RU2077068C1 - Optical adaptive module - Google Patents

Abstract

FIELD: laser technology. SUBSTANCE: optical adaptive module has union body 1 where there are input optical window 2, optical compensating device composed by dynamic adjusting head 5 with adaptive mirror 4 and right angle separating prism 6. Separating prism is set on such manner that optical radiation passing through input window 2 is reflected by adaptive mirror to frontal cathetus plane of prism 6 and then it is directed to output window 3 in body 1. Optical radiation passing through separating prism is reflected by prism second cathetus plane. Both rays are passed through lenses 7 and 9, respectively, to radiation receivers 8 and 10 which outputs are connected to electronic amplifier-converter connected to dynamic adjusting head 5. EFFECT: less laser radiation divergence, higher laser radiation wave front control. 5 dwg

Description

 The invention relates to controlled optics and can be used to reduce the divergence of laser radiation during their operation, as well as to control the wavefront of laser beams in optical instruments and systems.

 Known intracavity adaptive system for compensating distortions of laser radiation, containing a correction device in the form of an adaptive mirror mounted inside the resonator, a lens in the focus of which is a photodetector with a point aperture located in front of it, amplifiers, synchronous detectors, master oscillators and mixers. The separation of the adaptive mirror control channels is achieved by the choice of various modulating frequencies of the master oscillators. The disadvantages of this system are the use of an intracavity correction scheme, since this involves interference with the laser design, the complexity of the system and its elements, low accuracy and reliability of distortion compensation.

 Known adaptive compensation system for thermal self-influence of laser radiation, containing a correction device consisting of cylindrical lenses and rotary mirrors, and its control system, consisting of a laser, an optical system and two control channels. One of the channels, containing a square radiation receiver located at the focus of the lens, differential and output amplifiers, generates control signals for the position of two rotary mirrors. Another channel containing a lens, the focus of which is a photodetector with a point diaphragm located in front of it, amplifiers, synchronous detectors, specifying generators, phase shifters, filters and adders, generates control signals for stepper motors that move cylindrical lenses along the optical axis, and the separation of control signals the position of the cylindrical lenses is achieved by the selection of various modulating frequencies of the master oscillators.

 The disadvantages of the known device are the complexity of the system as a whole, as well as the devices included in it, low accuracy and reliability of distortion compensation.

 The technical result from the use of the invention is to simplify the system of dynamic compensation for defocusing and tilting the wavefront of the laser radiation while improving the accuracy and reliability of compensation.

 This result is achieved by the fact that the optical adaptive module containing the correction device and two radiation detectors located in the foci of the lenses, one of which is square, and in front of the other there is a point diaphragm, is equipped with an input optical window located in a single housing, a correction device containing a dynamic alignment head with an adaptive mirror located in it and a rectangular prism, the side legs of which are partially transparent, with an input optical m window, the two radiation receivers and an electronic amplifier-converter, the inputs of which are connected to the outputs of detectors, and outputs a dynamic aligning head and an adaptive mirror.

 Simplification of the dynamic compensation system for defocusing and tilting the wavefront of laser radiation is achieved by eliminating the laser, synchronous detectors, master oscillators, phase shifters, filters and adders and replacing the converter with a direct dividing prism and electronic amplifier. Improving the accuracy and reliability of compensating for defocusing and tilting the wavefront is achieved through the use of a bimorph adaptive mirror instead of cylindrical lenses moved by stepper motors, and a dynamic alignment head with piezoelectric drives instead of rotary mirrors.

 In FIG. 1 shows a schematic diagram of an optical adaptive module; in FIG. 2 the location of the focal spot on the square radiation receiver in the initial state; in FIG. 3 the same, in the presence of wavefront distortions; in FIG. 4 schematic diagram of an electronic amplifier-converter; in FIG. 5 composition and principle of operation of the dynamic alignment head.

 The device consists of a housing 1, in which there are input 2 and output 3 optical windows. Behind the input window 2, an adaptive mirror 4 is mounted in series, mounted in the dynamic alignment head 5, and a dividing prism 6, after which there are two receiving optical channels and an output optical window 3. One of the receiving optical channels contains a lens 7 and a square radiation receiver 8, the other a lens 9, in the focus of which there is a radiation receiver 10 with a point diaphragm located in front of it 11. The outputs of the radiation receivers 8 and 10 are connected through an electronic amplifier-converter 12 to dynamic ovochnoy head 5 and the adaptive mirror 4.

 The optical adaptive module operates as follows.

