockwise or counterclockwise in the φ=45° plane and the internal angle θ of the crystal rotates from 56.9° to 75.9°, a tunable laser output in the ultraviolet band with a wavelength range of 330-275 nm is obtained;

[0037] When the external angle of the crystal rotates 8.1°, the internal angle rotates 5.4° accordingly. The light propagates in the direction of θ=61° in the crystal, and the output light wavelength is 311nm.

[0038] It can be seen from the above technical solution that compared with the prior art, it has the following advantages:

[0039] This method realizes the cascade of two physical mechanisms, self-phase modulation and five-wave mixing, in a single nonlinear optical crystal, thereby obtaining a laser output with a frequency in the ultraviolet band that can be continuously tuned. To achieve this frequency conversion process, the nonlinear optical crystal must simultaneously meet the following three conditions: (1) the crystal is non-centrosymmetric; (2) the incident pump light intensity must exceed the self-phase modulation threshold to produce spectral broadening and provide the fundamental frequency wave for tunable five-wave mixing; (3) the phase matching condition of five-wave mixing is met. This method uses an ultrafast near-infrared light source with a central wavelength of λ p The pump light is injected into the nonlinear optical crystal, and the crystal generates self-phase modulated light λ through the self-phase modulation effect. s , the newly generated self-phase modulated light λ s With pump light λ p According to the phase matching condition it meets, five-wave mixing is performed, and the output frequency is ω o , the corresponding wavelength is λ o The laser is located in the ultraviolet band. Continuously changing the five-wave mixing phase matching condition satisfied by the ultrafast laser propagation in the nonlinear optical crystal will continuously change the output light frequency ω o , and obtain a continuously tunable laser in the ultraviolet band. This method uses a simple device to obtain a tunable ultraviolet laser, which has the advantages of only one-step frequency conversion from near-infrared to ultraviolet, a large tunable range, high conversion efficiency, narrow spectral linewidth, low production cost, stable and reliable performance, etc. It can be widely used in laser medical treatment, photon storage, ultraviolet processing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0041] Figure 1 This is a diagram of an optical frequency conversion device;

[0042] Figure 2 The theoretical and experimental data diagram of the β-BBO crystal frequency conversion and 1030nm pumping described in Example 1;

[0043] Figure 3 This is a comparison chart of the effects of Example 1 and three-wave mixing and four-wave mixing technologies; the left picture shows the output light intensity, and the right picture shows the output spectral line width.

[0044] Figure 4 This is a theoretical data diagram of the β-BBO crystal frequency conversion and 800nm ​​pumping described in Example 2;

[0045] Figure 5 This is a theoretical data diagram of KBBF crystal frequency conversion and 1030nm pumping described in Example 3;

[0046] Figure 6 This is a theoretical data diagram of KBBF crystal frequency conversion and 800nm ​​pumping described in Example 4;

[0047] Figure 7 This is a theoretical data diagram of the CLBO crystal frequency conversion and 1030nm pumping described in Example 5;

[0048] Among them, 1. Pump light source, 2. Wavelength is λ p 1. Ultrafast pump light, 2. Focusing lens, 3. Nonlinear optical crystal, 4. Color filter, 5. Wavelength λ o The output light. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] The embodiment of the present invention discloses a method for generating ultraviolet band tunable laser, using an optical frequency conversion device, and utilizing a single nonlinear optical crystal to realize the cascade of two physical effects of self-phase modulation and five-wave mixing, thereby obtaining a continuously tunable output of ultraviolet laser. Figure 1 As shown, it comprises: a pump light source 1, a focusing lens 3, a nonlinear optical crystal 4 and a color filter 5 arranged in sequence along the optical path; the pump light source 1 emits a wavelength of λ p The ultrafast pump light 2 is focused by the focusing lens 3 and then incident on the nonlinear optical crystal 4 and enters the color filter 5, finally obtaining a wavelength of λ o The output light 6.

[0051] This method uses a fixed central wavelength λ p The near-infrared ultrafast laser is used as the pump source, and tunable frequency up-conversion is achieved by combining the two nonlinear optical effects of self-phase modulation and five-wave mixing in a single nonlinear optical crystal.

