A method for generating tunable laser in the visible to deep ultraviolet band

Abstract

The present invention discloses a method for generating a tunable laser in the visible to deep ultraviolet band, comprising: providing a laser with a center frequency of ω p , wavelength is λ p The near-infrared ultrafast laser is used as the pump light source, and the pump light intensity exceeds the self-phase modulation threshold; the pump light is focused and incident on the nonlinear optical crystal to stimulate the self-phase modulation effect in the crystal, generating a center frequency of ω p The method involves adjusting the position or orientation of the nonlinear optical crystal so that the pump light and the broadened spectrum generated by self-phase modulation meet the phase matching conditions of four-wave mixing (FWM) in the NLO crystal, resulting in laser output from the visible to deep ultraviolet range. By continuously changing the phase matching conditions of the NLO crystal, the output laser frequency can be continuously tuned from the visible to deep ultraviolet range. This method overcomes the current problem of four-wave mixing technology that prevents wide-range frequency tuning of the output light and has potential applications in ultra-fine machining, UV lithography, air pollution monitoring, microsurgery, and other fields.

Description

Technical Field

[0001] The present invention relates to the field of lasers and nonlinear optics, and in particular to a method for generating tunable lasers in the visible to deep ultraviolet band, and more specifically to a method for generating tunable lasers in the visible to deep ultraviolet band by utilizing the combined effects of self-phase modulation and four-wave mixing. Background Art

[0002] Since the first appearance of lasers in 1960, laser technology has made great progress and has received widespread attention and application. Utilizing nonlinear frequency conversion technology, laser output has covered a wide spectrum from the deep ultraviolet to the far infrared; through mode locking technology, laser pulse width has also been significantly shortened, from nanoseconds to attoseconds and even shorter time scales. In 1961, Franken et al. discovered frequency-doubled light by irradiating a quartz wafer with a ruby ​​laser. Phase matching technology was subsequently developed and became a key method for nonlinear optical frequency conversion. Phase matching is divided into two categories: frequency up-conversion and frequency down-conversion. Frequency up-conversion includes sum frequency, frequency doubling, and frequency tripling, while frequency down-conversion includes difference frequency, optical parametric generation, optical parametric amplification, and optical parametric oscillation.

[0003] Phase matching is a key technique in nonlinear optics. It optimizes the phase relationship between the frequency and wave vector of a light wave to maximize the efficiency of the nonlinear optical process. When the beam propagation direction is misaligned with the crystal's optical axis, birefringence causes light with different polarization directions to propagate at different speeds. Achieving phase alignment is crucial for efficient nonlinear output because, when phases are aligned, the harmonics superimpose and enhance each other; otherwise, the harmonics cancel each other out, resulting in reduced or even vanishing intensity.

[0004] Patent document CN102751653A discloses a mid-infrared fiber parametric oscillator based on degenerate four-wave mixing of photonic crystal fibers. It uses a 1030-1070nm pump laser coupled to a photonic crystal fiber to stimulate the nonlinear effect of fiber four-wave mixing, achieving mid-infrared laser output. The signal and idler wavelengths are 641 and 2611nm respectively. The basic principle of the four-wave mixing technology is ω p +ω p =ω s +ω i (where the subscripts p, s, and i represent pump light, signal light, and idler light, respectively), which is a third-order nonlinear optical effect. In terms of effect, from a single center frequency (ω p ) of the pump source and the new wavelength laser generated has a fixed frequency (ω s ,ω i ), cannot be tuned.

[0005] In recent years, some literatures have reported direct triple frequency generation of different nonlinear optical crystals (Optics Letters, 36, 18, 3627, 2011; Optics Letters, 43, 8, 1734, 2018; Optik, 262, 169325, 2022). The basic principle of the four-wave mixing technology is ω p +ω p +ω p =ω o (where subscripts p and o represent pump light and output light respectively), which also belongs to the third-order nonlinear optical effect. In terms of effect, from a single center frequency (ω p ) of the pump source and the new wavelength laser generated also has a fixed frequency (ω o ) and cannot be tuned. Only by changing the center frequency of the pump source can the output light achieve limited frequency adjustment. For example, when the pump source provides a tunable fundamental frequency light of 620-800nm, the spectral tunable width of the output light for calcite crystal and α-BBO crystal is 54nm (213-267nm) and 17nm (250-267nm), respectively (Optik, 262, 169325, 2022).

