RU2082263C1 - Method for driving self-limited-junction pulsed lasers - Google Patents

Abstract

FIELD: quantum electronics; development of pulsed lasers around vapors of chemical elements operating in self-heating mode. SUBSTANCE: method involves shaping one additional pulse along with each driving pulse in case definite conditions are satisfied. Novelty is that time position of additional pulse relative to driving pulse is varied starting from oscillating pulse origin towards preceding driving pulse; additional pulse DC voltage amplitude is chosen between 15 and 50% of driving pulse voltage amplitude. EFFECT: improved laser driving conditions. 2 dwg

Description

 The invention relates to the field of quantum electronics and can be used to create pulsed lasers for vapor of chemical elements.

A known method of excitation of pulsed lasers on self-limited transitions of vapors of chemical elements, which consists in the fact that the excitation of the active medium and heating of the active substance to the working temperature is carried out by periodically repeating high-frequency pulses, which, firstly, due to the energy released during the discharge in the gas mixture, produce heating of the active medium to operating temperature, and secondly, create an inverse population in the active medium [1]
This method of excitation is the easiest way to obtain vapors of the active substance and their excitation. However, this method implements a stationary laser mode and it is impossible to control the energy characteristics of laser generation (pulse repetition rate, average and pulsed power of laser radiation), since a change in the parameters of the pulse excitation necessary to control the energy characteristics of the generation leads to a violation of the thermal laser mode.

A known method of excitation of pulsed lasers on self-limited transitions, which consists in the formation of excitation pulses and additional pulses that do not cause generation [2]
This method allows stabilization of the output characteristics of laser radiation at a given level, but does not allow you to control the energy characteristics of the laser generation.

 The closest in technical essence to the proposed method is a method of excitation of pulsed lasers on self-limited transitions, operating in self-heating mode [3] consisting in the formation with each pulse of the excitation of an additional pulse with an adjustable delay between pulses.

This method was widely used to study the limiting energy characteristics of laser radiation, however, it also does not allow controlling the energy characteristics of laser generation. To ensure thermal operation of the laser, when two pulses are applied to the active medium, the following conditions must be met:
(E ₁ + E ₂ ) f P,
where E _{1 the} energy of the excitation pulse;
E ₂ energy of an additional impulse;
f repetition rate of the excitation pulses;
P the power required to heat the working volume of the laser and maintain it at operating temperature.

 An object of the present invention is to control the energy characteristics of a generation.

The solution of the technical problem is achieved by the fact that, like the well-known method of excitation of pulsed lasers at self-limited transitions operating in the self-heating mode, the proposed method consists in the formation with each excitation pulse of one additional pulse with an adjustable delay between pulses subject to the conditions:
(E ₁ + E ₂ ) f P,
where E _{1 the} energy of the excitation pulse;
E ₂ energy of an additional impulse;
f repetition rate of the excitation pulses;
P the power required to heat the working volume of the laser and maintain it at operating temperature.

 In contrast to the known method, in the proposed method, the temporary location of the additional pulse relative to the excitation pulse is changed from the moment the generation pulse starts to the side of the previous excitation pulse, while the voltage amplitude of the additional pulse is chosen constant within 15-50% of the amplitude of the excitation pulse voltage.

 The authors know how to excite lasers at self-limited transitions due to the formation of an excitation pulse and an additional pulse [2, 3] There is also a method for controlling the energy characteristics of generation (energy of the generation pulse and average generation power) by changing the amplitude of the excitation pulse during two-pulse excitation [4] the excitation method is not known, which makes it possible to control over a wide range from zero to a maximum value the energy characteristics of generation, such as a laser pulse energy, average power generation, power distribution lines between the generation and the repetition frequency of the laser pulse.

The main mechanism for creating an inverse population in lasers based on self-limited transitions of atoms of chemical elements is a higher excitation rate of the upper laser level than the lower one during the course of the excitation pulse. An important role in creating an inverse population is played by such plasma parameters as the concentration of atoms of the working substance n _a , the electron concentration n _e and the electron temperature _Te . The concentration of atoms of the working substance in self-heating lasers is determined by thermal heating of the working volume of the laser tube during the dissipation of gas discharge energy. According to Jerry's theory, the power of generation [5]
P _gene = [n _a n _e <σ ₁₃ ν _e > -n _a n _e <σ ₁₂ ν _e >] / 2, (1)
where <σ ₁₃ ν _e >, <σ ₁₂ ν _e > are the rates of excitation of the upper and lower laser levels by electron impact from the ground state. Excitation rates are directly related to the electron temperature, which is determined by the voltage applied to the laser tube. The maximum lasing power is realized at the maximum value of the first term and the minimum value of the second term of the given expression (1). In practice, this is achieved by optimizing the parameters of the excitation pulse. In pulse-periodic lasers operating with a high pulse repetition rate, the plasma does not have time to completely recombine. Therefore, before the excitation pulse there is a relatively high residual electron concentration, of the order of 10 ¹² 10 ¹³ / cm ³ . If we introduce an additional pulse before the excitation pulse, which, on the contrary, is optimized so that the second term is maximum and the first term of expression (1) is minimum, then inversion will not occur in the active medium when an additional pulse passes. Since the lower laser level in lasers at self-limited transitions is metastable, with a lifetime of the order of 10 ^-5 s, when an excitation pulse is applied immediately after an additional pulse, inversion will not occur in the active medium even if an excitation pulse is applied. If an additional pulse is placed in front of the excitation pulse with a delay equal to the settling time of the lower laser level, then this is equivalent to the initial condition (in the absence of an additional pulse or it is placed behind the generation pulse). In this case, the maximum energy of the generation pulse is realized. By changing the delay between the additional and exciting pulses, it is possible to control the energy characteristics of the generation from zero to the maximum value. It has been experimentally established that an additional pulse satisfies the above requirements with a voltage amplitude of a selectable constant within 15 50% of the voltage pulse amplitude of the excitation pulse. When the temporary location of the additional pulse gradually changes from the moment of the generation pulse to the side of the previous excitation pulse, the average generation power changes from the maximum value to zero and then increases from zero to the maximum value. In this case, the decrease in average power from the maximum value to zero occurs more sharply than an increase from zero to the maximum value.

