CN104297825B - Light laser vortex reflecting mirror - Google Patents

Abstract

A kind of strong laser vortex reflector, it is characterized in that: on the optical glass or fused silica substrate, the microstructure of N steps in N lobe sectors is etched by photolithography, and the etching depth corresponding to the nth step is Where l is the topological charge of the vortex carried by the vortex mirror; n=1, 2, ..., N, where N is taken as a high-order power value of 2, such as N=4, 8, 16, 32 and so on. Then, a high-efficiency, high-damage-threshold dielectric reflective film is coated on the microstructure to form a strong laser vortex reflector. Thus, the intense laser light incident at 45 degrees is reflected by the vortex reflector and becomes a strong vortex laser with a topological charge of 1 emitted at 45 degrees. This ultra-intense laser with vortex phase wavefront has important scientific research significance and potential practical value for inertial confinement nuclear fusion.

Description

Strong laser vortex mirror

technical field

The invention relates to an inertial-constrained ultra-intensive vortex laser, in particular to an intense laser vortex reflector for generating an ultra-intensive vortex laser.

Background technique

Laser technology has been proposed to produce inertial confinement fusion since the invention of lasers in 1960. We know that the mode distribution of the laser light field is mainly determined by the laser resonator, which is the Hermitian Gaussian mode for the rectangular cavity mirror and the Laguerre Gaussian mode for the circular symmetric cavity mirror. In general, the Gaussian beam of the fundamental mode has smaller spatial localization and higher energy density, so the Gaussian beam of the general fundamental mode is widely used. For laser targeting, although the usual Gaussian laser can generate extremely high energy density, a strong plasma cloud is generated on the metal target surface. However, with the further increase of laser energy, the plasma cloud forms a strong shielding effect on the metal surface, which affects the further absorption of laser energy. The focused laser center drifts and diffuses with the axial propagation of the focused point due to the strong plasma cloud shielding effect, which makes the laser targeting effect worse.

The so-called vortex laser refers to a laser beam with a spiral phase wavefront, and there is a phase singularity in the center of its optical axis, so a hollow light field structure carrying angular momentum can be generated, that is, the center of the optical axis is a dark spot. The energy density vector of this vortex laser has a spiral cone structure, so it has an angular momentum component in the circumferential tangential direction, so that this tangential angular momentum can be transmitted to the irradiated object. The special properties of the vortex laser can be expected to be used in the fast ignition scheme in laser inertial confinement fusion. Particle simulation research has initially found that it can produce a drilling effect similar to that of a screw [Phys.Rev.Lett.112 ,235001(2014)] On the one hand, compared with the traditional linear polarization laser, it may form a better "drilling" effect, making the laser closer to the center of the compressed target, forming a faster ignition. On the other hand, this screw-like advancement may be beneficial for the alignment of the hole punching process. The vortex ultra-intensive laser will make the plasma rotate along the center, so that the generated protons are confined to the center of the axial propagation, which is conducive to the transmission of laser energy to the metal target surface, which will be very important in the research and application of laser targeting value.

Contents of the invention

The object of the present invention is to provide a strong laser vortex reflector for realizing super strong vortex laser.

Technical solution of the present invention is as follows:

A kind of strong laser vortex reflector, which is characterized in that the microstructure of N-lobe sector N steps is etched on the optical glass or fused silica substrate by photolithography, and the etching depth corresponding to the nth step is And the step depth differences of adjacent sectors are equal, both Where n=1,2,...,N; N is taken as a high-order power value of 2, such as N=4, 8, 16, 32, etc.; l is the topological charge of the vortex carried by the strong laser vortex mirror ; Then, a high-efficiency dielectric reflection film is coated on the microstructure for the working wavelength to form a strong laser vortex mirror.

The working mode of the strong laser vortex reflector is 45 degrees incident and 45 degrees exit.

The incident spot projection on the described strong laser vortex mirror is elliptical, wherein the ratio of the semi-major axis to the semi-minor axis is And the elliptical area of the incident light is divided into N equal-area parts by the N-lobe sectors.

