CN103278251B - Ultra-strong femto-second laser pulse population parameter in-situ measurement system and measuring method and application - Google Patents
Ultra-strong femto-second laser pulse population parameter in-situ measurement system and measuring method and application Download PDFInfo
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Abstract
本发明公开了一种超强飞秒激光脉冲全参数原位测量系统及测量方法和应用。本发明用X-射线测量超强飞秒激光脉冲,从一个测量得到的光电子能谱就能推导出飞秒激光脉冲所有参数:强度,脉冲时间宽度,载波-包络相位,脉冲形状等;它是一种物理的方法,不需要做任何假设;它是一种解析方法,不需要时间分辨测量、数据拟合和迭代计算。本发明的测量方法是一个原位测量方法,对待测量的飞秒激光脉冲的状态不需要作任何改变,测量结果直接反映了各个参数之间的物理关联性,并且实时、快速、高精度;激光强度的量程能达到4-5个数量级,方法的相对精度对于激光强度好于0.1%,对于其他参数好于1%,可以广泛地应用到科学实验和工程测量中。
The invention discloses a full-parameter in-situ measurement system, a measurement method and an application of a super-powerful femtosecond laser pulse. The present invention uses X-rays to measure ultra-strong femtosecond laser pulses, and can deduce all parameters of femtosecond laser pulses from a measured photoelectron energy spectrum: intensity, pulse time width, carrier-envelope phase, pulse shape, etc.; it is a physical approach that does not require any assumptions; it is an analytical approach that does not require time-resolved measurements, data fitting, and iterative calculations. The measurement method of the present invention is an in-situ measurement method, and the state of the femtosecond laser pulse to be measured does not need to be changed. The measurement result directly reflects the physical correlation between each parameter, and is real-time, fast and high-precision; The range of the intensity can reach 4-5 orders of magnitude, the relative accuracy of the method is better than 0.1% for the laser intensity and better than 1% for other parameters, and can be widely applied in scientific experiments and engineering measurements.
Description
技术领域technical field
本发明属于超强超快光学,具体涉及一种超强飞秒激光脉冲全参数原位测量系统及测量方法和应用。The invention belongs to ultra-strong and ultra-fast optics, and in particular relates to an in-situ measurement system, measurement method and application of all parameters of ultra-strong femtosecond laser pulses.
背景技术Background technique
各种超强、超短激光脉冲已经广泛地应用于科学实验和工程技术中,如高次谐波辐射、阈上电离、非线性激光-电子康普顿散射、激光离子加速等。对于激光频率的测量,目前已经有较为成熟的方法,但对于超强激光脉冲的强度(即能量密度)、脉宽、载波-包络相位和脉冲强度时间分布等全参数的原位测量,一直是科学难题之一。当激光脉冲强度较低时,可以用光敏二极管、光电倍增管、各种硅等探测器、条纹相机等测量。但是当激光强度达到比如I>109W/cm2时,测量介质会被激光脉冲破坏,无法直接测量。目前采用的办法较多的是用估算的办法,即通过测量光脉冲的总能量,再测量光脉冲的空间分布和脉冲时间宽度,从而计算出强度值。也可以通过测量原子或高价态惰性气体离子在强激光电场中的电离谱,从分析电子或离子的动量提取激光脉冲强度数据。前者估算的方法误差很大(甚至达到真实值的几倍),后者测量的灵敏度和动态范围很小(与工作介质的电离特性有关)。另外,用于计算测量结果的脉冲的各种参数是用不同的测量方法、不同的实验装置和不同的时间分别单独测量的,测量和计算结果是一种统计值,与各种参数的物理关联性和实时性差。总之,如何快速、精确地测量这些光脉冲具体细致的时间结构,一直是科学界的一个挑战。Various ultra-intense and ultra-short laser pulses have been widely used in scientific experiments and engineering technologies, such as high-order harmonic radiation, suprathreshold ionization, nonlinear laser-electron Compton scattering, and laser ion acceleration. For the measurement of laser frequency, there are relatively mature methods at present, but for the in-situ measurement of all parameters such as the intensity (ie, energy density), pulse width, carrier-envelope phase and pulse intensity time distribution of ultra-intense laser pulses, it has been is one of the scientific problems. When the laser pulse intensity is low, it can be measured with photosensitive diodes, photomultiplier tubes, various silicon and other detectors, and streak cameras. However, when the laser intensity reaches, for example, I>10 9 W/cm 2 , the measurement medium will be damaged by the laser pulse and cannot be directly measured. Most of the methods currently used are estimation methods, that is, by measuring the total energy of the light pulse, and then measuring the spatial distribution and pulse time width of the light pulse to calculate the intensity value. Laser pulse intensity data can also be extracted from the momentum of analyzed electrons or ions by measuring the ionization spectrum of atoms or high-valence noble gas ions in a strong laser electric field. The estimation method of the former has a large error (even reaching several times of the real value), while the sensitivity and dynamic range of the latter measurement are very small (related to the ionization characteristics of the working medium). In addition, the various parameters of the pulse used to calculate the measurement results are separately measured with different measurement methods, different experimental devices, and different times, and the measurement and calculation results are a statistical value that is physically related to various parameters. Poor performance and real-time performance. In short, how to quickly and accurately measure the specific and detailed time structure of these light pulses has always been a challenge for the scientific community.
