CN101290451A - Nonlinear optical crystal laser frequency multiplier capable of expanding embient temperature adaptation range - Google Patents

Abstract

The invention provides a nonlinear optical crystal laser frequency multiplier capable of extending the environmental temperature adaptation range, comprising a first nonlinear optical crystal and a second nonlinear optical crystal, wherein, the two nonlinear optical crystals are made of the same materials and are cut at different cutting angles, incident end surfaces and emergent end surfaces of the first nonlinear optical crystal and the second nonlinear optical crystal are plated with reflection reducing coatings with a fundamental frequency optical wavelength lambda1 and a frequency multiplication optical wavelength lambda 2, an emergent end surface of the first nonlinear optical crystal and an incident end surface of the second nonlinear optical crystal are attached. The laser frequency multiplier compensates the influence of the change in the environmental temperature on the frequency multiplication converting efficiency of the nonlinear optical crystals, extends the environmental temperature adaptation range of the nonlinear optical crystals in the frequency multiplication process, and provides an important way for the application of the nonlinear optical crystals.

Description

Can expand the nonlinear optical crystal laser frequency multiplier of environment temperature adaptation scope

Technical field

The present invention relates to a kind of nonlinear optical crystal laser frequency multiplier, particularly a kind of nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope.

Background technology

Phase matching is important concept in the nonlinear optics, be meant that the phase velocity (or refractive index) of fundamental frequency light in nonlinear optical crystal equals the phase velocity (or refractive index) of frequency doubled light, when fundamental frequency light passed through nonlinear optical crystal, the frequency multiplication polarization field that excites in the direction of propagation was strengthened mutually because of having identical phase place.

With KTP (potassium titanium oxide phosphate) crystal is example, and ktp crystal belongs to positive biaxial crystal, and 3 main shaft refractive indexes satisfy relational expression n _x＞n _y＞n _z, its refractive index surface equation is:

In the formula, θ and

Wave vector for arbitrary incident light correspondence

At intracrystalline polar coordinates angle, θ is ripple a--vector

With the angle of Z axle,

Be wave vector

At the projection of XOY plane and the angle of X-axis.Respectively with fundamental frequency light λ ₁The main shaft refractive index n _x, n _y, n _zWith frequency doubled light λ ₂The main shaft refractive index n _x, n _y, n _zSubstitution (1) formula, solving equation can obtain respectively with θ and The fundamental frequency light of expression and the o optical index n of frequency doubled light _o(λ ₁, θ,

), n _o(λ ₂, θ,

) and e optical index n _e(λ ₁, θ,

), n _e(λ ₂, θ,

).In the frequency multiplication process of ktp crystal II class phase matching, phase-matching condition is: $\mathrm{\Δk}={\stackrel{\→}{K}}_{1o}+{\stackrel{\→}{K}}_{1e}-{\stackrel{\→}{K}}_{2o}=0,$ That is:

(2) establishment computer numerical calculation procedure by formula, to θ and Scanning can be obtained optimum phase matching angle θ within the specific limits _mWith

Relational expression.

Nonlinear optical crystal is pressed phase matching angle θ _mWith

Cutting, fundamental frequency light incides on the crystal with certain angle, accurately rotates crystal, adjusts incident angle to phase matching angle θ _mWith

Make crystal reach phase matching and realize the output of effective frequency multiplication, obtain maximum frequency-doubling conversion efficiency.

Yet phase matching angle θ _mWith

Be in the certain environment temperature T ₀(room temperature) calculated down, and in general, the refractive index of nonlinear optical crystal changes with the variation of environment temperature T:

$n_x(\mathrm{\λ},T)=n_x\left(\mathrm{\λ}\right)+\frac{{\mathrm{dn}}_x}{\mathrm{dT}}(T-T_0)$

$n_y(\mathrm{\λ},T)=n_y\left(\mathrm{\λ}\right)+\frac{{\mathrm{dn}}_y}{\mathrm{dT}}(T-T_0)---\left(3\right)$

$n_z(\mathrm{\λ},T)=n_z\left(\mathrm{\λ}\right)+\frac{{\mathrm{dn}}_z}{\mathrm{dT}}(T-T_0)$