[0006] In summary, the existing four-wave mixing technology has the problem that the fundamental frequency light source cannot be tuned or the tuning range is limited, resulting in the output light being unable to be tuned or having a limited tuning range (<60nm). In order to solve the above problem, the present invention is proposed. Summary of the Invention

[0007] In view of this, the present invention provides a method for generating tunable laser in the visible to deep ultraviolet band, which makes up for the shortcomings of the existing technology and solves the problem that the current four-wave mixing technology cannot achieve large-scale frequency tuning of the output light.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for generating tunable laser light in the visible to deep ultraviolet band, using an optical frequency conversion device to achieve tunable frequency up-conversion; 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:

[0010] a) Provide a center frequency of ω p , corresponding to wavelength λ p A near-infrared ultrafast laser is used as a pump light source, wherein the pump light intensity of the pump light source exceeds a self-phase modulation threshold;

[0011] b) focusing the pump light and injecting it into a nonlinear optical crystal to stimulate the self-phase modulation effect in the crystal, thereby generating a phase shift at the center frequency ωp spectral broadening nearby;

[0012] c) adjusting the position or direction of the nonlinear optical crystal so that the pump light and the broadened spectrum generated by self-phase modulation meet the phase matching condition of four-wave mixing in the nonlinear optical crystal, thereby outputting laser light in the visible to deep ultraviolet band;

[0013] d) continuously changing the phase matching condition of the nonlinear optical crystal to achieve continuous tuning of the output laser frequency in the visible to deep ultraviolet band.

[0014] Furthermore, the phase matching condition of the four-wave mixing satisfies at least one of the following energy conservation and momentum conservation conditions:

[0015] (1)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 o ω o The momentum conservation condition of

[0016] (2)ω p +ω s +ω s =ω o The energy conservation condition and n p ω p +n s ω s +n s ω s =n o ω o Momentum conservation conditions;

[0017] (3)ω p +ω p +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n s ω s =n o ω o Momentum conservation conditions;

[0018] Among them, ω p represents the frequency of the pump light, ω srepresents 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.

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

[0020] By continuously adjusting the spatial orientation of the nonlinear optical crystal, the refractive index of the crystal is continuously changed, and then the four-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 from visible to 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 800 nm;

[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: four-wave mixing phase matching capability, good transmittance, and high light damage resistance threshold in the deep ultraviolet to near infrared band;

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

[0027] β-BBO, LBO, CLBO, BIBO, YCOB, KDP followed by ADP.

[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=45° and φ=30°, step d) includes: rotating the β-BBO crystal so that the internal angle of the crystal is rotated from 30.5° to 49.5°, thereby being able to output tunable laser light in the range of 450-280 nm.

[0029] Furthermore, 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=40.4° and φ=30°, the step d) includes: rotating the β-BBO crystal so that the internal angle of the crystal is rotated from 37.4° to 44.6°, thereby being able to output tunable laser light in the range of 350-298 nm.

[0030] Furthermore, when the nonlinear optical crystal is KDP, when the Yb 3+ When a femtosecond laser is used as a pump source and the tangential angle of the KDP crystal is θ=75° and φ=45°, step d) includes: rotating the KDP crystal so that the internal angle of the crystal is rotated from 62° to 90°, thereby being able to output tunable laser light in the range of 450-295 nm.

[0031] 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=54° and φ=0°, step d) includes: rotating the CLBO crystal so that the internal angle of the crystal is rotated from 40° to 68°, thereby being able to output tunable laser light in the range of 450-274 nm.

[0032] Furthermore, when the nonlinear optical crystal is CLBO, when a titanium sapphire femtosecond laser with a central wavelength of 800 nm is used as the pump source, and the tangential angle of the CLBO crystal is θ=62° and φ=0°, step d) includes: rotating the CLBO crystal so that the internal angle of the crystal is rotated from 56° to 68°, so as to output a tunable laser in the range of 310-275 nm.