где

амплитуда пучка;

радиус вектор;
ω_o угловая частота лазерного излучения;
t временная координата;
k волновое число;
Φ_o постоянный сдвиг фазы
создает в центре каждого приемника излучения фокальное пятно минимального диаметра. На фиг. 2 показано расположение фокального пятна на квадратном приемнике излучения 8 при входном пучке 1 в исходном состоянии, когда для выходных сигналов U₁ U₄ этого приемника, пропорциональных площадям засветки соответствующих светочувствительных площадок П1,П4, справедливо
U_{1 исх}=U_{3 исх} (2)
U_{2 исх}=U_{4 исх} (3)
Выходной сигнал U₅ второго приемника излучения 10, пропорциональный интенсивности излучения в центре фокального пятна, в исходном состоянии при входном пучке (1) имеет свое максимальное значение U_макс
U_{5 исх}=U_макс
Электронный усилитель-преобразователь 12 (фиг. 4) имеет три канала усиления, каждый из которых содержит два последовательно расположенных дифференциальных усилителя 13, причем последние из них имеют обратную связь через резистор 14, а первые регулировку коэффициента усиления. Один из каналов усиления дополнительно содержит схему запоминания и сравнения 15, а также потенциометр 16. Выходные сигналы U₁.U₅ приемников излучения 8, 10 поступают на входы электронного усилителя-преобразователя 12, как показано на фиг. 4, который формирует управляющие сигналы адаптивного зеркала 4 V₃ и динамической юстировочной головки 5 V₁, V₂

где U₁.U₄ выходные сигналы квадратного приемника излучения;
U₅ выходной сигнал второго приемника излучения;
U_макс выходной сигнал второго приемника в исходном состоянии;
K₁.K₃ коэффициенты усиления каналов электронного усилителя-преобразователя;
' обозначение предыдущих значений сигналов U₁.U₅, V₁.V₃,
причем знак перед вторым слагаемым в (7) меняется на противоположный, если:

В исходном состоянии справедливо:
V_{1 исх}=V_{2 исх}=V_{3 исх}=0 (9)
При наличии в лазерном пучке (1) искажений типа наклонов и дефокусировки волнового фронта, описываемых соответственно функциями

где C₁, C₂, C₃ постоянные коэффициенты,
фокальное пятно на квадратном приемнике излучения 8 смещается (фиг. 3) так, что на динамическую юстировочную головку 5 поступают управляющие сигналы V₁, V₂ в соответствии с (5), (6). Интенсивность излучения в центре фокального пятна на приемнике 10 в этом случае снижается так, что на адаптивное зеркало 4 поступает управляющий сигнал V₃ в соответствии с (7), (8). Динамическая юстировочная головка 5 содержит неподвижное основание 17 ( фиг. 5) с установленными на нем опорой 18 и пьезоэлектрическим приводом 19, на которых расположено подвижное основание 20, причем соединение его с опорой 18 представляет собой шаровой шарнир. На подвижном основании 20 с помощью опоры 21 и пьезоэлектрического привода 22 аналогично установлена подвижная оправка 23, в которой неподвижно закрепляется адаптивное зеркало 4, причем угол между прямыми, соединяющими элементы 18 и 19, 21 и 22, составляет 90^o. Пьезоэлектрические приводы 19 и 22 деформируются под воздействием управляющих сигналов V₂ и V₁ соответственно так, что наклоны отражающей поверхности адаптивного зеркала 4 описываются функциями S₁ и S₂
S₁=V₁•a₁•x (13)
S₂=V₂•a₂•y (14)
где f₁, a₂ постоянные коэффициенты.The laser beam through the input window 2 enters the adaptive mirror 4 and then to the separation prism 6, with which a small fraction of the radiation is allocated to the receiving optical channels, and the main beam through the output window 3 is output from the laser adaptive module. In the initial state, the shape of the reflective surface of the adaptive mirror 4 is flat, and the elements 4 11 are aligned so that a laser beam E with a plane wavefront feeding the adaptive mirror 4

Where

beam amplitude;

radius vector;
ω _{o the} angular frequency of the laser radiation;
t time coordinate;
k wave number;
Φ _o constant phase shift
creates a focal spot of minimum diameter in the center of each radiation receiver. In FIG. 2 shows the location of the focal spot on the square radiation receiver 8 with the input beam 1 in the initial state, when for the output signals U ₁ U _{4 of} this receiver, which are proportional to the illumination areas of the corresponding photosensitive areas P1, P4,
U _{1 ref} = U _{3 ref} (2)
U _{2 ref} = U _{4 ref} (3)
The output signal U _{5 of the} second radiation receiver 10, which is proportional to the radiation intensity at the center of the focal spot, has its maximum value U _max in the initial state with the input beam (1)
U _{5 ref} = U _max
The electronic amplifier-converter 12 (Fig. 4) has three amplification channels, each of which contains two differential amplifiers 13 located in series, the last of them having feedback through the resistor 14, and the first adjusting the gain. One of the amplification channels further comprises a memory and comparison circuit 15, as well as a potentiometer 16. The output signals U ₁ .U _{5 of} the radiation receivers 8, 10 are fed to the inputs of the electronic amplifier-converter 12, as shown in FIG. 4, which generates control signals of the adaptive mirror 4 V ₃ and the dynamic alignment head 5 V ₁ , V ₂

where U ₁ .U _{4 the} output signals of the square radiation receiver;
U _{5 the} output signal of the second radiation receiver;
U _{max the} output signal of the second receiver in the initial state;
K ₁ .K ₃ channel gains of the electronic converter amplifier;
'designation of the previous values of the signals U ₁ .U ₅ , V ₁ .V ₃ ,
moreover, the sign in front of the second term in (7) is reversed if:

In the initial state, it is true:
V _{1 ref} = V _{2 ref} = V _{3 ref} = 0 (9)
In the presence of distortions in the laser beam (1) such as slopes and defocusing of the wavefront, described by the

where C ₁ , C ₂ , C ₃ constant coefficients,
the focal spot on the square radiation receiver 8 is shifted (Fig. 3) so that the control signals V ₁ , V ₂ are supplied to the dynamic alignment head 5 in accordance with (5), (6). The radiation intensity in the center of the focal spot at the receiver 10 in this case decreases so that the control signal V ₃ is supplied to the adaptive mirror 4 in accordance with (7), (8). The dynamic alignment head 5 comprises a fixed base 17 (Fig. 5) with a support 18 and a piezoelectric actuator 19 mounted on it, on which a movable base 20 is located, and its connection with the support 18 is a ball joint. On the movable base 20 with the support 21 and the piezoelectric actuator 22, a movable mandrel 23 is likewise mounted in which the adaptive mirror 4 is fixedly fixed, the angle between the straight lines connecting the elements 18 and 19, 21 and 22 is 90 ^° . Piezoelectric actuators 19 and 22 are deformed under the influence of control signals V ₂ and V _1, respectively, so that the slopes of the reflective surface of the adaptive mirror 4 are described by functions S ₁ and S ₂
S ₁ = V ₁ • a ₁ • x (13)
S ₂ = V ₂ • a ₂ • y (14)
where f ₁ , a ₂ constant coefficients.

Значения коэффициентов усиления K₁, K₂, K₃ каналов усилителя-преобразователя 12 устанавливаются на этапе юстировки так, чтобы для некоторых пробных искажений (10),(12) выполнялись условия (19),(21), и, следовательно, (18), что соответствует плоскому волновому фронту выходного лазерного пучка и полной компенсации дефокусировки и наклонов.4-bimorph adaptive mirror with a control electrode in the form of a circle and response function f:
f = a ₃ (x ² + y ² ) (15)
where a ₃ constant coefficient;
is deformed under the influence of the control signal V ₃ so that its reflecting surface is described by the function S ₃
S ₃ = V ₃ f = V ₃ a ₃ • (x ² + y ² ). (16) phase Φ _neg. reflected from the adaptive mirror 4 of the laser beam (1) containing the slopes (10), (11) and the defocusing (12) of the wave front, is
Φ _neg = Φ _o + Φ ₁ + Φ ₂ + Φ ₃ -2K • cosθ _o • (S ₁ + S ₂ + S ₃ ), (17)
where θ is the angle of incidence of the laser beam on the mirror and for some values of the gain K ₁ , K ₂ , K ₃ in (5), (7) channels of the amplifier-transducer 12 is valid
v _neg = Φ _o (18)
at

The gain coefficients K ₁ , K ₂ , K ₃ of the amplifier-converter 12 channels are set at the adjustment stage so that for some test distortions (10), (12) conditions (19), (21) are satisfied, and, therefore, (18 ), which corresponds to a plane wavefront of the output laser beam and full compensation for defocusing and tilting.

выходные сигналы U₁,U₅ приемников излучения 8, 10 и, следовательно, управляющие сигналы динамической юстировочной головки 5 - V₁, V₂ и адаптивного зеркала 4 V₃ также изменяются со временем, при этом работа лазерного адаптивного модуля представляет собой итерационный процесс достижения условий (2),(4), соответствующих компенсации дефокусировки и наклонов волнового фронта выходного излучения.In the presence of tilts and defocusing of the wavefront in the laser beam (1), which change with time
Φ ₁ (t) = C ₁ (t) • x, (22)

the output signals U ₁ , U _{5 of} the radiation receivers 8, 10 and, therefore, the control signals of the dynamic alignment head 5 - V ₁ , V ₂ and the adaptive mirror 4 V ₃ also change with time, while the operation of the laser adaptive module is an iterative process of achieving conditions (2), (4), corresponding to compensation for defocusing and slopes of the wavefront of the output radiation.

Claims (1)

 An optical adaptive module containing a correction device, an electronic amplifier-converter, two radiation detectors located in the foci of the lenses, one of which is square, and a dot aperture is located in front of the other, and a beam-splitting system, while the outputs of the radiation receivers are connected to the input of the electronic amplifier-converter the outputs of which are connected to a corrective device, characterized in that the corrective device is made in the form of a dynamic alignment head and installed in adaptive mirror, the beam splitting system is made in the form of a rectangular prism, the first leg of which is located in the course of the beam reflected from the adaptive mirror, the lenses are located in the course of the beam, which passed through the second leg of the rectangular prism in the course of the beam reflected from it, the module is equipped with an input an optical window located in front of the adaptive mirror and an output optical window located in the course of the beam reflected from the first leg of the rectangular prism, while the optical windows are located in fully inserted housing.

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