Mechanism for pulse laser shaping frequency shift and adjusting method

Abstract

The invention discloses a mechanism for pulse laser shaping frequency shift and an adjusting method, and relates to the technical field of pulse laser shaping frequency shift, the mechanism comprises a laser source, a reflector, a spatial light modulator, a focusing lens, a frequency shift piece and a detector, and the laser source, the reflector, the spatial light modulator, the focusing lens, the frequency shift piece and the detector are sequentially arranged. According to the waveform shaping frequency shift method based on the molecular collimation effect, directional adjustment of the nonlinear effect can be realized by accurately regulating and controlling parameters of pulse waveforms, such as steep degree and direction, and frequency shift of the nonlinear effect can be accurately controlled by optimizing pulse parameters, so that the frequency shift efficiency is improved. And a new method is provided for improving the performance of the ultrafast light source and expanding the application of the ultrafast light source. According to the scheme, a novel light source scheme which is large in bandwidth, tunable, efficient and compact and more flexible and diverse regulation and control means are provided, and important application value is achieved for research in the fields of strong field optics, precision spectroscopy, optical communication, optical imaging and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of pulse laser shaping frequency shift, and in particular to a mechanism and an adjustment method for pulse laser shaping frequency shift. Background Art

[0002] The development of ultrashort pulse lasers provides an important opportunity for humans to better understand and transform the natural world, especially in the field of frequency-adjustable short-cycle laser pulses in a wide spectral range, which has broad application prospects. However, the spectral range and pulse length that ultrafast lasers can currently cover are limited by the laser crystal materials. Therefore, the development of large-bandwidth, wavelength-adjustable, and highly robust high-energy ultrashort laser pulses has become an important challenge facing nonlinear optical technology.

[0003] In the prior art, the conversion of pulse frequency is mainly achieved by nonlinear frequency shifting based on the Kerr effect. The Kerr effect is a kind of optical nonlinear effect. It uses the dependence of the refractive index of the medium on the light intensity to achieve the frequency conversion of light waves. When a beam of light passes through a specific nonlinear medium, the refractive index of the medium will change due to the Kerr effect. This change is directly related to the intensity of the incident light. As the light intensity increases, the refractive index of the medium will also increase, resulting in a unique frequency conversion process for the light wave when passing through the medium. In traditional Kerr effect frequency shifting technology, when the light field intensity reaches a high level, the nonlinear optical effect becomes more significant. However, this enhanced nonlinear response is often accompanied by severe distortion. Specifically, the phase and amplitude of the light wave will be distorted due to multi-photon absorption, scattering and other nonlinear interactions in the nonlinear medium, resulting in a decrease in the quality of the output light. This distortion not only affects the integrity of the signal, but may also introduce additional noise, reduce the signal-to-noise ratio of the system, and thus limit the performance in high-power laser applications. Summary of the invention

[0004] The object of the present invention is to provide a mechanism and an adjustment method for pulse laser shaping frequency shift to solve the technical problems mentioned in the above background technology.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A mechanism for pulse laser shaping frequency shift comprises a laser source, a reflector, a spatial light modulator, a focusing lens, a frequency shifter and a detector, wherein the laser source, the reflector, the spatial light modulator, the focusing lens, the frequency shifter and the detector are arranged in sequence.

[0007] The laser source is used to emit pulsed laser, which enters the spatial light modulator after being reflected by a reflector, is incident on the focusing lens after waveform adjustment by the spatial light modulator, is refracted by the focusing lens and input into the frequency shifter for frequency shifting, and finally is output as a pulsed laser after waveform adjustment and frequency shifting.

[0008] As a further solution of the present invention: the laser source is a titanium sapphire laser with a central wavelength of 800 nm.

[0009] As a further solution of the present invention: the reflector is made of ultraviolet fused quartz, has a thickness of 12 mm, and has an operating wavelength of 750 nm to 1100 nm.

[0010] As a further solution of the present invention: the spatial light modulator is a liquid crystal spatial light modulator or a multi-quantum well light modulator.

[0011] As a further solution of the present invention: the focusing lens is made of borosilicate crown glass, has a focal length of 10 cm, and an operating wavelength of 350 nm to 2000 nm.

