RU2069431C1 - Multichannel coherent optical radiation source - Google Patents

Abstract

FIELD: laser technology. SUBSTANCE: lasers 1 are disposed periodically along the arc of the circle about semitransparent communication mirror 2, which is made in form of annular cylinder. Lasers are mounted at the plane being perpendicular to axis of symmetry of mirror, and oriented radically in relation to the axis. Radius of mirror and distance from apertures of lasers to axis of the mirror satisfies to the relation got on the base of diffraction theory from the condition of complete representation of periodical field of laser set for Talbo cylindrical resonator. The relation given in the description s the following: $$$, where r is radius of the mirror, R is distance from apertures of lasers to axis of the mirror, $$$ is angle between axes of adjacent lasers, $$$ is generation wavelength. EFFECT: improved efficiency of operation. 2 dwg

Description

 The invention relates to laser technology, in particular to multichannel lasers with a new shape of the optical resonator, in particular, cylindrical.

Multichannel sources of optical radiation are known [1, 2], which are a set of parallel waveguide CO ₂ lasers.

 The disadvantage of such multichannel sources is the large divergence of the radiation and, as a consequence, the limitation of the maximum achievable power density. The reason for this is the independent generation of lasers, in which the radiation divergence is determined by the size of the aperture of an individual laser.

The closest in technical essence to the proposed device is a multi-channel source of coherent optical radiation [3] made in the form of a set of periodically arranged lasers with diffraction coupling in the Talbot resonator. In this source, the mirror connecting the lasers is located from their output apertures at a distance z _t = 2a ² / λ Talbot distance, a set period, λ wavelength. Such a system forms a Talbot resonator in which the radiation returning to the lasers after reflection from the coupling mirror most fully reproduces the field structure of the periodic set of lasers. As a result, in-phase generation of all lasers is achieved, in which the radiation divergence is significantly reduced, since it is determined by the size of the aperture of the entire set.

The disadvantage of the above radiation source is the following:
diffraction losses in the Talbot cavity caused by incomplete reproduction of the periodic field of a set of lasers due to their finite number;
large size of the source, since the Talbot distance z _t increases quadratically with the set period a and can be several meters;
a decrease in the radiation power density due to leakage into the side lobes of the radiation pattern formed by a set of lasers;
a limited (of the order of several degrees) value of the angle at which the radiation converges upon focusing, which is due to the finite dimensions of the aperture of the set.

 The technical problem of the invention to be solved is to eliminate these drawbacks, that is, to develop a compact device that provides in-phase radiation of a circular array of lasers and, as a result, obtains a high power density with minimal diffraction losses in the general resonator.

где r радиус зеркала связи,
R расстояние от апертур лазеров до оси зеркала,
Φ_o угол между осями соседних лазеров,
λ длина волны генерации.This task is achieved by the fact that in a multichannel source of coherent optical radiation containing a periodic set of lasers and a communication mirror forming the Talbot resonator, the communication mirror is translucent in the form of a circular cylinder, the lasers are mounted in a plane perpendicular to the symmetry axis of the mirror, and oriented in the radial direction along relative to this axis, the laser apertures being located on an arc of a circle centered on the axis of the mirror, and the radius of this mirror r and the distance R from the laser apertures to the mirror axis satisfy the ratio:

where r is the radius of the communication mirror,
R is the distance from the laser apertures to the mirror axis,
Φ _{o the} angle between the axes of adjacent lasers,
λ generation wavelength.

The technical result of the present invention is as follows:
1. the absence of losses due to diffraction of radiation by the angular coordinate, since due to the angular periodicity of the circular dialing in a Talbo cylindrical resonator, the structure of the optical field of the lasers is completely reproduced along this coordinate;
2. high compactness, since with a decrease in the radius of curvature of the communication mirror r, the distance R from the laser apertures to the mirror axis decreases;
3. high power density due to the volume nature of coherent radiation generated by a circular array of lasers;
4. The size of the radiating aperture in the angular coordinate is 2π ..

