RU2579548C1 - Laser with modulated resonator q-factor - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: invention relates to laser engineering. Q-switched laser resonator includes an active element and a resonator consisting of two mirrors, one of which is fixedly secured, while second actuator is provided and is rotatable in such a way that in operative position mirrors are parallel. Rotating mirror in original position deployed relative to operating position at an angle φ, drive is a conductive rod having one end secured to a stationary base, while second has possibility of longitudinal displacement and eccentric rests on a rotating mirror so that longitudinal movement of movable rod end mirror could rotate, moving to a working position, wherein conducting rod is connected with their ends through switch to power supply, and angle

where W₀ - set angular velocity of rotating mirror at moment of highest resonator Q, J - moment of inertia of mirror rotation, M - torque generated by drive.

EFFECT: technical result consists in increasing reliability and efficiency of laser.

2 cl, 5 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.

, гдеThis problem is solved due to the fact that in the known laser with a modulated Q-factor of the resonator, which includes an active element and a resonator consisting of two mirrors, one of which is fixed motionless, and the second is equipped with a drive and is able to rotate so that the mirrors are in the working position parallel, the rotating mirror in the initial position is deployed relative to the working position at an angle φ, the drive is a conductive rod, one end of which is fixed to a fixed base, and the second and EET possibility of longitudinal displacement and eccentrically supported on a rotating mirror so that the longitudinal movement of the movable rod end mirror could rotate, moving to a working position, wherein the conducting rod is connected at its ends through a switch to a power source, and the angle

where

W ₀ - the given angular velocity of the rotating mirror at the time of the highest quality factor of the resonator,

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

M is the torque generated by the drive.

The conductive rod may be provided with a lateral strain limiter.

In FIG. 1 shows a laser circuit. FIG. 2 explains the principle of operation of the device. In FIG. 3 shows an arrangement of a drive with a lateral deformation limiter. In FIG. 4 depicts an embodiment with several conductors fastened together and connected in series with current. In FIG. 5 shows a configuration of a device with a rotating mirror in the form of a prism of total internal reflection.

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 a conductive rod (Fig .2) supported at one end into a fixed base, and the other into a rotating mirror 2. The ends of the rod are connected to the power source 5 through a key 6. To fix the rod in its original position, use the stop 7, and to return to its original position - spring 8.

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, a current begins to flow through the conductive rod 4, causing the rod to heat up. Due to the thermal expansion of the rod, its loose end presses on the mirror 2, causing it 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 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 conductive rod may have a circular or rectangular cross section - to provide rigidity in one of the transverse directions. In order to increase the stiffness, several conductors can also be used with the ends mechanically fastened with a ferrule 11 (Fig. 4). In the latter case, as shown in the drawing, it is advisable to connect the conductors in series with the current. This increases the electrical resistance of the conductive rod and increases the efficiency of the power source.

The volume of the conductive rod should be minimal for its quick heating and reduce energy consumption. For this purpose, at a given length, it should have a minimum cross section. To ensure its rigidity in the transverse direction, lateral deformation limiters can be introduced. This allows you to increase the force generated by the rod in the longitudinal direction. In FIG. 2 shows an embodiment of such a construction. The conductive tape rod 4 with the left end is mounted on the laser housing 9 and can move freely during thermal expansion. A limiter 10 is installed on the opposite side of the housing. The gap Δ in which the rod moves does not allow it to bend in the transverse direction, thereby ensuring its ability to withstand specified loads in the longitudinal direction. For example, with the length of the conductive rod L ₀ = 20 mm, the gap width Δ = 0.05 mm and the working force F = 0.1 N, the maximum transverse force does not exceed 2FΔ / L ₀ = 2 · 0.1 · 0.05 / 20 = 0.0005 N, which is acceptable for a nichrome rod supported on two ends with its thickness of 0.1 mm and a width of 0.1 mm or more.

If the rotating mirror is made in the form of a prism of total internal reflection with equal sides of its hypotenuse face (Fig. 5), 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:

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 = Eτ of the prism after time τ after the onset of force F.

Linear displacement S = Аτ 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.

The temperature increment of the length of the conductive rod S = αLΔT (Fig. 3).

where α is the coefficient of linear expansion;

ΔT is the temperature difference.

Energy E _T = βm _T ΔT required to heat the conductive 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.

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

With r = 2 mm.

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

α = 18 · 10 ^-6 1 / deg (rod of nichrome); L = 10 mm; ΔL = 0.1 mm.

ΔT = ΔL / αL = 0.1 / (18 · 10 ^-6 · 10) = 10000/18 ~ 555 °.

Let the dimensions of the conductive rod be 0.01 × 0.01 × 1 cm. Volume V _T = 10 ^-4 cm ³ .

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. Rod mass

m _T = ρ _T · V _T = 7.94 · 10 ^-4 = 8 · 10 ^-4 g = 8 · 10 ^-7 kg.

E _t = βm _T ΔT = 0.57 · 8 · 10 ^-7 · 555 = 0.25 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 = 0.25 mJ / 0.1 ms = 2.5 W.

Power released in the conductor by resistance R _T

$$P_T=I_{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="00000006.png,00000007.png"\; state="\{\{state\}\}">T</figure-callout>}}^2\cdot R_T$$

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

where ρ _R ~ 1 μOhm · m is the specific resistance of nichrome, L _T = 0.01 m is the length of the conductive rod; St is the cross section of the rod.

Current consumption

I _T = (P _T / R _T ) ^0.5 = (2.5 / 1) ^0.5 = 1.6 A.

Source voltage

U _T = P _T / I _T = 2.5 / 1.6 ~ 1.6 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 2.5 mW.

According to the above results, the proposed Q-switched laser has minimum dimensions of mechanical components and 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. 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. 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. The laser with a modulated Q-factor of the resonator, comprising an active element and 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 the working position the mirrors are parallel, characterized in that the rotating mirror in the initial position is deployed relative to the working position at an angle φ, the drive is a conductive rod, one end of which is fixed on a fixed base, and the second has the ability to longitudinally motion and eccentrically rests on a rotating mirror so that during longitudinal movement of the movable end of the rod, the mirror can rotate, moving to its working position, with the conductive rod connected at its ends through a key to a power source, and the angle

Where
W ₀ - the given angular velocity of the rotating mirror at the time of the highest quality factor of the resonator,
J is the moment of inertia of rotation of the mirror,
M is the torque generated by the drive. 2. The laser under item 1, characterized in that the conductive rod is equipped with a limiter of lateral deformations.

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