发明内容Contents of the invention
为了解决强脉冲激光的精确快速测量的难题,本发明提出一种超强飞秒激光脉冲全参数原位测量系统及测量方法和应用,采用X-射线增强电离技术,可以精确地获取每个飞秒激光脉冲的全部参数,包括脉冲的强度、脉宽、载波-包络相位和脉冲强度分布。In order to solve the problem of accurate and rapid measurement of intense pulsed laser, the present invention proposes a super-powerful femtosecond laser pulse full-parameter in-situ measurement system and measurement method and application. X-ray enhanced ionization technology can be used to accurately obtain each femtosecond laser pulse All parameters of the second laser pulse, including pulse intensity, pulse width, carrier-envelope phase and pulse intensity distribution.
本发明的一个目的在于提出一种超强飞秒激光脉冲全参数原位测量系统。An object of the present invention is to propose a full-parameter in-situ measurement system for ultra-powerful femtosecond laser pulses.
本发明的超强飞秒激光脉冲全参数原位测量系统包括:皮秒或亚皮秒激光脉冲、分光镜、分离器、激光脉冲压缩单元、第一惰性气体原子和第二气体原子、第一和第二会聚镜、光电子能谱仪及光路调整装置;其中,皮秒或亚皮秒激光脉冲经过分光镜后分裂为两束激光;其中一束经过第一会聚镜后直接激发第一惰性气体原子产生前向发射的高次谐波辐射即X-射线;X-射线与激光脉冲经分离器后过滤掉激光,其中的窄带的X-射线变成直径很小的光束;分光镜分裂出的另一束激光,进入激光脉冲压缩单元后,变成线性极化的少周期待测的飞秒激光脉冲;经光路调整装置该脉冲与X-射线同轴、共线混合和传输;飞秒激光脉冲经第二会聚镜聚焦,与X-射线共同激发第二气体原子,产生光电子,在激光的极化方向用光电子能谱仪测量其能量分布。The ultra-strong femtosecond laser pulse full-parameter in-situ measurement system of the present invention includes: picosecond or subpicosecond laser pulse, beam splitter, separator, laser pulse compression unit, first inert gas atom and second gas atom, first and a second converging mirror, a photoelectron energy spectrometer and an optical path adjustment device; wherein, the picosecond or sub-picosecond laser pulse is split into two laser beams after passing through the beam splitter; one of them directly excites the first inert gas after passing through the first converging mirror Atoms produce forward-emitting high-order harmonic radiation, that is, X-rays; X-rays and laser pulses pass through a separator to filter out the laser, and the narrow-band X-rays become beams with a small diameter; the beams split by the beam splitter Another beam of laser light, after entering the laser pulse compression unit, becomes a linearly polarized femtosecond laser pulse with a few cycles to be expected; the pulse is coaxially and collinearly mixed and transmitted with the X-ray through the optical path adjustment device; the femtosecond laser pulse The pulse is focused by the second converging mirror, and together with the X-rays, the second gas atoms are excited to generate photoelectrons, and the energy distribution is measured with a photoelectron energy spectrometer in the polarization direction of the laser.
光路调整装置包括第一至第三反射镜,皮秒或亚皮秒激光脉冲经过分光镜后分裂为两束激光;其中一束经过第一会聚镜后直接激发第一惰性气体原子产生前向发射的高次谐波辐射即X-射线;X-射线与激光脉冲经分离器后过滤掉激光,其中的窄带的X-射线经过第一反射镜后变成垂直方向的直径很小的光束;分光镜分裂出的另一束激光,经第二反射镜后进入激光脉冲压缩单元,变成平行方向的线性极化的少周期待测的飞秒激光脉冲;该脉冲在第三反射镜处与X-射线在垂直方向同轴、共线混合和传输。The optical path adjustment device includes first to third mirrors, and the picosecond or sub-picosecond laser pulse is split into two laser beams after passing through the beam splitter; one beam directly excites the first inert gas atoms to generate forward emission after passing through the first converging mirror The high-order harmonic radiation is X-ray; the X-ray and laser pulse pass through the separator to filter out the laser, and the narrow-band X-ray becomes a beam with a small diameter in the vertical direction after passing through the first reflector; Another laser beam split by the mirror enters the laser pulse compression unit after passing through the second mirror, and becomes a femtosecond laser pulse with a few cycles to be predicted in the linear polarization of the parallel direction; - Rays are mixed and transmitted coaxially and collinearly in the vertical direction.