[0033] It can be seen from the above technical solution that compared with the existing technology, it has the following advantages:

[0034] 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 two third-order nonlinear optical effects, self-phase modulation and four-wave mixing, in a single nonlinear optical crystal. For the first time, self-phase modulation technology is introduced into four-wave mixing, which provides an ultra-wide band of fundamental frequency light and rich phase matching possibilities for the four-wave mixing process. The output light wavelength can be tuned over a wide range from the visible to the deep ultraviolet band, which makes up for the shortcomings of the existing technology and solves the problem that the current four-wave mixing technology cannot achieve large-scale frequency tuning of the output light.

[0035] The optical frequency conversion device used has the characteristics of simple structure, convenient use, stable performance and low production cost.

[0036] In addition, this method has the advantages of being applicable to a variety of nonlinear optical crystals, having a wide tuning range, high conversion efficiency, and narrow spectral line width. It can be widely used in ultra-fine processing, ultraviolet lithography, atmospheric pollution monitoring, micro-surgery and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0038] Figure 1 This is a diagram of an optical frequency conversion device;

[0039] Figure 2 The theoretical and experimental data diagram of the β-BBO crystal frequency conversion and 1030nm pumping described in Example 1;

[0040] Figure 3 The following figure compares the effects of Example 1 and three-wave mixing technology. The left figure shows the output light intensity, and the right figure shows the output spectral line width.

[0041] Figure 4 The theoretical and experimental data diagram of the β-BBO crystal frequency conversion and 800nm ​​pumping described in Example 2;

[0042] Figure 5 This is a graph showing theoretical data for the KDP crystal frequency conversion and 1030nm pumping described in Example 3;

[0043] Figure 6 This is a theoretical data diagram of the CLBO crystal frequency conversion and 1030nm pumping described in Example 4;

[0044] Figure 7 This is a graph showing theoretical data for the CLBO crystal frequency conversion and 800nm ​​pumping described in Example 5;

[0045] Among them, 1. Pump light source, 2. Wavelength is λ p Ultrafast pump light, 3. focusing lens, 4. nonlinear optical crystal, 5. color filter, 6. wavelength λ o output light. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0047] The embodiment of the present invention discloses a method for generating a tunable laser in the visible to deep ultraviolet band, using an optical frequency conversion device to achieve tunable frequency up-conversion; wherein the optical frequency conversion device, with reference to Figure 1 As shown, it includes: 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, and finally obtains the wavelength λ o The output light 6.

[0048] This method uses a near-infrared ultrafast laser with a fixed wavelength λp as the pump source and utilizes the combination of two third-order nonlinear optical effects, self-phase modulation and four-wave mixing, in a single nonlinear optical crystal to achieve tunable frequency up-conversion.

[0049] The specific process includes:

[0050] a) Provide a center frequency of ω p , corresponding to wavelength λ p A near-infrared ultrafast laser is used as a pump light source, wherein the pump light intensity of the pump light source exceeds a self-phase modulation threshold;

[0051] b) focusing the pump light and injecting it into a nonlinear optical crystal to stimulate the self-phase modulation effect in the crystal, thereby generating a phase shift at the center frequency ω p spectral broadening nearby;

[0052] c) adjusting the position or direction of the nonlinear optical crystal so that the pump light and the broadened spectrum generated by self-phase modulation meet the phase matching condition of four-wave mixing in the nonlinear optical crystal, thereby outputting laser light in the visible to deep ultraviolet band;

[0053] d) continuously changing the phase matching condition of the nonlinear optical crystal to achieve continuous tuning of the output laser frequency in the visible to deep ultraviolet band.

[0054] In this embodiment, the center frequency is ω p , corresponding to wavelength λ p The near-infrared ultrafast laser is focused and incident on the nonlinear optical crystal, and the incident laser intensity is increased 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 four-wave mixing phase matching condition, the crystal will output a frequency of ω o , corresponding to wavelength λ o The laser is located in the visible to deep ultraviolet band. Continuously changing the four-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 , obtaining continuously tunable lasers in the visible to deep ultraviolet band.

[0055] 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 two third-order nonlinear optical effects, self-phase modulation and four-wave mixing, in a single nonlinear optical crystal. It has the advantages of being applicable to a variety of nonlinear optical crystals, having a wide tuning range, high conversion efficiency, and a narrow spectral line width. It can be widely used in ultra-fine processing, ultraviolet lithography, atmospheric pollution monitoring, micro-surgery and other fields.