When the environment temperature T of nonlinear optical crystal departs from T ₀The time, produce phase mismatch Δ k:

$\mathrm{\Δk}=\frac{2\mathrm{\π}}{{\mathrm{\λ}}_1}[n_o({\mathrm{\λ}}_1,T)+n_e({\mathrm{\λ}}_1,T)-{2n}_o({\mathrm{\λ}}_2,T)]---\left(4\right)$

Cause the reduction of conversion efficiency in the nonlinear optical crystal frequency multiplication process:

$\mathrm{\η}=c{\left[\frac{\sin (\mathrm{L\Δk}/2)}{\mathrm{L\Δk}/2}\right]}^2---\left(5\right)$

In the formula, η=c is the maximal value of nonlinear optical crystal frequency-doubling conversion efficiency, and L is the length of nonlinear optical crystal.With the long λ of fundamental light wave ₁=1064nm, the frequency doubled light wavelength X ₂=532nm, the long ktp crystal of 1cm is an example, by formula (5) work out the computer numerical calculation procedure, frequency-doubling conversion efficiency when calculating the varying environment temperature, get c=1, obtain normalized frequency-doubling conversion efficiency η with curve η～T that environment temperature T changes, can obtain in the frequency multiplication process of II class phase matching, the temperature half-peak value width of frequency-doubling conversion efficiency is 25 ℃ of Δ T ≈.

These characteristics that the nonlinear optical crystal frequency-doubling conversion efficiency changes with variation of ambient temperature have greatly limited its application in many aspects, application especially militarily.Traditional solution is the measure of adopting frequency-doubling crystal constant temperature at present.Promptly no matter under what environment temperature, remain the ktp crystal temperature and be fixed in a certain definite scope, make that the variations in refractive index of ktp crystal is very little, so frequency-doubling conversion efficiency does not have obvious variation.

Summary of the invention

The objective of the invention is to: overcome the defective that existing laser frequency multiplier needs frequency-doubling crystal is taked constant temperature measures; In order to expand nonlinear optical crystal accommodation for environment temperature in the frequency multiplication process, thereby providing a kind of utilizes two blocks of different nonlinear optical crystals of cutting angle closely to arrange placement, the nonlinear optical crystal laser frequency multiplier of forming, this laser frequency multiplier is simple in structure, compactness has reduced device cost.

The object of the present invention is achieved like this:

The nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope provided by the invention comprises first nonlinear optical crystal 1; It is characterized in that, also comprise second nonlinear optical crystal 2; Described first nonlinear optical crystal 1 is the identical nonlinear optical crystals of two block of material with described second nonlinear optical crystal 2, two blocks of nonlinear optical crystals are with different cutting angle cuttings, and the incident end face of first nonlinear optical crystal 1 and second nonlinear optical crystal 2 and outgoing end face all are coated with the long λ of fundamental light wave ₁With the frequency doubled light wavelength X ₂Anti-reflection film, the outgoing end face of described first nonlinear optical crystal 1 and the incident end face of second nonlinear optical crystal 2 paste mutually to arrange and place.

The cutting angle of described first nonlinear optical crystal 1 is according to being adapted to the cutting of environment temperature condition with higher; The cutting angle of described second nonlinear optical crystal 2 is according to being adapted to the lower situation cutting of environment temperature.

The long λ of described fundamental light wave ₁Being the wavelength that can satisfy nonlinear optical crystal laser freuqency doubling phase-matching condition, can be 1064nm, and 800nm also can be other wavelength.

Described nonlinear optical crystal comprises potassium titanyl oxygenic phosphate(KTP) crystal (hereinafter to be referred as KTP), potassium dihydrogen phosphate crystal (hereinafter to be referred as KDP), and barium metaborate crystal (hereinafter to be referred as BBO) also can be other nonlinear optical crystal.

Advantage of the present invention:

The nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope provided by the invention, closely arrange placement owing to adopt two blocks of different nonlinear optical crystals of cutting angle, a nonlinear optical crystal cutting angle is adapted to the cutting of environment temperature condition with higher, another piece cutting angle is adapted to the lower situation cutting of environment temperature, compensated the influence of environment temperature like this, expanded nonlinear optical crystal accommodation for environment temperature in the frequency multiplication process frequency-doubling conversion efficiency.This laser frequency multiplier is simple in structure, and compactness has also reduced device cost simultaneously.