第二气体原子为惰性气体原子或氢原子。The second gas atoms are noble gas atoms or hydrogen atoms.
皮秒(picosecond)ps或亚皮秒激光脉冲经激光脉冲压缩单元产生待测量的飞秒激光脉冲,本发明采用在激光脉冲压缩单元前放置分束器,从而将皮秒激光脉冲分成两束,一束用来产生待测量的飞秒激光,另一束用来产生X-射线,从而待测的飞秒激光脉冲与X-射线在垂直方向同轴、共线混合和传输,共同激发惰性气体原子产生光电子,用光电子能谱仪测量其能量分布。本发明采用巧妙的系统设计,对待测量的飞秒激光脉冲的状态不需要作任何改变,测量结果直接反映了各个参数之间的物理关联性,是一种原位测量方法。一方面,由于皮秒激光脉冲产生的X-射线的时间宽度为皮秒或亚皮秒量级,经光路控制后容易与待测量的飞秒(femtosecond)fs激光脉冲同步;另一方面,要求X-射线的束流尺寸远小于飞秒激光脉冲,且同轴共线。因此,飞秒激光脉冲持续期间,X-射线的强度变化很小,可以认为是连续的;而飞秒激光脉冲的空间分布值变化很小(Single-Intensity)SI,其强度的最大值即激光脉冲的峰值I。A picosecond (picosecond) ps or sub-picosecond laser pulse generates a femtosecond laser pulse to be measured through a laser pulse compression unit. The present invention uses a beam splitter before the laser pulse compression unit to divide the picosecond laser pulse into two beams. One beam is used to generate the femtosecond laser to be measured, and the other is used to generate X-rays, so that the femtosecond laser pulses to be measured and X-rays are mixed and transmitted coaxially and collinearly in the vertical direction to jointly excite the inert gas The atoms generate photoelectrons, whose energy distribution is measured with a photoelectron spectrometer. The invention adopts ingenious system design, does not need to make any changes to the state of the femtosecond laser pulse to be measured, and the measurement result directly reflects the physical correlation between various parameters, which is an in-situ measurement method. On the one hand, since the time width of X-rays generated by picosecond laser pulses is on the order of picoseconds or sub-picoseconds, it is easy to synchronize with the femtosecond fs laser pulses to be measured after optical path control; on the other hand, it is required The X-ray beam size is much smaller than the femtosecond laser pulse, and it is coaxial and collinear. Therefore, during the duration of the femtosecond laser pulse, the X-ray intensity changes very little, which can be considered as continuous; while the spatial distribution value of the femtosecond laser pulse changes very little (Single-Intensity) SI, the maximum intensity of which is the laser The peak I of the pulse.
线性极化的飞秒激光脉冲的电场载波包络用高斯函数表示:The electric field carrier envelope of a linearly polarized femtosecond laser pulse is represented by a Gaussian function:
其中t是时间变量,τL为脉冲时间宽度即半高宽度FWHM。激光脉冲电场EL的变化(幅度E0)可以用下式表示:Among them, t is a time variable, and τ L is the pulse time width, that is, the half-maximum width FWHM. The change (amplitude E 0 ) of the laser pulse electric field E L can be expressed by the following formula:
其中为激光脉冲角频率,Φ为载波-包络相位。类似地,X-射线脉冲电场EX的变化(幅度恒定,简单地设为1)可以用下式表示:in is the laser pulse angular frequency, Φ is the carrier-envelope phase. Similarly, the variation of X -ray pulsed electric field E (constant amplitude, simply set to 1) can be expressed by the following formula:
其中为X-射线脉冲角频率。in is the X-ray pulse angular frequency.
因此,只要得到待测的飞秒激光脉冲的强度(即峰值功率密度)I、载波-包络相位Φ及激光脉冲时间宽度(半高宽FWHM)τL,便可得到飞秒激光脉冲的全部信息,(I,Φ,τL)为激光脉冲的全参数。Therefore, as long as the intensity (i.e., peak power density) I, carrier-envelope phase Φ, and laser pulse time width (full width at half maximum) τ L of the femtosecond laser pulse to be measured are obtained, all femtosecond laser pulses can be obtained. Information, (I, Φ, τ L ) is the full parameters of the laser pulse.