The invention is illustrated in figure 1, which schematically shows the proposed multi-channel source of coherent optical radiation, and figure 2, which shows the change in the distance Rr from the laser apertures to the communication mirror depending on the curvature of the communication mirror r ^-1 .

The device contains a periodic set of lasers 1 located along an arc of a circle of radius R around a translucent communication mirror 2 in the form of a circular cylinder of radius r. The circle lies in a plane perpendicular to the axis of symmetry O of the coupling mirror, its center lies on this axis. The optical axes of the lasers are oriented in the radial direction with respect to the axis of symmetry O; their output apertures 3 facing the axis O are transparent; on opposite windows
blind mirrors 4.

 The device operates as follows. The radiation from each laser 1 propagates to the communication mirror 2 and vice versa. Due to the divergence in the process of diffraction and reflection from the convex coupling mirror 2, the radiation of each laser enters the apertures of 3 other set lasers. Thus, optical diffraction coupling between the lasers is realized, due to which phase synchronization of the lasers occurs and collective generation occurs in the set. When choosing the radius of the coupling mirror in accordance with the condition for reproducing periodic fields (see below for details), a circular array of lasers 1 with such a coupling mirror 2 forms a cylindrical Talbo resonator. In this case, for the circular periodic array of lasers, the losses due to diffraction of radiation by the angular coordinate disappear, and the common-mode generation threshold reaches a minimum.

 During in-phase generation, the phases for obtaining lasers coincide, and in the vicinity of the axis of the semitransparent mirror, their fields are coherently added. As a result, the power density of radiation converging to the axis of the system is significantly increased, compared with the case of independent laser generation. The angular size of the aperture of a multichannel source with a Talbo cylindrical resonator is 2π in a plane perpendicular to its axis.

(1)
где r радиус зеркала связи,
R расстояние от апертур лазеров до оси зеркала,
Φ_o угол между осями соседних лазеров,
λ длина волны генерации,
s характерный размер поперечной моды.The parameters of a Talbot cylindrical resonator are determined on the basis of diffraction theory from the conditions for reproducing the periodic structure of the field of a set of lasers. For real systems, the following conditions apply:

(one)
where r is the radius of the communication mirror,
R is the distance from the laser apertures to the mirror axis,
Φ _{o the} angle between the axes of adjacent lasers,
λ generation wavelength,
s characteristic size of the transverse mode.

:

(2)
Из условия (1) следует, что применимо малоугловое приближение, при котором поле отдельного лазера E(r,Φ′) на зеркале связи согласно формуле Кирхгофа для скалярной задачи дифракции имеет вид:

(3)
Аналогично представляется на окружности R поле, отраженное от зеркала связи:

(4)
Здесь Φ угловая координата для выходного излучения лазеров E(R,Φ) на окружности радиуса R;
Φ′ координата на зеркале связи;
Φ″ координата на окружности R для излучения E(R,Φ″),, падающего обратно на апертуры лазеров;
При поперечной моде лазера f(R,Φ_n), где Φ_n= Φ - nΦ_o,, n его номер в наборе, коэффициент оптической связи n-го и m-го лазеров в цилиндрическом резонаторе в соответствии с (3, 4) определяется выражением:

(5)
Для основной поперечной моды лазера вида

матричный коэффициент связи вычисляется по формуле:

(6)
где

волновой параметр цилиндрической системы,
m, n 1, 2, N, N число лазеров в наборе.This allows us to use the asymptotics valid for the source function of the two-dimensional diffraction problem

:

(2)
It follows from condition (1) that the small-angle approximation is applicable, in which the field of an individual laser E (r, Φ ′) on the coupling mirror according to the Kirchhoff formula for the scalar diffraction problem has the form:

(3)
Similarly, on the circle R, the field reflected from the coupling mirror is represented:

(4)
Here Φ is the angular coordinate for the output radiation of the lasers E (R, Φ) on a circle of radius R;
Φ ′ coordinate on the communication mirror;
Φ ″ coordinate on the circle R for radiation E (R, Φ ″), incident back on the laser apertures;
In the transverse laser mode f (R, Φ _n ), where Φ _n = Φ - nΦ _o ,, n its number in the set, the optical coupling coefficient of the nth and mth lasers in a cylindrical cavity in accordance with (3, 4) defined by the expression:

(5)
For the main transverse laser mode of the form

matrix coupling coefficient is calculated by the formula:

(6)
Where

wave parameter of a cylindrical system,
m, n 1, 2, N, N the number of lasers in the set.