[0056] The self-phase modulation threshold varies depending on the pump light source and nonlinear optical crystal used. For a pump light source of 1030nm, 200fs, and 100kHz, the experimentally measured self-phase modulation threshold of a 10mm long β-BBO crystal is 199.15GW / cm 2 For a pump source of 800nm, 35fs, and 2kHz, the threshold of self-phase modulation of a 10mm-long β-BBO crystal was experimentally measured to be 139.15GW / cm 2 The prerequisite for the application of this technology is that the power density exceeds the self-phase modulation threshold. Above the threshold and below the damage threshold, the higher the pump power density, the wider the self-phase modulation spectrum generated, and the larger the tunable range of the output light after four-wave mixing.

[0057] In step c), satisfying the four-wave mixing phase matching condition means satisfying both the energy conservation condition and the momentum conservation condition. According to the different properties of the participating light, the four-wave mixing phase matching condition can be divided into the following three categories:

[0058] (1)Meanwhile satisfying 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 o ω o Momentum conservation conditions;

[0059] (2)Meanwhile satisfying ω p +ω s +ω s =ω o The energy conservation condition and n p ω p +n s ω s +n s ω s =n o ω o Momentum conservation conditions;

[0060] (3)Meanwhile satisfying ω p +ω p +ω s =ω o The energy conservation condition and n p ω p +n p ω p +n s ω s =n o ω o The momentum conservation condition.

[0061] 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.

[0062] The so-called satisfying of the four-wave mixing phase matching condition refers to satisfying any one or more of the above three conditions, which are all within the scope of protection claimed by this patent.

[0063] During use, by continuously adjusting the spatial orientation of the nonlinear optical crystal, the refractive index of the crystal can be continuously changed, thereby continuously changing the four-wave mixing phase matching condition satisfied by the ultrafast laser propagation in the crystal, thereby making the output light frequency ω o Continuously changing, the output is tunable laser from visible to deep ultraviolet band.

[0064] In one embodiment, with a fixed wavelength λ p The near-infrared ultrafast laser pump source refers to a Ti:Sapphire femtosecond laser with a central wavelength of 800 nm or a Yb:Sapphire femtosecond laser with a central wavelength of 1030 nm. 3+Femtosecond laser, or Er with a central wavelength of 1550nm 3+ Femtosecond laser.

[0065] The above-mentioned nonlinear optical crystals must meet the following characteristics:

[0066] 1) Four-wave mixing phase matching capability in the deep ultraviolet to near-infrared band;

[0067] 2) Good permeability;

[0068] 3) and a high light damage resistance threshold;

[0069] Specific options include β-BBO (β-BaB2O4), LBO (LiB3O5), CLBO

[0070] (CsLiB6O 10 ), BIBO(BiB3O6), YCOB(YCa4O(BO3)3), KDP(KH2PO4), ADP(NH4H2PO4), etc.

[0071] The above-mentioned technology combining self-phase modulation and four-wave mixing overcomes the defect of previous four-wave mixing technology that cannot achieve large-range frequency tuning of the output light. During the actual measurement process, the spectral tuning width can reach 170nm (tuned from 450nm to 280nm).

[0072] The applicant's prior application: Patent document CN114185223A (publication date 2022-03-15) discloses a method for generating parametric light and its application, and provides a nonlinear optical material that meets the sum frequency phase matching condition, that is, simultaneously meets ω p +ω i =ω s The energy conservation condition and n p ω p +n i ω i =n s ω s Momentum conservation condition. When the wavelength is λ p When the laser is incident as pump light into the nonlinear optical material, the material will output a wavelength of λ s The signal light is tunable sum frequency parametric light. However, the mechanism of the patent document is three-wave mixing, a second-order nonlinear optical effect, which requires the nonlinear crystal to be non-centrosymmetric. Compared with the patent document, the mechanism of the present invention is four-wave mixing, a third-order nonlinear optical effect. It does not require the symmetry of the nonlinear crystal and can be either centrosymmetric or non-centrosymmetric, thus expanding the selection range of nonlinear optical crystals. In addition, compared with the patent document, the present invention has many advantages, such as high conversion efficiency in the ultraviolet band, strong output light, and narrow spectral lines.