[0012] As a further solution of the present invention: the frequency shifter is a gas chamber, which is filled with nitrogen and has an internal gas pressure of five MPa.

[0013] As a further solution of the present invention: the frequency shifting element is a waveguide.

[0014] As a further solution of the present invention: the detector is a fiber optic spectrometer.

[0015] A method for adjusting a pulse laser shaping frequency shift mechanism comprises the following steps:

[0016] Step 1: First, check and wipe each component to ensure that the input and output surfaces of each component are smooth. Then start the laser source, spatial light modulator and detector, and fill the frequency shifter with nitrogen to make the internal pressure of the frequency shifter reach 5 MPa.

[0017] Step 2: The pulse laser emitted by the laser source is incident on the surface of the reflector, and then the angle of the reflector is adjusted so that the pulse laser reflected by the reflector can accurately be incident on the spatial light modulator (3).

[0018] Step 3: The time domain waveform of the input light field is adjusted by a spatial light modulator to change its transient refractive index, so that the light field exhibits a desired waveform change in the time domain.

[0019] For the spatial light modulator with additional v(t), the output sine wave is:

[0020] E(t)=E0sin(ω c +pv(t))

[0021] E0 is the amplitude of the input wave, ω c is the incident wave frequency, p is the modulation coefficient of the input signal, when the modulation signal changes linearly with time, that is, v(t) = ω m t / p, the output signal is:

[0022] E(t)=E0sin[(ω c +ω m )t]

[0023] The output wave produces ω compared to the input wave m Considering the periodicity of the sine function, the modulation signal should have an amplitude of 2π / p and a period of 2π / ω. m The sawtooth waveform signal can be converted from linear amplitude modulation to linear phase ramp by the above formula.

[0024] Step 4: During the light field adjustment process, an additional iterative optimization algorithm is introduced to further optimize the time domain waveform so that it can achieve any controllable effect. Through multiple iterative adjustments of the algorithm, the precise shaping of the light field waveform in the time domain is ensured, thereby providing ideal initial conditions for the subsequent frequency shift process.

[0025] Step 5: The pulse light field shaped by the spatial light modulator is incident on the focusing lens, and then enters the frequency shifter after being focused by the focusing lens. The pulse light field generates a Raman molecular collimation effect in the frequency shifter, generating a Raman frequency shift.

[0026] Step 6: Use a detector to detect the pulse laser emitted by the frequency shifter. The magnitude and direction of the frequency shift of the pulsed light field undergoing molecular collimation can be calculated, where Δω represents the transient frequency and Δn represents the transient refractive index.

[0027] Beneficial effects of the present invention:

[0028] In the present invention, the waveform shaping frequency shift method based on the molecular collimation effect can achieve directional regulation of the nonlinear effect by precisely controlling the parameters of the pulse waveform, such as steepness and direction. By optimizing the pulse parameters, the nonlinear effect frequency shift can be precisely controlled, opening up new possibilities for improving the performance of ultrafast light sources and innovative applications. This scheme provides a new type of light source scheme with large bandwidth, tunability, high efficiency and compactness, as well as more flexible and diverse control methods, which is of great value to the research in the fields of strong field optics, precision spectroscopy, optical communications, optical imaging, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] Figure 1It is a structural schematic diagram of the shaping frequency shift mechanism in the present invention;

[0031] Figure 2 It is a flow chart of the shaping frequency shift mechanism adjustment method in the present invention;

[0032] Figure 3 It is a schematic diagram of the additional iterative optimization algorithm flow in the present invention.

[0033] In the figure: 1. laser source; 2. reflector; 3. spatial light modulator; 4. focusing lens; 5. frequency shifter; 6. detector. DETAILED DESCRIPTION

[0034] 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.

[0035] See also Figure 1-2 As shown, a mechanism for pulse laser shaping frequency shift includes a laser source 1, a reflector 2, a spatial light modulator 3, a focusing lens 4, a frequency shifter 5 and a detector 6. The laser source 1, the reflector 2, the spatial light modulator 3, the focusing lens 4, the frequency shifter 5 and the detector 6 are arranged in sequence.