Description of drawings

Fig. 1 is the laser frequency multiplier structural representation of traditional nonlinear optical crystal, is used for comparing with the nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of the present invention.

Fig. 2 is the synoptic diagram of the embodiment of the nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of the present invention.

The drawing explanation

A-fundamental frequency light λ ₁=1064nm

B-frequency doubled light λ ₂=532nm and remaining fundamental frequency light λ ₁=1064nm

W-1064nm, quarter wave plate

Z-nonlinear optical crystal optic axis Z axle

1-the first nonlinear optical crystal (cutting angle is adapted to the environment temperature condition with higher)

2-the second nonlinear optical crystal (cutting angle is adapted to the lower situation of environment temperature)

3-the three nonlinear optical crystal (with traditional phase matching angle cutting)

Embodiment

Make a traditional nonlinear optical crystal (3) by Fig. 1.

The 3rd nonlinear optical crystal 3 is selected the ktp crystal of II class phase matching for use, with traditional phase matching angle cutting, overall dimensions: 7 * 7 * 10mm ³, cutting angle: θ _m=90 °,

The incident end face of nonlinear optical crystal 3 and outgoing end face are coated with the long λ of fundamental light wave respectively ₁=1064nm and frequency doubled light wavelength X ₂The anti-reflection film of=532nm is placed on the rotary turntable of horizontal direction.Allow a branch of wavelength X ₁=1064nm, single pulse energy 100mJ, the fundamental frequency light of pulse width 3～5ns by quarter wave plate W, incides on the nonlinear optical crystal 3 then, obtains λ ₂The frequency doubled light output of=532nm.Regulate the level angle of turntable, obtain maximum frequency doubled light output ENERGY E _Shg=65.1mJ.Change the environment temperature of nonlinear optical crystal 3, frequency doubled light output energy difference when finding the varying environment temperature, the output energy value of frequency doubled light during record varying environment temperature obtains frequency doubled light output ENERGY E _ShgCurve E with environment temperature T variation _Shg～T is by frequency multiplication output energy trace E _ShgThe temperature half-peak value width that～T obtains the frequency multiplication output efficiency is Δ T=19 ℃.

Embodiment 1

Make a kind of nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of the present invention by Fig. 2.

First nonlinear optical crystal 1 is selected the ktp crystal of II class phase matching, overall dimensions: 7 * 7 * 5mm for use ³, cutting angle: θ _m=90 °,

Second nonlinear optical crystal 2 is selected the ktp crystal of II class phase matching, overall dimensions: 7 * 7 * 5mm for use ³, cutting angle: θ _m=90 °,

The cutting angle of first nonlinear optical crystal 1 and second nonlinear optical crystal 2 differs 0.5 °.The incident end face of described first nonlinear optical crystal 1 and described second nonlinear optical crystal 2, outgoing end face are coated with the long λ of fundamental light wave respectively ₁=1064nm and frequency doubled light wavelength X ₂The anti-reflection film of=532nm, the outgoing end face of first nonlinear optical crystal 1 pasted side by side mutually with the incident end face of second nonlinear optical crystal 2 be fixed together, form the nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of the present invention, be placed on the rotary turntable of horizontal direction.Allow with a branch of wavelength X ₁=1064nm, single pulse energy 100mJ, the fundamental frequency light of pulse width 3～5ns by quarter wave plate W, incides on the laser frequency multiplier of first nonlinear optical crystal 1 and second nonlinear optical crystal, 2 compositions then, obtains λ ₂The frequency doubled light output of=532nm.Regulate the level angle of turntable, obtaining maximum frequency doubled light output energy is E _Shg=60.84mJ.Change the environment temperature of the laser frequency multiplier of first nonlinear optical crystal 1 and second nonlinear optical crystal, 2 compositions, frequency doubled light output energy difference when finding the varying environment temperature, the output energy value of frequency doubled light during record varying environment temperature obtains frequency doubled light output ENERGY E _ShgCurve E with environment temperature T variation _Shg～T is by frequency doubled light output energy trace E _ShgThe temperature half-peak value width that～T obtains the frequency multiplication output efficiency is Δ T=76 ℃, is to use 4 times of traditional nonlinear optical crystal KTP frequency multiplication.

