CN103278251B - Ultra-strong femto-second laser pulse population parameter in-situ measurement system and measuring method and application - Google Patents

Abstract

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

Ultra-intense femtosecond laser pulse full-parameter in-situ measurement system, measurement method and application

technical field

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.

Background technique

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.

Contents of the invention

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.

An object of the present invention is to propose a full-parameter in-situ measurement system for ultra-powerful femtosecond laser pulses.

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.

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.

The second gas atoms are noble gas atoms or hydrogen atoms.

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.

The electric field carrier envelope of a linearly polarized femtosecond laser pulse is represented by a Gaussian function:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; ln</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

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:

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:

in is the X-ray pulse angular frequency.

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.

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

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Phi;</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 8</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Phi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

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.

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 :

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

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.

Another object of the present invention is to propose an in-situ measurement method for all parameters of ultra-powerful femtosecond laser pulses.

A method for in-situ measurement of full parameters of ultra-strong femtosecond laser pulses of the present invention comprises the following steps:

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) 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) Lock the carrier-envelope phase Φ of the femtosecond laser pulse, determine three peak positions W _a , W _b and W _c from the measured photoelectron spectrum n(W), and use the half-height of these peak positions The energy value W′ _i =0.5n(W _j ) is used 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 momentum offset value of the photoelectron, $\mathrm{\&Delta;}{p}_i\&equiv;\sqrt{2{W^{\&prime;}}_i}-\sqrt{2W_0},$ Substitute them into the following calculation:

$\mathrm{<span\; class="notranslate">\; \&Phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>$

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) 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.

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.

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.

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.

Advantages of the present invention:

(1) Measurement of ultra-intense femtosecond laser pulses with X-rays;

(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) It is a physical method without any assumptions;

(4) It is an analytical method that does not require time-resolved measurements, data fitting, and iterative calculations;

(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).

Description of drawings

Fig. 1 is the schematic diagram of the full parameter in-situ measurement system of ultra-strong femtosecond laser pulse of the present invention;

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;

Fig. 3 is a theoretical photoelectron energy spectrum n'(W) calculated by quantum mechanics method according to an embodiment of the present invention.

Detailed ways

The present invention will be further elaborated below through specific embodiments in conjunction with the accompanying drawings.

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.

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.

The method for in-situ measurement of all parameters of super-strong femtosecond laser pulses in this embodiment includes the following steps:

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) 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) 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:

$\mathrm{<span\; class="notranslate">\; \&Phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>$

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) 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,

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.

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.

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.

Claims (4)

1. A kind of ultra-strong femtosecond laser pulse full parameter in-situ measurement system, it is characterized in that, described in-situ measurement system comprises: picosecond or sub-picosecond laser pulse (1), spectroscope (2), splitter ( 5), laser pulse compression unit (8), first inert gas atom (4) and second gas atom (11), first and second converging mirrors (3 and 10), photoelectron spectrometer (12) and optical path Adjusting device; wherein, the picosecond or sub-picosecond laser 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) after passing through the first converging mirror (3) ) to generate X-rays emitted in the forward direction; X-rays and laser pulses pass through the separator (5) to filter out the laser light, wherein the narrow-band X-rays become beams with very small diameters; the other split by the beam splitter (2) A beam of laser light, after entering the laser pulse compression unit (8), becomes a linearly polarized femtosecond laser pulse with few cycles to be expected; through the optical path adjustment device, the optical path adjustment device includes first to third reflectors (6 , 7 and 9), the picosecond or sub-picosecond laser pulse (1) is split into two laser beams after passing through the beam splitter (2); one of them directly excites the first noble gas atom ( 4) Generate X-rays emitted in the forward direction; X-rays and laser pulses pass through the separator (5) to filter out the laser light, and the narrow-band X-rays pass through the first reflector (6) and become the diameter of the vertical direction A very small light beam; another beam of laser light split by the beam splitter (2) enters the laser pulse compression unit (8) after passing through the second reflector (7), and becomes a linear polarization in a parallel direction with few cycles to be measured Femtosecond laser pulse; the femtosecond laser pulse to be measured is coaxially and collinearly mixed and transmitted with the X-ray at the third reflector (9) place; the femtosecond laser pulse is focused by the second converging mirror (10) , to excite the second gas atoms (11) together with X-rays to generate photoelectrons, and measure their energy distribution with a photoelectron spectrometer (12) in the polarization direction of the laser. 2. The in-situ measurement system according to claim 1, characterized in that, the second gas atoms (11) are inert gas atoms or hydrogen atoms. 3. A method for in-situ measurement of full parameters of ultra-strong femtosecond laser pulses, characterized in that the method for in-situ measurement comprises the following steps: 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 Femtosecond laser pulses to be measured with fewer cycles, the femtosecond laser pulses to be measured by the optical path adjustment device are mixed and transmitted coaxially and collinearly with X-rays at the third mirror; 2) The femtosecond laser pulse is focused by the second converging mirror, and the second gas atoms are excited together with X-rays to generate photoelectrons, and the energy distribution is measured with a photoelectron spectrometer in the polarization direction of the laser, and the photoelectron energy spectrum n(W ); 3) Lock the carrier-envelope phase Φ of the femtosecond laser pulse, determine three peak positions W _a , W _b and W _c from the measured photoelectron spectrum n(W), and use the half-height of these peak positions The energy value W' _i =0.5n(W _j ) is used 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 momentum offset value of the photoelectron, ${\mathrm{\&Delta;p}}_i=\sqrt{{{2W}^{\&prime;}}_i}-\sqrt{{2W}_0},$ Substitute them into the following calculation: $\mathrm{<span\; class="notranslate">\; \&Phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>$ From the three numerical values on the left side of formula (1) and Calculate the full parameters (I,Φ,τ _L ) of the femtosecond laser pulse, that is, the preliminary solution (I,Φ,τ _L ) ₁ , where i∈(1,2,3), j∈(a,b, c), I is the intensity of the femtosecond laser pulse, Φ is the carrier-envelope phase of the laser pulse, τ _L is the laser pulse time width, U _p is the photoelectron mass kinetic energy, is the laser angular frequency, W ₀ is the initial kinetic energy of photoelectrons; 4) With the above preliminary solution (I, Φ, τ _L ) ₁ as input parameters and the known photon energy of narrow-band X-rays, the theoretical photoelectron energy spectrum n'(W) is calculated by quantum mechanical method, and from this Three peaks W _a ', W _b ' and W _c ' are determined on the theoretical photoelectron energy spectrum, and the peak positions W” ₁ , W” ₂ and W” ₃ of the semi-classical predicted values are calculated, so as to calculate the Three ratios (ε ₁ ,ε ₂ ,ε ₃ ) ₁ related to the semiclassical 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 '), and then according to these ratios, the semiclassical Predict the peak positions W ₁ , W ₂ and W ₃ of the value n _c (W), and calculate the momentum offset value of the photoelectron, Substituting them into formula (1) and calculating again, the exact solution (I,Φ,τ _L ) of all parameters of the femtosecond laser pulse is obtained. 4. The high-precision data of the femtosecond laser pulse full parameters that the in-situ measurement method of claim 3 obtains is used for the scale experiment system, and the purposes of evaluating the comprehensive index of the femtosecond laser system.