[0073] The advantages of the present invention are further illustrated by several specific embodiments below:

[0074] Example 1

[0075] A scheme for "generating tunable lasers from the visible to deep ultraviolet bands by utilizing the combined effects of self-phase modulation and four-wave mixing" using β-BBO crystal as the nonlinear optical material and 1030nm pumping.

[0076] Devices such as Figure 1 As shown, each component is 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 β-BBO with a size of 6mm×6mm×10mm and a cutting direction of (θ=45°, φ=30°). Here, any spatial direction is represented by polar coordinates (θ, φ), where θ is the angle between the direction and the crystal optical axis Z, and φ is the azimuth angle, which is the angle between the projection of the direction in the crystal XY main plane and the X-axis. The measured points obtained by rotating the β-BBO crystal are as follows Figure 2 、 Figure 3 The independent points in .

[0077] According to the conditions of Example 1, the corresponding four-wave mixing phase matching curve can be obtained by calculation, as shown in FIG. Figure 2 As shown in the curve. Figure 2 The graph includes three different four-wave mixing phase matching situations and measured data points. It can be seen from the figure that the theoretical and measured data are in good agreement, which confirms the practicality of this embodiment. When the phase matching angle θ of the crystal is rotated from 30.5° to 49.5°, a tunable laser output in the visible to deep ultraviolet band of 450-280nm can be obtained. We used the same device to compare the four-wave mixing measured in Example 1 with the three-wave mixing measured using the technology of patent document CN114185223A. Figure 3 shown. Figure 3 The middle left half of the figure shows a comparison of the output light intensity. It can be seen that in the ultraviolet band of 320-400nm, compared with the three-wave mixing in patent document CN114185223A, the method of the present invention has a greater output light intensity and a correspondingly higher optical conversion efficiency. Figure 3The figure on the right shows a comparison of the output spectral linewidths. It shows that within the broad wavelength range of 290-415 nm, the method of the present invention exhibits a narrower output spectral linewidth and greater monochromaticity than the three-wave mixing method described in patent document CN114185223A. This is a significant advantage of third-order nonlinear optical frequency conversion over second-order nonlinear optical frequency conversion. The measured results above demonstrate that the method of the present invention offers significant advantages over CN114185223A in terms of higher output light intensity, narrower spectral linewidth, and higher conversion efficiency.

[0078] Example 2

[0079] A scheme for "generating tunable laser in the visible to deep ultraviolet band by utilizing the combined effect of self-phase modulation and four-wave mixing" using β-BBO crystal as nonlinear optical material and 800nm ​​pumping. Figure 1 As shown, each component is 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 dimensions of 6mm×6mm×10mm and a cutting direction of (θ=40.4°, φ=30°). The measured points obtained by rotating the β-BBO crystal are shown in the figure below. Figure 4 The independent points in .

[0080] According to the conditions of Example 2, the corresponding four-wave mixing phase matching curve can be obtained by calculation, as shown in FIG. Figure 4 As shown in the curve. Figure 4 It includes three different four-wave mixing phase matching situations and measured data points. Theoretically, when the phase matching angle θ of the crystal is rotated from 35° to 50°, a 370-270nm ultraviolet band tunable laser output can be obtained. In actual measurement, when the crystal internal angle is rotated from 37.4° to 44.6°, a 350-298nm ultraviolet band tunable laser output is obtained. Figure 4 The theoretical and measured data are generally consistent, confirming the practicality of this embodiment. The measured tuning range is smaller than the theoretical tuning range, primarily due to limitations in the test conditions. This can be optimized through various means, such as increasing the pump power to enhance the intensity and width of the self-phase modulation spectrum and machining the crystal with a larger θ angle.

[0081] Example 3

[0082] A scheme for "generating tunable lasers in the visible to deep ultraviolet bands by utilizing the combined effects of self-phase modulation and four-wave mixing" using KDP crystal as nonlinear optical material and 1030nm pumping. Figure 1As shown, each component is 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 KDP with a size of 10mm×10mm×20mm and a cutting direction of (θ=75°, φ=45°). The KDP crystal is rotated to adjust the four-wave mixing phase matching condition. When the internal angle of the crystal is rotated from 62° to 90°, a tunable laser output in the visible to ultraviolet band of 450-295nm can be obtained, as shown in FIG. Figure 5 shown.