[0036] The laser source 1 is used to emit a pulsed laser, which is reflected by the reflector 2 and enters the spatial light modulator 3. After waveform adjustment by the spatial light modulator 3, it is incident on the focusing lens 4, and is refracted by the focusing lens 4 and input into the frequency shifter 5 for frequency shifting. Finally, the pulsed laser is output after waveform adjustment and frequency shifting.

[0037] As a further solution of the present invention: laser source 1 is a titanium sapphire laser with a central wavelength of 800nm. Titanium sapphire laser, that is, titanium sapphire doped laser, is a solid tunable laser that can output continuously tunable laser from 660nm to 1200nm and has a wide range of output. Using it as a laser output source can adapt to the changing output requirements during actual operation.

[0038] As a further solution of the present invention: the reflector 2 is made of ultraviolet fused quartz, has a thickness of 12 mm, and has an operating wavelength of 750 nm to 1100 nm.

[0039] As a further solution of the present invention: the spatial light modulator 3 is a liquid crystal spatial light modulator or a multi-quantum well light modulator. The liquid crystal spatial light modulator is based on optical phased array technology. It mainly controls the orientation of liquid crystal molecules by voltage to achieve modulation of light waves. It can achieve continuous or binary modulation. It is usually composed of one or more liquid crystal layers, a transparent electrode layer, a control circuit and an optical interface. The multi-quantum well light modulator is an optoelectronic device that utilizes a multi-quantum well structure to modulate light waves. It mainly utilizes the quantum confined Stark effect. The multi-quantum well is a system composed of multiple quantum wells. These quantum wells are usually composed of two materials with different energy band gaps. A periodic structure is formed by layered growth technology. In the multi-quantum well modulator, the absorption coefficient of the excitons in the quantum wells can be adjusted by changing the external electric field, thereby achieving modulation of the light waves.

[0040] As a further solution of the present invention: the focusing lens 4 is made of borosilicate crown glass, has a focal length of 10 cm, and an operating wavelength of 350 nm to 2000 nm.

[0041] As a further solution of the present invention: the frequency shifter 5 is a gas chamber filled with nitrogen, and the internal pressure is 5 MPa. By filling the gas chamber with nitrogen, conditions are provided for the molecular collimation effect of the pulse laser.

[0042] As a further solution of the present invention, the frequency shifting element 5 is a waveguide, and the waveguide can be set to limit the propagation of electromagnetic waves on a specific path to achieve the frequency shift of the pulsed laser.

[0043] As a further solution of the present invention: the detector 6 is a fiber optic spectrometer, and the finally output pulse laser can be detected by the fiber optic spectrometer.

[0044] A method for adjusting a pulse laser shaping frequency shift mechanism comprises the following steps:

[0045] Step 1: First, check and wipe each component to ensure that the input and output surfaces of each component are smooth, then start the laser source 1, spatial light modulator 3 and detector 6, and fill nitrogen into the frequency shifter 5 to make the internal air pressure of the frequency shifter 5 5 MPa.

[0046] Step 2: The pulse laser emitted by the laser source 1 is incident on the surface of the reflector 2, and then the angle of the reflector 2 is adjusted so that the pulse laser reflected by the reflector 2 can accurately be incident on the spatial light modulator 3.

[0047] Step 3: The time domain waveform of the input light field is adjusted by the spatial light modulator 3 to change its transient refractive index. The spatial light modulator is an advanced optical device that can accurately control the phase, amplitude and polarization state of the light field. Using this modulator, we can achieve precise control of the input light field so that the light field exhibits the desired waveform change in the time domain. Specifically, the spatial light modulator can adjust the transient refractive index of the light field by changing the phase leading edge and trailing edge of the light field, thereby affecting the propagation characteristics of the light field in the time domain.

