CN1169008C - Non-linear frequency changeover crystal - Google Patents

Abstract

The present invention relates to a nonlinear frequency conversion crystal, which comprises two of three kinds of four optical elements as follows: a nonlinear crystal 1, a nonlinear crystal 2, one half of a wave plate 5 and a dual-wavelength wave plate 6, wherein the nonlinear crystal 1 and the nonlinear crystal 2 are nonlinear crystals KTP with the same length and are cut in a phase matching direction according to the II class; the surface 1a of the nonlinear crystal 1 is plated with anti-reflection film @ 1064 NM, and the surface 1b of the nonlinear crystal 1 is plated with anti-reflection film @ 1064 NM & 532 NM; both surfaces of the nonlinear crystal 2, the half of a wave plate 5 and the dual-wavelength wave plate 6 are plated with anti-reflection film @ 1064 NM & 532 NM. The present invention has one of four combined structures. N pieces of crystals can form nonlinear frequency conversion crystal plate piles with arbitrarily lengths through optical cement or deepened optical cement, wherein the N is an integer. The present invention can simultaneously compensate phase difference caused by the going of light waves in spaces and the passing of fundamental frequency light through the nonlinear frequency conversion crystal, is not sensitive to environment temperatures, has the advantages of simple structure, compact volume, etc. and is suitable for being used as an inner cavity double frequency doubling and an outer cavity frequency doubling crystal with low noise.

Description

A kind of novel non-linear frequency conversion crystal

Technical field

The present invention relates to a kind of non-linear frequency conversion crystal, belong to the light wavelength conversion device technical field.

Background technology

Under critical phase-matching condition, because the influence of following factor has limited the raising of nonlinear crystal frequency conversion efficiency.

At first, fundamental frequency light is divided into two orthogonal polarization components incide the nonlinear crystal with birefringence effect with certain polarization direction after, because the refractive index that different polarized components is corresponding different, at the inner phase mismatch that takes place of nonlinear crystal, promptly when fundamental frequency light during from the nonlinear crystal outgoing two polarized components one phase difference is arranged

Δ＝(n ₂ ^ω-n ₁ ^ω)L·2π/λ

Wherein, λ is the fundamental frequency light wavelength, and L is the effective length of nonlinear crystal, n ₁ ^ω, n ₂ ^ωBe respectively the refractive index of two polarized component correspondences.Polarization direction when phase difference makes the outgoing of fundamental frequency light changes, and causes the angle of fundamental frequency polarisation of light direction and nonlinear crystal optical axis to change, and this will inevitably cause the fluctuation of nonlinear crystal frequency conversion efficiency.

Secondly, in nonlinear crystal, because the birefringence effect of light wave, in general, the phase place direction of propagation of light wave and can spread that to broadcast direction be inconsistent.Angle α between wave vector and the Poynting vector is called the deviation angle of light wave.The light wave of walking interaction in making crystal of light wave is separated from each other after through a segment distance, thereby has reduced interaction length, has reduced the frequency conversion efficiency of nonlinear crystal.

In the background technology, developed the multiple method that under critical phase-matching condition, improves the nonlinear crystal frequency conversion efficiency.U.S. Pat 4,913,533 control control phase difference Δ by nonlinear crystal being carried out temperature, but this method can not compensate light wave spatially walk from, very high to temperature requirements, and this device is very sensitive to the variation of surrounding environment.Japanese unexamined patent Nos.1 (1989)-152781 uses the nonlinear crystal with trapezoid cross section, changes the light path of light wave by nonlinear crystal by moving up and down trapezoidal nonlinear crystal, realizes the adjusting to phase difference.But this method can not compensate light wave the space walk from, and to the requirement on machining accuracy height of crystal, also very sensitive to the variation of surrounding environment.The U.S. Pat 5 that on July 29th, 1997 was authorized people such as Yoji Okazaki, 652,757 disclose the non-linear frequency conversion crystal of another kind of structure, and the optical axis direction that is about to the nonlinear crystal of the same race of two equal length, identical cutting angle is placed along logical optical axis half-twist.This non-linear frequency conversion crystal not only can compensate the phase differential that fundamental frequency light causes through nonlinear crystal, and ambient temperature is changed insensitive, but can't compensate light wave spatially walk from.March nineteen ninety-five, people such as Gao Jiangrui publish an article on Applied Optics, the nonlinear crystal of the same race of having introduced two equal length of employing, identical cutting angle in the laser instrument of intracavity frequency doubling is as frequency-doubling crystal, wherein, second nonlinear crystal optical axis direction with respect to first nonlinear crystal optical axis direction along logical optical axis Rotate 180 ° placement.This non-linear frequency conversion crystal not only can compensate light wave the space walk from, and ambient temperature is changed insensitive, but this non-linear frequency conversion crystal can't compensate the phase differential that fundamental frequency light causes through nonlinear crystal.

