阅读说明：本技术 一种超连续谱产生装置及超连续谱产生方法 (Super-continuum spectrum generation device and super-continuum spectrum generation method ) 是由 陶镇生 田传山 朱冰冰 于 2020-06-27 设计创作，主要内容包括：本发明涉及一种超连续谱产生装置及超连续谱产生方法,装置包括依次设置的飞秒激光器、反射镜、半波片、偏振片、聚焦透镜、多片等腔长排列的介质薄片组成的介质薄片谐振腔和准直透镜；方法包括：设定和获得预置参数,计算得到介质薄片上有效光斑半径,获得空间自相似模式曲线,计算得到介质薄片谐振腔的腔长,产生超连续谱以及超连续谱的优化。与现有技术相比,通过激光器参数推导谐振系统的物理参数,避免了人工摆放介质薄片带来的不确定性,可保证获得能量转换效率高、空间自相似模式优的超连续输出；占用比充气中空光纤更小的空间,适用于多种不同激光功率、脉冲能量以及波长的入射激光。(The invention relates to a super-continuum spectrum generating device and a super-continuum spectrum generating method, wherein the device comprises a femtosecond laser, a reflector, a half-wave plate, a polaroid, a focusing lens, a dielectric sheet resonant cavity consisting of a plurality of dielectric sheets arranged in equal cavity length and a collimating lens which are arranged in sequence; the method comprises the following steps: setting and obtaining preset parameters, calculating to obtain the effective spot radius on the dielectric sheet, obtaining a spatial self-similarity mode curve, calculating to obtain the cavity length of the dielectric sheet resonant cavity, and generating the supercontinuum and optimizing the supercontinuum. Compared with the prior art, the method has the advantages that the physical parameters of the resonance system are deduced through the laser parameters, so that the uncertainty caused by manually placing the medium sheets is avoided, and the super-continuous output with high energy conversion efficiency and excellent spatial self-similarity mode can be ensured; occupies smaller space than the inflatable hollow optical fiber, and is suitable for incident laser with various laser powers, pulse energies and wavelengths.)

1. A super-continuum spectrum generation device comprises a femtosecond laser, a reflector, a half-wave plate, a polaroid, a focusing lens, a dielectric sheet resonant cavity and a collimating lens which are sequentially arranged, and is characterized in that the dielectric sheet resonant cavity is composed of a plurality of dielectric sheets which are arranged in an equal cavity length mode, the thicknesses of the plurality of dielectric sheets are consistent, and the cavity length of the dielectric sheet resonant cavity is obtained by calculating the effective light spot radius, the incident wavelength and a spatial self-similar mode curve on the dielectric sheet.

2. The apparatus according to claim 1, wherein the length L of said dielectric slab resonator is calculated as:

wherein w is the effective spot radius on the dielectric sheet, λ is the incident pulse laser wavelength, f (b) is the ordinate corresponding to the selected nonlinear phase b in the spatial self-similar mode curve, and the ordinate is positively correlated with the square of the effective spot radius on the dielectric sheet.

3. The apparatus according to claim 2, wherein the selected nonlinear phase b is ≦ 1.2 rad.

4. The apparatus according to claim 1, wherein the effective spot radius on the dielectric sheet is obtained by the following formula:

wherein n is₂The Kerr coefficient of the dielectric sheet as a resonant cavity of the dielectric sheet_effIs the equivalent thickness of the dielectric sheet, E₀For incident pulsed laser energy, τ_FWHMB is the selected nonlinear phase for the full width at half maximum of the time domain of the incident pulsed laser.

5. The apparatus according to claim 4, wherein said dielectric sheet has an equivalent thickness/, of_effThe calculation formula of (2) is as follows:

wherein l is the real thickness of the dielectric sheet, theta_BIs the brewster angle.

6. The apparatus according to claim 1, wherein the spatial self-similarity mode curve isA curve is obtained by solving a spatial self-similarity mode of the dielectric sheet resonant cavity for each selected nonlinear phase b through Fox-Li iteration and further counting a convergence solution;

the expression of the Fox-Li iteration is:

wherein, U_i(p ') is the light field at the front surface p' of a sheet of dielectric material, U_i+1(p) is lowerLight field, U, at the front surface ρ of a dielectric sheet₁(ρ₀) Front surface rho of first medium sheet₀Light field of (J)₀(. cndot.) is a zero order Bessel function,

the constraints of the spatial self-similarity mode are as follows:

max(|U_i(ρ')|)＝1

wherein the content of the first and second substances,

7. The apparatus according to claim 6, wherein the head position of the dielectric slab resonator is determined by the abscissa and the ordinate corresponding to the selected nonlinear phase b in the spatial self-similar mode curve.

8. The apparatus according to claim 7, wherein the head position d is₀The calculation formula of (2) is as follows:

β＝α_b×f(b)

wherein β is a ratio of a distance between the first medium sheet and the focal point of the focusing lens to a rayleigh length of the light beam, and f (b) is a vertical coordinate corresponding to a selected nonlinear phase b in the spatial self-similarity mode curve.