Technical effect of the present invention:

The invention can realize high-efficiency conversion of ultra-intensive laser to ultra-intensive vortex laser.

Description of drawings

Figure 1. The step height distribution and corresponding phase delay distribution of a typical eight-lobed intense laser vortex mirror: ①～⑧The corresponding step heights are respectively The corresponding phase delays are π/4, π/2, 3π/4, π, 5π/4, 3π/2, 7π/4, 2π.

Fig. 2 is a schematic diagram of the wavefront transformation of the intense laser vortex mirror of the present invention.

Figure 3 is the surface three-dimensional morphology of the processed strong laser vortex mirror.

Figure 4 shows the far-field diffraction spot intensity distribution of the processed strong laser vortex mirror.

detailed description

As shown in Figure 1, the number of steps of the strong laser vortex reflector is N=8, that is, the elliptical area in Figure 1 is divided into 8 sectors, and the etching depth corresponding to each sector is sequentially numbered for The corresponding phase delays are π/4, π/2, 3π/4, π, 5π/4, 3π/2, 7π/4, 2π. For the working wavelength of 800nm, the etching depth of each step is 35nm, 70nm, 105nm, 140nm, 175nm, 210nm, 245nm, 280nm in sequence. In this embodiment, this multi-sector and multi-step microstructure is processed on an optical glass or fused silica substrate by photolithography. In order to make full use of the effective lithography area of the lithography machine, in this embodiment, the four corners of the rectangular substrate are cut off to form an octagonal substrate. The cut-off size design is marked in Figure 1, where the length and width of the original rectangular substrate are and a, so the maximum clear aperture is a. Using a lithography machine with an effective lithography area of Φ80mm, the maximum clear aperture of the strong laser vortex mirror that can be processed is about a=50mm. Through three-step overlaying, we can obtain the 8-step microstructure of the 8-sector intense laser vortex mirror. Then, by coating a high-efficiency, high-damage-threshold dielectric high-reflection film on the microstructure, the above-mentioned strong laser vortex mirror is formed. Figure 3 shows the surface 3D topography of the intense laser vortex mirror processed by this method. Figure 4 shows the far-field spot intensity distribution generated by the corresponding strong laser vortex mirror, from which it can be seen that the vortex laser has an obvious central dark spot effect.

In summary, the present invention proposes a strong laser vortex reflector working under super strong laser conditions. The vortex reflector can introduce a vortex phase wavefront into the ultra-intensive laser, so it has important scientific research value and important potential application prospects in ultra-intensive laser targeting and ultra-intensive laser physics.

The implementation of the above-mentioned strong laser vortex reflector is only a specific implementation of the present invention, and should not be construed as limiting the protection scope of the present invention. It should be pointed out that for those skilled in the art, without departing from the basic idea of the present invention, some deformations and improvements can be made to the technical details such as the processing technology and the shape of the substrate proposed in this patent. All belong to the protection scope of the present invention.

Claims (3)

1. A kind of strong laser vortex reflector, it is characterized in that on optical glass or fused silica substrate, the microstructure of N lobe sector N steps is etched by the method of photolithography, the etching depth corresponding to the nth step for And the step depth differences of adjacent sectors are equal, both Wherein n=1,2,...,N; N is taken as a high-order power value of 2, that is, N=4,8,16,32,...; l is the topology of the vortex carried by the strong laser vortex mirror charge, λ is the working wavelength; then, a high-efficiency, high-damage-threshold dielectric reflection film is coated on the microstructure for the working wavelength to form a strong laser vortex mirror. 2. The powerful laser vortex reflector according to claim 1, characterized in that the working mode of the powerful laser vortex reflector is 45-degree incident and 45-degree outgoing. 3. The strong laser vortex reflector according to claim 1, characterized in that the projection of the incident light spot on the described strong laser vortex reflector is elliptical, wherein the ratio of the semi-major axis to the semi-minor axis is And the elliptical area of the incident light is divided into N equal-area parts by the N-lobe sectors.