从半经典力学观点来看,由X-射线和激光电场共同激发、在t时刻产生、激光的极化方向上飞出的光电子的能量W(t)为From the point of view of semi-classical mechanics, the energy W(t) of photoelectrons that are excited by X-rays and laser electric field at time t and fly out in the polarization direction of laser is given by
其中W0=ωX-Ip为光电子的初动能,而ωX和Ip分别为窄带X-射线脉冲的光子能量及气体原子或分子的电离能。为光电子的质动能。Where W 0 =ω X -I p is the initial kinetic energy of photoelectrons, and ω X and I p are the photon energy of the narrow-band X-ray pulse and the ionization energy of gas atoms or molecules, respectively. is the mass-kinetic energy of the photoelectron.
光电子能谱是单位能量内测量到的光电子数,能谱有明显的边界,并且成三个峰,成峰位置Wa、Wb和Wc,从小到大排列为Wa、Wc和Wb。光电子能谱n(W)上分别与Wa、Wb和Wc位置对应的半经典预言值W1、W2和W3无法测量,但在激光脉冲参数已知的情况下,可以计算出半经典预言值能谱nc(W)的成峰位置如W1、W2和W3,它们分别与Wa、Wb和Wc对应,并且还可以计算出三个比值ε1、ε2和ε3:Photoelectron energy spectrum is the number of photoelectrons measured per unit energy. The energy spectrum has obvious boundaries and forms three peaks. The peak positions W a , W b and W c are arranged as W a , W c and W from small to large. b . The semiclassical predicted values W 1 , W 2 and W 3 corresponding to the positions of W a , W b and W c on the photoelectron spectrum n(W) cannot be measured, but they can be calculated when the laser pulse parameters are known. The peak positions of the semi-classical predicted energy spectrum n c (W) are W 1 , W 2 and W 3 , which correspond to W a , W b and W c respectively, and three ratios ε 1 , ε can also be calculated 2 and ε 3 :
研究和大量计算表明,对于特定的激光载波-包络相位Φ,比值ε1、ε2和ε3随着激光强度的变化非常小。因此,在很大的激光强度范围内,可以认为比值ε1、ε2和ε3基本相近。Research and extensive calculations have shown that for a specific laser carrier-envelope phase Φ, the ratios ε 1 , ε 2 and ε 3 vary very little with laser intensity. Therefore, in a large laser intensity range, it can be considered that the ratios ε 1 , ε 2 and ε 3 are basically similar.
本发明的另一个目的在于提出一种超强飞秒激光脉冲全参数原位测量方法。Another object of the present invention is to propose an in-situ measurement method for all parameters of ultra-powerful femtosecond laser pulses.
本发明的一种超强飞秒激光脉冲全参数原位测量方法,包括以下步骤:A method for in-situ measurement of full parameters of ultra-strong femtosecond laser pulses of the present invention comprises the following steps:
1)皮秒或亚皮秒激光脉冲经过分光镜后分裂为两束激光,其中一束经过第一会聚镜后直接激发第一惰性气体原子产生前向发射的高次谐波辐射即X-射线,X-射线与激光脉冲经分离器后过滤掉激光,其中的窄带的X-射线变成直径很小的光束,分光镜分裂出的另一束激光,进入激光脉冲压缩单元,变成线性极化的少周期待测的飞秒激光脉冲,经光路调整装置待测量的飞秒激光脉冲与X-射线同轴、共线混合和传输;1) The picosecond or sub-picosecond laser pulse is split into two laser beams after passing through the beam splitter, one of which directly excites the first inert gas atoms after passing through the first converging mirror to generate forward-emitting high-order harmonic radiation, that is, X-rays , X-rays and laser pulses pass through the separator to filter out the laser, and the narrow-band X-rays become a beam with a small diameter, and another beam of laser split by the beam splitter enters the laser pulse compression unit and becomes a linear pole The femtosecond laser pulses to be measured with fewer cycles, the femtosecond laser pulses to be measured and the X-rays are coaxially and collinearly mixed and transmitted through the optical path adjustment device;
2)飞秒激光脉冲与X-射线经第二会聚镜聚焦,共同激发第二气体原子,产生光电子,在激光的极化方向用光电子能谱仪测量其能量分布,得到光电子能谱n(W);2) Femtosecond laser pulses and X-rays are focused by the second converging mirror to jointly excite the second gas atoms to generate photoelectrons, and measure their energy distribution with a photoelectron spectrometer in the polarization direction of the laser to obtain the photoelectron energy spectrum n(W );