[0048] Frequency shift is achieved by modulating the phase of the input wave through a phase modulator. It is widely used in frequency shift in RF, microwave and optical bands. For the spatial light modulator 3 with additional v(t), the output sine wave is:

[0049] E(t)=E0sin(ω c t+pv(t))

[0050] E0 is the amplitude of the input wave, ω c is the incident wave frequency, p is the modulation coefficient of the input signal, when the modulation signal changes linearly with time, that is, v(t)=E0sin[(ω c +ω m )t], the output signal is:

[0051] E(t)=E0sin[(ω c +ω m )t]

[0052] The output wave produces ω compared to the input wave m Considering the periodicity of the sine function, the modulation signal should have an amplitude of 2π / p and a period of 2π / ω. m The sawtooth waveform signal can be converted from linear amplitude modulation to linear phase ramp by the above formula.

[0053] Step 4: In the process of adjusting the light field, an additional iterative optimization algorithm is introduced to further optimize the time domain waveform so that it can achieve any controllable effect. Through multiple iterative adjustments of the algorithm, the accurate shaping of the light field waveform in the time domain is ensured, thereby providing ideal initial conditions for the subsequent frequency shift process. The introduction of the optimization algorithm is to overcome non-ideal factors that may exist in practical applications, such as noise, nonlinear effects, etc. Through multiple iterative adjustments, the optimization algorithm can gradually approach the ideal waveform, making the shaping of the light field waveform in the time domain more accurate. First, according to the initially set target waveform, the error between the current light field output and the target waveform is calculated. Then, the modulation phase loaded by the spatial light modulator is adjusted according to the error, and the adjusted waveform is recorded. This process is repeated until the error between the output light field and the target waveform reaches the preset tolerance range. The gradient descent optimization algorithm is used to optimize the network parameters. First, all the parameters of the optimization network are randomly generated, and then the output waveform of the problem is recorded. By calculating the loss function Loss(w0,w Target ), and then the gradient of the network parameters ω and the loss function ▽Loss(w0,w Target ), and make the weight of each layer in the network change ω along the gradient direction according to the learning rate η t+1 =ω t -η·▽ ω Loss(w0,w Target ).

[0054] Step 5, the pulse light field waveform-shaped by the spatial light modulator 3 is incident on the focusing lens 4, and after being focused by the focusing lens 4, it enters the frequency shifter 5. The pulse light field undergoes a molecular collimation effect in the frequency shifter 5, generating a Raman frequency shift. The pulse light field waveform-shaped is input into the gas chamber, which is pre-filled with molecular gas. The input light field undergoes a Raman frequency shift process in the gas chamber. In this process, due to the delayed response of the molecular collimation effect, the magnitude of the frequency shift and the change of the transient refractive index are asymmetric. The molecular collimation effect refers to the directional arrangement of molecules under the action of the light field. The delayed response of this effect makes the magnitude of the frequency shift of the light field and the change of the transient refractive index asymmetric, that is, the frequency shift of the light field not only depends on the current refractive index, but also is affected by the previous refractive index change. By accurately controlling the waveform of the input light field, the frequency shift process can be regulated in the gas chamber, thereby forming a customized frequency shift result.

[0055] Step 6: Detect the pulse laser emitted by the frequency shifter 5 through the detector 6. The magnitude and direction of the frequency shift of the pulsed light field that has undergone molecular collimation can be calculated, where Δω represents the transient frequency and Δn represents the transient refractive index. The frequency change caused by the laser pulse passing through the molecular gas mainly comes from the delayed response of the laser to the molecular collimation of the gas.

[0056] Working principle: The pump laser is reflected by the reflector 2 onto the spatial light modulator 3, and the input pulse is pulse-shaped into a sawtooth pulse by the spatial light modulator 3. The shaped sawtooth pulse is focused by the focusing lens 4 and enters the gas chamber. The gas chamber of the frequency shifter 5 is filled with nitrogen, and the nitrogen is ionized by the light field to form light filaments. The pulse is frequency-shifted after the molecular collimation effect. Customized frequency shift can be achieved by changing the waveform of the pulse, such as the ratio and direction of the sawtooth wave. The frequency shift result can be measured and collected by the fiber optic spectrometer.