Summary of the invention

The technical problem to be solved in the present invention is to release a kind of non-linear frequency conversion crystal, this non-linear frequency conversion crystal can compensate light wave walking from passing through the phase mismatch that nonlinear crystal causes with fundamental frequency light in the space simultaneously, make the nonlinear crystal frequency conversion efficiency reach maximum, and for any wave band all is full-wave plate, simultaneously, this non-linear frequency conversion crystal changes insensitive to ambient temperature, need not the serviceability temperature control system, simple in structure, volume is small and exquisite.

The present invention makes above-mentioned technical matters be resolved by following technical solution: a kind of non-linear frequency conversion crystal, contain following four kinds of optical elements: in first nonlinear crystal, second nonlinear crystal, 1/2nd wave plates and the dual wavelength wave plate two～three kinds, it is characterized in that, first nonlinear crystal is the identical nonlinear crystal KTP of length with second nonlinear crystal, press the cutting of II class phase matching direction, a surface of first nonlinear crystal is coated with Zeng Toumo @1064nm, and another surface is coated with Zeng Toumo @1064nm﹠amp; 532nm, two surfaces of second nonlinear crystal, 1/2nd wave plates and dual wavelength wave plate all are coated with anti-reflection film; 532nm, this non-linear frequency conversion crystal has one of following four kinds of unitized constructions: first type non-linear frequency conversion crystal closely is adjacent to arrange place by first nonlinear crystal and three second nonlinear crystals and forms, the optical axis direction of first second nonlinear crystal with respect to the optical axis direction of first nonlinear crystal along logical optical axis Rotate 180 ° placement, the optical axis direction of second second nonlinear crystal is placed along logical optical axis half-twist with respect to the optical axis direction of first second nonlinear crystal, the optical axis direction of the 3rd block of second nonlinear crystal with respect to the optical axis direction of second second nonlinear crystal along logical optical axis Rotate 180 ° placement; Second type non-linear frequency conversion crystal closely is adjacent to arrange place by first nonlinear crystal and three second nonlinear crystals and forms, the optical axis direction of first second nonlinear crystal is placed along logical optical axis half-twist with respect to the optical axis direction of first nonlinear crystal, along logical optical axis Rotate 180 ° placement, place along logical optical axis half-twist with respect to the optical axis direction of second second nonlinear crystal by the optical axis direction of the 3rd block of second nonlinear crystal with respect to the optical axis direction of first second nonlinear crystal for the optical axis direction of second second nonlinear crystal; The 3rd type non-linear frequency conversion crystal closely is adjacent to arrange place by first nonlinear crystal, 1/2nd wave plates and second nonlinear crystal and forms, second nonlinear crystal is placed in the identical mode of optical axis direction of its optical axis direction and first nonlinear crystal, and 1/2nd wave plates are placed between the above two in the mode of its optical axis direction while and the above two optical axis direction angle at 45; Closely being adjacent to arrange placement with the 4th type non-linear frequency conversion crystal by first nonlinear crystal, dual wavelength wave plate and second nonlinear crystal forms, second nonlinear crystal is placed in the identical mode of optical axis direction of its optical axis direction and first nonlinear crystal, and the dual wavelength wave plate is placed between the above two in the mode of its optical axis direction while and the above two optical axis direction angle at 45.

Technical solution of the present invention is further characterized in that, but first nonlinear crystal and the second nonlinear crystal nonlinear crystal KNbO ₃, LiB ₃O ₅, β-BaB ₂O ₄, MgO: LiNbO ₃, KDP.