3)锁定飞秒激光脉冲的载波-包络相位Φ,从测量得到的光电子能谱n(W)中确定三个峰位置Wa、Wb和Wc,用这些峰位置的半高度处的能量值W′i=0.5n(Wj)来近似代替光电子能谱的半经典预言值能谱nc(W)的成峰位置,并计算出光电子的动量偏移值,
从式(8)左边三个数值和可以计算出飞秒激光脉冲的全参数(I,Φ,τL)的即初步解(I,Φ,τL)1,其中,i∈(1,2,3),j∈(a,b,c);From the three numerical values on the left side of formula (8) and The preliminary solution (I, Φ, τ L ) 1 of the full parameters (I, Φ, τ L ) of the femtosecond laser pulse can be calculated, where, i∈(1, 2, 3), j∈(a, b , c);
4)以上述初步解(I,Φ,τL)1为输入参数和已知的窄带X-射线的光子能量(用角频率表示),用量子力学方法计算出理论的光电子能谱n′(W),并从这个理论的光电子能谱上确定出三个峰值Wa′、Wb′和Wc′,以及计算出半经典预言值的成峰位置W″1、W″2和W″3,从而计算出与半经典预言值相关的三个比值(ε1,ε2,ε3)1,其中ε1=n′(W″1)/n′(Wa′),ε2=n′(W″2)/n′(Wb′),ε3=n′(W″3)/n′(Wc′),再根据这些比值,从初始测量得到的光电子能谱n(W)读出半经典预言值nc(W)的成峰位置W1、W2和W3,并计算出光电子的动量偏移值,将它们代入式(8)再次计算,得到飞秒激光脉冲的全参数的精确解(I,Φ,τL)。4) Take the above preliminary solution (I, Φ, τ L ) 1 as input parameters and the known photon energy of narrowband X-rays (using angular frequency Expressed), the theoretical photoelectron spectrum n'(W) is calculated by quantum mechanics method, and three peaks W a ', W b ' and W c ' are determined from this theoretical photoelectron spectrum, and half The peak positions W″ 1 , W″ 2 and W″ 3 of the classical prediction value, thus calculating the three ratios (ε 1 , ε 2 , ε 3 ) 1 related to the semi-classical prediction value, where ε 1 =n′ (W″ 1 )/n′(W a ′), ε 2 =n′(W″ 2 )/n′(W b ′), ε 3 =n′(W″ 3 )/n′(W c ′ ), according to these ratios, read out the peak positions W 1 , W 2 and W 3 of the semi-classical predicted value n c (W) from the photoelectron energy spectrum n(W) obtained from the initial measurement, and calculate the momentum deviation of the photoelectron transfer value, Substituting them into formula (8) for calculation again, the exact solution (I, Φ, τ L ) of all parameters of the femtosecond laser pulse is obtained.
X-射线与激光脉冲激发氢原子或惰性气体原子产生的光电子能谱n(W),有明显的边界,并且成三个峰,成峰位置Wa、Wb和Wc。光电子能谱的半经典预言值nc(W)在实验上无法测量,但在激光脉冲参数已知的情况下,可以计算出nc(W)的成峰位置如W1、W2和W3,它们分别与Wa、Wb和Wc对应,并且还可以根据公式(5)、(6)和(7)计算出三个比值ε1、ε2和ε3。在步骤3)中,近似的取εi=0.5,将近似的半经典预言值能谱nc(W)的成峰位置代入公式(8)进行计算,得到初步解,然后步骤4)中进行第二步计算,从而得到比较精确的比值εi。研究和大量计算表明,对于特定的激光载波-包络相位Φ,比值ε1、ε2和ε3随着激光强度的变化非常小。因此,在很大的激光强度范围内,可以认为比值ε1、ε2和ε3基本相近。The photoelectron energy spectrum n(W) produced by X-ray and laser pulse excitation of hydrogen atoms or inert gas atoms has obvious boundaries and forms three peaks, which form peak positions W a , W b and W c . The semiclassical predicted value n c (W) of photoelectron energy spectrum cannot be measured experimentally, but when the laser pulse parameters are known, the peak positions of n c (W) can be calculated such as W 1 , W 2 and W 3 , which correspond to W a , W b and W c respectively, and three ratios ε 1 , ε 2 and ε 3 can also be calculated according to formulas (5), (6) and (7). In step 3), ε i =0.5 is approximately taken, and the peak position of the approximate semi-classical predicted value energy spectrum n c (W) is substituted into formula (8) for calculation to obtain a preliminary solution, and then proceed in step 4) In the second step of calculation, a more accurate ratio ε i can be obtained. Research and extensive calculations have shown that for a specific laser carrier-envelope phase Φ, the ratios ε 1 , ε 2 and ε 3 vary very little with laser intensity. Therefore, in a large laser intensity range, it can be considered that the ratios ε 1 , ε 2 and ε 3 are basically similar.