[0052] The specific process includes:

[0053] a) Provide a central wavelength of λ p A near-infrared ultrafast laser is used as a pump light source, and the pump light intensity of the pump light source exceeds a self-phase modulation threshold;

[0054] b) focusing the pump light and injecting it into a nonlinear optical crystal, and generating a self-phase modulated light λ through a self-phase modulation effect s ; The nonlinear optical crystal is non-centrosymmetric;

[0055] c) Self-phase modulated light λ s With pump light λ p Five-wave mixing occurs according to the phase matching condition, generating an output frequency of ω o , the corresponding wavelength is λ o UV laser;

[0056] d) Adjust the spatial direction of the nonlinear optical crystal to change the phase matching condition of five-wave mixing, thereby achieving the output optical frequency ω o Continuous tuning.

[0057] In this embodiment, the center frequency is ω p , the corresponding wavelength is λ p The near-infrared ultrafast laser is focused or beam-contracted and then incident on the nonlinear optical crystal, increasing the incident laser intensity until it exceeds the self-phase modulation threshold. p When the incident pump light and the newly generated self-phase modulated light propagate in the nonlinear optical crystal and meet the five-wave mixing phase matching condition, the crystal will output a frequency of ω o, the corresponding wavelength is λ o The laser is located in the ultraviolet band. Continuously changing the five-wave mixing phase matching condition satisfied by the ultrafast laser propagation in the nonlinear optical crystal will continuously change the output light frequency ω o , and obtain continuously tunable laser in the ultraviolet band.

[0058] This method uses a simple device to obtain a tunable ultraviolet laser, which has the advantages of only one-step frequency conversion from near-infrared to ultraviolet, a large tunable range, high conversion efficiency, narrow spectral linewidth, low production cost, stable and reliable performance, etc. It can be widely used in laser medical treatment, photon storage, ultraviolet processing and other fields.

[0059] The above self-phase modulation threshold varies according to the difference of the pump light source and nonlinear optical crystal used. For example, for a pump light source with a wavelength of 1030nm, a pulse width of 200fs, and a repetition frequency of 100kHz, the experimentally measured self-phase modulation threshold of a 10mm long β-BBO crystal is 199.15GW / cm 2 The pump light power density of the five-wave mixing output optical signal is 249.2GW / cm 2 For a pump light source with a wavelength of 800nm, a pulse width of 35fs, and a repetition rate of 2kHz, the self-phase modulation threshold of a β-BBO crystal of the same length is 139.15GW / cm 2 The pump light power density of the five-wave mixing output optical signal is 177.1 GW / cm 2 Under the premise that the crystal is not damaged, the higher the pump light power density, the wider the self-phase modulation spectrum generated, the higher the intensity of the output light after five-wave mixing, and the larger the tunable range.

[0060] In step c), satisfying the five-wave mixing phase matching condition means satisfying both the energy conservation condition and the momentum conservation condition, which can be divided into the following four categories according to the different properties of the participating light:

[0061] (1) Both satisfy ω s +ω s +ω s +ω s =ω o The energy conservation condition and n s ω s +n s ω s +n s ω s +n s ω s =n o ω o The momentum conservation condition of

[0062] (2) Both satisfy ω p+ω s +ω s +ω s =ω o The energy conservation condition and n p ω p +n s ω s +n s ω s +n s ω s =n o ω o The momentum conservation condition of

[0063] (3) At the same time, ω p +ω p +ω s +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n s ω s +n s ω s =n o ω o The momentum conservation condition of

[0064] (4) At the same time, ω p +ω p +ω p +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n p ω p +n s ω s =n o ω o The momentum conservation condition.

[0065] Where p represents pump light, s represents self-phase modulated light, and o represents output light; ω p represents the frequency of the pump light, ω s represents the frequency of the self-phase modulated light, ω o Indicates the frequency of the output light; n p represents the refractive index of the pump light in the nonlinear optical crystal, n s represents the refractive index of the self-phase modulated light in the nonlinear optical crystal, n o Represents the refractive index of the output light in the nonlinear optical crystal.

[0066] The so-called satisfying the five-wave mixing phase matching condition refers to satisfying any one or more of the above four conditions, which are all within the scope of protection required by the present invention.

