SU1748128A1 - Laser emission special filter - Google Patents

Abstract

Using the selection of part of the laser beam to obtain a given structure of radiation. SUMMARY OF THE INVENTION The filter includes an input focusing lens located on an optical axis, a diffusing lens, a diaphragm device, and an output focusing lens. The total optical power of the lenses is zero, and the diaphragm device is located behind the first component of the diffusion filter. The diaphragm device is made of two or more elements. 1 silt

Description

The invention relates to laser optics, namely, devices for separating a part of a laser beam in order to obtain a given radiation structure, and can be used in laser systems with varying divergence, power and transverse distribution of radiation intensity.

A device is known in which, in order to reduce the radiation load on the diaphragm, the input focusing lens of the spatial filter (PF) is designed as a concave output mirror of a laser resonator that transmits 80% of the radiation, and about 20% reflects the aperture of 0.2 mm in diameter

However, in this version of the filter design, the diaphragm is placed in focus and is subjected to high radiation loads.

Closest to the proposed is a spatial filter containing an input focusing lens.

aperture, output focusing lens.

Due to the fact that the diaphragm is carried out in the focal plane of the input object, the radiation loads on the diaphragm are very large. When working with pulsed and pulsed periodic radiation, this filter must be placed in a vacuum, since the atmosphere inevitably causes a laser spark near the aperture shielding it. Moreover, it is known that the shape of the orifice of the diaphragm must correspond to the Fourier transform of the beam otherwise, the losses due to vignetting increase, the angular spectrum of the beam is distorted, the proportion of the energy absorbed by the diaphragm and, accordingly, the probability of its destruction increases. If the cross section of the incident beam is , then the round hole is optimal for filtration. However, for laser beams with a section other than round, the shape of the hole should

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significantly different from the round, and in these devices to fulfill this condition due to the small hole size is technically difficult, if not impossible. In the PF optical schemes, the tolerance for the misalignment of the aperture of the diaphragm with the axis of the focused laser beam does not exceed 10% of the size of the aperture. When the tolerance is exceeded, the radial loads on the diaphragm sharply increase, therefore in such PF U you need its careful time-consuming adjustment with an error of 0.01-0.05 mm.

The aim of the invention is to expand the power range of the filter while simplifying its adjustment.

The goal is achieved by the fact that in a spatial laser radiation filter between the input and output focusing lenses there is a 20 scattering lens, consisting of at least two components, the total optical power of the input, scattering and output lenses being zero. laid behind the first component of the scattering lens.

The diaphragm device is made of two or more elements, and for each successive element of the diaphragm device as compared to the previous one, the ratio ap2 / ief ef-12 / 1n-1eff, where ap, ap-i, is at least part of the perimeter of the through-hole. , ..., ai, ..., ai is the distance from the optical axis 35 to the edge of the aperture of the corresponding diaphragm element; Ln, Ln-1 is the effective optical path length between the main plane of the input focusing lens and the corresponding diaphragm element, which is equal to LiMi + XiM-i2 when placing a diaphragm element between the components of a scattering lens or LiMi + + X2M2 between the second component of the scattering lens and the output focusing lens, where LI is the distance between the main planes of the input focusing lens and 50 of the first component of the scattering lens; Mi - the multiplicity of the system, educated-. Noah these two elements; Xi is the distance from the main plane of the first component of the scattering lens to 55 of the plane of the corresponding diaphragm element; La is the distance between the main planes of the components of the scattering lens; X2 is the distance from the main plane of its second component.

to the plane of the corresponding diaphragm element; Ma is the multiplicity of the system formed by the second component scattering lens and the output focusing lens. The value ai satisfies the relation as Dj / 2, where O | —the light aperture of the filter in the plane of the corresponding diaphragm element, and the effective removal of the last of these elements is equal to or greater than DO / OO, where D0 is the input light aperture of the filter, Oo is the specified angular value by which the divergence of the filtered laser radiation must be reduced.

The drawing shows the optical layout of the device.

The device comprises a focusing lens 1, a first component 2 of a diffusing lens, a second component 3 of a diffusing lens, an output focusing lens 4, a diaphragm element or a device 5. The optical axis is designated O2. the distance between the main planes of the input focusing lens and the first component of the diverging lens Li; the distance between the main planes of the components of the scattering lens L.2,1 the distance between the main planes of the second component of the scattering lens and the output focusing lens, the distance from the main plane of the first component of the scattering lens to the plane of the corresponding diaphragm element X-to the head plane of the second component of the scattering lens to the plane of the corresponding X2 diaphragm element, the input light aperture of the filter D0; the light aperture of the filter in the plane of the corresponding diaphragm element Di.

The spatial laser radiation filter works as follows.

The laser beam with a diameter of D0 is focused by the lens 1, then scattered by components 2 and 3 of the scattering lens, of which the first along the beam of component 2 is located closer to the input focusing lens 1 than its focal plane. After that, the beam is transformed into a paraxial one using the output focusing lens 4. The total optical power of all the lenses is zero. The beam diaphragm is produced by one or several diaphragm elements 5. placed behind the first component 2 of the diffusing lens.