[0057] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A mechanism for pulse laser shaping frequency shift, characterized in that: The invention comprises a laser source (1), a reflector (2), a spatial light modulator (3), a focusing lens (4), a frequency shifter (5) and a detector (6), wherein the laser source (1), the reflector (2), the spatial light modulator (3), the focusing lens (4), the frequency shifter (5) and the detector (6) are arranged in sequence respectively; The laser source (1) is used to emit pulsed laser light, which is reflected by a reflector (2) and then enters a spatial light modulator (3). After waveform adjustment by the spatial light modulator (3), the laser light is incident on a focusing lens (4), refracted by the focusing lens (4), and then input into a frequency shifting element (5) for frequency shifting. Finally, the pulsed laser light is output after waveform adjustment and frequency shifting.

2. A mechanism for pulse laser shaping frequency shift according to claim 1, characterized in that: The laser source (1) is a titanium sapphire laser with a central wavelength of 800 nm.

3. The mechanism for pulse laser shaping frequency shift according to claim 1, characterized in that: The reflector (2) is made of ultraviolet fused quartz, has a thickness of 12 mm, and an operating wavelength of 750 nm to 1100 nm.

4. The mechanism for pulse laser shaping frequency shift according to claim 1, characterized in that: The spatial light modulator (3) is a liquid crystal spatial light modulator or a multi-quantum well light modulator.

5. The mechanism for pulse laser shaping frequency shift according to claim 1, characterized in that: The focusing lens (4) is made of borosilicate crown glass, has a focal length of 10 cm, and an operating wavelength of 350 nm to 2000 nm.

6. The mechanism for pulse laser shaping frequency shift according to claim 1, characterized in that: The frequency shifter (5) is a gas chamber filled with nitrogen, and the internal pressure is 5 MPa.

7. The mechanism for pulse laser shaping frequency shift according to claim 1, characterized in that: The frequency shifting element (5) is a waveguide.

8. The mechanism for pulse laser shaping frequency shift according to claim 1, characterized in that: The detector (6) is a fiber optic spectrometer.

9. A method for adjusting a pulse laser shaping frequency shift mechanism according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: First, check and wipe each component to ensure that the input and output surfaces of each component are smooth, then start the laser source (1), spatial light modulator (3) and detector (6), and fill nitrogen into the frequency shifter (5) to make the internal pressure of the frequency shifter (5) 5 MPa. Step 2: The pulse laser emitted by the laser source (1) is incident on the surface of the reflector (2), and then the angle of the reflector (2) is adjusted so that the pulse laser reflected by the reflector (2) can accurately be incident on the spatial light modulator (3). Step three: The time domain waveform of the input light field is adjusted by the spatial light modulator (3) to change its transient refractive index, so that the light field exhibits a desired waveform change in the time domain. For the spatial light modulator (3) with additional v(t), the output sine wave is: E(t)=E0sin(ω c t+pv(t)) E0 is the amplitude of the input wave, ω c is the incident wave frequency, p is the modulation coefficient of the input signal, when the modulation signal changes linearly with time, that is, v(t) = ω m t / p, the output signal is: E(t)=E0sin[(ω c +w m )t] The output wave produces ω compared to the input wave m Considering the periodicity of the sine function, the modulation signal should have an amplitude of 2π / p and a period of 2π / ω. m The sawtooth waveform signal can be converted from linear amplitude modulation to linear phase ramp by the above formula. Step 4: During the light field adjustment process, an additional iterative optimization algorithm is introduced to further optimize the time domain waveform so that it can achieve any controllable effect. Through multiple iterative adjustments of the algorithm, the precise shaping of the light field waveform in the time domain is ensured, thereby providing ideal initial conditions for the subsequent frequency shift process. Step 5: The pulse light field that has been waveform-shaped by the spatial light modulator (3) is incident on the focusing lens (4), and after being focused by the focusing lens (4), it enters the frequency shifter (5). The pulse light field generates a molecular collimation effect in the frequency shifter (5), generating a Raman frequency shift. Step 6: The pulse laser emitted by the frequency shifting element (5) is detected by a detector (6). The magnitude and direction of the frequency shift of the pulsed light field undergoing molecular collimation can be calculated, where Δw represents the transient frequency and Δn represents the transient refractive index.

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