[0083] Example 4

[0084] A scheme for "generating tunable laser in the visible to deep ultraviolet band by utilizing the combined effect of self-phase modulation and four-wave mixing" using CLBO crystal as nonlinear optical material and 1030nm pumping. Figure 1 As shown, each component is 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 CLBO with a size of 10mm×10mm×10mm and a cutting direction of (θ=54°, φ=0°). The CLBO crystal is rotated to adjust the four-wave mixing phase matching condition. When the internal angle of the crystal is rotated from 40° to 68°, a tunable laser output in the visible to deep ultraviolet band of 450-274nm can be obtained, as shown in FIG. Figure 6 shown.

[0085] Example 5

[0086] A scheme for "generating tunable laser in the visible to deep ultraviolet band by utilizing the combined effect of self-phase modulation and four-wave mixing" using CLBO crystal as nonlinear optical material and 800nm ​​pumping. Figure 1 As shown, each component is 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 CLBO with a size of 10mm×10mm×10mm and a cutting direction of (θ=62°, φ=0°). The CLBO crystal is rotated to adjust the four-wave mixing phase matching condition. When the internal angle of the crystal is rotated from 56° to 68°, a tunable laser output in the ultraviolet band of 310-275nm can be obtained, as shown in FIG. Figure 7 shown.

[0087] Example 6

[0088] The application of the method in ultraviolet lithography is described in conjunction with the above embodiment 1:

[0089] Ultraviolet lithography, a key process in semiconductor manufacturing, requires a high-precision, narrow-spectrum UV laser source. Traditional UV light sources struggle to meet the increasingly complex demands of lithography. However, tunable lasers, generated through the combined effects of self-phase modulation and four-wave mixing, offer a highly efficient and tunable laser source for this application.

[0090] Implementation steps:

[0091] 1. Device preparation:

[0092] Use Figure 1 The device configuration shown includes a pump light source 1 (ultrafast femtosecond laser), a focusing lens 3, a nonlinear optical crystal 4, a color filter 5, and an output light receiving device. All components are arranged in sequence along the optical path.

[0093] 2. Pump light source settings:

[0094] Using Yb with a central wavelength of 1030nm 3+ A femtosecond laser was used as the pump light source. The pulse width of the laser was set to 200fs, the repetition rate was 100kHz, and the average output power was 1200mW.

[0095] After passing through the focusing lens 3, the laser is focused into the β-BBO (β-BaB2O4) nonlinear optical crystal 4. The size of the crystal is 6 mm×6 mm×10 mm, and the cutting direction is θ=45° and φ=30°.

[0096] 3. Self-phase modulation and four-wave mixing:

[0097] By adjusting the power density of the laser to exceed the self-phase modulation threshold of the β-BBO crystal, a significant spectral broadening effect is stimulated.

[0098] Based on spectral broadening, the β-BBO crystal is rotated to meet the phase-matching conditions for four-wave mixing. When the phase-matching angle θ of the crystal is rotated from 30.5° to 49.5°, the system outputs a tunable laser with a wavelength range of 450nm to 280nm.

[0099] 4. Photolithography applications:

[0100] The generated tunable laser beam passes through the color filter 5 to filter out redundant frequency components, thereby obtaining the required narrow-band ultraviolet laser output.

[0101] The UV laser output light is guided to the photolithography system, using different wavelengths in the range of 450-280nm to perform high-precision exposure on different layers of the semiconductor wafer.

[0102] By adjusting the angle of the β-BBO crystal, the laser wavelength can be quickly switched to adapt to the requirements of different lithography levels, significantly improving the flexibility and efficiency of the lithography process.

[0103] 5. Performance verification:

[0104] Experimental results show that in the lithography process using this method, ultraviolet laser has high conversion efficiency and narrow spectral line width, and can accurately control the lithography pattern to achieve nanometer-level precision.

[0105] Compared with traditional laser lithography systems, this method can achieve multi-band operation in the same lithography system, greatly improving equipment utilization and reducing manufacturing costs.