[0067] The above-mentioned nonlinear optical crystal refers to a crystal that can meet the five-wave mixing phase matching condition. This requirement is different from the patent document CN114185223A (publication date 2022-03-15) and the application with patent application number 202411245661.0. It is a special requirement for nonlinear optical materials. The patent document CN114185223A requires that the material meet the three-wave mixing phase matching condition, while the present invention requires that the material meet the five-wave mixing phase matching condition. The requirements for the material are more stringent and there are fewer types of materials available, such as KDP (KH2PO4) crystals and ADP (NH4H2PO4) crystals known in the art. They meet the three-wave mixing phase matching condition but do not meet the five-wave mixing phase matching condition. Therefore, they are applicable to the patent document CN114185223A, but not to the present invention. The application with patent application number 202411245661.0 requires that the material meet the four-wave mixing phase matching condition, which belongs to the third-order nonlinear optical effect, and has no requirements for the symmetry of the material, while the five-wave mixing of the present invention belongs to the fourth-order nonlinear optical effect, requiring the crystal to be non-centrosymmetric. Overall, from the perspective of symmetry and refractive index, the application with patent application number 202411245661.0 has a larger material selection range than the patent document CN114185223A, and the material selection range of the patent document CN114185223A is larger than the present invention. In addition, since the higher the order of nonlinear optical frequency conversion, the smaller the nonlinear coefficient, the higher the required fundamental frequency power density, and the higher the requirement for the material's resistance to light damage, the material selection range of this patent is also the smallest and most demanding from the perspective of light damage resistance.

[0068] During use, by continuously adjusting the spatial orientation of the nonlinear optical crystal, the crystal refractive index can be continuously changed, thereby continuously changing the five-wave mixing phase matching condition satisfied by the ultrafast laser propagation in the crystal, so that the output light frequency ω o Continuously changing, outputting tunable laser in the ultraviolet band.

[0069] In one embodiment, with a fixed central wavelength λ p The near-infrared ultrafast laser pump source refers to a Ti:Sapphire femtosecond laser with a central wavelength of 800nm ​​or a Yb:Sapphire laser with a central wavelength of 1030nm. 3+ Femtosecond laser, or Er with a central wavelength of 1550nm 3+ Femtosecond laser.

[0070] The above-mentioned nonlinear optical crystals have good transmission performance, stable physical and chemical properties, high light damage resistance threshold, and five-wave mixing phase matching ability in the ultraviolet to near-infrared band, such as β-BBO (β-BaB2O4) crystal, CLBO (CsLiB6O 10 ) crystal, KBBF (KBe2BO3F2) crystal.

[0071] Previously, five-wave mixing has only been realized in quasi-phase-matched periodically polarized materials (Applied Optics, 44, 6, 1028-1031, 2005) and thin film materials (Photonics Research, 9, 317-323, 2021), all of which have limited independent wavelength output and cannot be continuously tuned. The present invention realizes five-wave mixing in bulk nonlinear crystals for the first time, and uses the change of phase matching conditions to achieve large-scale continuous tuning of five-wave mixing light, filling the gap in the current nonlinear optical frequency conversion technology. In summary, the advantages of the present invention are mainly reflected in:

[0072] (1) Special physical mechanism: The present invention adopts five-wave mixing, which is different from the three-wave mixing in the patent document CN114185223A and the four-wave mixing in the patent application No. 202411245661.0.

[0073] (2) Special material selection and processing methods. The present invention uses a non-centrosymmetric crystal with a high light damage threshold that meets the five-wave mixing phase matching conditions, and processes it along the five-wave mixing phase matching direction, which is different from the patent document CN114185223A that processes along the three-wave mixing phase matching direction, and the patent application No. 202411245661.0 that processes along the four-wave mixing phase matching direction.

[0074] (3) The pumping conditions used are different. The present invention requires an ultrafast laser with sufficiently large energy as a pump source to produce a five-wave mixing laser output, and the pumping threshold is higher than that of the patent document CN114185223A and the application with patent application number 202411245661.0. Nevertheless, since the order of the nonlinear optical effect used is higher, the output light energy increases faster as the pump light energy increases, so the overall output energy and conversion efficiency are not inferior to those of the patent document CN114185223A and the application with patent application number 202411245661.0.