 This is explained by the fact that in the first case, the change in average power occurs due to the population of the lower level during the passage of the additional pulse, and in the second case, the relaxation of the population of the lower working level after the passage of the additional pulse.

 The method can be implemented as follows.

 In FIG. 1 shows a block diagram of a device that implements this method, which depicts adjustable high-voltage power supplies 1, 2, a trigger pulse generator 3, switches 4, 5, delay lines 6, 7 (which can be used, for example, waiting multivibrators), a resonator 8, laser tube 9, charging inductance 10, working capacities 11, 12.

 The laser operates as follows.

 A working capacitance 11 is charged from an adjustable high-voltage power source 1, and a working capacitance is charged from an adjustable high-voltage power supply 2. Capacities are charged through a charging inductance 10. A triggering pulse generator 3 starts a switch 4 through a delay line 6, which generates excitation pulses on a laser tube 9 placed in the resonator 8. In parallel, the trigger pulse generator 3 through the delay line 7 (adjustable delay line) starts the switch 5, which forms on the laser tubes ke 9 additional impulse.

 Laser tuning is as follows.

Both power supplies 1, 2 are turned on, the working volume of the laser tube 9 is heated up to the working temperature, voltage, current, generation pulses, operating temperature are recorded using recording equipment. Using the delay line 7, the beginning of the additional pulse is combined with the moment of generation. Then, the laser is tuned for excitation, selecting the optimal parameters of the exciting pulse. After adjusting the laser for excitation, having received the maximum energy output from the laser tube, using an adjustable source 2 set the voltage amplitude of the additional pulse within 15 50% of the amplitude of the voltage of the excitation pulse. In this case, the condition must be fulfilled: (E ₁ + E ₂ ) f P, where E ₁ and E _2, respectively, are the energies of the additional and exciting pulses, f is the pulse repetition rate, P is the power h needed to heat up and maintain the working volume of the laser tube at the operating temperature . The fulfillment of this condition is necessary in order to maintain the thermal regime of the laser. By changing the delay (delay line 7), it is possible to control the energy characteristics of the generation from the maximum value to zero.

Practically the implementation of this method was carried out by the authors in a copper vapor laser. An UL-102 Quantum industrial laser tube was used as an active element, the working channel of which was made of alundum ceramics Al ₂ O _{3 with a} diameter of 20 mm and a length of 400 mm. Buffer gas pressure neon-400 Torr. The rated average power according to the manufacturer’s passport is 5 W on two generation lines (510.6 and 578.2 nm) at a pulse repetition rate of 8 kHz.

 The TGIZ-500/20 thyratrons were used as switches, and two waiting multivibrators, which were launched from a single generator, were used as delay lines.

 The operating voltage at the rectifier of the power source generating the excitation pulse was 5 kV, the operating capacitance was 3300 pF, the pulse repetition rate was 8 kHz, and the power consumption from the rectifier was 1.5 kW.

 The operating voltage at the rectifier of the power source forming the additional pulse was 750 V, the operating capacitance was 3300 pF, and the power consumption from the rectifier was 100 W.

 With these parameters of the exciting and additional pulses and the placement of the additional pulse at the time of the generation pulse, an average output power of 5 W was obtained on two generation lines (510.6 and 578.2 nm). When the delay was changed in the above range between the additional and exciting pulses, the average generation power and the generation energy in the pulse were controlled from the maximum value to zero. In this case, at the beginning, the generation energy decreases at a wavelength of 510.6 nm, then at a wavelength of 578.2 nm.

 When controlling a laser from a computer, it is possible to control the output parameters according to a predetermined law, for example, to change the repetition rate of the generation pulses, to carry out any sequence of generation pulses, to switch along the generation lines, to set a certain value of the generation energy per pulse, to control the average generation power, etc. d.

 In FIG. Figure 2 shows the dependences obtained during testing of the total average output power of a copper vapor laser and in each generation line (510.6 and 578.2 nm) on the time interval between the additional pulse and the excitation pulse. The origin from the moment the start of the generation pulse.

 This technical solution allows you to significantly expand the functionality of lasers on self-limited transitions.

 It is of interest in almost all areas where these lasers are used.

Claims (1)

The method of excitation of pulsed lasers at self-limited transitions operating in the self-heating mode, which consists in the formation with each pulse of the excitation of one additional pulse with an adjustable delay between pulses, while observing the condition
(E ₁ + E ₂ ) _f P,
where E _{1 the} energy of the excitation pulse;
E ₂ energy of an additional impulse;
f repetition rate of the excitation pulses;
P the power required to heat the working volume of the laser and maintain it at operating temperature,
characterized in that the energy characteristics of the generation are controlled by changing the temporal location of the additional pulse relative to the excitation pulse from the moment the generation pulse starts to the side of the previous excitation pulse, while the voltage amplitude of the additional pulse is chosen constant within 15-50% of the amplitude of the excitation pulse voltage.

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