High-power ultrashort pulse optical parameter tuning simple device

Abstract

The invention provides a high-power ultrashort pulse optical parameter tuning simple device. A slide array, a chirp mirror group, a diffraction assembly, a slit and a first reflector are sequentially arranged along the propagation direction of a light path. The invention provides a compact high-power ultrashort pulse optical parameter tuning device, which realizes high-efficiency spectrum broadening of femtosecond laser through a slide array, performs pulse width compression in combination with a chirp mirror group, and realizes high-precision large-amplitude continuous tuning of wavelength, bandwidth, pulse width and power through a gradual filter, a blazed grating and a slit. The invention has the advantages of high conversion efficiency, strong stability, wide tuning range, good compactness and the like. The device can accurately control multiple output parameters of laser, is suitable for the fields of ultrahigh time resolution spectrum testing, ultrafast laser processing and the like, overcomes the defects that a traditional device is low in conversion efficiency, limited in tuning range and the like, and is an integrated and high-flexibility optical tuning solution.

Description

Technical Field

[0001] The invention relates to the technical field of optical parameter tuning, and more specifically, to a simple device for high-power ultrashort pulse optical parameter tuning. Background Art

[0002] Ultrashort pulse laser, also known as ultrafast laser, generally refers to a pulse laser with a pulse width of picoseconds, femtoseconds or even sub-femtoseconds. The ultra-high instantaneous power and ultra-short pulse width of ultrafast laser make it widely used in micro-nano processing, transient spectroscopy and other fields.

[0003] First, in the process of laser micro-nano processing, due to the diversity of materials, different materials have different bond energies and different absorption energy gaps, which inevitably leads to different materials requiring different laser parameter combinations (wavelength, pulse width and power, etc.) to achieve the desired processing effect. This requires the control of the parameters of the laser output laser. Similarly, in the research process of transient spectroscopy, different materials have different band structures, different absorption cross-sections, and different lifetimes of dynamic signals. This also requires the best combination of the wavelength, pulse width and power of the excitation light to achieve the best dynamic signal extraction. Then, in the application of transient spectroscopy, the energy level structure and carrier dynamics of different materials are different, and different wavelengths, pulse widths, etc. are needed to detect the dynamic process, which also requires the control of the output laser parameters.

[0004] Among the products that have been commercialized internationally, the tuning of optical parameters mainly adopts optical parametric amplifiers (OPA) and nonlinear optical parametric amplifiers (NOPA). These two products are mainly aimed at the output of Ti:Sapphire femtosecond lasers. The former's advantage lies mainly in the tuning of wavelength, and it cannot achieve the tuning of pulse width and power. Although the latter can compress the pulse width of the laser, it adopts the laser crystal spectrum broadening and compression scheme. Under the condition of low nonlinear light conversion efficiency (usually 10%-30%), the output power is very low, and it is generally rarely used in laser processing. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a simple device for high-power ultrashort pulse optical parameter tuning to overcome the disadvantage of low nonlinear light conversion efficiency in the existing optical parameter tuning equipment.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions: a simple device for tuning optical parameters of high-power ultrashort pulses, wherein a glass array, a chirped mirror group, a diffraction component, a slit and a first reflector are sequentially arranged along the propagation direction of the optical path; the glass array is used to receive an incident femtosecond laser in a focused state, and perform spectral broadening on the incident femtosecond laser to form an ultra-wideband white light; the chirped mirror group is used to perform dispersion compensation on the ultra-wideband white light to achieve pulse width compression; the diffraction component is used to diffract the ultra-wideband white light after pulse width compression to generate parallel light bands distributed continuously in space; the slit is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band; the first reflector is used to reflect the light beam passing through the slit, and adjust the reflection direction of the light beam so that the reflected light beam is no longer parallel to the incident light beam; the diffraction component is also used to receive and compress the light beam reflected by the first reflector to generate an outgoing laser, and the diffraction component is also used to perform dispersion compensation on the received light beam to achieve pulse width compression.

[0007] In one embodiment, the glass slide array includes: at least two groups of glass slides, each glass slide group includes two glass slides, and the glass slides are arranged in sequence along the propagation direction of the incident femtosecond laser, so that the incident femtosecond laser passes through each glass slide in sequence to achieve nonlinear broadening; the angle between the surface of each glass slide and the incident femtosecond laser is at the Brewster angle.

[0008] In one embodiment, the two glass slides in the glass slide set are arranged in a V shape, so that the incident femtosecond laser can propagate along the original optical path after passing through the two glass slides in the glass slide set in sequence.

[0009] In one embodiment, the installation position of the glass slide is constrained by the power of the incident femtosecond laser at the installation position, specifically including:

[0010] in, is the critical power for the glass slide to produce a self-focusing effect; is the power of the incident femtosecond laser at the installation position of the glass slide; the distance between any two adjacent glass slides maintains a minimum distance under the premise of satisfying the incident femtosecond laser power constraint.

[0011] In one embodiment, a gradient filter is further arranged between the chirped mirror assembly and the diffraction component; The gradient filter is slidably arranged, the filtering gradient of the gradient filter is parallel to the sliding direction of the gradient filter; the sliding direction of the gradient filter is perpendicular to the propagation direction of the light path; the laser power is continuously tuned after matching the bandwidth selected by the slit.

[0012] In one embodiment, an aperture is further arranged between the glass slide array and the chirped mirror group, and the aperture is used to block the halo formed by the diffraction of the incident femtosecond laser after passing through the glass slide array. A through hole is opened in the center of the aperture, so that the ultra-wideband white light located in the central area of ​​the incident femtosecond laser passes through the through hole and is emitted into the chirped mirror group; the diameter of the through hole is less than or equal to the spot diameter formed by the ultra-wideband white light at the aperture position.