[0075] (4) The use effects and application directions are different. Under the same pumping conditions, the high energy output band of patent document CN114185223A is located above 400nm, mainly concentrated in the visible light band; the high energy output band of patent application number 202411245661.0 is located at 320-400nm, mainly concentrated in the near ultraviolet band; the high energy output band of the present invention is located below 320nm, mainly concentrated in the deep ultraviolet band (see Example 1 and Figure 3 ). In comparison, the present invention has the significant advantages of short wavelength, high intensity and narrow line width, which improves the overall performance of deep ultraviolet laser output, can meet the special application requirements of many short-wavelength ultraviolet lasers, and makes up for the defects of previous technologies.

[0076] The advantages of the present invention are further illustrated by several specific embodiments below:

[0077] Example 1

[0078] β-BBO crystal was used as the nonlinear optical crystal, and Yb with a central wavelength of 1030nm was used. 3+ The scheme of "generating deep ultraviolet tunable laser through self-phase modulation and five-wave mixing cascade" with femtosecond laser as pump source. Figure 1 As shown, the components of the device are arranged along the optical path. The pump light source 1 is an ultrafast femtosecond laser with a wavelength of 1030nm, a pulse width of 200fs, a repetition rate of 100kHz, and a power of 1200mW. The focal length of the focusing lens 3 is 300mm, and the nonlinear optical crystal 4 is a β-BBO with a size of 6mm×6mm×10mm and a cutting direction of (θ=60.8°, φ=30°). Here, any spatial direction of the nonlinear optical crystal is represented by polar coordinates (θ, φ), where θ is the angle between the direction and the optical axis Z of the crystal, and φ is the azimuth, which is the angle between the projection of the direction in the XY principal plane of the crystal and the X-axis. The measured data obtained by rotating the β-BBO crystal are shown in the attached figure. Figure 2 and attached Figure 3 The independent points in .

[0079] According to the conditions of Example 1, the corresponding five-wave mixing phase matching curve can be obtained by calculation, as shown in the attached figure. Figure 2 The curve in Figure 2 is shown in Figure 2. Figure 2 It includes four different five-wave mixing phase matching situations and measured data points. It can be seen that the three theoretical curves (ω s +ω s +ω s +ω s =ω o ,ω p +ω s +ω s +ω s =ωo ,ω p +ω p +ω s +ω s =ω o ) is completely consistent with the measured data, and another theoretical curve (ω p +ω p +ω p +ω s =ω o ) is consistent with the measured data in most bands, verifying the practicality of this technical solution. When the phase matching angle θ of the crystal is rotated from 42.8° to 78.8°, a tunable laser output in the deep ultraviolet band with a wavelength of 330-227nm can be achieved.

[0080] Using the same device, in addition to observing the five-wave mixing phenomenon, the four-wave mixing reported in the patent application No. 202411245661.0 and the three-wave mixing reported in the patent document CN114185223A were also observed. The comparison of the output light of these three phenomena is shown in the attached figure. Figure 3 Attached Figure 3 The left figure shows the comparison results of the output light intensity. It can be seen that in the deep ultraviolet band of 260-310nm, compared with three-wave mixing and four-wave mixing, the output light intensity of this method is greater and the corresponding optical conversion efficiency is higher. Figure 3 The right figure shows the comparison results of the output spectral line width. In the wide band of 260-330nm, compared with three-wave mixing and four-wave mixing, the output spectral line width of this method is narrower and more monochromatic, which is also a significant advantage of fourth-order nonlinear optical frequency conversion over second-order and third-order nonlinear optical frequency conversion. From the above measured results, it can be seen that the present invention has significant advantages of greater output light intensity, narrower spectral line width and higher conversion efficiency in the ultraviolet band with a wavelength less than 300nm.

[0081] The outer angle of the crystal is rotated by 1°, and the inner angle is rotated by 0.6°. The light propagates in the direction of θ=60.2° in the crystal. At this time, the output light wavelength is 254nm. This wavelength is suitable for ultraviolet sterilization, which can destroy the molecular structure of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) in bacteria and viruses, causing growth cell death and regenerative cell death, achieving the effect of sterilization and disinfection.

