CN201166588Y - Apparatus for measuring high power ultra-short laser pulse contrast - Google Patents

Abstract

A measuring device with high power used for measuring the ultra-short laser pulse contrast is characterized by comprising a first convex lens, a BBO frequency doubling crystal, a second convex lens and a beam splitter which are orderly arranged in the laser pulse incident direction, wherein the frequency doubling light which is generated after the incident beam passes through the BBO frequency doubling crystal and the base frequency light which originally enters are divided into the transmitted base frequency light and the reflected frequency doubling light by the beam splitter, wherein the transmitted base frequency light enters a third convex lens through a delayed regulator, the reflected frequency doubling light passes through a flat glass and then enables the frequency doubling light to be divided into a plurality of the frequency doubling light with certain delay time and decreased strength, which enters the third convex lens, and the base frequency light and a plurality of the frequency doubling light enter a BBO frequency mixing crystal in parallel through the third convex lens, which generates harmonic wave signals for three times, then is aligned by a collimation lens, and is received by a photoelectric detecting element after passing through a filter. The measuring device can measure the single ultra-short laser pulse contrast, and the utility model has the advantages that the light path regulation is flexible and convenient, the dynamic range of measuring is big, and the accuracy is high.

Description

High power ultra-short laser pulse contrast measurement mechanism

Technical field

The utility model relates to high power ultra-short laser pulse, it is a kind of high power ultra-short laser pulse contrast measurement mechanism, it adopts the sheet glass of a plated film to the frequency-doubled signal beam splitting, then respectively and frequently with fundamental frequency signal, produce corresponding frequency tripling signal, thereby effectively obtain the strength information of pulse diverse location to be measured, realize measurement single ultrashort laser pulse contrast.

Background technology

In ultrashort ultra-intense laser and matter interaction process, contrast be one extremely important, and directly influence the parameter index of laser and matter interaction effect.Because the pulse front edge of laser can produce pre-plasma, it is determining the original state of plasma, and and then influences the mechanism of laser and matter interaction.So accurately the contrast of Laser Measurement pulse is a very important problem.In order to obtain the information of laser pulse contrast, the measuring method that generally adopts is technology such as secondary correlation method, three correlations methods at present.Though the secondary correlation method also can provide some information of intensity contrast, because the signal that obtains is symmetrical before and after being in this way, so it can not provide the parameter of pulse front edge exactly; And interact in the three correlations methods with what produce coherent signal is two different pulses, so can distinguish the forward position and the edge, back of pulse more accurately, thus the position of accurate given noise, and can realize the measurement of the dynamic range that contrast is higher.

Fig. 1 is the measurement mechanism of existing ultrashort laser pulse contrast.Its basic structure is: at first pulse concentration to be measured is incided on barium metaborate (the being designated hereinafter simply as BBO) crystal 2 of one two frequency multiplication by condenser lens 1, produce second harmonic signal, with Wollaston prism 5 parallel fundamental frequency signal and frequency-doubled signal are spatially separated then, again the fundamental frequency signal that will disperse by a biprism 6 and frequency-doubled signal converge at again optical path axis to, place mixer crystal BBO7 to produce harmonic signal at the meet of two signals, wave plate 9 after filtration at last, receive the frequency tripling signal with CCD10, thereby draw end product.This device can carry out the measurement of single ultrashort laser pulse contrast, but its time range that can survey is subjected to the restriction of the size of the angle of fundamental frequency signal and frequency-doubled signal and biprism 6, generally can only measure ± 10ps～± scope of 20ps.In addition, the pulse of corresponding a pair of fundamental frequency of each fixing optical path difference and frequency multiplication is right, be to cutting apart before the interference wave, and the inhomogeneous meeting of beam intensity space distribution directly causes surveying reducing of contrast dynamic range, and it can survey dynamic range can only reach 10 ⁴

Summary of the invention

The purpose of this utility model will remedy above-mentioned the deficiencies in the prior art exactly, and a kind of high power ultra-short laser pulse contrast measurement mechanism is provided.This device can be realized the measurement to single high power ultra-short laser pulse contrast, has bigger dynamic range, also can effectively avoid to preventing the saturated error that attenuator brought that adds of optical detection device by regulating simultaneously.