[0013] In one embodiment, a concave mirror and a second reflector are further arranged between the aperture and the chirped mirror group; the concave mirror is used to focus the ultra-wideband white light passing through the through hole into a collimated light beam; the second reflector is used to adjust the propagation direction of the collimated light beam; The spot diameter on the concave mirror The following constraints need to be met:

[0014] in is the spot diameter on the concave mirror; is the focal length of the concave mirror; is the central wavelength of the ultra-broadband white light passing through the through hole; is the focal spot radius where the last slide is located.

[0015] In one embodiment, the chirped mirror group specifically includes two parallel planar chirped mirrors, and the two planar chirped mirrors are both rectangular or circular; The diameter or length of the two planar chirped mirrors Equal and satisfy:

[0016] The distance between the two planar chirped mirrors satisfy:

[0017] in is the spot diameter on the plane chirped mirror; is the number of times the laser spot is reflected on the chirped mirror, is the specific laser incident angle of the chirped mirror. The number of reflections depends on the dispersion compensation amount given by the chirped mirror after one reflection. The dispersion caused by the thickness of the glass and the length of the gas Sure.

[0018] In one embodiment, the diffraction component specifically includes: a blazed grating, which is used to diffract the ultra-wideband white light after pulse width compression to generate a light band continuously distributed in space; a cylindrical concave mirror, which is used to focus the light band continuously distributed in space to generate a parallel light band continuously distributed in space; the parallel light band and the axis of the cylindrical concave mirror are parallel to each other; the distance between the blazed grating and the cylindrical concave mirror is equal to the focal length of the cylindrical concave mirror.

[0019] In one embodiment, the slit includes a first light-shielding sheet and a second light-shielding sheet; the first light-shielding sheet and the second light-shielding sheet can both be slidably adjusted, and the sliding directions of the first light-shielding sheet and the second light-shielding sheet are perpendicular to the propagation direction of the parallel light band; the sliding distance ranges of the first light-shielding sheet and the second light-shielding sheet are both equal to the cross-sectional diameter of the cylindrical concave mirror; the positions of the first light-shielding sheet and the second light-shielding sheet are both controlled by motor drive to achieve continuous adjustment of the slit position and slit width.

[0020] In summary, the present invention has the following beneficial effects: a compact high-power ultrashort pulse optical parameter tuning device, wherein a glass slide array, a chirped mirror group, a diffraction component, a slit and a first reflector are sequentially arranged along the propagation direction of the optical path; the glass slide array is used to receive incident femtosecond laser in a focused state, and perform spectral broadening on the incident femtosecond laser to form ultra-wideband white light; the chirped mirror group is used to perform dispersion compensation on the ultra-wideband white light to achieve pulse width compression; the diffraction component is used to diffract the ultra-wideband white light after pulse width compression to generate parallel light bands continuously distributed in space; the slit is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band; the first reflector is used to reflect the light beam passing through the slit, and adjust the reflection direction of the light beam so that the reflected light beam is no longer parallel to the incident light beam; the diffraction component is also used to receive and compress the light beam reflected by the first reflector to generate an outgoing laser, and the diffraction component is also used to perform dispersion compensation on the received light beam to achieve pulse width compression. This application provides a compact high-power ultrashort pulse optical parameter tuning device, which realizes efficient spectrum broadening of femtosecond lasers through a glass slide array, combines a chirped mirror group for pulse width compression, and realizes high-precision adjustment of wavelength, bandwidth and pulse width through gradient filters, blazed gratings and slits. It has the advantages of high conversion efficiency, strong stability, wide tuning range, good compactness, etc. The device can accurately control the output parameters of the laser and is suitable for fields such as ultra-high time-resolution spectral testing and ultrafast laser processing. It overcomes the shortcomings of low conversion efficiency and limited tuning range of traditional devices, and is an integrated and highly flexible optical tuning solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of a simple device for tuning high-power ultrashort pulse optical parameters of the present invention; Figure 2 Schematic diagram of light propagation when four slides are arranged in parallel; Figure 3 A schematic diagram of light propagation when four glass slides are arranged in a V shape in the present invention; Figure 4 It is a schematic diagram of the structure in which four glass slides are installed in an inert gas sealed chamber in the present invention; Figure 5 is a schematic diagram of a light beam reflected by a planar chirped mirror in the present invention; Figure 6 Schematic diagram of the filter glass turntable in an embodiment of the present invention; In the figure: 1. glass slide; 2. aperture; 3. concave mirror; 4. second reflector; 5. plane chirped mirror; 6. gradient filter; 61. rotating disk; 62. filter; 7. blazed grating; 8. cylindrical concave mirror; 9. slit; 10. first reflector; 11. exit triangular prism; 12. inert gas sealed chamber. DETAILED DESCRIPTION

[0022] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. Several embodiments of the present invention are shown in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0023] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0024] In order to facilitate the understanding of the technical solution of this patent by those skilled in the art, the prior art in this field is first described: Ultrashort pulse laser, also known as ultrafast laser, generally refers to a pulse laser with a pulse width of picoseconds (ps), femtoseconds (fs) or even sub-femtoseconds. The ultra-high instantaneous power and ultra-short pulse width of ultrafast laser make it widely used in micro-nano processing, transient spectroscopy and other fields.

