CN100575897C - Picosecond Pulse Contrast Single Shot Meter - Google Patents

Abstract

A picosecond pulse contrast single-shot measurement device is composed of a spectroscope, a first reflector, a second reflector, a third reflector, a fourth reflector, a base frequency Dammann grating, a base frequency compensation grating group, a fifth reflector, a sixth reflector, a double frequency crystal, a double frequency Dammann grating, a double frequency compensation grating group, a reflector group, a beam combining mirror group, a triple frequency crystal group, a filter group and a photomultiplier tube group. The present invention adopts Dammann grating to realize multi-path splitting of the pulse to be measured and its double frequency signal to realize contrast measurement of more than 10 ^8. Moreover, the different angles generated when the Dammann grating is split can be used to obtain a gradual optical path delay. By changing the distance between the Dammann gratings and the distance between the Dammann grating and the compensation grating, the maximum value of the optical path delay can be adjusted to realize the time delay measurement of 100ps.

Description

Picosecond Pulse Contrast Single Shot Meter

technical field

The invention relates to laser parameter diagnosis, in particular to a single measurement device for picosecond pulse contrast.

Background technique

High-power laser pulses are widely used in strong-field physics research such as laser-plasma interaction, X-ray laser, multi-photon ionization, and high-order harmonic generation. When using ultra-short and ultra-intense laser pulses to target, if the noise signal before the main pulse exceeds a certain intensity, it will destroy the target surface and generate plasma, which will cause complex adverse effects. Therefore, it is necessary to monitor the noise signal intensity preceding the laser pulse.

In order to obtain ultra-short and ultra-intense petawatt laser, the optical parametric chirped pulse amplification (OPCPA) technology is adopted. This technology is to broaden a beam of low-energy femtosecond broadband seed signal optical pulses to be amplified in the time domain through the method of positive chirp dispersion, and the widened pulses appear as chirped pulses in the time domain. Then, a beam of high-energy nanosecond narrow-band pump light and the broadened chirped seed light are parametrically coupled in the nonlinear crystal to amplify the seed light pulse. The amplified seed light pulse is then compressed into a femtosecond pulse output by negative chirp dispersion. The petawatt laser device transformed into the Shenguang II ninth-channel system uses OPCPA technology to achieve a pulse output of 1000J and 1ps.

In OPCPA, a grating pair is used to realize pulse stretching and compression, which are called stretcher and compressor respectively. Due to the surface defect of the grating itself and the incomplete match between the stretcher and the compressor, the pulse shape after compression will be different from the pulse shape of the seed light. In terms of time, there is a very long step (pedestral) before and after the main pulse, as shown in FIG. 4 . In order to monitor and control the time waveform of the compressed picosecond pulse to meet the needs of physical experiments, it is necessary to measure the signal intensity 10 ps before the main pulse and beyond to ensure the ratio of the laser signal intensity at these moments to the intensity of the main pulse Less than <10 ^-8 , that is, pulse contrast <10 ^-8 .

The basic structure of the existing short-pulse laser contrast single-shot diagnostic device is shown in Fig. 1 . The pulse to be measured is used as the fundamental frequency light, and the focusing lens 1 is focused on a double frequency crystal 2 to generate double frequency light. Then use the collimating lens 3 to obtain the parallel light beams of the fundamental frequency and the double frequency, the cylindrical lens 4 focuses the incident rectangular light beams into a straight line, and the parallel fundamental frequency signal and the double frequency signal are spaced by the Wollaston prism 5 separate. Then, a Fresnel double prism 6 is used to deflect the separated base frequency signal and frequency multiplied signal to realize oblique intersection. By placing a frequency-tripling crystal 7 at the intersection of the two signals, frequency-tripling light can be obtained. Through the imaging lens 8 and using the filter 9 to filter out the residual fundamental frequency light and the double frequency light, the triple frequency signal is received on the CCD 10 , and the final result is obtained through certain calculations.

The problem with this technique is that high dynamic range contrast measurements cannot be achieved and the time delay is limited. The generation of its optical path delay is based on the principle of splitting the wavefront, obliquely intersecting the two wide beams of the fundamental frequency and the double frequency. When the two beams reach the surface of the triple frequency crystal, at different positions on the crystal surface, the fundamental frequency light and There is a gradually changing optical path difference between the double-frequency light, so that the simultaneous measurement of different time delay positions can be realized. In the existing contrast single-shot measurement technology, multiple time-delayed positions are measured simultaneously in the same crystal, so that beams corresponding to different time-delays will interfere with each other. Therefore, its measurable dynamic range can only reach the order of 10 ⁴ . On the other hand, the measurable time delay is limited by the beam width of the fundamental frequency signal and the double frequency signal and the size of the double prism, so it can only be measured within ±10ps. Therefore, neither the dynamic range nor the time delay of the existing single-shot measurement system can meet the application requirements.