Technical solution of the present utility model is as follows:

A kind of high power ultra-short laser pulse contrast measurement mechanism, characteristics are that its formation is: set gradually first convex lens in the high power ultra-short laser pulse incident direction, the BBO frequency-doubling crystal, second convex lens and beam splitter, incident beam produces frequency doubled light through the BBO frequency-doubling crystal, the fundamental frequency light of this frequency doubled light and former incident is divided into the fundamental frequency light of transmission and the frequency doubled light of reflection by described beam splitter, the fundamental frequency light of described transmission enters the 3rd convex lens by delay modulator, the frequency doubled light of described reflection enters sheet glass through catoptron, behind this sheet glass, this frequency doubled light is divided into and has certain hour and postpone, a few bundle frequency doubled lights that intensity weakens, enter the 3rd convex lens, fundamental frequency light and a few bundle frequency doubled light through the 3rd convex lens enter the BBO mixer crystal concurrently, produce harmonic signal, this harmonic signal collimates through collimation lens again, received by optical detection device behind the filter plate.

Utilize above-mentioned measurement mechanism to measure the method for high power ultra-short laser pulse contrast, comprise the following steps:

1. high power ultra-short laser pulse to be measured is imported this device, adjusts the position of described sheet glass, determine to count N from the light beam of two frequencys multiplication of this sheet glass output:

I _n(2ω) n＝1、2、3、……、N；

2. adjust the delay of the fundamental frequency light of transmission by delay modulator, make the main peak and the described the most weak frequency multiplication light beam I of the fundamental frequency light of transmission from sheet glass output _N(2 ω) mixing produces I _N(3 ω);

3. import high power ultra-short laser pulse to be measured, the fundamental frequency signal in the light path is restrainted two frequency-doubled signals and frequently with N respectively, receives with optical detection device then, obtain different postpone Δ t ∈ (∞, 0] the frequency tripling intensity spectrum I that locates _n(3 ω) (n=1,2,3,4,5 ... N);

4. 3. go on foot in the frequency tripling intensity spectrum of gained the and find out maximum I _N(3 ω) and time maximum I _n(3 ω);

5. ask the contrast of high power ultra-short laser pulse:

I _N(ω)/I _n(ω)＝(r ₁r ₂) ^(1-N+n)I _N(3ω)/I _n(3ω)

In the formula: r ₁And r ₂Be respectively the reflectivity of sheet glass (2-7) two inside surfaces.

Technical solution of the present utility model is based on following principle:

Fig. 3 is the sheet glass of a plated film, and establishing its refractive index is n, and thickness is d, and beam incident angle is i ₁, the refraction angle is i ₂, the optical path difference of adjacent two bundle frequency doubled lights is:

$\mathrm{\ΔL}=n(\mathrm{OA}+\mathrm{AB})-\mathrm{AP}=2d\sqrt{n^2-{\sin }^2{i}_1}---\left(1\right)$

Other establishes r ₁, r ₂Be respectively the reflectivity of sheet glass OF face and AG face two sides inside surface, then have

I _n(2ω)＝(r ₁r ₂) ^n-1I ₁(2ω) n＝1，2，3，4，5，…… (2)

In the formula: I _n(2 ω) expression is respectively restrainted the frequency multiplication light intensity from the glass plate outgoing

In nonlinear medium, the optical electric field E (ω of two different frequencies ₁, z), E (ω ₂, can produce polarized electric field E (ω during z) with medium interaction ₃, z), suppose that their wave vector is respectively k ₁, k ₂, k ₃, have following coupledwave equation to set up:

$\frac{\mathrm{dE}({\mathrm{\&omega;}}_1,z)}{\mathrm{dz}}=\frac{{\mathrm{i\&omega;}}_1^2}{k_1{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="Y20072007767700081.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}{\mathrm{\&chi;}}_{\mathrm{eff}}^{\left(2\right)}E({\mathrm{\&omega;}}_3,z)E^{*}({\mathrm{\&omega;}}_2,z)e^{-\mathrm{i\&Delta;kz}}---\left(3\right)$

$\frac{\mathrm{dE}({\mathrm{\&omega;}}_2,z)}{\mathrm{dz}}=\frac{{\mathrm{i\&omega;}}_2^2}{k_2{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="Y20072007767700081.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}{\mathrm{\&chi;}}_{\mathrm{eff}}^{\left(2\right)}E({\mathrm{\&omega;}}_3,z)E^{*}({\mathrm{\&omega;}}_1,z)e^{-\mathrm{i\&Delta;kz}}---\left(4\right)$

$\frac{\mathrm{dE}({\mathrm{\&omega;}}_3,z)}{\mathrm{dz}}=\frac{{\mathrm{i\&omega;}}_3^2}{k_3{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="Y20072007767700081.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}{\mathrm{\&chi;}}_{\mathrm{eff}}^{\left(2\right)}E({\mathrm{\&omega;}}_1,z)E({\mathrm{\&omega;}}_2,z)e^{\mathrm{i\&Delta;kz}}---\left(5\right)$