Let us consider in more detail / the work of the proposed PF laser radiation. Suppose that the input focusing lens 1 includes a laser beam with a diameter D0 and a divergence Po. As the beam shrinks, its angular spectrum expands M times, where M is the multiplicity of the reducing system. This means that the unit of length traveled by a beam compressed M times is equivalent to a length that is M2 times the length traveled by a beam with a diameter Do. Thus, the concept of effective length is introduced. For the region bounded by lens 1 and component 2, LiMi, where LI is the distance between the main planes of lens 1 and component 2; Mi is the multiplicity of the system formed by these elements.

For the section bounded by the first 2 and second 3 components of the scattering lens, 1-eff L.2M 1, where L2 is the distance between the main planes of the components 2 and 3 of the scattering lens. For the section between elements 3 and 4, the effective length of Zf UM2, where h is the distance between the main planes of the second component of the scattering and output focusing objectives; Ma is the multiplicity of the system formed by these elements. The total effective length of the FS is equal to the sum of the effective lengths of the indicated segments.

With proper selection of Mi and Ma, the effective length of the LF can be many times more geometric. The choice of CP is determined from the condition of the formation of the far zone of the beam at the location of the diaphragm element. For a laser beam with a diffraction divergence, its structure takes on a form corresponding to the far zone when the laser beam travels the distance D0 / 4A from the radiator, where I is the wavelength. In the case of a beam with a real divergence, significant mixing of the rays occurs in the beam. nii D0 / «o.

Thus, in the proposed device, due to the large effective length, the mixing of the rays and the approach of the beam structure to the far-field beam to the artinian occur with small geometric lengths. The smallest section of the filtered beam has, on the order of time, a larger area than the area of the filtered beam in the focal plane of the objective lens of the prototype device. For example, in a prototype device with Do 100 mm, ab 2, focus 5-10 mm, the diaphragm diameter should be 1 mm and it is located in the focal plane of the input lens, where there are very high radiation loads. In addition, it is necessary to ensure the misalignment of the focused beam and the aperture of the diaphragm of no more than 0.05-0.1 mm, which, with a filter length of 10 m, causes certain difficulties (due to thermal deformations, vibrations, etc.). The small size of the hole does not allow to give it a shape that differs from a round one.

In the proposed device, even with the diffraction divergence of the Dal'opolsk, the picture is formed if Scf D0 / 4 A is 250 m. Prien in MI M2 S; Li 1 m,

5 L2 3 m, we have Zf 10 + 3 -1 (G + 10 320 m, i.e. the condition of the far zone is fulfilled, and the diaphragm section is two orders of magnitude larger than in the device-prototype. Thanks to this, it is easy to provide any form of hole 0 requirements, and the requirements for accuracy in maintaining the coaxiality are drastically reduced. To increase the radiation resistance of the diaphragm 5, it can be placed not between the components 2 and 3 of the diffusing lens, but

5 between component 3 and lens 4, or even past.

Heat transfer during diaphragming can be significantly increased, and the formation of a hole of a complex shape is facilitated,

0 if we use a series of diaphragm elements so that each element along the beam shading the beam would be on one of the sides of the cross section or part of it. This is ensured, if only

5, the ratio an2 / 1 pef an-i2 / Ln-i3, where an, an-i, ..., ajai, is the distance from the optical axis to the edge of the aperture of the corresponding diaphragm element; Ln, 1-п-1э - effective optical path length between the main plane of the input focusing lens and the corresponding diaphragm element. Otherwise, the first di5 afragmiruyuschiy element vignette all others that will no longer be needed.

The proposed device with an extended operating power range and simplified adjustment allows to solve

This task, namely, the adjustment of the power, the divergence and the transverse distribution of the intensity of the laser radiation, as well as the reduction of the dimensions of the proposed FS compared to the prototype.

Example. The experimental layout has dimensions of 3 m. The input and output focusing lenses are made in the form of concave metal mirrors with a focus of 1.1 m and an aperture of 120x120 mm. The diffusing two-component lens is made of two convex metal mirrors, the distance between which is 3 m. The effective length of such a PF corresponds to 320 m, which allows to solve the problem with the same effect as in the device-prototype. However, the dimensions of the proposed IF are 3 times smaller, the diaphragm elements experience a low radiation load, and the requirements for their adjustment are very low.

Claims (1)

Based on the proposed device, laser light can be created with simple alignment and small dimensions for working with high-power laser beams. Thus, the proposed device is advantageously different from the known ones and can be effectively used for the purpose of correcting the spatial-energy characteristics of laser radiation, for example, in wavefront reversal circuits. Formula of the invention radiation, which includes an input focusing lens, an aperture device, and an output focusing lens placed on the non-optical axis, so that, in order to expand range of the filter's operating powers while simplifying its adjustment, there is a diffusing lens between the input and output focusing lenses, consisting of at least two components, the total optical power of the input, scattering and output lenses is zero, and the diaphragm device is located behind the first component of the scattering lens. lens.