[0025] OPA (Optical Parametric Amplifier) ​​is a device based on nonlinear optical effects, mainly used to amplify and tune the wavelength of laser signals within a specific wavelength range. The main working principle of OPA relies on the optical parametric amplification effect of nonlinear crystals. OPA generates different frequency components in the output light through interaction with pump light. The working principle of OPA mainly includes: the input signal interacts with the pump light through a nonlinear process to generate a new signal light (output light). This process usually occurs in a nonlinear crystal, and its nonlinear properties are used to amplify the signal light (or enhance weak light signals). The gain process of OPA mainly affects the intensity of the signal light, but does not directly change the temporal characteristics (pulse width) of the light. Although in some cases, OPA will produce some dispersion effects through interaction with pump light, this usually does not significantly change the pulse width. The gain efficiency of OPA is related to the power of the pump light and the initial intensity of the signal light. By increasing the power of the pump light, the power of the signal light can be increased, but the gain amplitude of OPA does not precisely control the power. The output power of the OPA is related to the power of the pump light and the efficiency of the nonlinear crystal, so its output power is determined by the characteristics of the pump and the crystal.

[0026] The gain process of the NOPA (Non-Linear Optical Parametric Amplifier) ​​system involves converting the pump light energy into signal light and idler light. The phase matching condition in the nonlinear optical process determines the energy exchange efficiency between the pump light and the signal light. Due to the strict requirements of the phase matching condition on the wavelength and beam shape, a perfect match cannot be achieved, which limits the effective conversion of energy. Different nonlinear crystal materials have different nonlinear coefficients, losses, and bandwidth characteristics. For efficient spectral broadening and compression, it is very important to choose the right crystal material, but these materials usually need to work at lower conversion efficiency. Due to the low nonlinear light conversion efficiency of NOPA, usually only , resulting in a relatively low power output signal, usually only a few millijoules.

[0027] Embodiment 1 In order to solve the above problems, the present invention provides a simple device for tuning high-power ultrashort pulse optical parameters, such as Figure 1−3, a glass slide array, a chirped mirror group, a diffraction component, a slit 9 and a first reflector 10 are sequentially arranged along the propagation direction of the optical path; the glass slide array is used to receive the incident femtosecond laser in a focused state, and perform spectral broadening on the incident femtosecond laser to form ultra-wideband white light; the chirped mirror group is used to perform dispersion compensation on the ultra-wideband white light to achieve pulse width compression; the diffraction component is used to diffract the ultra-wideband white light after pulse width compression to generate parallel light bands that are continuously distributed in space; the slit 9 is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light bands; the first reflector 10 is used to reflect the light beam passing through the slit 9, and adjust the reflection direction of the light beam so that the reflected light beam is no longer parallel to the incident light beam; the diffraction component is also used to receive and compress the light beam reflected by the first reflector 10 to generate an outgoing laser, and the diffraction component is also used to perform dispersion compensation on the received light beam to achieve pulse width compression.

[0028] Specifically, in the present application, the incident femtosecond laser is generated by a laser. In order to broaden the spectrum of the incident femtosecond laser, the incident femtosecond laser needs to be in a focused state to increase the power of the incident femtosecond laser. A plurality of glass slides are arranged in the glass slide array, and when receiving the incident laser, the incident laser can be nonlinearly broadened. When the incident laser passes through the glass slide, the instantaneous phase of the pulse will change, causing the spectrum to expand to the low-frequency and high-frequency sides respectively, thereby broadening the pulse of the incident laser and generating ultra-wideband white light. Under the condition of fixed incident laser parameters, the broadening amplitude of ultra-wideband white light is related to the glass slide material, glass slide thickness, gas pressure in the environment where the glass slide is located, and gas type. After the femtosecond laser passes through the glass slide array, its pulse width broadening is mainly caused by group velocity dispersion. As an ultra-short pulse with a wide spectrum, light of different frequencies (wavelengths) in the femtosecond laser has different group velocities in the glass. Since each glass slide in the glass slide array causes different propagation speeds for light of different wavelengths, the phases of high-frequency (short-wave) and low-frequency (long-wave) light accumulated in the glass differ, resulting in a relative time delay or advance of each frequency component in the pulse. This dispersion effect stretches the temporal width of the laser pulse, ultimately leading to a broadened pulse width.

[0029] In order to avoid pulse width broadening, which will cause the pulse energy of the femtosecond laser to be distributed over a longer time range, thereby reducing the peak power of the laser, a chirped mirror group is set behind the glass slide array. By introducing group velocity dispersion that is opposite to the laser pulse broadening process, the delay of the high-frequency component is corrected, the advance of the low-frequency component is alleviated, and the compensated pulse frequency component is realigned to restore to a pulse width close to the initial one, thereby achieving pulse width compression. The ultra-wideband white light after pulse width compression is transmitted to the diffraction component, which is used to diffract the ultra-wideband white light into spatially continuous parallel light bands. By adjusting the position and size of the slit, the parallel light bands are frequency-selected, the central wavelength of the frequency-selected light beam is determined based on the center point of the slit, and the bandwidth of the frequency-selected light beam is determined based on the width of the slit. After the light beam passing through the slit is reflected by the reflector, it passes through the slit again, and is re-compressed by the diffraction component to form an output laser, which is emitted from the output port of the tuning device.

[0030] In summary, the present application provides a simple device for tuning high-power ultrashort pulse optical parameters. The device uses a femtosecond laser to broaden the spectrum through an ultra-thin glass slide, uses a chirped mirror group to compress the pulse width of the femtosecond laser, and uses a slit for frequency selection. It is particularly suitable for high-power hundred-femtosecond and sub-hundred-femtosecond lasers. The input light conversion efficiency of the device is high, and the pulse width and spectral bandwidth can be continuously adjusted to a large extent. After the spectrum is doubled and differentiated, the wavelength adjustable range can be wider. Compared with the method of using a femtosecond laser to achieve spectrum broadening only through high-pressure inert gas, the stability of the laser output is greatly improved. It is particularly suitable for tuning the light source parameters in ultra-high time-resolution spectral testing and ultrafast laser processing systems.

