RU2579642C1 - Laser with optical-mechanical gate - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: invention relates to laser engineering. Laser with optical-mechanical gate includes a housing, an active element and resonator consisting of two mirrors, one of which is rigidly fixed relative to body, and second one is equipped with drive and has possibility of rotation so that in working position of mirrors are parallel. Rotating mirror in original position is deployed relative to operating position at an angle φ. Drive is a flexible rod with electro-dependent curvature, one end of which is fixed to housing, and a second eccentric mounted on a rotating mirror so that rod axis joining its ends, oriented in direction of point of coupling second end of shaft with a rotating mirror from its initial position to working, and rod is connected by its electrical contacts through switch to power source, and angle of

, where W₀ - predetermined angular velocity of rotating mirror when high Q resonator, J - moment of inertia of rotating mirror, M - torque generated by flexible rod on rotating mirror with closed switch position.

EFFECT: technical result consists in improvement of reliability of laser.

6 cl, 2 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 laser with a resonator, consisting of two mirrors, one of which is fixed motionless, and the second is equipped with a drive and has the ability to rotate so that in one of the positions of the rotating and stationary resonator mirrors become 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 laser, including the housing, the active element and the resonator, consisting of two mirrors, one of which is fixed motionless relative to the housing, and the second is equipped with a drive and has the ability to rotate so that in the working position of the mirror parallel, the rotating mirror in the initial position is deployed relative to the working position at an angle φ, the drive is a flexible rod with electrically dependent curvature, one end of which is fixed to the housing, and the second eccentric adic fixed on a rotating mirror so that the rod axis joining its ends, oriented in the direction of the point of coupling the second end of the rod with a rotating mirror from its initial position to the working, wherein the rod is connected through its electrical contacts of the key to the power source, and the angle

,

,

where W ₀ is the given angular velocity of the rotating mirror at the moment of the highest quality factor of the resonator,

J is the moment of inertia of rotation of the mirror,

M - torque created by a flexible rod on a rotating mirror with the key closed.

A flexible rod can be made in the form of traction, the curvature of which increases when connected to a power source.

A flexible rod can be made in the form of a pusher, the curvature of which decreases when connected to a power source.

The flexible rod can be made in the form of a bimetallic tape, its ends connected through a key to a power source.

The flexible rod can be made in the form of at least a two-layer metal-glass or cermet tape, its ends connected through a key to a power source.

The flexible rod can be made of a piezoelectric tape, on the side surfaces of which are applied metal plates connected via a key to a power source.

In the drawing of FIG. 1 shows a laser circuit. FIG. 2 illustrates the principle of operation of the device with a thrust (Fig. 2a) and a pusher (Fig. 2b).

The device (Fig. 1) consists of a resonator formed by a movable 1 and a rotating 2 mirrors, between which the active element of the laser 3 is placed. The rotating mirror is equipped with a drive 4, connected to the power supply 5 through a key 6. The drive 4 is made in the form of traction (Fig. 2a), with one end connected to the housing 7, and the other with a rotating mirror at a distance r from its axis of rotation. In the initial position, the rod holds the rotating mirror 2 at an angle φ to the working position, in which the rotating mirror is parallel to the stationary mirror 1. In the embodiment of FIG. 2b) drive 4 is made in the form of a pusher.

The laser operates as follows.

In the initial state, the rotating mirror 2 is located at an angle φ to the fixed mirror 1. In this case, the quality factor of the resonator formed by these mirrors is insufficient for laser generation. When the key 6 is closed through a flexible rod in the form of a rod 4 (Fig. 2a) or a pusher (Fig. 2b), a current begins to flow, causing it to heat up. Due to thermal lateral deformation of the rod, its movable end presses on mirror 2 (Fig. 2b) or pulls it onto itself (Fig. 2a), causing the mirror to rotate. When the mirror thus driven into rotation becomes parallel to the stationary mirror, the quality factor of the resonator increases to a level sufficient to generate a 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.

A flexible rod with electrically dependent curvature may be a bimetallic, metal-glass or cermet composition. When the conductive layer is heated by the current flowing through it, the curvature of the two-layer rod k, that is, the reciprocal of the radius of bending of the rod, changes according to the dependence [3]

where ε = (α ₁ -α ₂ ) ΔT;

E ₁ and E ₂ - the modulus of elasticity of materials 1 and 2;

h ₁ and h ₂ - the thickness of the materials 1 and 2;

α ₁ and α ₂ - coefficient of thermal expansion of materials 1 and 2;

ΔТ is the temperature difference before and after heating the flexible rod.

In the initial state, the rod in the form of traction (Fig. 2A) can be given preliminary curvature. In each case, its value is determined by the complex requirements for the longitudinal movement of the rod, which is developed in this case by the acceleration of the rotating mirror and the maximum permissible temperature of the rod with a minimum energy consumption for its heating.

The preliminary curvature of the rod in the form of a pusher (Fig. 2b) should be greater than the curvature in its working position, that is, the rod should be bent in the opposite direction, for which the orientation of the bimorph composition should be opposite.

The calculation of a flexible rod in the form of a piezoelectric beam is given in [4].

A mechanical calculation of a rod in the form of a loaded beam is contained in [5].

The volume of a flexible rod should be minimal for its quick heating and reduction of energy consumption. For this purpose, at a given length, it should have a minimum cross section.

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 [6].

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: E = M / J,

where F is the force; r is the shoulder (Fig. 2).

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 displacement S = Aτ 2/2 ^{of the} point of application of the force F exerted by the conductive rod during its thermal expansion.

