RU2585799C1 - Pulsed laser with modulated q-factor - Google Patents

Abstract

FIELD: optics; instrument engineering.

SUBSTANCE: pulse laser with modulated q-factor has active element and resonator consisting of two mirrors, one of which is rigidly fixed and the second one is equipped with drive and has possibility of rotation so that in working position mirrors are parallel. Laser includes elastic element and brace which fix the second mirror relative to body in initial position at angle φ to working position. Brace is represented by conductive thread and elastic element is installed so that in initial position the brace is stretched counteracting torque moment M created at the second mirror by elastic element. Besides there are series-connected switch and power supply connected to the ends of current-conducting thread, wherein angle is

where W₀ is given angular velocity of second mirror in its working position, J is total inertia moment of second mirror and elastic element rotation, M is torque created by elastic element on second mirror element.

EFFECT: higher reliability and efficiency of laser.

1 cl, 3 dwg

Description

The invention relates to laser technology, namely to lasers with Q-switching of a laser resonator by changing the position of one of its mirrors.

Known lasers for the formation of giant laser pulses [1] by turning on the quality factor of a laser resonator using Q-switches (gates). All of them have certain disadvantages - high cost, high control voltage, insufficient reliability and operational stability.

The closest in technical essence to the present invention is a pulsed Q-switched laser, comprising a housing, an active element and a resonator, consisting of two mirrors, one of which is fixed motionless relative to the housing, and the second has the ability to rotate so that in the working position of the mirror are parallel [2]. In this position of the mirrors, a high Q-factor of the resonator is provided, which is sufficient for the development of laser generation. The speed of rotation of the mirror at the moment of high Q-factor of the resonator should be sufficient for the emergence of an avalanche-like generation of a giant pulse. The optimal mirror rotation speed for different types of lasers is 10-20 thousand rpm. As a rotating mirror, a prism of total internal reflection is usually used, which has high reflective characteristics and is not critical to the inclination of the axis of rotation. In the known device [2], the prism drive is a high-speed electric motor. The disadvantages of this solution are the relatively high dimensions and insufficient reliability of existing engines, as well as the electrical and magnetic interference created by them. The latter is especially unacceptable if the system including the laser contains devices sensitive to such interference, such as an electronic compass.

The objective of the invention is to increase the reliability and speed and reduce electrical and magnetic interference and interference with minimum dimensions and minimum cost of the laser.

This problem is solved due to the fact that in the known pulsed Q-switched laser, which includes a housing, an active element and a resonator consisting of two mirrors, one of which is fixed motionless relative to the housing, and the second has the ability to rotate so that in the working position of the mirror were parallel, an elastic element and an extension were introduced, with which the second mirror was fixed relative to the housing in the initial position at an angle φ to the working position, the extension was a conductive thread, and the ugly element is installed so that in the initial position the stretch is stretched, counteracting the torque M created by the elastic element on the second mirror, as well as a series-connected key and a power source connected to the ends of the conductive thread, and the angle

where W ₀ is the given angular velocity of the second mirror in its working position,

J is the total moment of inertia of rotation of the second mirror and the elastic element,

M is the torque created on the second mirror by an elastic element.

In FIG. 1 shows a laser circuit. FIG. 2 explains the principle of operation of the device with the opposite position of the elastic element and the stretch relative to the axis of rotation of the second mirror. In FIG. 3 shows an arrangement with the one-sided position of the elastic element and the extension relative to the axis of rotation of the mirror.

The device (Fig. 1) consists of a resonator formed by a fixed 1 and rotating 2 mirrors, between which the active element of the laser 3 is placed. The rotating mirror is fixed in a fixed position relative to the housing 4 by two stretch marks, the first of which is an elastic element 5, and the second is conductive thread 6 connected to the power source 7 through the key 8. Stretch marks can be placed on opposite sides of the axis of rotation of the mirror 2 (Fig. 2) or on one side (Fig. 3). In this case, the elastic element (spring) 5 must be previously stretched in its original position (Fig. 2A, Fig. 3) or compressed (Fig. 2b).

The laser operates as follows.

In the initial state, the rotating mirror 2 is located at an angle φ to its working position. In this case, the quality factor of the resonator formed by these mirrors is insufficient for laser generation. When the key 8 is closed, a current begins to flow through the conductive filament 6, causing the filament to heat up. Due to the thermal expansion of the filament, its loose end releases mirror 2, causing it to rotate under the action of the moment of rotation M created by the elastic element (spring) 5. When the mirror thus brought into rotation becomes parallel to the stationary mirror, the quality factor of the resonator increases to a level sufficient for generation giant laser pulse. The rate of increase in the Q factor of the resonator should be commensurate with the rate of development of generation known for each type of laser. This imposes corresponding requirements on the rotation speed W of the mirror 2, which in the high-Q position should be of the order of 500-2000 rad / s.

The volume of the conductive filament 6 should be minimal for its rapid heating and reduce energy consumption. For this purpose, it should have a minimum cross-section and a minimum length necessary for the mirror 2 to rotate through an angle φ during thermal expansion of the thread.

If a rotating mirror is made in the form of a prism of total internal reflection with equal sides of its hypotenuse face, then the following calculated relations are valid [3].

The moment of inertia of rotating prisms J = J _x ~ ma ^2/10 where

a - side of the hypotenuse face of the prism;

m = ρ · a ^3/4 - mass of the prism;

ρ is the density of the prism material.

The angular acceleration E of the prism under the action of a torque M = Fr, where

E = M / J,

where F is the strength of the elastic element; r is the shoulder of the application of force F (Fig. 2, 3).

Linear acceleration of the point of application of force A = Er.

The angular velocity W = Еτ of the prism after time τ after the onset of force F.