(7)
где

матрица оптической связи, элементы которой суть коэффициенты M_mn.The steady-state collective generation of lasers in a set is described by the eigenvalue problem:

(7)
Where

optical coupling matrix whose elements are coefficients M _mn .

определяет дифракционные потери k-ой коллективной моды генерации. Из решения собственной задачи (7) следует, что потери синфазной моды k=1 минимальны, если система образует цилиндрический резонатор Тальбо, то есть расстояние между выходными апертурами лазеров и зеркалом связи составляет половину расстояния Тальбо для цилиндрической геометрии. Зависимость расстояния Тальбо

от кривизны зеркала связи r^-1 изображена на фигуре 2 в единицах, отнесенных к величине z = 2(RΦ_o)²/λ.. Зависимость, представленная на фигуре 2, с удовлетворительной точностью (не хуже 3%) аппроксимируется следующей формулой:

где r радиус зеркала связи,
R расстояние от апертур лазеров до оси зеркала,
Φ_o угол между осями соседних лазеров,
λ длина волны генерации.Eigenvalue module

determines the diffraction loss of the kth collective generation mode. It follows from the solution of the intrinsic problem (7) that the in-phase mode losses k = 1 are minimal if the system forms a Talbo cylindrical resonator, i.e., the distance between the output apertures of the lasers and the coupling mirror is half the Talbot distance for cylindrical geometry. Talbot distance dependence

the curvature of the communication mirror r ^{-1 is} shown in figure 2 in units related to the value z = 2 (RΦ _o ) ² / λ .. The dependence shown in figure 2, with satisfactory accuracy (not worse than 3%) is approximated by the following formula:

where r is the radius of the communication mirror,
R is the distance from the laser apertures to the mirror axis,
Φ _{o the} angle between the axes of adjacent lasers,
λ generation wavelength.

 In the two-dimensional system, the in-phase mode losses vanish, which indicates the complete reproduction of the periodic field structure of this mode in the angular coordinate in the cylindrical Talbot resonator.

 Example.

Parameters of a multi-channel optical radiation source with a Talbo cylindrical resonator using an example of a set of semiconductor lasers:
wavelength l = 1.3 μm;
communication mirror radius r = 2 cm;
Talbot distance 2 (Rr) = 6 cm;
circle radius R = 5 cm;
the distance between the axes of adjacent lasers RΦ _o = 350 μm;
the number of lasers in the set N = 10 ³ .

 Thus, a scheme is proposed for a multichannel source of coherent optical radiation, which differs from known similar devices by a high concentration of the light field power density on the axis of the system, which is achieved as a result of interference of coherent radiation converging from lasers located around the circumference in phase synchronization mode.

 The proposed multichannel source can be used to create laser technology systems, in particular for circular processing of a product, as well as laser controlled thermonuclear fusion systems for bulk compression and heating of a target.

 The proposed scheme can be generalized to a multichannel coherent source with a Talbo spherical resonator.

Claims (1)

A multichannel optical radiation source containing a set of lasers and a communication mirror forming a Talbot resonator, characterized in that the communication mirror is translucent in the shape of a round cylinder, while the lasers are mounted in a plane perpendicular to the symmetry axis of the mirror and are oriented in the radial direction with respect to this axis, and the laser apertures are located on an arc of a circle centered on the mirror axis, and the radius of the mirror and the distance from the laser apertures to the mirror axis satisfy the following relation:

where r is the radius of the mirror;
R is the distance from the laser apertures to the mirror axis;
Φ _{o the} angle between the axes of adjacent lasers;
λ generation wavelength.

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