Technical solution of the present invention is further characterized in that, but N first type non-linear frequency conversion crystal, second type non-linear frequency conversion crystal, the 3rd type non-linear frequency are changed crystal or the 4th type non-linear frequency conversion crystal optical cement or in-depth optical cement and are become the non-linear frequency conversion crystal wafer heap of length arbitrarily, and wherein N is a positive integer.

Compare with background technology, the present invention has following outstanding effect:

Non-linear frequency provided by the invention conversion crystal can compensate light wave walking from the phase differential that causes through non-linear frequency conversion crystal with fundamental frequency light spatially simultaneously, and the nonlinear interaction distance can strengthen greatly, all shows as full-wave plate for any wave band; Simultaneously, this non-linear frequency conversion crystal changes insensitive to ambient temperature, need not the serviceability temperature control system, simple in structure, volume is small and exquisite; And the length of each ktp crystal needs only identical, need not to be worked into a certain particular value, greatly reduces the requirement to the nonlinear crystal machining precision.

Description of drawings

Fig. 1 is the structural representation of first type non-linear frequency conversion crystal 10, and wherein, 1 is first nonlinear crystal, and 1a and 1b are respectively two surfaces of first nonlinear crystal 1, and 2 is second nonlinear crystals.Fig. 2 is the structural representation of second type non-linear frequency conversion crystal 11.Fig. 3 is the structural representation of the 3rd type non-linear frequency conversion crystal 12.Fig. 4 is the structural representation of the 4th type non-linear frequency conversion crystal 13.Fig. 5 is the structural representation that 10 in the crystal of first type non-linear frequency conversion of 2 (N=2) optical contants or in-depth optical contant piles non-linear frequency conversion crystal wafer heap 14, wherein, 1a is the surface of first first nonlinear crystal 1, and 4b is the surface of second second nonlinear crystal 2.Fig. 6 is the structural representation that 11 in the crystal of non-linear frequency conversion of 2 (N=2) optical contants or in-depth optical contant piles non-linear frequency conversion crystal wafer heap 15, wherein, 1a is the surface of first first nonlinear crystal 1, and 4b is the surface of second second nonlinear crystal 2.

Embodiment

Existing accompanying drawings principle of work of the present invention:

(1) first type non-linear frequency conversion crystal 10:

The optical axis direction of first second nonlinear crystal 2 with respect to the optical axis direction of first nonlinear crystal 1 along logical optical axis Rotate 180 ° placement, the optical axis direction of second second nonlinear crystal 2 is placed along logical optical axis half-twist with respect to the optical axis direction of first second nonlinear crystal 2, the optical axis direction of the 3rd block of second nonlinear crystal 2 with respect to the optical axis direction of second second nonlinear crystal 2 along logical optical axis Rotate 180 ° placement.Ktp crystal is a biaxial crystal, and first nonlinear crystal 1, second nonlinear crystal 2 are along the YZ plane cutting around Z axle rotation Φ, and Φ is 23.5 °.As shown in Figure 1, frequency be the fundamental frequency light of 1064nm with perpendicular to the Z axle, the direction that becomes phase matching angle Φ with X-axis by first type non-linear frequency conversion crystal 10 after, change the frequency doubled light that frequency is 532nm into.In frequency conversion, fundamental frequency light is successively through first nonlinear crystal 1, first piece second nonlinear crystal 2, second piece second nonlinear crystal 2, the 3rd block of second nonlinear crystal 2.When fundamental frequency light during through first nonlinear crystal 1, fundamental frequency light is divided into the polarization mode of two orthogonal directionss: the polarization direction is perpendicular to the basic mode e on the XY plane of first nonlinear crystal 1 ₁Be parallel to the basic mode e on the XY plane of first nonlinear crystal 1 with the polarization direction ₂In the XY plane of first nonlinear crystal 1, basic mode e ₁In first nonlinear crystal 1, propagate basic mode e along logical optical axis direction ₂Downward bias is propagated from logical optical axis direction, with basic mode e ₁Walk from.When fundamental frequency light during from 1 outgoing of first nonlinear crystal, basic mode e ₂With basic mode e ₁The phase differential that produces is

$\mathrm{\Δ}1=({n_2}^{e_2}-{n_1}^{e_1})L\·2\mathrm{\π}/\mathrm{\λ}---\left(a\right)$