Linear movement Aτ S = ^2/2 points of application of force F.

Angular displacement φ = arctan (S / r) of the point of application of force F.

The temperature increment of the length L of the conductive filament S = αLΔT.

where α is the coefficient of linear expansion;

ΔT is the temperature difference.

Energy E _T = βm _T ΔT required for heating the conductive filament.

where β is the heat capacity;

m _T = ρ _T V _T is the mass of the thread;

ρ _T is the density of the material of the thread;

V _T is the volume of the thread.

Example.

ρ = 2550 kg / m ³ ; a = 2 · 10 ^-3 m.

m = ρa ^3/4 = 2550 · 8 · 10 ^-9 / 4 ~ 5 · 10 ^-6 kg.

J _X ~ ma ^2/10 = 5 · 4 · 10 ^-6 · 10 ^-6 / 10 ~ 2 × 10 ^-12 kgm ^2.

Let F = 0.02 H; r = 2 · 10 ^-3 m.

Then M = 4 · 10 ^-5 Nm.

E = 4 · 10 ^-5 / 2 · 10 ^-12 = 2 · 10 ⁷ rad / s ² .

The linear acceleration of the point of application of force A = Er = 2 · 10 ⁷ · 2 · 10 ^-3 = 4 · 10 ⁴ m / s ² .

At τ = 10 ^-4 s.

W = Eτ = 2 · 10 ⁷ · 10 ^-4 = 2 · 10 ³ rad / s.

Equivalent rotational speed w = W / 6.28 ~ 320 rpm ~ 20,000 rpm.

A = 4 · 10 ⁴ m / s ² ; τ = 10 ^-4 s.

S = 4 · 10 ⁴ · 10 ^-8 / 2 = 2 · 10 ^-4 m = 0.2 mm.

With r = 2 mm.

φ = arctan (S / r) = arctan (0.2 / 2) ~ 5.7 °.

α = 18 · 10 ^-6 1 / deg (thread of nichrome); L = 20 mm; ΔL = 0.2 mm.

ΔТ = ΔL / αL = 0.2 / (18 · 10 ^-6 · 20) = 10000/18 ~ 555 °

The dimensions of the conductive filament are 0.01 × 0.01 × 2 cm. Volume V _T = 2 · 10 ^-4 cm ³ .

The mass of nichrome thread m _T = V _T ρ _T = 2 · 10 ^-7 · 7.94 ~ 16 · 10 ^-7 kg.

For nichrome ρ _T = 7.94 g / cm ³ ; β = 0.48 J / kgK at 25 ° C; 0.76 J / kgK at 800 ° C. On average, for a temperature of 25 + 250 = 275 ° C, the specific heat is β = 0.57 J / kgK.

Е _T = βm _T ΔТ = 0.57 · 16 · 10 ^-7 · 555 = 0.5 mJ.

Characteristics of the power source.

Power Consumption

P _T = E _T / τ.

For the example in question

P _T = E _T / τ = 0.5 mJ / 0.1 ms = 5 W.

Power released in the conductor by resistance R _T

Resistance R _T = ρ _R L _T / S _T ~ 10 ^-6 · 2 · 10 ^-2 / (0,1 0,1) · 10 ^-6 = 2 Ohm,

where ρ _R ~ 1 μOhm · m is the specific resistance of nichrome, L _T = 0.02 m is the length of the conductive thread; S _T is the cross section of the thread.

Current consumption

I _T = (P _T / Rt) ^0.5 = (5/2) ^0.5 = 1.6 A.

Source voltage

U _T = P _T / I _T = 5 / 1.6 ~ 3.1 V.

The average power consumption P _cf = E _T · f _rad , where f _rad - the frequency of the laser radiation.

When f _rad = 1 s ^{-1, the} average power consumption is 5 mW.

According to the results, the proposed Q-switched laser has the minimum dimensions of the mechanical components and the minimum power consumption. The simplicity and low power consumption of the device ensure its high reliability. In these parameters, as well as in speed, the proposed laser is superior to the closest and other known analogues. Low voltage and the absence of rubbing contacts and magnetic elements provide a minimum level of spurious electrical effects on other elements of the laser and the integrated system with it.

Thus, the proposed device provides a solution to the problem, namely increasing reliability and speed and reducing electrical and magnetic interference and interference with minimum dimensions and minimum cost of the laser.

Information sources

1. V.A. Volokhatyuk et al. Optical location issues. Ed. P.P. Krasovsky. Ed. "Soviet Radio", Moscow, 1971, p. 196.

2. "Handbook of laser technology." Ed. Yu.V. Bayborodina, L.Z. Kriksunova, O.N. Litvinenko. Ed. "Technique", Kiev, 1978, pp. 152-154. - The prototype.

3. Sivukhin D.V. General physics course. T. 1. Mechanics. 3rd ed. M .: Nauka, 1989, §53 (http://genphys.phys.msu.ru/rus/lab/mech/opis7/i2.htm).

Claims (1)

Q-switched pulsed laser, comprising a housing, an active element and a resonator consisting of two mirrors, one of which is fixed motionless relative to the housing, and the second has the ability to rotate so that in the working position the mirrors are parallel, characterized in that the elastic element is introduced and a stretch, by which the second mirror is fixed relative to the housing in the initial position at an angle φ to the working position, the stretch is a conductive thread, and the elastic element is set so so that in the initial position the stretch is stretched, counteracting the torque M created by the elastic element on the second mirror, as well as a series-connected key and a power source connected to the ends of the conductive thread, and the angle

,
where W ₀ is the given angular velocity of the second mirror in its working position,
J is the total moment of inertia of rotation of the second mirror and the elastic element,
M is the torque created on the second mirror by an elastic element.

Images