Embodiment 2

Make the another kind of nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of the present invention by Fig. 2.

First nonlinear optical crystal 1 is selected the ktp crystal of II class phase matching, overall dimensions: 7 * 7 * 5mm for use ³, cutting angle: θ _m=90 °,

Second nonlinear optical crystal 2 is selected the ktp crystal of II class phase matching, overall dimensions: 7 * 7 * 5mm for use ³, cutting angle: θ _m=90 °,

The cutting angle of first nonlinear optical crystal 1 and second nonlinear optical crystal 2 differs 1.0 °.The incident end face of described first nonlinear optical crystal 1 and described second nonlinear optical crystal 2, outgoing end face are coated with the long λ of fundamental light wave respectively ₁=1064nm and frequency doubled light wavelength X ₂The anti-reflection film of=532nm, the outgoing end face of first nonlinear optical crystal 1 and the incident end face of second nonlinear optical crystal 2 pasted to arrange mutually be fixed together, form the nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of the present invention, be placed on the rotary turntable of horizontal direction.Allow with a branch of wavelength X ₁=1064nm, single pulse energy 100mJ, the fundamental frequency light of pulse width 3～5ns by quarter wave plate W, incides on the laser frequency multiplier of first nonlinear optical crystal 1 and second nonlinear optical crystal, 2 compositions then, obtains λ ₂The frequency doubled light output of=532nm.Regulate the level angle of turntable, obtaining maximum frequency doubled light output energy is E _Shg=56.98mJ.Change the environment temperature of the laser frequency multiplier of first nonlinear optical crystal 1 and second nonlinear optical crystal, 2 compositions, frequency doubled light output energy difference when finding the varying environment temperature, the output energy value of frequency doubled light during record varying environment temperature obtains frequency doubled light output ENERGY E _ShgCurve E with environment temperature T variation _Shg～T is by frequency doubled light output energy trace E _ShgThe temperature half-peak value width that～T obtains the frequency multiplication output efficiency is Δ T=95 ℃, is to use 5 times of traditional nonlinear optical crystal KTP frequency multiplication.

Claims (4)

1. the nonlinear optical crystal laser frequency multiplier that can expand environment temperature adaptation scope comprises first nonlinear optical crystal (1); It is characterized in that, also comprise second nonlinear optical crystal (2); Described first nonlinear optical crystal (1) is the identical nonlinear optical crystals of two block of material with described second nonlinear optical crystal (2), two blocks of nonlinear optical crystals are with different cutting angle cuttings, and incident end face, the outgoing end face of described first nonlinear optical crystal (1) and described second nonlinear optical crystal (2) are coated with the long λ of fundamental light wave respectively ₁With the frequency doubled light wavelength X ₂Anti-reflection film, the incident end face of the outgoing end face of described first nonlinear optical crystal (1) and second nonlinear optical crystal (2) pastes mutually arrange to be placed.

By the described nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of claim 1, it is characterized in that 2, the cutting angle of described first nonlinear optical crystal (1) is according to being adapted to the cutting of environment temperature condition with higher; The cutting angle of described second nonlinear optical crystal (2) is according to being adapted to the lower situation cutting of environment temperature.

3, by the described nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of claim 1, it is characterized in that the long λ of described fundamental light wave ₁Be the wavelength that can satisfy nonlinear optical crystal laser freuqency doubling phase-matching condition, comprise 1064nm, 800nm or other wavelength.

4, by the described nonlinear optical crystal laser frequency multiplier of expanding environment temperature adaptation scope of claim 1, it is characterized in that described first nonlinear optical crystal (1) and second nonlinear optical crystal (2) comprise potassium titanyl oxygenic phosphate(KTP) crystal, potassium dihydrogen phosphate crystal, barium metaborate crystal or other nonlinear optical crystal.

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