[0031] In one embodiment, the glass slide array includes: at least two groups of glass slides, each glass slide group includes two glass slides 1, and the glass slides 1 are arranged in sequence along the propagation direction of the incident femtosecond laser, so that the incident femtosecond laser passes through each glass slide 1 in sequence to achieve nonlinear broadening; the angle between the surface of each glass slide 1 and the incident femtosecond laser is at the Brewster angle.

[0032] In practical applications, Brewster's Angle refers to the angle at which the reflected light is completely polarized and the power of the transmitted light is maximized when the incident angle meets certain conditions when light is incident from one medium to another. The specific angle of Brewster's Angle is related to the refractive index of the two media, specifically satisfying:

[0033] in, represents the Brewster angle, which is the angle between the incident light and the interface; is the refractive index of the incident medium; is the refractive index of the transmission medium. When light is incident from air to the glass slide, part of the light will be reflected and part of the light will be transmitted. The intensity of the reflected light and the transmitted light depends on the incident angle. At the Brewster angle, the intensity of the reflected light is minimized and the intensity of the transmitted light is maximized. Therefore, controlling the angle between the glass slide and the incident femtosecond laser can effectively improve the transmission efficiency of the incident femtosecond laser.

[0034] In one embodiment, the two glass slides 1 in the glass slide set are arranged in a V shape, so that the incident femtosecond laser can propagate along the original optical path after passing through the two glass slides in the glass slide set in sequence.

[0035] In practical applications, such as Figure 2 , Figure 3 As shown, the two glass slides 1 in each glass slide group are arranged in a V shape, so that the laser can be slightly corrected in the optical path after being deflected in the thick glass slide, avoiding a large position offset between the optical path and the original incident femtosecond laser, which affects the integration of the equipment.

[0036] In one embodiment, the installation position of the glass slide is constrained by the power of the incident femtosecond laser at the installation position, specifically including:

[0037] in, is the critical power for the glass slide to produce a self-focusing effect; is the power of the incident femtosecond laser at the installation position of the glass slide; the distance between any two adjacent glass slides maintains a minimum distance under the premise of satisfying the incident femtosecond laser power constraint.

[0038] In practical applications, when ultrashort lasers propagate in the air, due to the high intensity of the laser, the refractive index of the air will change, usually increasing. This change will cause the laser beam to focus, further increasing its intensity and forming a self-focusing effect. After focusing, ultrashort laser pulses usually form a high-intensity concentrated light spot in the near-focus area. As the laser propagates, the focus will expand. However, the high intensity and nonlinear effects of the laser pulse may cause the laser to refocus or deform in the area away from the focus, forming a layered propagation effect, that is, the layered effect of laser propagation in the air. Therefore, during the propagation process, the laser usually focuses-diverges-focuses alternately, and the laser will form numerous focal spots on the propagation optical path. Because the thinner the laser beam, the higher the peak power of the laser, the more obvious the nonlinear effect of the interaction between the laser and the glass slide. The peak power cannot be too high, as too high peak power will damage the glass slide. When setting the position of the glass slide, it is usually necessary to set the glass slide near the focal spot position to balance the relationship between the nonlinear effect and the peak power. Specifically, the position of the glass slide can be adjusted to achieve the maximum value of the spectrum broadening at the position of the glass slide.

[0039] Based on the hierarchical effect of the nonlinear laser, it is necessary to determine the power of the incident femtosecond laser at each position. , and the critical power of the self-focusing effect of the glass slide , to determine the placement of the slide, that is, it is necessary to meet the requirements at the placement position. In order to improve the integration of the device and reduce the size of the device, it is necessary to control the distance between the two glass slides to be kept at a minimum value when the glass slides are placed while satisfying the incident power. The position of the glass slide can also be adjusted to achieve the maximum value of the spectrum broadening at the position of the glass slide.

[0040] In one embodiment, the glass slide 1 is made of one or more of BBO crystal, sapphire crystal, and quartz glass.

[0041] In practical applications, the power of the input ultrashort laser is controlled so that the peak power threshold Pin of the input ultrashort laser pulse is greater than the power threshold Pspm of the glass slide to achieve self-phase modulation (SPM). The refractive index of the material through which the glass slide or laser passes has nonlinear characteristics, and the refractive index n of the optical material is related to the light intensity I. When the electric field intensity changes, the refractive index of the material also changes, and the phase of the light wave passing through the medium also changes, which is SPM. The frequency adjustment caused by SPM broadens the spectrum. Its frequency shift Δφ can be expressed by the following formula:

[0042]

[0043] Among them, Pav is the average power of the laser, f is the repetition frequency of the laser, S is the focal spot area, Ts is the duration of a single pulse, λ is the laser wavelength, Aeff is the effective area, Leff is the effective length, and n2 is the nonlinear refractive index of the medium. At the same time, the power threshold Pin of the input laser should be greater than the critical power Pcr of the self-focusing effect of the glass slide, but less than twice the latter, specifically satisfying:

[0044]

[0045] Where λ is the laser wavelength, is the linear refractive index, is the nonlinear refractive index of the medium. By changing the glass slides of different materials and thicknesses, the spectrum can achieve a bandwidth broadening of 10 times or more. In particular, the ultra-thin micron-level glass slide design is more suitable for high-peak power femtosecond laser spectrum broadening than the currently commonly used spectrum broadening designs, such as sapphire, CaF2, water film, etc.