本发明用两步计算精确测量激光脉冲全参数,测量方法是一个原位测量方法,对待测量的飞秒激光脉冲的状态不需要作任何改变,测量结果直接反映了各个参数之间的物理关联性,并且实时、快速、高精度。激光强度的量程能达到4-5个数量级,方法的相对精度对于激光强度好于0.1%,对于其他参数好于1%,可以广泛地应用到科学实验和工程测量中。The invention uses two-step calculations to accurately measure the full parameters of the laser pulse. The measurement method is an in-situ measurement method. The state of the femtosecond laser pulse to be measured does not need to be changed, and the measurement results directly reflect the physical correlation between the parameters. , and real-time, fast, and high-precision. The measuring range of the laser intensity can reach 4-5 orders of magnitude, the relative accuracy of the method is better than 0.1% for the laser intensity and better than 1% for other parameters, and can be widely applied in scientific experiments and engineering measurements.
本发明的又一个目的在于提出上述原位测量方法得到的飞秒激光脉冲全参数的高精度数据用于刻度实验系统,评估飞秒激光系统的综合指标的用途。这些高精度数据在科学研究和实际应用上具有重要意义。Another object of the present invention is to propose the use of the high-precision data of the full parameters of the femtosecond laser pulse obtained by the above-mentioned in-situ measurement method for the calibration experiment system and the evaluation of the comprehensive index of the femtosecond laser system. These high-precision data are of great significance in scientific research and practical applications.
本发明的优点:Advantages of the present invention:
(1)用X-射线测量超强飞秒激光脉冲;(1) Measurement of ultra-intense femtosecond laser pulses with X-rays;
(2)从一个测量得到的光电子能谱就能推导出飞秒激光脉冲所有参数:强度,脉冲时间宽度,载波-包络相位,脉冲形状等;(2) All parameters of the femtosecond laser pulse can be deduced from a measured photoelectron spectrum: intensity, pulse time width, carrier-envelope phase, pulse shape, etc.;
(3)它是一种物理的方法,不需要做任何假设;(3) It is a physical method without any assumptions;
(4)它是一种解析方法,不需要时间分辨测量、数据拟合和迭代计算;(4) It is an analytical method that does not require time-resolved measurements, data fitting, and iterative calculations;
(5)它具有快速、高精度(相对精度理论预言值,对于激光强度好于0.1%,其他参数好于1%),方法简单,测量动态范围大(激光强度测量范围达几个数量级)。(5) It is fast, high-precision (relative accuracy theoretical prediction value is better than 0.1% for laser intensity, and better than 1% for other parameters), simple method, and large dynamic range of measurement (laser intensity measurement range reaches several orders of magnitude).
附图说明Description of drawings
图1为本发明的超强飞秒激光脉冲全参数原位测量系统的示意图;Fig. 1 is the schematic diagram of the full parameter in-situ measurement system of ultra-strong femtosecond laser pulse of the present invention;
图2为本发明的一个实施例的X-射线与激光脉冲激发氢原子产生的光电子能谱n(W);Fig. 2 is the photoelectron energy spectrum n (W) that X-ray and laser pulse excite hydrogen atom generation of an embodiment of the present invention;
图3为本发明的一个实施例的用量子力学方法计算出的理论的光电子能谱n′(W)。Fig. 3 is a theoretical photoelectron energy spectrum n'(W) calculated by quantum mechanics method according to an embodiment of the present invention.
具体实施方式Detailed ways
下面结合附图,通过具体实施例,进一步阐述本发明。The present invention will be further elaborated below through specific embodiments in conjunction with the accompanying drawings.
如图1所示,本实施例的超强飞秒激光脉冲全参数原位测量系统包括:皮秒或亚皮秒激光脉冲1、分光镜2、分离器5、激光脉冲压缩单元8、第一惰性气体原子4和第二气体原子11、第一和第二会聚镜3和10、第一至第三反射镜6、7和9及光电子能谱仪12;其中,皮秒或亚皮秒激光脉冲1经过分光镜2后分裂为两束激光;其中一束经过第一会聚镜3后直接激发第一气嘴A出射的第一惰性气体原子4产生前向发射的高次谐波辐射即X-射线;X-射线与激光脉冲经分离器后过滤掉激光,其中的窄带的X-射线经过第一反射镜6后变成z方向的直径很小的光束;分光镜2分裂出的另一束激光,经第二反射镜7后进入激光脉冲压缩单元8,变成极化方向x的线性极化的少周期待测的飞秒激光脉冲;该脉冲在第三反射镜9处与X-射线在z方向同轴、共线混合和传输;飞秒激光脉冲经第二会聚镜10聚焦,与X-射线共同激发第二气嘴B出射的第二气体原子11,产生光电子,在激光的极化方向用光电子能谱仪12测量其能量分布。其中,分离器5采用铍窗或其他合适材料;第二气体原子11为氢原子。As shown in Figure 1, the in-situ measurement system for all parameters of the ultra-powerful femtosecond laser pulse in this embodiment includes: a picosecond or sub-picosecond laser pulse 1, a beam splitter 2, a splitter 5, a laser pulse compression unit 8, a first Inert gas atom 4 and second gas atom 11, first and second converging mirrors 3 and 10, first to third mirrors 6, 7 and 9 and photoelectron spectrometer 12; wherein, picosecond or subpicosecond laser The pulse 1 is split into two laser beams after passing through the beam splitter 2; one of them directly excites the first inert gas atom 4 emitted from the first gas nozzle A after passing through the first converging mirror 3 to generate forward-emitted high-order harmonic radiation, namely X - ray; X-ray and laser pulse filter out the laser after the separator, wherein the narrow-band X-ray becomes a beam with a very small diameter in the z direction after passing through the first reflector 6; another beam splitted by the beam splitter 2 A beam of laser light enters the laser pulse compression unit 8 after passing through the second reflector 7, and becomes a femtosecond laser pulse with few cycles to be expected in the linear polarization of the polarization direction x; The rays are mixed and transmitted coaxially and collinearly in the z direction; the femtosecond laser pulse is focused by the second converging mirror 10, and together with the X-rays excites the second gas atoms 11 emitted by the second gas nozzle B to generate photoelectrons, The energy distribution of the polarization direction is measured with a photoelectron spectrometer 12 . Wherein, the separator 5 adopts a beryllium window or other suitable materials; the second gas atoms 11 are hydrogen atoms.
