CN1259469C - Realization of Gd2(MoO4) 3Method for periodic domain inversion of crystal - Google Patents

Abstract

A method for achieving periodic domain inversion of a _Gd2 ( _MoO4 ) ₃ crystal is characterized in that a _Gd2 ( _MoO4 ) ₃ crystal sheet is first polished along the polarization direction (001), an ultra-strong ultrafast laser is divided into two laser beams by a wave splitter, the interval between interference fringes is changed by adjusting the incident angle of the laser beam, and the periodic domain inversion is achieved under the action of the strong electric field of the femtosecond laser. The preparation process of the periodic domain structure of the invention is simple, easy to operate, accurate in size, low in cost, and easy to achieve rapid and large-scale production. The nonlinear optical crystal with such a structure is suitable for high-energy frequency-doubling laser output.

Description

A Method to Realize Periodic Domain Inversion of Gd2(MoO4)3 Crystal

technical field

The present invention relates to gadolinium molybdate (hereinafter referred to as Gd ₂ (MoO ₄ ) ₃ ) crystal, in particular a method for realizing periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ crystal. The periodic domain inversion of this crystal can be used for frequency doubling output of laser.

Background technique

In 1962, Bloembergen et al. proposed the theory of quasi phase matching (Quasi phase matching, hereinafter referred to as QPM): through the periodic modulation of the nonlinear susceptibility of the crystal (periodic domain inversion) to compensate for the fundamental wave and phase caused by the refractive index dispersion. The phase mismatch between harmonics has been enhanced by nonlinear optical effects. Replacing homogeneous materials with microstructured materials and using QPM to achieve enhanced laser frequency-doubling conversion efficiency is technically very attractive. The use of crystal periodic domain inversion to achieve quasi-phase matching has a series of major advantages over birefringent phase matching:

First, since the user controls the periodicity, it can choose a certain period to match the desired nonlinear interaction;

Second, there is no need to use orthogonal beam polarizations, which means that the nonlinear coefficients are no longer restricted to asymmetric d-tensor elements;

Third, quasi-phase matching is critical phase matching in the absence of birefringence-induced divergence of orthogonally polarized propagating beams.

In addition, various grating pitches can be set on the periodically poled crystal and simple tuning can be realized by changing the temperature of the crystal.

At present, the methods to achieve periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ crystals include electron beam scanning, ion diffusion and external electric field induction. Their disadvantages are that they cannot achieve periodic phase matching of micro-regions (only on the order of microns), and the accuracy is not very high.

3. Contents of the invention

The technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a method for periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ crystals, so as to realize nanoscale periodic domain inversion.

The basic idea of the present invention is: in the Gd ₂ (MoO ₄ ) ₃ single crystal along the [001] direction, under the strong electric field of the interference fringes formed by the mutual interference of two ultra-strong and ultra-fast lasers, the polarizability inversion is realized, and the The domain structure is reversed, resulting in a quasi-phase match.

Technical solution of the present invention is as follows:

A method for realizing periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ crystal, which is characterized in that the Gd ₂ (MoO ₄ ) ₃ crystal sheet is firstly polished along the polarization direction (001), and an ultra-strong ultra-fast laser is used to The split-wave plate is divided into two laser beams, and the spacing between the interference fringes is changed by adjusting the incident angle of the laser beams. Under the action of the strong electric field of the ultra-intense-ultrafast laser, the periodic inversion of domains is realized.

The specific process steps of the method for realizing periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ crystal in the present invention are as follows:

<1> Orientate the Gd ₂ (MoO ₄ ) ₃ single crystal first, cut the Gd ₂ (MoO ₄ ) ₃ single crystal into a single wafer with a certain thickness perpendicular to the [001] direction, and after polishing (the finish is greater than grade III), Monodomain treatment is performed by annealing, and the crystal annealing temperature is 870±20°C;

<2>Optical path adjustment, the titanium sapphire femtosecond laser is divided into two beams through the beam splitter, and then focused by the lens to achieve an energy density of 9-11J/ ^cm2 . By adjusting the incident angle Θ between the two beams, Adjust the width of interference fringes;

<3> Place the single wafer processed by <1> at the focal point of the laser beam, and irradiate the single wafer with the laser for 19-30 minutes, that is, the periodic domains of Gd ₂ (MoO ₄ ) ₃ crystals are realized reverse.

The femtosecond laser is 800nm, titanium sapphire 120fs, 200kHz laser.