In the formula: χ _Eff ²Be the non-linear susceptibility of crystal, that commonly used is nonlinear factor d in actual applications _EffFor with the frequency process, ${\mathrm{\&chi;}}_{\mathrm{<figure-callout\; id="2"\; label="eff"\; filenames="Y20072007767700081.png"\; state="\{\{state\}\}">eff</figure-callout>}}^2=d_{\mathrm{eff}}$ , consider the small-signal process, can obtain small-signal separate into:

$E({\mathrm{\&omega;}}_3,L)=\frac{{\mathrm{i\&omega;}}_3^2}{k_3{c}^2}{d}_{\mathrm{eff}}E({\mathrm{\&omega;}}_1,0)E({\mathrm{\&omega;}}_2,0)e^{\mathrm{i\&Delta;kL}/2}\frac{\sin (\mathrm{\&Delta;kL}/2)}{\mathrm{\&Delta;k}/2}---\left(6\right)$

Consider I _ω=ε ₀Cn|E _ω| ²/ 2, and sinc (x)=sin (x)/x is arranged, can obtain

$I_{3\mathrm{\&omega;}}=K{d}_{\mathrm{eff}}^2{L}^2{I}_{1\mathrm{\&omega;}}{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="Y20072007767700081.png"\; state="\{\{state\}\}">I</figure-callout>}}_{2\mathrm{\&omega;}}{\sin c}^2(\mathrm{\&Delta;kL}/2)---\left(7\right)$

In the following formula $K={2\mathrm{\&omega;}}_3^2/\left({\mathrm{\&epsiv;}}_0{c}^3{n}_1{n}_2{n}_3\right)$ 。Δ k=k ₃-k ₁-k ₂(θ, T λ), are the functions about θ, temperature T, wavelength X to=Δ k.In three rank autocorrelation processes, if (θ, T's Δ k λ) remain unchanged, and can think

I _3ω∝I _1ωI _2ω (8)

Also can be expressed as herein:

I _n(3ω)∝I _n(ω)I _n(2ω)∝(r ₁r ₂) ^n-1I _n(ω)I ₁(2ω) (n＝1，2，3，4，5……) (9)

Then have

I _n(ω)∝(r ₁r ₂) ^1-nI _n(3ω)/I ₁(2ω) (n＝1，2，3，4，5……) (10)

Respectively and frequently,, accept with CCD then by the fundamental frequency signal in the light path with a few bundle two frequency-doubled signals, can obtain different postpone Δ t ∈ (∞, 0] locate with frequency light intensity I _n(3 ω) (n=1,2,3,4,5 ...), can obtain the contrast of high power ultra-short laser pulse to be measured again in conjunction with following formula:

I _N(ω)/I _n(ω)＝(r ₁r ₂) ^(1-N+n)I _N(3ω)/I _n(3ω)。(11)

Technique effect of the present utility model is as follows:

1, core of the present utility model is to adopt the sheet glass beam splitting of a plated film, obtains the information of its contrast by the multimetering to the single ultrashort laser pulse.Reflection and the transmission of light beam by sheet glass is easy to realize that the aplanatism of adjacent outgoing pulse is poor, in addition, adjusts also better controlled light path extent within the specific limits of incident angle in conjunction with the thickness of glass plate.So having light path, this device regulates flexible advantage;

2, the utility model has effectively overcome the size of fundamental frequency signal and frequency-doubled signal angle in the prior art and biprism size to can surveying the restriction of time range, and adopted divide amplitude, avoided minimizing, thereby obtained higher dynamic range because of the inhomogeneous dynamic range surveyed that causes of beam intensity space distribution;

3, by regulating the time delay of fundamental frequency signal and frequency-doubled signal, make the main pulse peak value that drops on fundamental frequency signal from the most weak frequency multiplication light beam of sheet glass outgoing, make stronger frequency multiplication light beam drop on the pulse front edge of more weak fundamental frequency signal, can effectively avoid error, improve measuring accuracy for preventing that the saturated attenuator that adds of optical detection device from bringing.

Description of drawings

Fig. 1 is existing single ultrashort laser pulse contrast measurement mechanism structural representation.

Fig. 2 is the structural representation of the utility model single ultrashort laser pulse contrast measurement mechanism.

Fig. 3 is the light path synoptic diagram in the described plated film sheet glass.

Embodiment

The utility model is described in further detail below in conjunction with accompanying drawing, but should not limit protection domain of the present utility model with this.