Wherein, n ₂ ^E2Be basic mode e ₂Refractive index in first nonlinear crystal 1, n ₁ ^E1Be basic mode e ₁Refractive index in first nonlinear crystal 1, L is the length of first nonlinear crystal 1, λ is the fundamental frequency light wavelength.Then, fundamental frequency light incides on first second nonlinear crystal 2 and since the optical axis direction of first second nonlinear crystal 2 with respect to the optical axis direction of first nonlinear crystal 1 along logical optical axis Rotate 180 ° placement, basic mode e ₁The polarization direction continues to propagate basic mode e along logical optical axis direction perpendicular to its XY plane in first second nonlinear crystal 2 ₂The polarization direction is parallel to its XY plane in first second nonlinear crystal 2, and will in its XY plane, upwards depart from logical optical axis direction and propagate, because the length of first second nonlinear crystal 2 is identical with the length of first nonlinear crystal 1, basic mode e ₂In first second nonlinear crystal 2, make progress walk from just in time can compensate it in first nonlinear crystal 1 downward walk from, make basic mode e ₂When arriving the another side of first second nonlinear crystal 2 can with basic mode e ₁In the same point outgoing.Basic mode e ₂With basic mode e ₁The phase differential that produces in first second nonlinear crystal 2 is

$\mathrm{\Δ}2=({n_2}^{e_2}-{n_1}^{e_1})L\·2\mathrm{\π}/\mathrm{\λ}---\left(b\right)$

Then, fundamental frequency light incides on second second nonlinear crystal 2, because the optical axis direction of second second nonlinear crystal 2 is placed basic mode e with respect to the optical axis direction of first second nonlinear crystal 2 along logical optical axis half-twist ₂Basic mode e is propagated perpendicular to its XY plane in the polarization direction along logical optical axis direction in second second nonlinear crystal 2 ₁The polarization direction is parallel to its XY plane in second second nonlinear crystal 2, will propagate from logical optical axis direction to left avertence in its XY plane, with basic mode e ₂Walk from.Basic mode e ₂With basic mode e ₁The phase differential that produces in second second nonlinear crystal 2 is

$\mathrm{\Δ}3=({n_1}^{e_2}-{n_2}^{e_1})L\·2\mathrm{\π}/\mathrm{\λ}---\left(c\right)$

At last, fundamental frequency light incides on the 3rd second nonlinear crystal 2 and since the optical axis direction of the 3rd block of second nonlinear crystal 2 with respect to the optical axis direction of second second nonlinear crystal 2 along logical optical axis Rotate 180 ° placement, basic mode e ₂The polarization direction continues to propagate basic mode e along logical optical axis direction perpendicular to its XY plane in the 3rd second nonlinear crystal 2 ₁The polarization direction is parallel to its XY plane in the 3rd second nonlinear crystal 2, will in its XY plane, propagate from logical optical axis direction to right avertence, because the length of the 3rd block of second nonlinear crystal 2 is identical with the length of second second nonlinear crystal 2, and basic mode e ₁In the 3rd second nonlinear crystal 2 to the right walk from just in time can compensate it in second block of nonlinear crystal 2 left walk from, make basic mode e ₁When arriving the another side of the 3rd second nonlinear crystal 2 can with basic mode e ₂In the same point outgoing.Basic mode e ₂With basic mode e ₁The phase differential that produces in the 3rd second nonlinear crystal 2 is

$\mathrm{\Δ}4=({n_1}^{e_2}-{n_2}^{e_1})L\·2\mathrm{\π}/\mathrm{\λ}---\left(d\right)$

N among formula (a) and (b), (c), (d) ₁ ^E1, n ₁ ^E2All be the refractive index of polarization direction perpendicular to the polarized component on nonlinear crystal XY plane, n ₂ ^E1, n ₂ ^E2So the refractive index that all is parallel to the polarized component on nonlinear crystal XY plane for the polarization direction is n ₁ ^E1With n ₁ ^E2, n ₂ ^E1With n ₂ ^E2Equate respectively, so fundamental frequency light is zero (being Δ 1+ Δ 2+ Δ 3+ Δ 4=0) through first nonlinear crystal 1, first piece second nonlinear crystal 2, second piece second nonlinear crystal 2, the 3rd total phase differential in second nonlinear crystal, 2 backs successively.Hence one can see that, by first nonlinear crystal 1 and three second nonlinear crystals 2 closely be adjacent to arrange place the first type non-linear frequency conversion crystal 10 that forms not only can compensate light wave spatially walk from, and can compensate the phase differential that fundamental frequency light causes through first type non-linear frequency conversion crystal 10.