Contents of the invention

The problem to be solved by the present invention is to overcome the above-mentioned deficiencies in the prior art, provide a picosecond pulse contrast single-time measurement device, improve the dynamic range of contrast measurement, and expand the time delay of contrast measurement, so as to meet the requirements of physical experiments for ultra-short and ultra-strong Contrast requirements for laser systems.

Technical solution of the present invention is:

A single measurement device for picosecond pulse contrast, characterized in that it consists of a beam splitter, a first reflector, a second reflector, a third reflector, a fourth reflector, a fundamental frequency Damman grating, a fundamental frequency compensation grating group, a second Five-mirror, sixth mirror, double frequency crystal, double frequency Damman grating, double frequency compensation grating group, mirror group, beam combiner group, triple frequency crystal group, filter group and photomultiplier The composition of the tube group is as follows:

The incident pulse to be measured is used as the fundamental frequency light, and is divided into a transmitted beam and a reflected beam through the beam splitter, and the transmitted beam is composed of a first reflector, a second reflector, a third reflector and a fourth reflector The optical path delay mechanism is incident on the fundamental frequency Damman grating to form multiple fundamental frequency sub-beams, each of which corresponds to a fundamental frequency compensation grating of the fundamental frequency compensation grating group, and then shoots to the beam combiner The corresponding beam-combining mirrors of the group, the reflected light beam passes through the fifth reflector and the sixth reflector, enters the double frequency crystal to obtain double frequency light, and the double frequency light is incident on the double frequency up to On the Mann grating, a frequency-doubled multi-path sub-beam is formed, and each double-frequency sub-beam corresponds to a double-frequency compensation grating in the double-frequency compensation grating group to obtain a double-frequency multi-path sub-beam, and the double-frequency multi-path sub-beam After being reflected by the corresponding mirrors of the mirror group, it enters the beam combining mirror group, combines with the fundamental frequency sub-beam and then transmits collinearly, and enters the triple frequency crystal group together to obtain triple frequency light. The beam of tripled frequency light passes through the filter group, and the intensity of the tripled frequency signal is detected by the photomultiplier tube group, and the contrast of the pulse to be measured can be obtained after calculation.

The base frequency compensation grating group is composed of five fundamental frequency compensation gratings with the same structure, the double frequency compensation grating group is composed of five double frequency compensation gratings with the same structure, and the mirror group is composed of five Mirrors with the same structure, the beam combining mirror group is composed of five beam combining mirrors with the same structure, the triple frequency crystal group is composed of five triple frequency crystals with the same structure, the The optical filter group is composed of five optical filters with the same structure, and the photomultiplier tube group is composed of five photomultiplier tubes with the same structure.

The present invention adopts the method of dividing the amplitude, obtains five identical sub-beams separated from each other through the Damman grating, and realizes the contrast measurement at different time delay positions in five triple frequency crystals respectively. Since each sub-beam is separated in space, there is an optical path difference between two adjacent beams when the angles are different. The larger the deflection angle, the longer the propagation distance, and the larger the optical path difference. Large time delays can thus be achieved with this method.

The basic principle of short-pulse contrast measurement is the third-order cross-correlation process.

The function of the pulse to be measured with respect to time t is I(t), and the corresponding third-order cross-correlation signal is

I ₃ (τ)＝∫I(t)I ² (t-τ)dt (1)

Where: τ is the time delay. I ² (t) can be obtained through a double frequency crystal, and after adding a time delay τ, the third-order cross-correlation signal is obtained in a triple frequency crystal.

The technical effect of the present invention is,

1) A contrast measurement with a dynamic range above 10 ⁸ can be realized. In this solution, each frequency tripler crystal corresponds to only one time delay position, so there is no interference of the above-mentioned prior art. This approach is similar to the superposition of contrast measurement devices at 5 repetition rates, each of which measures a time-delayed position, enabling high dynamic range contrast measurements.

2) The time delay can be extended to 100ps. Because the optical path delay between the fundamental-frequency photon beam and the double-frequency photon beam is determined by the angle and the transmission distance in the air, changing the distance between two Damman gratings, or the distance between the Damman grating and the compensation grating The distance between them can realize the adjustment of optical path delay.

