RU2585798C1 - Pulsed laser with modulated resonator q-factor - Google Patents

Abstract

FIELD: optics; instrument engineering.

SUBSTANCE: invention relates to laser equipment. 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 two braces. First brace is stretched between the second mirror and body counteracting to elastic element installed between the second mirror and body, and the second brace is stretched between middle part of the first brace and body so that in initial position of the second mirror condition is fulfilled

where φ is the angle between initial and working position of the second mirror, W₀ is the given angular velocity of the second mirror in its working position, J is total inertia moment of rotation of the second mirror and elastic element, M is torque, created at the second mirror by elastic element. Second brace is made from conducting material. Laser also includes subsequently connected switch and power supply source connected to the second brace ends, wherein the first and second brace length with closed switch is sufficient for free rotation of the second mirror in its working position.

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 two extensions were introduced, the first of which was stretched between the second mirror and the housing, counteracting the elastic element installed between the second mirror and the housing, and the second stretched between the middle part of the first extension and the body so that in the initial position of the second mirror the condition is satisfied:

 where φ is the angle between the initial and working positions of the second mirror,

W ₀ - a 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 by the elastic element on the second mirror, the second extension is made of conductive material, and a key and a power source are connected in series, connected to the ends of the second extension, and the length of the first extension and the second extension when the key is closed is sufficient for free rotation of the second mirrors in its working position.

The elastic element can be combined with the first stretch.

In FIG. 1 shows a laser circuit. FIG. 2 explains the principle of operation of the device. In FIG. 3 shows the combination of the elastic element and the first stretch.

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 2 in its initial position is fixed relative to the housing 4 by an elastic element and two stretch marks, the first of which is suspended between the second mirror and the casing, and the second is stretched between the middle of the first stretch and the casing so that together with the first stretch and the elastic element to keep the mirror 2 in its original position (Fig. 2). The elastic element and the first stretch can be placed on different sides of the axis of rotation of the mirror 2 or on one side (Fig. 1). In this case, the elastic element (spring) 5 must be pre-stretched in its original position or compressed depending on its location relative to the first thread and the axis of rotation of the mirror 2. The first stretch can be made elastic, for example in the form of a tension spring. Then it can fulfill the function of an elastic element (Fig. 3).

The laser operates as follows.

In the initial state, the rotating mirror 2 is fixed by a stretch 6, drawn by the second stretch 7 so that the mirror 2 is located at an angle φ to its working position. In this case, the force of the elastic element F acts on mirror 2 (Fig. 2). The quality factor of the resonator formed by these mirrors is insufficient for laser generation. When the key 9 is closed through a conductive extension 7 from the power supply 8, a current begins to flow, causing it to heat. Due to the thermal expansion of the stretch, its loose end releases the first stretch 6, which is straightened by the action of the elastic element 5, which causes the mirror 2 to rotate under the action of the force F, which creates a moment of rotation M = Fr, where r is the radius of the force. 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 relevant 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 extension (filament) 7 should be minimal for its quick 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 is the 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 ΔТ, necessary 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 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 = Еτ = 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.

The relationship between the displacement S and the temperature extension ΔL of the second thrust is determined by the Pythagorean theorem (Fig. 2).

h ² = (L / 2) ² - (L ′ / 2) ² ,

where h is the amount of sagging of the first thrust in its initial position; L is the length of the first thrust; L ′ is the distance between the attachment points of the first link.

From here:

The derivative of this quantity:

With small increments Δh of the parameter h (Fig. 2), the relation

By varying the h / L ratio, it is possible to control the Δh / S ratio depending on the restrictions on the temperature of the second stretch and the force F required to spin the second mirror at a given angular speed for the required time to enter the mode:

.Δh = S for $$h=L/\sqrt{12}$$

.

Example

With r = 2 mm and Δh = S;

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

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

ΔT = S / 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.

Power Supply Specifications

Power consumption of a conductive thread:

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 with 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 / R _T ) ^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 ,

_rad where f - 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. M., Soviet Radio, 1971, p. 196.

2. Handbook of laser technology. Ed. Yu.V. Bayborodina, L.Z. Kriksunova, O.N. Litvinenko. Kiev, Technics, 1978, p. 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/ras/lab/mech/opis7/i2.htm).

Claims (2)

1. A Q-switched pulse 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 the mirrors are parallel in the working position, characterized in that an elastic element and two extensions, the first of which is stretched between the second mirror and the housing, counteracting the elastic element installed between the second mirror and the housing, and the second extension is stretched between the middle part of the first stretch and the casing so that in the initial position of the second mirror the condition is satisfied:

,
where φ is the angle between the initial and working positions of the second mirror,
W ₀ - a 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 by the elastic element on the second mirror, the second extension is made of conductive material, and a key and a power source are connected in series, connected to the ends of the second extension, and the length of the first extension and the second extension when the key is closed is sufficient for free rotation of the second mirrors in its working position. 2. The pulsed laser according to claim 1, characterized in that the elastic element is combined with the first stretching.

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