SU1189322A1 - Device for producing impulsive optical discharge - Google Patents

Description

I.

The invention relates to plasma technology, specifically to devices for producing optical discharge (laser spark) in a substance and can be used to create pulsed light sources, waveguides and channels of reduced density, plasma electrodes and gaps of discharge gaps, plasma reflectors and antennas. .

The aim of the invention is to increase the time of existence of a linear optical discharge and its geometric dimensions with a constant total energy of laser radiation.

The drawing shows a diagram of the proposed device.

The device for obtaining an optical discharge contains optically coupled igniting laser 1, axicon focusing system 2, a pump laser 3, an elliptical hole mirror 4, and a synchronization unit 5. Lasers 1 and 3 are installed at a right angle, and the beam at the igniting laser has an annular cross section. Mirror 4 is set at its center at the point of intersection of the axes of the laser beams so that the normal to the reflecting surface is directed along the bisector of the angle I, waiting for these beams, and the projections of the aperture on the normal beam sections are equal to the pump beam 3 and the inside beam of the firing laser 1.

The axicon focusing system 2 is made of two coaxially located axicons, central 6 and ring 7, the diameters of which are equal to the diameters of the laser beams falling on them, but the ratio of the refractive angle of the ring axicon | C / - to the refractive angle of the central axicon ot is equal to the ratio of the external diameter ring emitting. aperture of the igniter laser 1) to the diameter of the radiating aperture of the pump laser 5 ".

For example, for an axicon focusing system with a refractive angle of a ring axicon o (10 and a refractive angle of a central axicon and a central axicon diameter of 60 mm, the spark parameters are as follows. The maximum length is caus323222

The tiki of the central axicon will be equal to:.

h

7 (p1t) 666

where 30 mm is the radius of the central

axicon; oi., 10 - refractive angle

central axicon;

 is the refractive index of the glass from which a xicon is made.

In order to agree on the maximum caustic lengths of both axicons, the condition L Lii must be fulfilled. -R. Ri

Then

d, () s (h-1)

 R- TT-60 MM.

Therefore, the outer diameter of the ring axicon will be 120 mm. Seed spark is generated from axicon

on distance Ы "t - g-g - 333 mm

 UG P-1)

and has a length L - L 333 mm.

The device works as follows. The beam of the igniting laser, after passing through the ring axicon. 7, creates in the focal segment a seed laser spark that is continuous in the case of an input energy input of 4 J / cm or has gaps in the event that this condition is not fulfilled.

Then a spark, the plasma of which effectively absorbs the laser. This radiation is illuminated through the central axicon 6 by a free-generation pulse with a duration of 1-5 ms.

In the case of a continuous spark, the first mode of discharge is realized, when only the transverse size of its plasma channel increases, and in the case of discontinuities in the seed, the second mode of combustion, during which certain areas are blown into a continuous linear discharge, simultaneously expanding transverse direction.

In the first mode, the optical discharge is more homogeneous, but the second mode is more energetically advantageous, since the formation of a discrete chain of bare sources of breakdown can be achieved over a long length with relatively small heat input, and much less laser radiation intensity is required to sustain combustion than for sample

Claims (1)

A device for producing a pulsed optical discharge containing optically coupled an ignition laser and an axicon focusing system, characterized in that, in order to increase the lifetime of the optical discharge and its geometric dimensions with a constant total laser energy, a pump laser is additionally introduced into the device free generation mode, installed at an angle other than 0 ° and 180 °, to the optical axis of the firing laser having a ring emitting aperture, the synchronization unit of the ignition laser and pump laser and a mirror with an elliptical hole, the center of which is aligned with the point of intersection of the optical axes of the laser beams, and the normal to the reflecting surface in the center of the hole is directed along the bisector of the angle between the laser beams, while the reflecting surface of the mirror faces the focusing system , and the projections of the elliptical hole on the plane normal to the optical axes of the laser beams are respectively equal to the inner diameter of the ring emitting aperture of the igniting laser and, and the diameter and of the pumping laser aperture, while the axicon focusing system is made of two coaxially arranged axicons whose diameters are equal to the diameters of the corresponding emitting laser apertures, and the ratio of the refractive angles of the axicons is equal to the ratio of the outer diameter of the ring emitting laser firing aperture to the diameter of the pumping laser aperture .