[0046] In one embodiment, the thickness of the glass slides of the glass slide array can be adjusted according to the pulse energy of the incident femtosecond laser. From the perspective of bandwidth broadening and the quality of supercontinuum light generated, the higher the power, the thinner the glass slide, so that the thickness of the medium through which the laser passes is small, which is conducive to reducing the divergence of the laser and improving the beam quality. In this embodiment, the thickness of the glass slide is between . Angle of incidence The Brewster angle is satisfied. Using the currently commercial titanium sapphire laser as the light source, the output laser pulse width is , the output power is , the repetition frequency is The device can achieve an input power of By adjusting the focal length of the laser passing through the concave mirror, the highest peak power at the shorter point can be achieved. By adjusting the position of the glass slide at the focus, the glass slide can be placed at the best peak power position to obtain the best widening effect and conversion efficiency without damaging the glass slide. After the slides are assembled, The conversion efficiency of ultra-broadband white light generated by the input laser can reach When injected into the slide cavity Atmosphere pressure of inert gas He, the spectrum width can reach In this application, the spectrum broadened by the glass slide in 1.5 atmospheres of He is passed through the slit 9, reflected by the reflector, and then compressed by the blazed grating 7. The pulse width can be continuously tuned from sub-5 femtoseconds to picoseconds, and the central wavelength and bandwidth can be adjusted in By combining the doubled and difference frequency lasers, the frequency can be selected through the slit 9 and the first reflector 10, and a large range of continuous tuning can be achieved from the ultraviolet 250nm to the infrared 1700nm band.

[0047] In one embodiment, Figure 4 As shown, it also includes: an inert gas sealed chamber 12; the inert gas sealed chamber 12 is arranged along the propagation direction of the incident femtosecond laser, and the glass slide array is arranged inside the inert gas sealed chamber 12 along the propagation direction of the incident femtosecond laser; the inert gas sealed chamber 12 is filled with one of helium, neon, argon, krypton or xenon, and the gas pressure in the inert gas sealed chamber is .

[0048] Specifically, in practical applications, the spectrum broadening effect is related to the medium through which the ultrafast laser passes. In an inert gas, the broadening effect of the ultrafast laser is more obvious than in an air medium, and in a gas medium, the greater the pressure of the gas medium, the greater the effect on the spectrum broadening. Therefore, by filling the inert gas sealed cavity 12 with an inert gas and controlling the pressure of the inert gas in the sealed cavity, the broadening effect of the ultrafast laser can be further improved. In the process of the laser passing through the glass slide group, the glass slide and the inert gas can both act as nonlinear media and have a broadening effect on the laser. In particular, the nonlinear refractive index of the inert gas increases with the increase of the gas pressure, thereby having a positive gain effect on the broadening of the spectrum.

[0049] In one embodiment, Figure 4 As shown, the inert gas sealed cavity is provided with an incident through hole and an exit through hole; The first glass slide in the glass slide array is covered on the incident through hole; The last glass slide in the glass slide array is covered on the exit through hole; The angle between the first glass slide in the glass slide array and the incident femtosecond laser satisfy:

[0050] in, is the Brewster angle of the interface between air and glass slide; is the Brewster angle of the interface between the glass slide and the inert gas; The angle between the last glass slide in the glass slide array and the incident femtosecond laser satisfy:

[0051] in, is the Brewster angle of the interface between the inert gas and the glass slide; is the Brewster angle of the glass slide-air interface.

[0052] Specifically, the high-pressure inert gas is filled into the inert gas sealed chamber 12, which improves the effect of ultrafast laser spectrum broadening and also changes the Brewster angle from the glass slide to the high-pressure inert gas. That is, on the first glass slide, the first Brewster angle of the ultrafast femtosecond laser incident from the air to the glass slide is , and the second Brewster angle of ultrafast femtosecond laser emitted from the glass slide into the inert gas In order to maximize the transmittance of the femtosecond laser, the average of the two Brewster angles can be taken. Similarly, the angle of the last slide also needs to be determined based on the average of the two Brewster angles.

[0053] In the inert gas sealed chamber 12, in order to prevent the high-pressure gas from crushing the glass slide on the incident through hole, the sizes of the incident through hole and the exit through hole need to be controlled within a predetermined size range, usually 1 mm to 3 mm.

[0054] Under one atmosphere of pressure, when the laser is refracted on the surface and inside of the glass slide through the inert gas medium, the refractive index of the inert gas is similar to that of air. However, the refractive index of the inert gas increases with the increase of gas pressure, thereby fine-tuning the direction of the laser emitted through the glass slide group.

[0055] Changes in the refractive index of noble gases ,satisfy:

[0056] in , and Refractive index, gas pressure and temperature under standard conditions. and are the expansion coefficient and temperature in Celsius of the gas respectively. It is the increase or change of gas pressure. By changing the gas pressure, the refractive index also changes proportionally, thereby modulating the Brewster angle. Under the same laser input parameters, if the inert gas He is replaced by Ne gas with a larger nonlinear refractive index, or even Xe gas, the spectrum broadening will be further increased to reach .

[0057] In one embodiment, the glass slide 1 is detachable so that the material and thickness of the glass slide 1 can be adjusted according to the pulse energy of the incident laser. From the perspective of bandwidth broadening and the quality of supercontinuum light generated, the higher the power, the thinner the glass slide, so that the thickness of the medium through which the laser passes is small, which is conducive to reducing the divergence of the laser and improving the beam quality.

[0058] In one embodiment, a gradient filter 6 is further arranged between the chirped mirror group and the diffraction component; the gradient filter 6 is slidably arranged, and the filtering gradient of the gradient filter 6 is parallel to the sliding direction of the gradient filter 6; the sliding direction of the gradient filter 6 is perpendicular to the propagation direction of the optical path; so as to continuously tune the laser power after matching the bandwidth selected by the slit.

[0059] In this application, ultra-wideband white light contains a large number of wavelength components, and many applications require a single wavelength or narrowband light source. The gradient filter is used to select a beam of predetermined wavelength from the ultra-wideband white light. The sliding direction of the filter is perpendicular to the optical path, which is convenient for integration into a compact optical system and reduces the error caused by mechanical adjustment. The gradient filter can be continuously adjusted within a large wavelength range. Combined with a diffraction component or a chirp mirror group, high-precision spectral tuning of ultra-wideband white light can be achieved. The use of gradient filters in conjunction with slits can more flexibly control the bandwidth range and further enhance the tuning capability of the system.