9. A stent as defined in claim 8A continuum generation apparatus, characterized in that the focal radius is obtained by β, the focal radius determining the spatial phase of the light field at the front surface of the first sheet of media, said focal radius w₀The calculation formula of (2) is as follows:

wherein w is the effective spot radius on the dielectric sheet.

10. A supercontinuum generation method using the supercontinuum generation apparatus according to any one of claims 1 to 9, characterized by comprising the steps of:

step S1: setting selected nonlinear phase b and incident pulsed laser energy E₀；

Step S2: obtaining a Kerr coefficient n of the dielectric sheet₂Dielectric sheet equivalent thickness l_effIncident pulse laser wavelength lambda and incident pulse laser time domain half-height width tau_FWHM；

Step S3: using selected nonlinear phase b, incident pulsed laser energy E₀K-factor n of dielectric sheet₂Dielectric sheet equivalent thickness l_effAnd half-width tau of incident pulse laser time domain_FWHMCalculating the effective spot radius w on the dielectric sheet by the following formula:

step S4: obtaining a spatial self-similarity mode curve by carrying out Fox-Li recursion on a light field;

step S5: and calculating the cavity length L of the dielectric sheet resonant cavity by using a spatial self-similar mode curve, the effective spot radius w on the dielectric sheet and the incident pulse laser wavelength lambda through the following formula:

step S6: setting a dielectric sheet resonant cavity according to the cavity length L of the dielectric sheet resonant cavity, and generating a supercontinuum by pulse laser emitted by a femtosecond laser sequentially through a reflector, a half-wave plate, a polarizing plate, a focusing lens, the dielectric sheet resonant cavity and a collimating lens;

step S7: and (3) finely adjusting the incident pulse laser energy and the cavity length L, and optimizing the supercontinuum width and the output laser pulse space mode.

Technical Field

The invention relates to the technical field of ultrafast optics and nonlinear optics, in particular to a supercontinuum generation device and a supercontinuum generation method.

Background

The supercontinuum light source has very important application in ultrafast optics and nonlinear optics research. The supercontinuum light source can cover a wide spectrum range and is an important tool for researching ultrafast spectroscopy of gas, liquid and solid materials. Meanwhile, the supercontinuum light source is widely applied to laser products such as an optical parametric amplifier and the like as a seed light source, and laser radiation with adjustable wavelength is generated according to needs after regeneration and amplification. On the other hand, the phase correction of the supercontinuum light source can compress laser pulses into ultrashort pulses in time, so that extremely strong light field intensity is generated.

The continuous spectrum generation stage is mainly realized by an inflatable hollow fiber supercontinuum generation device, and the device comprises the following parts: one hollow optical fiber; one mounting platform with a V-shaped optical fiber mounting groove; brewster angle entrance and exit windows; an observation window; air inlet and outlet and cavity mounted on the two-dimensional moving platform.

The existing gas-filled hollow fiber supercontinuum generation device meets the supercontinuum generation of pulse energy laser from 0.4mJ to 13mJ, and the transmission efficiency is about 70%. The disadvantages of the device for generating the super-continuum spectrum by utilizing the inflatable hollow optical fiber are as follows: 1) the installation operation is complex, and special training personnel are required for maintenance; 2) the coupling stability of the laser and the optical fiber is poor, so that the instability of parameters such as output intensity, phase, frequency spectrum width and the like is brought; 3) fiber systems have a limited lifetime and are easily damaged by high energy laser pulses.

Continuous spectrum generation devices based on multi-media sheets have also been implemented and used in recent years. The existing scheme for generating the continuous spectrum based on the multi-medium sheet is mainly to select a proper medium material, a sheet thickness and a sheet placement position based on experimental experience so as to obtain the widest spectrum. Meanwhile, in the existing method, the system is not close to the nonlinear resonance state and reaches proper operation parameters, and the transverse spatial self-similarity mode of the light spot is greatly damaged by the conical scattering effect in the propagation process. Therefore, a good laser propagation mode needs to be achieved by spatial filtering, and the filtering efficiency is usually only about 60%.

Disclosure of Invention

The present invention is directed to a supercontinuum generation apparatus and a supercontinuum generation method, which overcome the above-mentioned shortcomings of the prior art.

The purpose of the invention can be realized by the following technical scheme:

a super-continuum spectrum generation device comprises a femtosecond laser, a reflector, a half-wave plate, a polaroid, a focusing lens, a dielectric sheet resonant cavity and a collimating lens which are sequentially arranged, wherein the dielectric sheet resonant cavity is composed of a plurality of dielectric sheets which are arranged in an equal cavity length mode, the thicknesses of the plurality of dielectric sheets are consistent, and the cavity length of the dielectric sheet resonant cavity is obtained by calculating the effective light spot radius, the incident wavelength and a spatial self-similar mode curve on the dielectric sheet.

The calculation formula of the cavity length L of the dielectric sheet resonant cavity is as follows:

wherein w is the effective spot radius on the dielectric sheet, λ is the incident pulse laser wavelength, f (b) is the ordinate corresponding to the selected nonlinear phase b in the spatial self-similar mode curve, and the ordinate is positively correlated with the square of the effective spot radius on the dielectric sheet.