[0082] Example 2

[0083] The scheme of "generating deep ultraviolet tunable laser through self-phase modulation and five-wave mixing cascade" uses β-BBO crystal as nonlinear optical crystal and Ti:Sapphire femtosecond laser with central wavelength of 800nm ​​as pump source. Figure 1As shown, the components of the device are arranged along the optical path. The pump light source 1 is an ultrafast femtosecond laser with a wavelength of 800nm, a pulse width of 35fs, a repetition rate of 2kHz, and a power of 600mW. The focal length of the focusing lens 3 is 350mm, and the nonlinear optical crystal 4 is β-BBO with a size of 6mm×6mm×10mm and a processing direction of (θ=58.4°, φ=30°). Rotate the β-BBO crystal to continuously change the five-wave mixing phase matching condition satisfied by the light transmission direction. When the phase matching angle θ of the crystal is rotated from 42.5° to 74.3°, a tunable laser output in the ultraviolet band with a wavelength of 330-230nm can be achieved, as shown in the attached figure. Figure 4 shown.

[0084] The outer angle of the crystal is rotated 4.3°, and the inner angle is rotated 2.6° accordingly. The light propagates in the crystal along the direction of θ=55.8°. At this time, the output light wavelength is 266nm. This wavelength is suitable for making ultraviolet laser imaging devices to reveal latent fingerprints. In the field of crime scene investigation and physical evidence inspection, it can reveal and extract some potential physical evidence that is not easy to observe with the naked eye, such as latent fingerprints on objects such as flower glass, mirrors, and incandescent bulbs. It has the advantages of small background interference, large contrast, and high clarity.

[0085] Example 3

[0086] KBBF crystal is used as nonlinear optical crystal, and Yb with a central wavelength of 1030nm is used as 3+ The scheme of "generating deep ultraviolet tunable laser through self-phase modulation and five-wave mixing cascade" with femtosecond laser as pump source. Figure 1 As shown, the components of the device are arranged along the optical path. The pump light source 1 is an ultrafast femtosecond laser with a wavelength of 1030nm, a pulse width of 200fs, a repetition rate of 100kHz, and a power of 1200mW. The focal length of the focusing lens 3 is 300mm, and the nonlinear optical crystal 4 is a KBBF with a size of 6mm×6mm×10mm and a processing direction of (θ=56.2°, φ=0°). The KBBF crystal is rotated to adjust different five-wave mixing phase matching conditions. When the phase matching angle θ of the crystal is rotated from 36° to 76.4°, a tunable laser output in the ultraviolet band with a wavelength of 330-180nm can be achieved, as shown in the attached figure. Figure 5 shown.

[0087] The outer angle of the crystal is rotated by 14.3°, and the inner angle is rotated by 9.5°. The light propagates in the crystal along the direction of θ=65.7°, and the output light wavelength is 193nm. This wavelength is suitable for ultraviolet laser dissociation, which can efficiently dissociate the non-denatured protein skeleton and retain the non-covalent interaction forces such as hydrogen bonds in the fragment ions, thereby realizing the protein dynamic structure and interaction mass spectrometry analysis with single amino acid site resolution.

[0088] Example 4

[0089] The scheme of "generating deep ultraviolet tunable laser through self-phase modulation and five-wave mixing cascade" uses KBBF crystal as nonlinear optical crystal and Ti:Sapphire femtosecond laser with central wavelength of 800nm ​​as pump source. Figure 1 As shown, the components of the device are arranged along the optical path. The pump light source 1 is an ultrafast femtosecond laser with a wavelength of 800nm, a pulse width of 35fs, a repetition rate of 2kHz, and a power of 600mW. The focal length of the focusing lens 3 is 350mm, and the nonlinear optical crystal 4 is a KBBF with a size of 6mm×6mm×10mm and a processing direction of (θ=56.4°, φ=0°). The KBBF crystal is rotated to adjust different five-wave mixing phase matching conditions. When the phase matching angle θ of the crystal is rotated from 36° to 76.8°, a tunable laser output in the ultraviolet band with a wavelength of 330-180nm can be achieved, as shown in the attached figure. Figure 6 shown.

[0090] The outer angle of the crystal is rotated by 4.1°, and the inner angle is rotated by 2.7°. The light propagates in the crystal along the direction of θ=59.1°. At this time, the output light wavelength is 206nm. This wavelength is suitable for cutting and ablation of sapphire crystals by ultraviolet lasers. Non-thermal laser ablation of sapphire crystals during processing can avoid cracking caused by heat accumulation and improve processing quality.