[0060] In one embodiment, Figure 6 As shown, a rotating disk 61 is also provided between the chirped mirror group and the diffraction component; filters 62 are arranged along the circumference of the rotating disk 61; the rotating disk 61 can be rotated under the drive of the motor so that different filters are rotated to the optical path to filter light. Multiple filters are installed on the rotating disk, each filter corresponds to a different wavelength range, and the rotating disk can be controlled by the motor to switch the filters, so that the selection of light of different wavelengths can be quickly realized; the filters are installed on the rotating disk, and multiple filters share one optical path position, which can significantly reduce the volume and complexity of the system compared to designing multiple filter components separately.

[0061] In one embodiment, an aperture 2 is further arranged between the glass slide array and the chirped mirror group. The aperture 2 is used to block the halo formed by the diffraction of the incident femtosecond laser after passing through the glass slide array. A through hole is opened at the center of the aperture 2 to allow the ultra-wideband white light located in the central area of ​​the incident femtosecond laser to pass through the through hole and then enter the chirped mirror group; the diameter of the through hole is less than or equal to the spot diameter formed by the ultra-wideband white light at the aperture position.

[0062] After passing through the glass slide, the ultrafast femtosecond laser will have its spectrum broadened and a colored halo will be generated around the laser. These colored halos may interfere with subsequent light after entering the grating. To solve this problem, an aperture with a through hole is needed to shield the colored halo around the laser and only allow the white light in the middle of the ultrafast femtosecond laser to pass through, while also being able to adjust the laser power.

[0063] In one embodiment, a concave mirror 3 and a second reflector 4 are further provided between the aperture 2 and the chirped mirror assembly; the concave mirror 3 is used to focus the ultra-wideband white light passing through the through hole into a collimated light beam; the second reflector 4 is used to adjust the propagation direction of the collimated light beam so that the collimated light beam can be transmitted to the chirped mirror assembly; The spot diameter on the concave mirror 3 The following constraints need to be met:

[0064] in is the spot diameter on the concave mirror 3; is the focal length of the concave mirror 3; is the central wavelength of the ultra-broadband white light passing through the through hole; is the focal spot radius where the last slide is located.

[0065] Since the ultrafast laser will produce a layering effect when propagating in the medium, it will diverge after passing through the last glass slide. Therefore, the ultrafast laser will still diverge after passing through the aperture. In order to allow the ultrafast laser to propagate smoothly backward, a concave mirror 3 is required to be set on the propagation light path of the ultrafast laser to focus the divergent ultra-broadband white light into parallel ultra-broadband white light. The spot diameter on the concave mirror 3 is The following constraints need to be met:

[0066] in is the maximum diameter of the light spot on the concave mirror 3; is the focal length of the concave mirror 3; is the central wavelength of the incident light beam; is the focal spot radius where the last slide is located.

[0067] In one embodiment, the chirped mirror assembly specifically includes two parallel planar chirped mirrors 5, both of which are rectangular or circular; the diameter or length of the two planar chirped mirrors 5 is Equal and satisfy: The distance between the two planar chirped mirrors 5 is satisfy: in is the spot diameter on the plane chirped mirror; is the number of times the laser spot is reflected on the chirped mirror, is the specific laser incident angle of the chirped mirror. The dispersion compensation amount given by the chirped mirror is Total dispersion caused by the thickness of the glass and the length of the gas Sure.

[0068] Specifically, the total dispersion Dispersion introduced by the glass of the chirped mirror and the dispersion introduced by the gas medium in which the chirped mirror is located Jointly determine:

[0069]

[0070]

[0071] in, is the thickness of the slide; is the length of the light beam propagating along the gas medium; is the refractive index of the slide; is the refractive index dispersion property of the gas; is the dispersion coefficient of the glass material; is the dispersion coefficient of the gas medium.

[0072] The number of reflections n is calculated based on the dispersion compensation amount z of the chirped mirror single reflection and the total dispersion G, specifically:

[0073] in, represents rounding up to ensure that the chirped mirror can fully compensate for the dispersion.

[0074] like Figure 5 As shown, is the spot diameter incident on the chirped mirror; is a specific laser incident angle of the chirped mirror. In this embodiment, the angle between the two plane chirped mirrors 5 and the ultra-wideband white light is between 5° and 15°, and the beam diameter is 10 mm. The ultra-wideband white light is reflected multiple times between the two plane chirped mirrors 5 to compress the pulse width of the ultra-wideband white light. The number of reflections is usually between 3 and 20 times. Taking 5 reflections as an example, the distance between the two plane chirped mirrors 5 is between 40 and 100 mm.

[0075] In practical applications, the purpose of the chirped mirror pair is to achieve pulse width compression of ultra-wideband white light by introducing dispersion compensation pulse width. Light of different wavelengths will have different reflection paths on the chirped mirror, resulting in changes in time delay (dispersion). The angle of the chirped mirror directly affects the propagation path length of the light beam, thereby affecting the dispersion of the spectrum. By adjusting the angle of the chirped mirror, the number of reflections of ultra-wideband white light between the two chirped mirrors can be adjusted accordingly. For a given chirped mirror, each reflection of ultra-wideband white light will introduce a wavelength-dependent time delay. The design of the chirped mirror will make the reflection time of light of different wavelengths on the mirror surface different. By accumulating the optical path length, the chirped mirror can introduce sufficient time delay for ultra-wideband white light, thereby achieving compensation for initial dispersion and pulse width compression.