图2为本实施例的X-射线与激光脉冲激发氢原子产生的光电子能谱n(W)。飞秒激光脉冲持续期间,X-射线的强度变化很小,可以认为是连续的;而飞秒激光脉冲的空间分布值变化很小(Single-Intensity)SI,其强度的最大值即激光脉冲的峰值I。计算图2所示能谱的参数如下:激光强度I=1014W/cm2,波长800nm,脉冲宽度τL=7.5fs,Φ=0°,X-射线光子能量135eV。X-射线强度简单地设为108W/cm2,没有特殊考虑,因为光电子能谱即单位能量内的光电子计数率与X-射线强度成简单的正比关系。Fig. 2 is the photoelectron energy spectrum n(W) generated by X-ray and laser pulse excitation of hydrogen atoms in this embodiment. During the duration of the femtosecond laser pulse, the intensity of X-rays changes very little, which can be considered as continuous; while the spatial distribution value of the femtosecond laser pulse changes very little (Single-Intensity) SI, and the maximum value of the intensity is the laser pulse Peak I. The parameters for calculating the energy spectrum shown in Fig. 2 are as follows: laser intensity I = 10 14 W/cm 2 , wavelength 800 nm, pulse width τ L = 7.5 fs, Φ = 0°, X-ray photon energy 135 eV. The X-ray intensity is simply set to 10 8 W/cm 2 , without special consideration, because the photoelectron spectrum, that is, the photoelectron count rate per unit energy, has a simple proportional relationship with the X-ray intensity.
本实施例的超强飞秒激光脉冲全参数原位测量方法包括以下步骤:The method for in-situ measurement of all parameters of super-strong femtosecond laser pulses in this embodiment includes the following steps:
1)皮秒或亚皮秒激光脉冲1经过分光镜2后分裂为两束激光;其中一束经过第一会聚镜3后直接激发第一气嘴A出射的第一惰性气体原子4产生前向发射的高次谐波辐射即X-射线;X-射线与激光脉冲经分离器后过滤掉激光,其中的窄带的X-射线经过第一反射镜6后变成z方向的直径很小的光束;分光镜2分裂出的另一束激光,经第二反射镜7后进入激光脉冲压缩单元8,变成极化方向x的线性极化的少周期待测的飞秒激光脉冲;该脉冲在第三反射镜9处与X-射线在z方向同轴、共线混合和传输;1) The picosecond or sub-picosecond laser pulse 1 is split into two laser beams after passing through the beam splitter 2; one beam directly excites the first inert gas atom 4 emitted from the first gas nozzle A after passing through the first converging mirror 3 to generate a forward direction The emitted high-order harmonic radiation is X-ray; the X-ray and laser pulse pass through the separator to filter out the laser, and the narrow-band X-ray becomes a beam with a small diameter in the z direction after passing through the first reflector 6 Another laser beam split by the beam splitter 2 enters the laser pulse compression unit 8 after the second reflector 7, and becomes a femtosecond laser pulse with few cycles to be expected in the linear polarization of the polarization direction x; The third reflector 9 is coaxial and collinearly mixed and transmitted with the X-ray in the z direction;
2)飞秒激光脉冲第二会聚镜10聚焦,与X-射线经共同激发第二气体原子11,产生光电子,在激光的极化方向用光电子能谱仪测量其能量分布,得到光电子能谱n(W),如图2所示;2) The second converging mirror 10 of the femtosecond laser pulse is focused, and the second gas atom 11 is jointly excited with the X-ray to generate photoelectrons, and its energy distribution is measured with a photoelectron energy spectrometer in the polarization direction of the laser to obtain the photoelectron energy spectrum n (W), as shown in Figure 2;