(2) second type non-linear frequencies conversion crystal 11:

The optical axis direction of first second nonlinear crystal 2 is placed along logical optical axis half-twist with respect to the optical axis direction of first nonlinear crystal 1, along logical optical axis Rotate 180 ° placement, place along logical optical axis half-twist with respect to the optical axis direction of second second nonlinear crystal 2 by the optical axis direction of the 3rd block of second nonlinear crystal 2 with respect to the optical axis direction of first second nonlinear crystal 2 for the optical axis direction of second second nonlinear crystal 2.As shown in Figure 2, the principle of work and the first type non-linear frequency of second type non-linear frequency conversion crystal 11 are changed the roughly the same of crystal 10, repeat no more here.

(3) the 3rd type non-linear frequencies conversion crystal 12:

Second nonlinear crystal 2 is placed in the identical mode of optical axis direction of its optical axis direction and first nonlinear crystal 1, and 1/2nd wave plates 5 are placed between the above two in the mode of its optical axis direction while and the above two optical axis direction angle at 45.As shown in Figure 3, in the frequency conversion, fundamental frequency light is successively through first nonlinear crystal 1,1/2nd wave plates 5 and second nonlinear crystal 2.When fundamental frequency light during through first nonlinear crystal 1, fundamental frequency light is divided into the polarization mode of two orthogonal directionss: the polarization direction is perpendicular to the basic mode e on the XY plane of first nonlinear crystal 1 ₁Be parallel to the basic mode e on the XY plane of first nonlinear crystal 1 with the polarization direction ₂In the XY plane of first nonlinear crystal 1, basic mode e ₁In first nonlinear crystal 1, propagate basic mode e along logical optical axis direction ₂Downward bias is propagated from logical optical axis direction, with basic mode e ₁Walk from.When fundamental frequency light during from 1 outgoing of first nonlinear crystal, basic mode e ₂With basic mode e ₁The phase differential that produces is

$\mathrm{\Δ}1=({n_2}^{e_2}-{n_1}^{e_1})L\·2\mathrm{\π}/\mathrm{\λ}---\left(e\right)$

Then, fundamental frequency light incides on 1/2nd wave plates 5, since the optical axis direction of 1/2nd wave plates 5 and the optical axis direction angle at 45 of first nonlinear crystal 1, the basic mode e in first nonlinear crystal 1 ₁, behind 1/2nd wave plates 5, the polarization direction becomes the XY plane that is parallel to first nonlinear crystal 1, second nonlinear crystal 2, enter second nonlinear crystal 2 after, downward bias is propagated the basic mode e in first nonlinear crystal 1 from logical optical axis direction ₂, behind 1/2nd wave plates 5, the polarization direction becomes the XY plane perpendicular to first nonlinear crystal 1, second nonlinear crystal 2, enter second nonlinear crystal 2 after, will propagate along logical optical axis direction.Because the length of second nonlinear crystal 2 is identical with the length of first nonlinear crystal 1, basic mode e ₁Downward walking in second nonlinear crystal 2 from just in time compensating basic mode e ₂In first nonlinear crystal 1 downward walk from, make basic mode e ₂When arriving the another side of second nonlinear crystal 2 can with basic mode e ₁In the same point outgoing.Basic mode e ₂With basic mode e ₁The phase differential that produces in second nonlinear crystal 2 is

$\mathrm{\Δ}2=({n_1}^{e_2}-{n_2}^{e_1})L\·2\mathrm{\π}/\mathrm{\λ}---\left(f\right)$