[0076] In one embodiment, the diffraction component specifically includes: a blazed grating 7, which is used to diffract the ultra-wideband white light after pulse width compression to generate a light band continuously distributed in space; a cylindrical concave mirror 8, which is used to focus the light band continuously distributed in space to generate a parallel light band continuously distributed in space; the parallel light band and the axis of the cylindrical concave mirror 8 are parallel to each other; the distance between the blazed grating and the cylindrical concave mirror is equal to the focal length of the cylindrical concave mirror 8.

[0077] After diffraction by the blazed grating 7, the ultra-wideband white light can be separated into different wavelengths of light and form a continuously distributed light band in space, which provides a basis for subsequent optical tuning; the cylindrical concave mirror has an asymmetric focusing characteristic, which can focus in one direction and keep the light beam parallel in another direction; through the focusing effect of the cylindrical concave mirror, the separated light band generated by the blazed grating 7 can be further adjusted to a continuously distributed and uniform parallel light band in space; the distance between the blazed grating 7 and the cylindrical concave mirror is equal to the focal length of the cylindrical concave mirror, which can ensure that the light diffracted from the blazed grating can be perfectly focused to the focal point of the cylindrical concave mirror and form an ideal parallel light band. The combination of the high diffraction efficiency of the blazed grating 7 and the high reflection efficiency of the cylindrical concave mirror ensures the efficient use of ultrafast laser energy by the system. This design reduces unnecessary energy loss in the optical path, thereby improving the overall output efficiency of the system.

[0078] In one embodiment, the slit includes a first light-shielding sheet and a second light-shielding sheet; the first light-shielding sheet and the second light-shielding sheet can both be slidably adjusted, and the sliding directions of the first light-shielding sheet and the second light-shielding sheet are perpendicular to the propagation direction of the parallel light band; the sliding distance ranges of the first light-shielding sheet and the second light-shielding sheet are both equal to the cross-sectional diameter of the cylindrical concave mirror; the positions of the first light-shielding sheet and the second light-shielding sheet are both controlled by motor drive to achieve continuous adjustment of the slit position and slit width.

[0079] The sliding position of the first shading sheet and the second shading sheet is controlled by a motor drive to achieve continuous adjustment of the slit position and width, which is highly flexible and adaptable. The sliding direction of the shading sheet is perpendicular to the propagation direction of the parallel light band, which can efficiently cut the target spectral area, avoid lateral interference, and improve the adjustment efficiency. The servo motor or stepper motor drive is used to accurately control the motor rotation angle based on the number of pulses, thereby achieving high-precision adjustment of the slit position and width to meet different experimental needs. The motor drive supports automated adjustment, simplifies the operating process, and reduces manual intervention. It is particularly suitable for application scenarios that require frequent switching of spectral settings, significantly improving the convenience and efficiency of the system.

[0080] The slit can be adjusted manually or electrically, and the slit can be adjusted by changing the position of the center point of the slit to select the position of the central wavelength, or by adjusting the width of the slit to select the bandwidth of the optical signal passing through the slit. Among them, the selection of the position of the central wavelength requires the overall adjustment of the upper and lower shading plates of the slit. While keeping the phase position unchanged, the two shading plates are moved simultaneously to achieve the selection of the central wavelength of the slit. The selection of the bandwidth is to control the relative position of the upper and lower shading plates of the slit 3 to adjust the width of the slit. According to the time-frequency uncertainty principle, the bandwidth of the ultrafast laser is inversely proportional to the pulse width. Therefore, by selecting the bandwidth of the light band formed by the broadening of the ultrafast laser, the pulse width of the ultrafast laser can be indirectly controlled. In the present application, the optical signal that passes through the slit and is reflected by the first reflector is compressed by the blazed grating 7. The pulse width can be continuously tuned between sub-5 femtoseconds and picoseconds, and the central wavelength and bandwidth can be adjusted within a certain range. Combined with the frequency-doubled and frequency-differenced lasers, the slit and the first reflector are integrated to select the frequency, which can achieve the effect of switching from ultraviolet to ultraviolet. arrive Largely continuously adjustable within the infrared band.

[0081] In traditional laser tuning equipment, the slit is used alone to select the spectrum, which can control the light flux passing through, thereby roughly adjusting the output power. The change of the slit width directly affects the bandwidth and power of the light. The adjustment is relatively mechanical, with limited accuracy, and will cause the power adjustment to be coupled with the bandwidth. In this embodiment, the filter glass and the slit are used to cooperate with each other. The filter can select different wavelengths or suppress specific wavelengths by rotating under a fixed slit width, thereby making more precise adjustments to the power, effectively decoupling the relationship between power and bandwidth, so that users can optimize the power and bandwidth separately. The filter further filters the light of non-target wavelengths and enhances the spectral purity. The combination of the slit and the filter can achieve higher selectivity for the target wavelength and is suitable for applications that require multi-wavelength switching. In some scenarios of nonlinear experiments of ultrafast laser tuning, stable power output is required but frequent wavelength switching is required. Therefore, the slit can be used to provide a fixed bandwidth, and the filter can achieve fast wavelength switching or power adjustment to meet the needs of dynamic experiments. When the power is high, the slit can prevent excessive broadband light flux from causing damage to optical components, while the filter can optimize the output under fixed conditions.

[0082] In one embodiment, the first reflector is rotatably arranged to adjust the position misalignment of the light spot of the light beam after passing through the slit and reaching the laser incident first grating, thereby ensuring the output of the laser and preventing it from returning to the original path, so as to facilitate the extraction of the output laser from the system.

[0083] Specifically, if Figure 1 As shown in the black part of the optical path, the plane mirror behind the slit needs to be rotated a small angle to ensure that the reflected light beam can be offset from the incident light spot on the grating by a suitable position, so that the light beam can be output from the system. Need to meet .in, is the focal length of the cylindrical concave mirror, l It is the vertical distance from the plane mirror behind the slit to the center line of the cylindrical concave mirror; It is the spot diameter formed by the light beam formed by the reflector on the cylindrical concave mirror.