[0091] Example 5

[0092] CLBO crystal is used as nonlinear optical crystal, and Yb with a central wavelength of 1030nm is used as 3+ The scheme of "generating deep ultraviolet tunable laser through self-phase modulation and five-wave mixing cascade" with femtosecond laser as pump source. Figure 1 As shown, the components of the device are arranged along the optical path. The pump light source 1 is an ultrafast femtosecond laser with a wavelength of 1030nm, a pulse width of 200fs, a repetition rate of 100kHz, and a power of 1200mW. The focal length of the focusing lens 3 is 300mm, and the nonlinear optical crystal 4 is a CLBO with a size of 6mm×6mm×10mm and a processing direction of (θ=66.4°, φ=45°). The CLBO crystal is rotated to adjust different five-wave mixing phase matching conditions. When the phase matching angle θ of the crystal is rotated from 56.9° to 75.9°, a tunable laser output in the ultraviolet band with a wavelength of 330-275nm can be achieved, as shown in the attached figure. Figure 7 shown.

[0093] The outer angle of the crystal is rotated 8.1°, and the inner angle is rotated 5.4° accordingly. The light propagates in the direction of θ=61° in the crystal, and the output light wavelength is 311nm. This wavelength is suitable for phototherapy to treat psoriasis, which can slow down the rapid growth of skin cells, inhibit the activation of immune cells, avoid excessive proliferation of epidermal keratinocytes, fight inflammation and kill bacteria, and effectively help the body recover.

[0094] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0095] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for generating ultraviolet tunable laser, characterized in that: The method uses an optical frequency conversion device to simultaneously realize self-phase modulation and five-wave mixing cascade effect in a single nonlinear optical crystal, thereby obtaining a tunable laser output with a frequency in the ultraviolet band. The method specifically includes the following steps: the optical frequency conversion device includes: a pump light source, a focusing lens, a nonlinear optical crystal and a color filter arranged in sequence along an optical path; the specific method includes: a) Provide a central wavelength of λ p A near-infrared ultrafast laser is used as a pump light source, and the pump light intensity of the pump light source exceeds the self-phase modulation threshold; b) focusing the pump light and injecting it into a nonlinear optical crystal, and generating a self-phase modulated light λ through a self-phase modulation effect s ; The nonlinear optical crystal is non-centrosymmetric; c) Self-phase modulated light λ s With pump light λ p Five-wave mixing occurs according to the phase matching condition, generating an output frequency of ω o , the corresponding wavelength is λ o UV laser; d) Adjust the spatial direction of the nonlinear optical crystal to change the phase matching condition of five-wave mixing, thereby achieving the output optical frequency ω o Continuous tuning.

2. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: The phase matching condition of the five-wave mixing satisfies at least one of the following energy conservation and momentum conservation conditions: (1)ω s +ω s +ω s +ω s =ω o The energy conservation condition and n s ω s +n s ω s +n s ω s +n s ω s =n o ω o The momentum conservation condition of (2)ω p +ω s +ω s +ω s =ω o The energy conservation condition and n p ω p +n s ω s +n s ω s +n s ω s =n o ω o The momentum conservation condition of (3)ω p +ω p +ω s +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n s ω s +n s ω s =n o ω o The momentum conservation condition of (4)ω p +ω p +ω p +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n p ω p +n s ω s =n o ω o The momentum conservation condition of Among them, ω p represents the frequency of the pump light, ω s represents the frequency of the self-phase modulated light, ω o Indicates the frequency of the output light; n p represents the refractive index of the pump light in the nonlinear optical crystal, n s represents the refractive index of the self-phase modulated light in the nonlinear optical crystal, n o Represents the refractive index of the output light in the nonlinear optical crystal.

3. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: The step d) specifically comprises: By continuously adjusting the spatial orientation of the nonlinear optical crystal, the refractive index of the crystal is continuously changed, and then the five-wave mixing phase matching condition satisfied by the ultrafast laser propagation in the crystal is continuously changed, so that the output light frequency ω o Continuously changing, the output is tunable laser in the visible deep ultraviolet band.

4. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: The pump light source is any one of the following: Ti:sapphire femtosecond laser with a central wavelength of 800nm; Yb with a central wavelength of 1030nm 3+ Femtosecond lasers; Or Er with a central wavelength of 1550nm 3+ Femtosecond laser.

5. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: The nonlinear optical crystal meets the following characteristics: five-wave mixing phase matching capability, good transmission performance, and high light damage resistance threshold in the ultraviolet to near-infrared band; The nonlinear optical crystal is made of any of the following materials: β-BBO, CLBO and KBBF.

6. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: When the nonlinear optical crystal is β-BBO, when the Yb 3+ When a femtosecond laser is used as a pump source and the tangential angle of the β-BBO crystal is θ=60.8° and φ=30°, the step d) comprises: adjusting the five-wave mixing phase matching condition by rotating the β-BBO crystal, and obtaining a tunable laser output in the ultraviolet band with a wavelength range of 330-227 nm when the crystal rotates clockwise or counterclockwise in a φ=30° plane and the internal angle θ of the crystal rotates from 42.8° to 78.8°; When the outer angle of the crystal rotates 1°, the inner angle rotates 0.6° accordingly. The light propagates in the direction of θ=60.2° in the crystal. At this time, the output light wavelength is 254nm.

7. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: When the nonlinear optical crystal is β-BBO, when a titanium sapphire femtosecond laser with a central wavelength of 800 nm is used as a pump source, and the tangential angle of the β-BBO crystal is θ=58.4° and φ=30°, the step d) includes: adjusting the five-wave mixing phase matching condition by rotating the β-BBO crystal, and when the crystal rotates clockwise or counterclockwise in a φ=30° plane, and the internal angle θ of the crystal rotates from 42.5° to 74.3°, a tunable laser output in the ultraviolet band with a wavelength range of 330-230 nm is obtained; When the outer angle of the crystal rotates 4.3°, the inner angle rotates 2.6° accordingly. The light propagates in the crystal along the direction of θ=55.8°. At this time, the output light wavelength is 266nm.

8. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: When the nonlinear optical crystal is KBBF, when the Yb 3+ When a femtosecond laser is used as a pump source and the tangential angle of the KBBF crystal is θ=56.2° and φ=0°, the step d) comprises: adjusting the five-wave mixing phase matching condition by rotating the KBBF crystal, and when the crystal rotates clockwise or counterclockwise in the φ=0° plane and the internal angle θ of the crystal rotates from 36° to 76.4°, a tunable laser output in the ultraviolet band with a wavelength range of 330-180 nm is obtained; When the external angle of the crystal rotates 14.3°, the internal angle rotates 9.5° accordingly. The light propagates in the crystal along the direction of θ=65.7°. At this time, the output light wavelength is 193nm.

9. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: When the nonlinear optical crystal is KBBF, when a titanium sapphire femtosecond laser with a central wavelength of 800 nm is used as a pump source, and the tangential angle of the KBBF crystal is θ=56.4° and φ=0°, the step d) includes: adjusting the five-wave mixing phase matching condition by rotating the KBBF crystal, and when the crystal rotates clockwise or counterclockwise in the φ=0° plane, and the internal angle θ of the crystal rotates from 36° to 76.8°, a tunable laser output in the ultraviolet band with a wavelength range of 330-180 nm is obtained; When the external angle of the crystal rotates 4.1°, the internal angle rotates 2.7° accordingly. The light propagates in the crystal along the direction of θ=59.1°. At this time, the output light wavelength is 206nm.

10. The method for generating ultraviolet tunable laser according to claim 1, characterized in that: When the nonlinear optical crystal is CLBO, when a Yb3+ femtosecond laser with a central wavelength of 1030 nm is used as a pump source, and the tangential angle of the CLBO crystal is θ=66.4° and φ=45°, the step d) includes: adjusting the five-wave mixing phase matching condition by rotating the CLBO crystal, and when the crystal rotates clockwise or counterclockwise in the φ=45° plane, and the crystal internal angle θ rotates from 56.9° to 75.9°, a tunable laser output in the ultraviolet band with a wavelength range of 330-275 nm is obtained; When the external angle of the crystal rotates 8.1°, the internal angle rotates 5.4° accordingly. The light propagates in the direction of θ=61° in the crystal, and the output light wavelength is 311nm.

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