3)锁定飞秒激光脉冲的载波-包络相位Φ,Φ=0°,从测量得到的如图2所示的光电子能谱n(W)中确定三个峰位置Wa、Wb和Wc,用这些峰位置的半高度处的能量值W′i=0.5n(Wj)来近似代替光电子能谱的半经典预言值能谱nc(W)的成峰位置,并计算出光电子的动量偏移值,将它们代入下式计算:3) Lock the carrier-envelope phase Φ of the femtosecond laser pulse, Φ=0°, determine the three peak positions W a , W b and W from the photoelectron spectrum n(W) obtained from the measurement as shown in Figure 2 c , use the energy value W' i =0.5n(W j ) at the half height of these peak positions to approximately replace the peak position of the semi-classical predicted value energy spectrum n c (W) of the photoelectron energy spectrum, and calculate the peak position of the photoelectron energy spectrum The momentum offset value of , Substitute them into the following calculation:
从式(8)左边三个数值和可以计算出飞秒激光脉冲的全参数(I,Φ,τL)的即初步解(I,Φ,τL)1==(0.981×1014W/cm2,3.691°,7.599fs);From the three numerical values on the left side of formula (8) and The preliminary solution (I, Φ, τ L ) 1 == (0.981×10 14 W/cm 2 , 3.691°, 7.599fs) of the full parameters (I, Φ, τ L ) of the femtosecond laser pulse can be calculated;
4)以上述初步解(I,Φ,τL)1为输入参数和已知的窄带X-射线的光子能量,用量子力学方法计算出理论的光电子能谱n′(W),并从这个理论的光电子能谱上确定出三个峰值Wa′、Wb′和Wc′,以及计算出半经典预言值能谱n′c(W)的成峰位置W″1、W″2和W″3,从而计算出与半经典预言值相关的三个比值(ε1,ε2,ε3)1:得到(ε1,ε2,ε3)1=(46.7%,41.4%,30.9%),ε1、ε2和ε3的值已经标记在图上,再根据这些比值,从初始测量得到的光电子能谱n(W)读出半经典预言值nc(W)的成峰位置W1、W2和W3,并由此计算出光电子的动量偏移值,4) With the above-mentioned preliminary solution (I, Φ, τ L ) 1 as the input parameter and the photon energy of the known narrow-band X-ray, calculate the theoretical photoelectron energy spectrum n'(W) with the method of quantum mechanics, and from this Three peaks W a ′, W b ′ and W c ′ were determined on the theoretical photoelectron energy spectrum, and the peak positions W″ 1 , W″ 2 and W″ 3 , thus calculating the three ratios (ε 1 , ε 2 , ε 3 ) 1 related to the semiclassical prediction value: get (ε 1 , ε 2 , ε 3 ) 1 = (46.7%, 41.4%, 30.9 %), the values of ε 1 , ε 2 and ε 3 have been marked on the graph, and according to these ratios, the peaking of the semi-classical predicted value n c (W) can be read from the photoelectron spectrum n(W) obtained from the initial measurement position W 1 , W 2 and W 3 , and thus calculate the momentum offset value of the photoelectron,
将它们代入式(8)再次计算,得到飞秒激光脉冲的全参数的精确解(I,Φ,τL)2=(0.99918×1014W/cm2,-0.862°,7.565fs)。 Substituting them into formula (8) for recalculation, the exact solution (I, Φ, τ L ) 2 = (0.99918×10 14 W/cm 2 , -0.862°, 7.565fs) of all parameters of the femtosecond laser pulse is obtained.
本发明的测量方法得到的飞秒激光脉冲全参数与原始输入参数(1014W/cm2,0°,7.5fs)相差极小,相对误差为(-0.082%,-0.2%,0.8%)。因此,本方法的理论精度的相对值,对于激光强度好于0.1%,其他参数好于1%。测量结果的误差由实验系统决定。The femtosecond laser pulse total parameters obtained by the measurement method of the present invention have very little difference from the original input parameters (1014W/cm2, 0°, 7.5fs), and the relative errors are (-0.082%, -0.2%, 0.8%). Therefore, the relative value of the theoretical accuracy of the method is better than 0.1% for laser intensity and better than 1% for other parameters. The error of the measurement result is determined by the experimental system.
上面描述的实施例并非用于限定本发明,任何本领域的技术人员,在不脱离本发明的精神和范围内,可做各种的变换和修改,因此本发明的保护范围视权利要求范围所界定。The embodiments described above are not intended to limit the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention depends on the scope of the claims. defined.
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