[0084] In one embodiment, the device further comprises an output triangular prism 11 for leading the re-compressed output laser out of the system.

[0085] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0086] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A simple device for tuning high-power ultrashort pulse optical parameters, characterized in that: A glass slide array, a chirped mirror group, a diffraction component, a slit and a first reflector are sequentially arranged along the propagation direction of the light path; The glass slide array is used to receive incident femtosecond laser light in a focused state, and perform spectrum broadening on the incident femtosecond laser light to form ultra-broadband white light; The chirped mirror group is used to perform dispersion compensation on the ultra-wideband white light to achieve pulse width compression; The diffraction component is used to diffract the ultra-wideband white light after pulse width compression to generate parallel light bands that are continuously distributed in space; The slit is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band; The first reflector is used to reflect the light beam passing through the slit and adjust the reflection direction of the light beam so that the reflected light beam is no longer parallel to the incident light beam; The diffraction component is also used to receive and compress the light beam reflected by the first reflector to generate an outgoing laser. The diffraction component is also used to perform dispersion compensation on the received light beam to achieve pulse width compression.

2. The high-power ultrashort pulse optical parameter tuning simple device according to claim 1, characterized in that: The glass slide array includes: at least two groups of glass slides, each glass slide group includes two glass slides, and the glass slides are arranged in sequence along the propagation direction of the incident femtosecond laser, so that the incident femtosecond laser passes through each glass slide in sequence to achieve nonlinear broadening; the angle between the surface of each glass slide and the incident femtosecond laser is at the Brewster angle.

3. The high-power ultrashort pulse optical parameter tuning simple device according to claim 2, characterized in that: The two glass slides in the glass slide group are arranged in a V shape, so that the incident femtosecond laser can propagate along the original light path after passing through the two glass slides in the glass slide group in sequence.

4. The high-power ultrashort pulse optical parameter tuning simple device according to claim 3, characterized in that: The installation position of the glass slide is constrained by the power of the incident femtosecond laser at the installation position, specifically including: in, is the critical power for the glass slide to produce a self-focusing effect; is the power of the incident femtosecond laser at the installation position of the glass slide; the distance between any two adjacent glass slides maintains a minimum distance under the premise of satisfying the incident femtosecond laser power constraint.

5. The high-power ultrashort pulse optical parameter tuning simple device according to claim 1, characterized in that: A gradient filter is also arranged between the chirped mirror group and the diffraction component; The gradient filter is slidably arranged, the filtering gradient of the gradient filter is parallel to the sliding direction of the gradient filter; the sliding direction of the gradient filter is perpendicular to the propagation direction of the light path; the laser power is continuously tuned after matching the bandwidth selected by the slit.

6. The high-power ultrashort pulse optical parameter tuning simple device according to claim 5, characterized in that: An aperture is also arranged between the glass slide array and the chirped mirror group. The aperture is used to block the halo formed by the diffraction of the incident femtosecond laser after passing through the glass slide array. A through hole is opened at the center of the aperture to allow the ultra-wideband white light located in the central area of ​​the incident femtosecond laser to pass through the through hole and then enter the chirped mirror group; the diameter of the through hole is less than or equal to the spot diameter formed by the ultra-wideband white light at the aperture position.

7. The high-power ultrashort pulse optical parameter tuning simple device according to claim 6, characterized in that: A concave mirror and a second reflector are also provided between the aperture and the chirped mirror group; the concave mirror is used to focus the ultra-wideband white light passing through the through hole into a collimated light beam; the second reflector is used to adjust the propagation direction of the collimated light beam; The spot diameter on the concave mirror The following constraints need to be met: in is the spot diameter on the concave mirror; is the focal length of the concave mirror; is the central wavelength of the ultra-broadband white light passing through the through hole; is the focal spot radius where the last slide is located.

8. The high-power ultrashort pulse optical parameter tuning simple device according to claim 7, characterized in that: The chirped mirror group specifically includes two parallel planar chirped mirrors, and the two planar chirped mirrors are both rectangular or circular; The diameter or length of the two planar chirped mirrors Equal and satisfy: The distance between the two chirped mirrors satisfy: in is the spot diameter on the plane chirped mirror; is the number of times the laser spot is reflected on the chirped mirror, is the specific laser incident angle of the chirped mirror. The number of reflections depends on the dispersion compensation amount given by the chirped mirror after one reflection. The dispersion caused by the thickness of the glass and the length of the gas Sure.

9. The high-power ultrashort pulse optical parameter tuning simple device according to claim 1, characterized in that: The diffraction component specifically includes: Blazed grating, used to diffract the ultra-broadband white light after pulse width compression to generate a light band that is continuously distributed in space; The cylindrical concave mirror is used to focus the light bands distributed continuously in space to generate parallel light bands distributed continuously in space; The parallel light band and the axis of the cylindrical concave mirror are parallel to each other; The distance between the blazed grating and the cylindrical concave mirror is equal to the focal length of the cylindrical concave mirror.

10. The high-power ultrashort pulse optical parameter tuning simple device according to claim 9, characterized in that: The slit includes a first light shielding sheet and a second light shielding sheet; the first light shielding sheet and the second light shielding sheet are both capable of sliding and adjusting, and the sliding directions of the first light shielding sheet and the second light shielding sheet are perpendicular to the propagation direction of the parallel light band; The sliding distance ranges of the first light shielding sheet and the second light shielding sheet are both equal to the cross-sectional diameter of the cylindrical concave mirror; The position of the first shading sheet and the position of the second shading sheet are both controlled by motor drive, so that the slit position and the slit width can be continuously adjusted.

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