N among formula (e), (f) ₁ ^E1, n ₁ ^E2All be the refractive index of polarization direction perpendicular to the polarized component on nonlinear crystal XY plane, n ₂ ^E1, n ₂ ^E2The refractive index that all is parallel to the polarized component on nonlinear crystal XY plane for the polarization direction, so ${n_1}^{e_1}={n_1}^{{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="C0211218700161.png"\; state="\{\{state\}\}">e</figure-callout>}}_2},{n_2}^{e_1}={n_2}^{{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="C0211218700161.png"\; state="\{\{state\}\}">e</figure-callout>}}_2}.$ So fundamental frequency light is zero (being Δ 1+ Δ 2=0) through first nonlinear crystal 1, the total phase differential in second nonlinear crystal, 2 backs successively.Hence one can see that, by first nonlinear crystal 1,1/2nd wave plates 5 and second nonlinear crystal 2 closely be adjacent to arrange place the 3rd type non-linear frequency conversion crystal 12 that forms not only can compensate light wave spatially walk from, and can compensate the phase differential that fundamental frequency light causes through the 3rd type non-linear frequency conversion crystal 12.

(4) the 4th type non-linear frequencies conversion crystal 13:

Second nonlinear crystal 2 is placed in the identical mode of optical axis direction of its optical axis direction and first nonlinear crystal 1, and dual wavelength wave plate 6 is placed between the above two in the mode of its optical axis direction while and the above two optical axis direction angle at 45.As shown in Figure 4, the 4th type non-linear frequency conversion crystal 13 adopts dual wavelength wave plate 6 when guaranteeing each polarized component difference half-twist of fundamental frequency light, the polarization characteristic that also guarantees frequency doubled light does not change, and makes the frequency doubled light of output have good polarization characteristic.The principle of work and the 3rd type non-linear frequency of the 4th type non-linear frequency conversion crystal 13 are changed the roughly the same of crystal 12, repeat no more here.

A kind of non-linear frequency conversion crystal wafer heap is formed by 10 heaps of N sheet first type non-linear frequency conversion crystal, and per four nonlinear crystal optical axis directions are placed as shown in Figure 1, gap d → 0 between any two non-linear frequencies conversion crystal.Fig. 5 is the synoptic diagram that 10 in the crystal of first type non-linear frequency conversion of 2 (N=2) optical contants or in-depth optical contant piles first type non-linear frequency conversion crystal wafer heap 14.The surperficial 1a of first first nonlinear crystal 1 is coated with anti-reflection film, and the surperficial 4b of second nonlinear crystal 2 of last a slice is coated with anti-reflection film; 532nm between any two non-linear frequencies conversion crystal, can plate Zeng Toumo @1064nm﹠amp; Behind the 532nm optical cement together, also plated film not, directly optical cement or in-depth optical cement be together in the polishing back.The principle of work and the first type non-linear frequency of first type non-linear frequency conversion crystal wafer heap 14 are changed the roughly the same of crystal 10, it is advantageous that can obtain the long arbitrarily non-linear frequency conversion crystal of length to improve frequency conversion efficiency.

A kind of non-linear frequency conversion crystal wafer heap is formed by 11 heaps of N sheet second type non-linear frequency conversion crystal, and per four nonlinear crystal optical axis directions are placed as shown in Figure 2, gap d → 0 between any two non-linear frequencies conversion crystal.Fig. 6 is the synoptic diagram that 11 in the crystal of second type non-linear frequency conversion of 2 (N=2) optical contants or in-depth optical contant piles second type non-linear frequency conversion crystal wafer heap 15.The surperficial 1a of first first nonlinear crystal 1 is coated with anti-reflection film, and the surperficial 4b of second nonlinear crystal 2 of last a slice is coated with anti-reflection film; 532nm between any two non-linear frequencies conversion crystal, can plate Zeng Toumo @1064nm﹠amp; Behind the 532nm optical cement together, also plated film not, directly optical cement or in-depth optical cement be together in the polishing back.The principle of work and the second type non-linear frequency conversion crystal 11 of second type non-linear frequency conversion crystal wafer heap 15 are roughly the same, it is advantageous that can obtain the long arbitrarily non-linear frequency conversion crystal of length to improve frequency conversion efficiency.

In like manner, but the 3rd type non-linear frequency crystal 12 or the 4th type non-linear frequency crystal 13 also sheet pile in addition two kinds of non-linear frequencies conversion crystal wafers heaps.