The selected nonlinear phase b is less than or equal to 1.2 rad.

The effective spot radius on the dielectric sheet is obtained by the following formula:

wherein n is₂The Kerr coefficient of the dielectric sheet as a resonant cavity of the dielectric sheet_effIs the equivalent thickness of the dielectric sheet, E₀For incident pulsed laser energy, τ_FWHMB is the selected nonlinear phase for the full width at half maximum of the time domain of the incident pulsed laser.

The equivalent thickness l of the dielectric sheet_effThe calculation formula of (2) is as follows:

wherein l is the real thickness of the dielectric sheet, theta_BIs the brewster angle.

The spatial self-similar pattern curve is

A curve is obtained by solving a spatial self-similarity mode of the dielectric sheet resonant cavity for each selected nonlinear phase b through Fox-Li iteration and further counting a convergence solution;

the expression of the Fox-Li iteration is:

wherein, U_i(p ') is the light field at the front surface p' of a sheet of dielectric material, U_i+1(p) is the light field at the front surface p of the next dielectric sheet, U₁(ρ₀) Front surface rho of first medium sheet₀Light field of (J)₀(. cndot.) is a zero order Bessel function,

the constraints of the spatial self-similarity mode are as follows:

max(|U_i(ρ')|)＝1

wherein the content of the first and second substances,

is a constant, and after convergence, the selected non-linear phase b corresponding to w is obtained by the following formula²/λL：

The head position of the dielectric sheet resonant cavity is determined by an abscissa and an ordinate corresponding to a selected nonlinear phase b in a spatial self-similarity mode curve.

The head position d₀The calculation formula of (2) is as follows:

β＝α_b×f(b)

wherein β is a ratio of a distance between the first medium sheet and the focal point of the focusing lens to a rayleigh length of the light beam, and f (b) is a vertical coordinate corresponding to a selected nonlinear phase b in the spatial self-similarity mode curve.

The focal radius, w, which determines the spatial phase of the light field at the front surface of the first sheet of media is obtained at β₀The calculation formula of (2) is as follows:

wherein w is the effective spot radius on the dielectric sheet.

A supercontinuum generation method using the supercontinuum generation device comprises the following steps:

step S1: setting selected nonlinear phase b and incident pulsed laser energy E₀；

Step S2: obtaining a Kerr coefficient n of the dielectric sheet₂Dielectric sheet equivalent thickness l_effIncident pulse laser wavelength lambda and incident pulse laser time domain half-height width tau_FWHM；

Step S3: using selected nonlinear phase b, incident pulsed laser energy E₀K-factor n of dielectric sheet₂Dielectric sheet equivalent thickness l_effAnd half-width tau of incident pulse laser time domain_FWHMCalculating the effective spot radius w on the dielectric sheet by the following formula:

step S4: obtaining a spatial self-similarity mode curve by carrying out Fox-Li recursion on a light field;

step S5: and calculating the cavity length L of the dielectric sheet resonant cavity by using a spatial self-similar mode curve, the effective spot radius w on the dielectric sheet and the incident pulse laser wavelength lambda through the following formula:

step S6: setting a dielectric sheet resonant cavity according to the cavity length L of the dielectric sheet resonant cavity, and generating a supercontinuum by pulse laser emitted by a femtosecond laser sequentially through a reflector, a half-wave plate, a polarizing plate, a focusing lens, the dielectric sheet resonant cavity and a collimating lens;

step S7: and (3) finely adjusting the incident pulse laser energy and the cavity length L, and optimizing the supercontinuum width and the output laser pulse space mode.

Compared with the prior art, the invention has the following advantages:

(1) existing methods of producing multi-media sheets rely on empirical selection of media sheet materials, thicknesses, and positioning. The scheme provided by the invention deduces the physical parameters of the resonance system through the laser parameters according to the nonlinear optical resonance principle, and reduces the uncertainty caused by manually placing the medium sheets by adopting a periodic structure, thereby ensuring to obtain the super-continuous output with high efficiency and excellent space self-similarity mode.

(2) Compared with a continuous spectrum generating device based on the inflatable hollow optical fiber, the continuous spectrum generating device has the advantages of stability, reliability, easiness in installation, low cost and the like, occupies a smaller space than the inflatable hollow optical fiber, and is suitable for incident lasers with different laser powers, pulse energies and wavelengths.

(3) By controlling the selected nonlinear phase below 1.2rad (including 1.2rad) on each dielectric slab under resonance conditions, the spatial self-similar mode of output light can be optimized, achieving > 90% high efficiency spatially uniform spectral broadening without the use of spatial filtering.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic diagram of a spatial self-similarity pattern curve according to the present invention;

FIG. 3 is a diagram illustrating a comparison of supercontinuum and fundamental frequency spectra in accordance with an embodiment of the present invention;

FIG. 4 is a diagram of an embodiment of the present invention showing a supercontinuum spatial self-similar model M²Measuring results;

FIG. 5 is a schematic diagram of the supercontinuum compensated compressed to 22fs pulse width according to an embodiment of the present invention;

FIG. 6 is a graph showing the relationship between the light field intensity U and ρ according to the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.