See also Fig. 2 earlier, Fig. 2 is the structural representation of the utility model single ultrashort laser pulse contrast measurement mechanism.As seen from the figure, the formation of the utility model high power ultra-short laser pulse contrast measurement mechanism is: set gradually the first convex lens 2-1 in the high power ultra-short laser pulse incident direction, BBO frequency-doubling crystal 2-2, the second convex lens 2-3 and beam splitter 2-4, incident beam produces frequency doubled light through BBO frequency-doubling crystal 2-2, the fundamental frequency light of this frequency doubled light and former incident is divided into the fundamental frequency light of transmission and the frequency doubled light of reflection by described beam splitter 2-4, the fundamental frequency light of described transmission enters the 3rd convex lens 2-8 by delay modulator 2-6, the frequency doubled light of described reflection enters sheet glass 2-7 through catoptron 2-5, behind this sheet glass 2-7, this frequency doubled light is divided into and has certain hour and postpone, a few bundle frequency doubled lights that intensity weakens, enter the 3rd convex lens 2-8, fundamental frequency light and a few bundle frequency doubled light through the 3rd convex lens 2-8 enter BBO mixer crystal 2-9 concurrently, produce harmonic signal, this harmonic signal collimates through collimation lens 2-10 again, received by optical detection device 2-12 behind the filter plate 2-11.

Fig. 3 is the light path synoptic diagram of a specific embodiment in the described plated film sheet glass.Here establish r in (2) formula ₁=0.2, r ₂=0.5, the position of adjusting sheet glass 2-7 produces 5 bundles, two frequency doubled lights, then has:

I _n(2ω)＝(0.1) ^n-1I ₁(2ω) n＝1，2，3，4，5 (12)

As seen, I ₁(2 ω) maximum is successively decreased I successively ₅(2 ω) minimum.

The situation of pulse ultrashort pulse centre wavelength 1053nm time domain width 1 psec that obtains after consideration titanium jewel (Ti:Sapphire) oscillator output broadening, amplification, the compression.

At first the fundamental frequency signal of 1053nm is focused into and is mapped on the BBO frequency-doubling crystal 2-2, to produce the frequency-doubled signal of 527nm, use beam splitter 2-4 (fundamental frequency full impregnated then, frequency multiplication is all-trans) fundamental frequency signal of transmission and the frequency-doubled signal of reflection are separated, frequency-doubled signal is repeatedly reflection in a plated film sheet glass 2-7, transmission, be divided into 5 bundles and have the parallel optical signal that certain hour postpones, make them parallelly with fundamental frequency signal enter a convergent lens 2-8, it is interior to produce the harmonic signal of 351nm to converge at frequency tripling bbo crystal 2-9, and wave plate 2-11 enters CCD2-12 after filtration.Wherein, by control lag regulator 2-6, make the most weak frequency-doubled signal I ₅The main pulse peak value of (2 ω) and fundamental frequency signal is synchronous, stronger frequency-doubled signal then with more weak pulse front edge effect, need not attenuator and can avoid that CCD2-12's is saturated.Easily know by analysis at I _n(ω) I in (n=1,2,3,4,5) ₅(ω) be maximal value, if I ₂(ω) be I _n(ω) maximal value in (n=1,2,3,4), then I ₅(ω)/I ₂(ω)=1000I ₅(3 ω)/I ₂(3 ω) is the contrast of ultrashort laser pulse to be measured.

Claims (1)

1, a kind of high power ultra-short laser pulse contrast measurement mechanism, be characterised in that its formation is: set gradually first convex lens (2-1) in the high power ultra-short laser pulse incident direction, BBO frequency-doubling crystal (2-2), second convex lens (2-3) and beam splitter (2-4), incident beam produces frequency doubled light through BBO frequency-doubling crystal (2-2), the fundamental frequency light of this frequency doubled light and former incident is divided into the fundamental frequency light of transmission and the frequency doubled light of reflection by described beam splitter (2-4), the fundamental frequency light of described transmission enters the 3rd convex lens (2-8) by delay modulator (2-6), the frequency doubled light of described reflection enters sheet glass (2-7) through catoptron (2-5), behind this sheet glass (2-7), this frequency doubled light is divided into and has certain hour and postpone, a few bundle frequency doubled lights that intensity weakens, enter the 3rd convex lens (2-8), fundamental frequency light and a few bundle frequency doubled light through the 3rd convex lens (2-8) enter BBO mixer crystal (2-9) concurrently, produce harmonic signal, this harmonic signal collimates through collimation lens (2-10) again, filter plate (2-11) back is received by optical detection device (2-12).

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