[0106] This specific example demonstrates the practical application of tunable laser light generated through the combined effects of self-phase modulation and four-wave mixing in ultraviolet lithography. This method not only meets the high light source requirements of ultraviolet lithography, but also improves the overall performance of the lithography process through its flexible tuning capabilities and high conversion efficiency. Similarly, Examples 1-5 described above can also be applied to fields such as ultrafine machining, ultraviolet lithography, air pollution monitoring, and microsurgery.

[0107] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0108] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for generating a tunable laser in the visible to deep ultraviolet band, characterized in that: Tunable frequency up-conversion using optical frequency conversion devices; 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 the optical path; the specific method includes: a) Provide a center frequency of ω p , corresponding to wavelength λ p A near-infrared ultrafast laser is used as a pump light source, wherein the pump light intensity of the pump light source exceeds a self-phase modulation threshold; b) focusing the pump light and injecting it into a nonlinear optical crystal to stimulate the self-phase modulation effect in the crystal, thereby generating a phase shift at the center frequency ω p spectral broadening nearby; c) adjusting the position or direction of the nonlinear optical crystal so that the pump light and the broadened spectrum generated by self-phase modulation meet the phase matching condition of four-wave mixing in the nonlinear optical crystal, thereby outputting laser light in the visible to deep ultraviolet band; d) continuously changing the phase matching condition of the nonlinear optical crystal to achieve continuous tuning of the output laser frequency in the visible to deep ultraviolet band.

2. The method for generating a tunable laser in the visible to deep ultraviolet band according to claim 1, characterized in that: The phase matching condition of the four-wave mixing satisfies at least one of the following energy conservation and momentum conservation conditions: (1)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 o ω o The momentum conservation condition of (2)ω p +ω s +ω s =ω o The energy conservation condition and n p ω p +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 o The energy conservation condition and 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 a tunable laser in the visible to deep ultraviolet band 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 four-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 from visible to deep ultraviolet band.

4. The method for generating a tunable laser in the visible to deep ultraviolet band 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 800 nm; 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 tunable laser in the visible to deep ultraviolet band according to claim 1, characterized in that: The nonlinear optical crystal has the following characteristics: four-wave mixing phase matching capability, good transmission performance, and high light damage resistance threshold in the deep ultraviolet to near infrared band; The nonlinear optical crystal is made of any of the following materials: β-BBO, LBO, CLBO, BIBO, YCOB, KDP or ADP.

6. The method for generating a tunable laser in the visible to deep ultraviolet band 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=45° and φ=30°, step d) includes: rotating the β-BBO crystal so that the internal angle of the crystal is rotated from 30.5° to 49.5°, thereby being able to output tunable laser light in the range of 450-280 nm.

7. The method for generating tunable laser in the visible to deep ultraviolet band 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=40.4° and φ=30°, step d) includes: rotating the β-BBO crystal so that the internal angle of the crystal is rotated from 37.4° to 44.6°, thereby being able to output tunable laser light in the range of 350-298 nm.

8. The method for generating tunable laser in the visible to deep ultraviolet band according to claim 1, characterized in that: When the nonlinear optical crystal is KDP, when the Yb 3+ When a femtosecond laser is used as a pump source and the tangential angle of the KDP crystal is θ=75° and φ=45°, step d) includes: rotating the KDP crystal so that the internal angle of the crystal is rotated from 62° to 90°, thereby being able to output tunable laser light in the range of 450-295 nm.

9. The method for generating tunable laser in the visible to deep ultraviolet band according to claim 1, characterized in that: 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=54° and φ=0°, step d) includes: rotating the CLBO crystal so that the internal angle of the crystal is rotated from 40° to 68°, thereby being able to output tunable laser light in the range of 450-274 nm.

10. The method for generating tunable laser in the visible to deep ultraviolet band according to claim 1, characterized in that: When the nonlinear optical crystal is CLBO, when a titanium sapphire femtosecond laser with a central wavelength of 800 nm is used as the pump source, and the tangential angle of the CLBO crystal is θ=62° and φ=0°, step d) includes: rotating the CLBO crystal so that the internal angle of the crystal is rotated from 56° to 68°, so as to output a tunable laser in the range of 310-275 nm.

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