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

Example 1

A prism of total internal reflection with characteristics ρ = 2550 kg / m ^{3 was} used as a rotating mirror; a = 2 · 10 ^-3 m. In this case

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 N; 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 = Et = 2 · 10 ⁷ · 10 ^-4 = 2 · 10 ³ rad / s.

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

S = 2 · 10 ⁴ · 10 ^-8 / 2 = 10 ^-4 m = 0.1 mm.

φ = arctan (S / r) = arctan (0.1 / 2) ~ 2.9 °.

The lateral displacement of the rod Q during its temperature bending is determined using expression (1).

where r = l / k is the bending radius of the rod (1);

l is the length of the rod.

The longitudinal (working) displacement of the movable end of the rod S _p is determined using formula (1) as the difference between the lengths C of the chords of the arc formed by the rod of length L at the initial and final values of ΔT.

Example 2

1) Starting position ΔT = 20 °.

k ₁ = 0.002 1 / mm. The radius of curvature ρ ₁ = 1 / k ₁ = 500 mm.

The angle θ covered by the arc, θ ₁ = L / ρ ₁ = 20/500 = 0.04 rad.

Chord C ₁ = 2ρ ₁ Sin (θ _1/2 ) = 19.998 mm.

2) Operating position ΔT = 200 °.

k ₂ = 0.02 1 / mm. The radius of curvature ρ ₂ = 1 / k ₂ = 50 mm

The angle θ covered by the arc, θ ₂ = L / ρ ₂ = 20/50 = 0.4 rad.

Chord C = 2ρ _{2 2} Sin (θ _2/2) = 19.87 mm.

Displacement Sп = C ₁ -C ₂ = 0.13 mm.

The energy E _T = βm _T ΔT required to heat the rod.

where β is the heat capacity;

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

ρ _T is the density of the rod material;

V _T is the volume of the rod.

Example 3

The flexible rod is a metal-glass tape with the characteristics of the conductive layer.

α = 18 · 10 ^-6 1 / degree (nichrome); L = 20 mm; ΔT = 200 °

Let the dimensions of the conductive rod be 0.01 × 0.01 × 2 cm. Volume V _T = 2-10 ^-4 cm ³ .

The density of 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. The mass of the rod m _T = ρ _T · V _T = 7.94 · 2 · 10 ^-4 = 1.6 · 10 ^-3 g = 1.6 · 10 ^-6 kg.

E _T = βm _T ΔТ = 0.57 · 1.6 · 10 ^-6 · 200 = 0.18 mJ.

Characteristics of the power source.

Power consumed by the conductive rod

P _T = E _T / τ.

For the example in question

P _T = E _T / τ = 0.18 mJ / 0.1 ms = 1.8 W.

Power released in the conductor by resistance R _T

P _T = I _T ² · 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 rod; S _T is the cross section of the rod.

Current consumption

I _T = (P _T / R _T ) ^0.5 = (1.8 / 2) ^0.5 = 0.95 A.

Source voltage

U _T = P _T / I _T = 1.8 / 0.95 ~ 1.9 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 1.8 mW.

According to the results, the proposed laser with an optical-mechanical shutter has the minimum dimensions of the mechanical components and the minimum power consumption at maximum speed: the acceleration time of a rotating mirror is 0.1 ms or less, while the closest analogue [2] has an acceleration time of at least 30 ms . The simplicity and low power consumption of the device ensure its high reliability. The time from the supply of a control pulse to the moment of laser radiation is minimal. In these parameters, the proposed laser is superior to the nearest 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. Clyne T.W. “Residual stresses in surface coatings and their effects on interfacial debonding.” Key Engineering Materials (Switzerland). Vol. 116-117, pp. 307-330. 1996.

4. A.B. Nasedkin. Some examples of finite element modeling of piezoelectric sensor systems and control objects with viscoelastic properties. http://www.pandia.ru/text/78/014/6789.php

5. Birger I.A., Mavlyutov R.R. Strength of materials. M .: Science. Ch., Ed. Phys.-Math. lit., 1986 - 560 s.

6. 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 (6)

1. The laser with an optical-mechanical shutter, 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 is equipped with a drive and can rotate so that the mirrors are parallel in the working position, different the fact that the rotating mirror in the initial position is deployed relative to the working position at an angle φ, the drive is a flexible rod with electrically dependent curvature, one end of which is fixed to the housing, and the second centric mounted on a rotating mirror so that the axis of the rod connecting its ends was oriented in the direction of the point of contact of the second end of the rod with the rotating mirror from its initial position to the working one, and the rod is connected by its electrical contacts through the key to the power source, and the angle

,
where W ₀ is the given angular velocity of the rotating mirror at the moment of the highest quality factor of the resonator,
J is the moment of inertia of rotation of the mirror,
M - torque created by a flexible rod on a rotating mirror with the key closed. 2. The laser under item 1, characterized in that the flexible rod is made in the form of traction, the curvature of which increases when connected to a power source. 3. The laser according to claim 1, characterized in that the flexible rod is made in the form of a pusher, the curvature of which decreases when connected to a power source. 4. The laser under item 1, characterized in that the flexible rod is made in the form of a bimetallic tape, its ends connected through a key to a power source. 5. The laser according to claim 1, characterized in that the flexible rod is made in the form of a composition of at least two layers, of which one is a metal and the other is a dielectric, for example glass. 6. The laser according to claim 1, characterized in that the flexible rod is made of a piezoelectric tape, on the side faces of which are applied metal plates connected through a key to a power source.

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