Description of drawings

Fig. 1 is a schematic diagram of an existing short-pulse contrast single-shot measurement device;

Fig. 2 is a schematic diagram of a picosecond contrast ratio single measuring instrument of the present invention;

Fig. 3 is a top view schematic diagram of the single picosecond contrast ratio measuring instrument in Fig. 2;

Fig. 4 is a schematic diagram of the time characteristic of the picosecond pulse output by the compressor in the petawatt laser device.

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

First please refer to Fig. 2 and Fig. 3, Fig. 2 and Fig. 3 are a schematic diagram of a specific embodiment of the present invention, as seen from the figure, the picosecond pulse contrast single-time measuring device of the present invention is composed of beam splitter 2-1, first reflecting mirror 2-2, the second reflector 2-3, the third reflector 2-4, the fourth reflector 2-5, the fundamental frequency Damman grating 2-6, the fundamental frequency compensation grating group 2-7, the fifth reflector 2-8, sixth reflector 2-9, double frequency crystal 2-10, double frequency Damman grating 2-11, double frequency compensation grating group 2-12, mirror group 2-13, beam combiner Group 2-14, triple frequency crystal group 2-15, optical filter group 2-16 and photomultiplier tube group 2-17 are formed, and its positional relationship is as follows: the incident pulse to be measured is used as the fundamental frequency light, and passes through described The beam splitter 2-1 is divided into a transmitted light beam and a reflected light beam, and the transmitted light beam passes through the first reflecting mirror 2-2, the second reflecting mirror 2-3, the third reflecting mirror 2-4 and the fourth reflecting mirror 2-5 The formed optical path delay mechanism is incident on the fundamental frequency Damman grating 2-6 to form five fundamental frequency sub-beams, each of which corresponds to a fundamental frequency compensation grating of the fundamental frequency compensation grating group 2-7 , and then shoot to the corresponding beam combiner of 2-14 of the beam combiner group, the reflected light beam passes through the fifth reflector 2-8, the sixth reflector 2-9, and enters the double frequency crystal 2- 10. Obtain double frequency light, which is incident on the double frequency Damman grating 2-11 to form five double frequency sub-beams, and each double frequency sub-beam corresponds to the double frequency compensation grating group 2 A double-frequency compensation grating at -12 obtains double-frequency five-way sub-beams, and the double-frequency five-way sub-beams enter the beam combining mirror group 2-14 after being reflected by the corresponding mirrors of the mirror group 2-13, After combining with the fundamental frequency sub-beams, they are transmitted collinearly, and enter the triple frequency crystal group 2-15 together to obtain triple frequency light. The five triple frequency light passes through the filter group 2-16, and is photoelectrically The multiplier tube group 2-17 detects the intensity of the triple frequency signal, and after calculation, the contrast of the pulse to be measured can be obtained.

In this embodiment, the fundamental frequency multi-path sub-beams and double frequency multi-path sub-beams all take 5 paths, therefore, the corresponding fundamental frequency compensation grating groups 2-7 are composed of five fundamental frequency compensation gratings, and the double frequency compensation grating group 2 -12 is composed of five double frequency compensation gratings, the beam combiner group 2-14 is composed of five beam combiner mirrors, and the triple frequency crystal group 2-15 is composed of five triple frequency crystals , the filter set 2-16 is composed of five filters, and the photomultiplier tube set 2-17 is composed of five photomultiplier tubes.

The incident pulse to be measured is used as the fundamental frequency light, which is divided into two by the beam splitter 2-1, and the transmitted beam passes through the first reflector 2-2, the second reflector 2-3, the third reflector 2-4 and the fourth reflector The optical path delay mechanism composed of mirrors 2-5 is incident on the fundamental frequency Damman grating 2-6, and converted into multiple fundamental frequency sub-beams, and each sub-beam corresponds to a compensation grating 2-7 to compensate the Damman grating resulting dispersion. The reflected light beam of the beam splitter 2-1 enters the double frequency crystal 2-10 through the fifth reflector 2-8 and the sixth reflector 2-9 to obtain the double frequency light, which also passes through the corresponding two Frequency-doubled Damman grating 2-11, double-frequency compensation grating 2-12, thereby obtaining double-frequency multi-path sub-beams. Then the double-frequency multi-path sub-beams are transmitted collinearly with the fundamental-frequency sub-beams through the reflector 2-13 and the beam combining mirror 2-14, and enter the triple-frequency crystal 2-15 together to obtain triple-frequency light. After the remaining fundamental frequency light and double frequency light are filtered out by the optical filter 2-16, the intensity of the triple frequency signal is detected by the photomultiplier tube 2-17, and the contrast of the pulse to be measured can be obtained after calculation. The optical path retarder composed of the first reflector 2-2, the second reflector 2-3, the third reflector 2-4, and the fourth reflector 2-5 is used to compensate the reflected light of the beam splitter during transmission. Additional delays from climbs and descents.