The incident angle Θ of the two beams of light is 37.5°.

The time of the femtosecond laser irradiation is 24±3 minutes.

Technical effect of the present invention is:

(1) A method for realizing periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ single crystal with femtosecond laser is proposed. Compared with the previous method of realizing quasi-phase matching, this method has the advantages of convenient operation and higher precision High, easy to realize automatic control and other advantages, can realize nanoscale periodic domain inversion.

(2) The present invention proposes a method for realizing periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ single crystal, compared with the previous method: it can realize nanoscale periodicity of Gd ₂ (MoO ₄ ) ₃ single crystal Domain inversion enables quasi-phase matching at the nanoscale. It can be applied to future all-optical system.

Description of drawings

Fig. 1 is a schematic diagram of a laser system of the method for realizing periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ crystals according to the present invention.

In the figure: M-mirror, 1-beam splitter, 2, 3-convex lens, 4-optical path adjuster

Detailed ways

Fig. 1 is a schematic diagram of a laser system of the method for realizing periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ crystals according to the present invention. The present invention utilizes femtosecond laser to realize the specific technological process of periodic domain inversion of Gd ₂ (MoO ₄ ) ₃ single crystal as follows:

<1> Orientate the Gd ₂ (MoO ₄ ) ₃ single crystal first, cut the Gd ₂ (MoO ₄ ) ₃ single crystal into a single wafer with a certain thickness perpendicular to the [001] direction, and after polishing (the finish is greater than grade III), Monodomain treatment is performed by annealing, and the crystal annealing temperature is 870±20°C;

<2>Optical path adjustment, the titanium sapphire femtosecond laser is divided into two beams through the beam splitter, and then focused by the lens to achieve an energy density of 9-11J/cm ² , by adjusting the incident angle between the two beams, adjust The width of the interference fringes;

<3> Place the single wafer processed by <1> at the focal point of the laser beam, and irradiate the single wafer with the laser for 19-30 minutes, that is, the periodic domains of Gd ₂ (MoO ₄ ) ₃ crystals are realized reverse.

A specific embodiment is given below:

The femtosecond laser is 800nm, 120fs, 200kHz Ti:Sapphire laser, the incident angle Θ of the two beams is 37.5°, the crystal annealing temperature is 870°C, and the femtosecond laser irradiation time is 24 minutes.

Claims (5)

1. realize Gd for one kind ₂(MoO ₄) ₃Crystal is the method for farmland counter-rotating periodically, it is characterized in that earlier with Gd ₂(MoO ₄) ₃Crystal wafer is divided into two bundle laser with femtosecond laser with componemt wave plate along polarised direction (001) direction polishing, and the incidence angle by adjusting laser beam changes the spacing between the interference fringe, under the effect of the electric field of femtosecond laser, realizes the periodic inversion on farmland.

2. Gd according to claim 1 ₂(MoO ₄) ₃Crystal is the method for farmland counter-rotating periodically, it is characterized in that the concrete technology step of this method is as follows:

＜1〉earlier with Gd ₂(MoO ₄) ₃Monocrystalline carries out orientation, perpendicular to the direction of [001] with Gd ₂(MoO ₄) ₃Be cut into certain thickness single-chip, through polishing, fineness is carried out poling by annealing and is processed greater than the III level, and described crystal annealing temperature is 870 ± 20 ℃;

＜2〉light path adjustment by spectroscope, is divided into two bundle laser with titanium jewel femtosecond laser, then through lens focus, reaches 9-11J/cm ²Energy density, by transferring the incident angle theta between the two-beam, adjust the width of interference fringe;

＜3〉will be through＜1〉process the focus place that single-chip places laser beam, this single-chip of laser irradiation, its exposure time is 19-30 minute, has namely realized Gd ₂(MoO ₄) ₃Periodically farmland counter-rotating of crystal.

3 Gd according to claim 2 ₂(MoO ₄) ₃Crystal is the method for farmland counter-rotating periodically, it is characterized in that described femtosecond laser is 800nm, titanium jewel 120fs, 200kHz laser.

4 Gd according to claim 2 ₂(MoO ₄) ₃Crystal is the method for farmland counter-rotating periodically, it is characterized in that the incident angle Θ of two-beam is 37.5 °.

5. Gd according to claim 3 ₂(MoO ₄) ₃Crystal is the method for farmland counter-rotating periodically, and the time that it is characterized in that described Gold Films Irradiated by Femtosecond Laser is 24 ± 3 minutes.

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