Non-linear frequency conversion crystal of the present invention is suitable for being used as low noise intracavity frequency doubling crystal and cavity external frequency multiplication crystal.Because the space is walked from eliminating, can use long crystal to increase the conversion efficiency of frequency multiplication; Walking from being compensated in time can be used for the frequency-doubling crystal as the femtosecond frequency multiplication.Conversion generation entangled photons is right down also to can be used for doing parameter conversion, especially parameter, and is significant in quantum information science.

Claims (3)

1. a non-linear frequency is changed crystal, contain following four kinds of optical elements: in first nonlinear crystal (1), second nonlinear crystal (2), 1/2nd wave plates (5) and the dual wavelength wave plate (6) two～three kinds, it is characterized in that, first nonlinear crystal (1) is the identical nonlinear crystal KTP of length with second nonlinear crystal (2), press the cutting of II class phase matching direction, a surface (1a) of first nonlinear crystal (1) is coated with Zeng Toumo @1064nm, and another surface (1b) is coated with Zeng Toumo @1064nm﹠amp; 532nm, two surfaces of second nonlinear crystal (2), 1/2nd wave plates (5) and dual wavelength wave plate (6) all are coated with anti-reflection film; 532nm, this non-linear frequency conversion crystal has one of following four kinds of unitized constructions: first type non-linear frequency conversion crystal (10) closely is adjacent to arrange place by first nonlinear crystal (1) and three second nonlinear crystals (2) and forms, the optical axis direction of first second nonlinear crystal (2) with respect to the optical axis direction of first nonlinear crystal (1) along logical optical axis Rotate 180 ° placement, the optical axis direction of second second nonlinear crystal (2) is placed along logical optical axis half-twist with respect to the optical axis direction of first second nonlinear crystal (2), the optical axis direction of the 3rd block of second nonlinear crystal (2) with respect to the optical axis direction of second second nonlinear crystal (2) along logical optical axis Rotate 180 ° placement; Second type non-linear frequency conversion crystal (11) closely is adjacent to arrange place by first nonlinear crystal (1) and three second nonlinear crystals (2) and forms, the optical axis direction of first second nonlinear crystal (2) is placed along logical optical axis half-twist with respect to the optical axis direction of first nonlinear crystal (1), along logical optical axis Rotate 180 ° placement, place along logical optical axis half-twist with respect to the optical axis direction of second second nonlinear crystal (2) by the optical axis direction of the 3rd block of second nonlinear crystal (2) with respect to the optical axis direction of first second nonlinear crystal (2) for the optical axis direction of second second nonlinear crystal (2); The 3rd type non-linear frequency conversion crystal (12) closely is adjacent to arrange place by first nonlinear crystal (1), 1/2nd wave plates (5) and second nonlinear crystal (2) and forms, second nonlinear crystal (2) is placed in the identical mode of optical axis direction of its optical axis direction and first nonlinear crystal (1), and 1/2nd wave plates (5) are placed between the above two in the mode of its optical axis direction while and the above two optical axis direction angle at 45; Closely being adjacent to arrange placement with the 4th type non-linear frequency conversion crystal (13) by first nonlinear crystal (1), dual wavelength wave plate (6) and second nonlinear crystal (2) forms, second nonlinear crystal (2) is placed in the identical mode of optical axis direction of its optical axis direction and first nonlinear crystal (1), and dual wavelength wave plate (6) is placed between the above two in the mode of its optical axis direction while and the above two optical axis direction angle at 45.

2. non-linear frequency according to claim 1 conversion crystal is characterized in that, first nonlinear crystal (1) and second nonlinear crystal (2) but nonlinear crystal KNbO ₃, LiB ₃O ₅, β-BaB ₂O ₄, MgO:LiNbO ₃, KDP.

3. non-linear frequency conversion crystal according to claim 1 and 2, it is characterized in that, N the first type non-linear frequency changed crystal (10), second type non-linear frequency conversion crystal (11), the 3rd type non-linear frequency conversion crystal (12) or the 4th type non-linear frequency conversion crystal (13) but the long arbitrarily non-linear frequency conversion crystal wafer heap of optical cement or in-depth optical cement one-tenth, and wherein N is a positive integer.

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