CN106911064A - Phase compensation type rastering laser resonator - Google Patents

Abstract

The invention is a phase compensation type grating laser resonant cavity, which relates to laser optical resonant cavity and laser frequency selection technology. The grating laser resonant cavity of the present invention is composed of a concave spherical reflector or a convex spherical reflector, a No. 1 grating, a No. 2 grating and a laser output mirror. The concave spherical reflector, the No. 1 grating, the No. 2 grating and the laser output mirror form the laser optical axis, and the angle between the optical axis and the grating normal is not equal to the blaze angle of the grating. The grating laser resonant cavity of the invention can solve the problem that the laser spot changes in the diffraction direction of the grating caused by the non-self-collimating operation of the grating. It is suitable for various tunable lasers such as carbon dioxide laser and hydrogen fluoride laser.

Description

Phase Compensation Grating Laser Resonator

technical field

The invention relates to the technical field of lasers, in particular to the light spot correction of a grating as a laser frequency selection device under the condition of non-self-collimation.

Background technique

Gratings have very good dispersion capabilities and are widely used in spectrometers and laser frequency-selective outputs. As an integral part of the cavity mirror, the grating utilizes its spectral dispersion ability on the one hand, and utilizes its planar reflection characteristics on the other hand. In general practical applications, the grating is mostly in a self-collimating manner (that is, the incident light is incident at the angle of the diffraction angle of the grating) and other optical elements to form a stable cavity or an unstable cavity. In some special laser resonators, the grating is applied in a non-self-collimation manner. Compared with the self-collimation method, this method will cause the spot to become larger or smaller in the diffraction direction of the grating, as shown in Figure 1 ( As shown in a) and (b), Figure 1(a) is the self-collimation method, and Figure 1(b) is the non-self-collimation method.

The grating equation is d(sin(β)+sin(θ))=nλ, where β is the angle between the incident light and the grating normal, and θ is the exit angle of different diffraction orders and diffraction wavelengths. When n = 1 and β = θ ₀ , it is the grating self-collimation condition, that is, the incident light is incident at the blaze angle θ ₀ of the grating, and the first-order main maximum blaze wavelength of the grating is λ at this time. If the angle between the optical axis and the grating normal is the blaze angle θ ₀ of the grating, then λ is the laser wavelength.

Figure 1(b) is a schematic diagram of a grating non-self-collimating stable cavity. When the diameter of the incident spot is D _i , the spot diameters of the exit spots of different orders in the diffraction direction are:

D _o ＝D _i /cos(β)*cos(θ)

The exit angle θ can be calculated by the grating equation, so the diameter ratio of the exit spot to the incident spot is:

Fig. 4 is the variation curve of the diameter ratio of the outgoing light spot to the incident light spot with the incident angle (the diffraction angle of the grating is θ ₀ =30°, n=1, λ/d=1). It can be seen from the figure that when the incident angle is larger than the diffraction angle of the grating, the spot is enlarged in the diffraction direction, and when the incident angle is smaller than the diffraction angle of the grating, the spot is reduced in the diffraction direction.

Contents of the invention

The purpose of the present invention is to provide a method for phase compensation and restoration of grating diffraction direction light spots for this type of grating optical resonant cavity.

In order to realize the purpose of the present invention, concrete technical scheme is:

For the grating non-self-collimating laser resonator in FIG. 1(b), the solution proposed by the present invention is to add an intracavity phase compensation grating in the exit direction of the grating, as shown in FIG. 2 . It is required that the blaze angle, blaze wavelength and grating constant of the phase compensation grating are the same as those of another grating. According to the grating equation, the angle between the outgoing light and the grating normal can be calculated as θ. To achieve phase compensation, the incident light angle of the phase compensation grating is very important, and the angle between the incident light of the phase compensation grating and the normal line of the grating should be θ. A cavity mirror is installed in the output direction of the phase compensation grating to form feedback and output.

The grating laser resonant cavity of the invention can solve the problem that the laser spot changes in the diffraction direction of the grating caused by the non-self-collimating operation of the grating.

Description of drawings

Figure 1 is a schematic diagram of the structure of a single grating self-collimation ((a)) and a non-self-collimation stable cavity ((b));

Fig. 2 is a structural representation of the present invention;

In the figure: (1): Resonator concave spherical mirror, (2): No. 1 grating, (3): Resonator output mirror, (4): Gain medium, (5): No. 2 grating;

Fig. 3 is an embodiment of the present invention;

In the figure: (1): Resonant cavity concave spherical mirror, (2): No. 1 grating, (3): Resonant output mirror, (4): Gain medium, (5): No. 2 grating: (6): Convex spherical reflector;

Figure 4 is a curve of the diameter ratio with the incident angle (the diffraction angle of the grating is 30°).

detailed description

In order to further illustrate the features and structures of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1(a) is a schematic diagram of a grating self-collimating laser resonator. The resonant cavity is composed of a concave spherical mirror 1 and a reflective grating 2, and the included angle between the normal direction of the concave spherical mirror and the normal line of the grating is the diffraction angle of the grating. When the reflectivity of the 0th order diffraction direction of the reflective grating is appropriate, the 0th order direction of the grating can be used as the light output direction of the laser. If the reflectivity of the 0th-order diffraction direction of the grating is not suitable, the concave spherical reflector can be replaced by a concave spherical transmission mirror, and the laser is output from the direction of the concave spherical mirror. In order to achieve higher power output, experiments were carried out using concave spherical mirrors with different transmittances.