The optical path delay mode in the Damman grating spectroscopy is shown in Figure 3. The sub-beams emitted from the two fundamental-frequency Damman gratings 2-6 and the double-frequency Damman grating 2-11 that are misplaced are incident on the corresponding fundamental-frequency compensation grating 2-7 and doubled in the top view. frequency compensation grating 2-12.

The 1×10 Damman grating used in Fig. 3, due to the symmetry of the Damman grating, only five of the sub-beams are used. L represents the vertical distance between the Damman grating and the compensation grating group, d ₁ is the grating constant of the fundamental frequency Damman grating, d ₂ is the constant of the double frequency Damman grating, d ₁ = 2 d ₂ , m ₁ , m ₂ , m ₃ , m ₄ , m ₅ are the distances from the five sub-beams on the fundamental frequency Daman grating to the corresponding small gratings in the compensation grating group, n ₁ , n ₂ , n ₃ , n ₄ , n ₅ are the fundamental frequency Daman The distances from the five sub-beams on the Mann grating to the corresponding small gratings in the compensation grating group, θ ₁ , θ ₂ , θ ₃ , θ ₄ , and θ ₅ are the diffraction angles of the five sub-beams on the fundamental frequency and double frequency Damman gratings . In this way, the corresponding optical path delay between the five sub-beams of the fundamental frequency and the five sub-beams of the double frequency can be expressed as

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}\\ {\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}\\ {\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}\\ {\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

The middle beam of the fundamental frequency light and the double frequency light is adjusted to have an equal optical path length, that is, m ₃ -n ₃ =0. Specifically, it is realized by an optical path delay mechanism composed of the first reflecting mirror 2-2, the second reflecting mirror 2-3, the third reflecting mirror 2-4, and the fourth reflecting mirror 2-5. When τ=0, the triple frequency light intensity output by it is recorded as I ₀ =I ₃ (τ=0). On both sides of the central beam, the optical path difference between the fundamental frequency sub-beam and the double frequency sub-beam gradually increases, thereby achieving different optical path delays. In the top view, on the upper side of the central beam, the optical path of the sub-beams of the fundamental frequency decreases successively, and the optical path of the sub-beams of the double frequency increases sequentially. When they are incident on the triple frequency crystal group 2-11, contrast intensity values at different time delay positions τ will be obtained.

When it is necessary to realize the measurement of 10ps optical path delay, taking the upper side of the central beam as an example, a system of equations between grating constants d ₁ and d ₂ , diffraction angles θ ₂ and θ ₄ , and vertical distance L can be established

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; mm</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; ps</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="d"\; filenames="C2008100416400011H1.png,C2008100416400011H2.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\\ {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="d"\; filenames="C2008100416400010H1.png,C2008100416400011H1.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 7</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the equation system, d ₁ =200um, d ₂ =100um, λ _1ω =1.053um, λ _2ω =0.527um, and the solutions give L=5352.86mm, θ ₂ =0.905°, θ ₄ =2.114°. At this time, in the second sub-beam on the upper side of the center beam, the time delay between the fundamental frequency and the double frequency is 20 ps. Two intensity values I ₊₁ =I ₃ (τ=+10ps) and I ₊₂ =I ₃ (τ=+20ps) are obtained after the cross-correlation of the triple frequency crystal group 2-11. On the lower side of the central beam, the optical path of the fundamental frequency sub-beam increases sequentially, and the optical path of the double frequency sub-beam decreases successively. After the cross-correlation of the triple frequency crystal group 2-11, two intensity values I _-1 are also obtained =I ₃ (τ=-10ps), I _-2 =I ₃ (τ=-20ps). .

In this way, the pulse contrast (Pulse contract) of the four time delay positions of ±10ps and ±20ps can be obtained by calculation:

SNR=I ₁ /I ₀

Wherein, i=-2, -1, +1, +2.