Figure 1(b) is a schematic diagram of a grating non-self-collimating laser resonator. The resonant cavity is composed of a concave mirror 1, a reflective grating 2 and a plane output mirror. The angle between the normal direction of the concave spherical mirror and the grating normal is larger or smaller than the diffraction angle of the grating. The laser output window of the non-self-collimating grating laser resonator is a plane mirror, and the best power output can be realized by changing the transmittance of the plane mirror.

Fig. 2 is a schematic diagram of the phase compensation grating laser resonator of the present invention. The laser resonant cavity of the present invention is composed of a concave spherical reflector 1, a No. 1 grating 2, a gain medium 4, a No. 2 grating 5 and a resonant cavity output mirror 3 (plane output mirror). Among them, the laser beam in the normal direction of the concave spherical mirror is amplified by the gain medium, and after being reflected by the No. 1 grating and No. 2 grating, it coincides with the normal of the output mirror of the resonator, and part of it is reflected on the surface of the output mirror of the resonator and returns to the original path to form a laser. Oscillating (another part of the transmitted output). In the case of laser resonator optical cavity collimation, the normal of the concave spherical mirror is the optical axis of the resonator. After being reflected by No. 1 grating and No. 2 grating, the laser coincides with the normal of the output mirror of the resonator. According to the design of the present invention, the key to solving the enlargement of the spot in the diffraction direction in FIG. 1(b) lies in the design parameters and placement position parameters of the No. 2 grating 5 . The grating constant d, blaze wavelength λ, and blaze angle θ ₀ of No. 2 grating 5 and No. 1 grating 2 are completely consistent. The best situation is that the two gratings are copied from the same master (original grating). The No. 2 grating is placed in the exit direction of the No. 1 grating and is parallel to the No. 1 grating. The angle between the diffracted light of the No. 1 grating and the normal line of the grating is the angle between the incident light of the No. 2 grating and the normal line of the grating.

Fig. 3 is an embodiment of the present invention, wherein the convex spherical reflector 6 is embedded on the plane output mirror (resonator output mirror 3). The surfaces of the concave spherical reflector 1 and the convex spherical reflector 6 are coated with a high reflection film, and the two reflectors and the two gratings 2 and 5 form a virtual confocal telescope cavity. The surface of resonant cavity output mirror 3 is coated with high-permeability filter medium film, and the laser outputs a hollow ring-shaped spot from this window; θ = 50 degrees (incident angle), θ ₀ = 30 degrees (blaze angle) of the No. 1 grating, and θ is greater than θ ₀ .

Claims (7)

1. A phase compensation grating laser resonator is made up of concave spherical reflector or convex spherical reflector, No. 1 reflective grating, No. 2 reflective grating and laser output coupling mirror, characterized in that: concave spherical reflector or convex spherical reflector The mirror and No. 1 reflective grating are respectively located on the left and right sides of the laser gain medium area, the No. 2 reflective grating and the laser output coupling mirror are placed outside the laser gain medium area, and the No. 1 reflective grating and No. 2 reflective grating are arranged parallel to each other; The mirror or the convex spherical mirror is arranged opposite to the No. 1 reflection grating; the laser output coupling mirror is arranged opposite to the No. 2 reflection grating. 2. The grating laser resonator as claimed in claim 1, characterized in that: a concave spherical reflector or a convex spherical reflector, No. 1 reflective grating, No. 2 reflective grating and the laser output coupling mirror form an optical axis, and the optical axis and The angle between the normals of the gratings is larger or smaller than the diffraction angle of the gratings, that is, the two gratings work under the condition of non-self-collimation. 3. The grating laser resonator as claimed in claim 1, characterized in that: between the No. 1 reflective grating and the concave spherical reflector or the convex spherical reflector is the laser gain region of the laser; the No. 1 reflective grating mainly functions as For laser frequency selection, the No. 2 reflective grating is mainly used for spot correction, and the optical parameters (grating constant d, blaze wavelength λ and blaze angle θ ₀ ) of No. 1 reflective grating and No. 2 reflective grating are strictly consistent. 4. The grating laser resonator as claimed in claim 1 or 3, wherein the angle between the No. 2 reflective grating and the optical axis is determined by the angle between the No. 1 reflective grating and the optical axis; if 1 The blaze angle of the No. 1 reflective grating is θ ₀ , and the angle between the incident light reflected by the concave spherical reflector or the convex spherical reflector onto the No. 1 reflective grating and the normal line of the No. 1 reflective grating is β, then the No. The included angle between the incident light on No. 2 reflective grating and the normal of No. 2 reflective grating should be asin(λ/d-sinβ), grating constant d, and blaze wavelength λ. 5. The grating laser resonator as claimed in claim 1, wherein the concave spherical reflector or the convex spherical reflector is a silicon substrate reflector with gold plating or a dielectric film, and the described laser output coupling mirror is plated Laser output mirror with a certain transmittance of dielectric film white sapphire or quartz. 6. The grating laser resonator according to claim 1, wherein the concave spherical reflector or the convex spherical reflector, No. 1 reflective grating, No. 2 reflective grating and laser output coupling mirror form a laser optical axis. 7. grating laser resonant cavity as claimed in claim 1, is characterized in that, a convex spherical reflector is embedded on the resonator output mirror; Concave spherical reflector (1) and convex spherical reflector surface are coated with high reflection film, this Two mirrors and two gratings form a virtual confocal telescope cavity.