In order to obtain an optical path delay of 100 ps between the fundamental frequency light and the double frequency light, it is only necessary to modify the equation group (3) as follows

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 30</span>}\mathrm{<span\; class="notranslate">\; mm</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 100</span>}\mathrm{<span\; class="notranslate">\; ps</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="d"\; filenames="C2008100416400011H1.png,C2008100416400011H2.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\\ {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="d"\; filenames="C2008100416400010H1.png,C2008100416400011H1.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 7</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\end{array}\right.<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>$

It can be obtained that L=53528.6mm, θ ₂ =0.905°, θ ₄ =2.114°. At this time, the pulse contrast at the four time delay positions of ±100ps and ±200ps can be obtained. In this case, however, the distance between the Damman grating and the compensating grating is relatively large. From the perspective of practical application, it is necessary to use 1×64 Damman grating instead of 1×10 Damman grating in the measurement system, and 32 sub-beams are available, which is the first-order diffraction and double of the fundamental frequency light. Corresponding to the 32nd order diffraction of frequency light, the equations are obtained

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 30</span>}\mathrm{<span\; class="notranslate">\; mm</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 100</span>}\mathrm{<span\; class="notranslate">\; ps</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="d"\; filenames="C2008100416400011H1.png,C2008100416400011H2.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\\ {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="d"\; filenames="C2008100416400010H1.png,C2008100416400011H1.png"\; state="\{\{state\}\}">d</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 32</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\end{array}\right.$

It can be obtained that L=499.4mm, θ ₁ =0.603°, θ ₄ =19.39°.

In this embodiment, each time delay position uses a single frequency tripler crystal, which can avoid interference and improve the dynamic range of contrast measurement. Using the angle and dislocation of the Damman grating in light splitting to form a statically distributed optical path delay can avoid using an optical path delay mechanism in each path and reduce the cost of the contrast measurement system.

Claims (2)

1, a kind of picopulse contrast single measurement device, be characterised in that by spectroscope (2-1), first catoptron (2-2), second catoptron (2-3), the 3rd catoptron (2-4), the 4th catoptron (2-5), fundamental frequency Darman raster (2-6), fundamental frequency null grating group (2-7), the 5th catoptron (2-8), the 6th catoptron (2-9), two frequency-doubling crystals (2-10), two frequency multiplication Darman rasters (2-11), two frequency multiplication null grating groups (2-12), reflector group (2-13), light combination mirror group (2-14), frequency tripling crystal group (2-15), filter set (2-16) and photomultiplier group (2-17) constitute, and its position relation is as follows:

The pulse to be measured of incident is as fundamental frequency light, be divided into transmitted light beam and folded light beam through described spectroscope (2-1), this transmitted light beam passes through by first catoptron (2-2), second catoptron (2-3), the optical path delay mechanism that the 3rd catoptron (2-4) and the 4th catoptron (2-5) are formed, incide on the fundamental frequency Darman raster (2-6), form fundamental frequency multichannel beamlet, a fundamental frequency null grating of all corresponding separately described fundamental frequency null grating group of each way light beam (2-7), (2-14) of directive light combination mirror group corresponding light combination mirror then, described folded light beam enters described two frequency-doubling crystals (2-10) by the 5th catoptron (2-8) and the 6th catoptron (2-9), obtain two frequency doubled lights, this two frequency doubled light incides on the two frequency multiplication Darman rasters (2-11), form two frequency multiplication multichannel beamlets, one two frequency multiplication null grating of all corresponding two frequency multiplication null grating groups (2-12) of every road two frequency multiplication beamlets, obtain two frequency multiplication multichannel beamlets, this two frequencys multiplication multichannel beamlet enters described light combination mirror group (2-14) after the mirror reflects accordingly by reflector group (2-13), close the conllinear transmission of bundle back with described fundamental frequency beamlet, enter frequency tripling crystal group (2-15) together, obtain frequency tripling light, this multi beam frequency tripling light is by filter set (2-16), by the intensity of photomultiplier group (2-17) detection frequency tripling signal, calculate the contrast that the back just can obtain pulse to be measured.

2, picopulse contrast single measurement device according to claim 1, it is characterized in that described fundamental frequency null grating group (2-7) is made of the identical fundamental frequency null grating of five block structures, described two frequency multiplication null grating groups (2-12) are made of two identical frequency multiplication null gratings of five block structures, described reflector group (2-13) is made of the identical catoptron of five block structures, (2-14) of described light combination mirror group is made of the identical light combination mirror of five block structures, described frequency tripling crystal group (2-15) is made of the identical frequency tripling crystal of five block structures, described filter set (2-16) is made of the identical optical filter of five block structures, and described photomultiplier group (2-17) is made of the identical photomultiplier of five block structures.

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