RU2177274C2 - Method for device for modulation of laser radiation - Google Patents

Abstract

FIELD: medical equipment for use in laser surgery. SUBSTANCE: method consists in production of pulsed-alternating generation in a laser radiation generator by placement of electron-mechanical interruption between the blind mirror of the resonator and the quadroon in the same optical axis. The pulse repetition frequency is selected up to 200 Hz with a frequency control discreteness of 10 Hz. The duration of operation of an open resonator is selected within K = t_gen/t_int= 15, where t_gen- time of generation, t_int-time of interruption that is ensured by production of the electron-mechanical interrupter in the form of a unit laser radiation generator coupled to the output of the power unit and consisting of a DC motor, whose shaft carries the interrupter representing a semi-circular flat plate with an operation indicator, the relation between whose are and the full circumference makes up 1: 15. The generator power unit is connected to the ignition unit connected to the laser radiation generator, which incorporates the quadroon with the pumping lamp. EFFECT: optimized condition of modulation for biologic tissues of various types, prevented excessive heating of their boundary edges and charring during surgical operation. 2 cl, 6 dwg

Description

 The invention relates to medical instrumentation and is intended for use in laser surgery for the treatment of cancer of various organs.

 A known method of pumping laser radiation, carried out by the device of the power supply SPIK-1, in which the lamp of the generator is ignited by supplying short high-voltage pulses of 25-30 kV, supplying a supply voltage of 1500 V to form a stable arc in the lamp, supplying power to the lamp. When the voltage to the lamp changes, the current passing through it changes, and when the pump current increases, generation appears at the output of the emitter (Power supply, testing and monitoring system of the emitter SPIK-1. Passport URM 2.625.004 PS).

 The disadvantages of the continuous method of pumping laser radiation is the limited range of the continuous mode, since during processing of the material, including biological tissues, the boundary edges overheat and break their structure. When using a continuous pump mode with stepwise adjustment of power, it is impossible to obtain stable parameters of laser radiation due to a decrease in energy parameters during lamp operating hours.

 As a prototype of the proposed method and device, a method for pumping a lamp of a laser radiation generator and a device for its implementation are considered (RU 2110382 C1, 05/10/98). The modulation of laser radiation in the known method is carried out in a pulsed-alternating mode of generation, as a result of ignition of the pump lamp of the laser radiation generator, the formation of an arc and the supply of an adjustable voltage to the lamp. The known circuit includes a power supply connected to the ignition unit, also a laser radiation generator including a quantron with a pump lamp.

 A disadvantage of the known device is a small gradation of frequencies and a purely pulsed pump and radiation mode. When a radiation pulse is exposed to biological tissue, the main longitudinal modes vaporize the cells without forming combustion products due to the high energy density at the peak of the pulse. The transverse modes present in the pulse heat the tissue to a combustion temperature (carbonization), since it has a lower energy density. Due to the high energy in the pulse, the boundary edges of the biological tissue overheat.

 The present invention is aimed at eliminating these disadvantages by eliminating overheating of the edges of the tissue during the surgical operation, and also to select the desired exposure mode, taking into account the type of tissue by choosing the modulation mode.

где t_ген - время генерации;
t_пр - время прерывания,
при этом t_ген + t_пр = Т, где Т - период лазерного извлечения.The essence of the invention lies in the fact that in the method of modulating laser radiation, carried out by igniting the pump lamp of the laser radiation generator, forming an arc and applying a regulating voltage to the lamp to obtain a pulse-variable generation mode. The resonator of the pump lamp is modulated by an electronic-mechanical chopper with a pulse repetition rate of up to 200 Hz and a frequency resolution of 10 Hz, while the duration of the open resonator is selected within a constant value

where t _gene is the generation time;
t _CR - time interruption,
wherein t _gene + t _CR = T, where T is the period of laser extraction.

 The task is also achieved by the fact that in the device for modulating laser radiation containing a generator power supply unit connected to the ignition unit, and a laser radiation generator including a quantron with a pump lamp, between a blind mirror of the resonator and a quantron, on the same optical axis as the output a mirror, a breaker is placed.

 The chopper is made in the form of a semicircular flat plate with a flag fixed on the DC motor shaft to ensure the plate is balanced during rotation of the motor shaft, and the ratio of the length of the arc that the flag occupies to the full circle described by this chopper in one revolution is 1:15. The chopper and the DC motor constitute an electronic-mechanical chopper, the input of the power supply unit of which is connected to the output of the power supply unit of the laser radiation generator.

 The invention is illustrated by drawings, where in FIG. 1 is a graph of a relaxation-vibrational regime of generating electromagnetic waves in a resonator; FIG. 2 is a graph of energy redistribution in the resonator; FIG. 3 shows a block diagram of a device; FIG. 4 shows the distribution of radiation power over the diameter of the beam at various pumping modes; FIG. 5 shows an electronic-mechanical chopper; FIG. 6 - chopper plate.

 A device for creating modulated laser radiation contains a series-connected power supply unit of the generator 1, an ignition unit 2 and a laser radiation generator 3, including a quantron 4, a blank 5 and an output 6 mirror, as well as a series-connected electronic-mechanical chopper 7 and a power supply unit of the chopper 8 moreover, the input of the chopper power supply unit is connected to the output of the generator power supply unit, and the chopper is installed between the blind mirror and the quantron on the same axis as the output mirror.

 Quantron 4 consists of a load block 9 (pump lamp), designed to excite quanta and the occurrence of spontaneous emission of excited active particles in the active element 10 (Fig. 3). Lamp pump power - minimum 3 kW, maximum 7 kW.

 The blind and output mirrors are a resonator that provides the buildup of oscillations with frequencies within the width of the gain line of the active medium and the output of a part of the excited electromagnetic wave to the outside through the output mirror.

 The electronic-mechanical chopper consists of a DC motor 11 with a chopper mounted on its shaft 12 in the form of a semicircular flat plate 13 with a flag 14, and the ratio of the length of the arc that the flag occupies to the full circle described by this chopper in one revolution is 1:15 .

 The laser radiation generator is a self-oscillating system with positive feedback, the generation of electromagnetic oscillations in which is due to coherent amplification as a result of induced quantum transitions. The resonator, consisting of one deaf 4 (opaque) mirror and an output 3 (translucent) mirror located parallel to it, oscillates with frequencies within the width of the gain line of the active element and outputs a part of the excited electromagnetic wave to the outside through the output mirror.

 The proposed device implements a method for modulating laser radiation, which consists in igniting a lamp, generating radiation with a continuous generation mode and implementing a modulation mode.

 The laser lamp is ignited in several stages.

 At the first stage, energy is accumulated in the power source of the generator 1 up to 1000 V, in the ignition unit 2 a short high-voltage pulse with a voltage of 18-25 kV is formed. There is a discharge of energy stored in the generator power source.

 Next, the power source of the generator is switched to the stabilization mode of the current of the pump lamp 9 of the laser radiation generator. Inside the generator, radiation with a continuous mode of generation is formed.

где t_ген - время генерации,
t_пр - время прерывания,
при этом t_ген + t_пр = Т, где Т - период лазерного излучения.To ensure the modulation mode, an electronic-mechanical chopper is switched on, which converts the continuous mode of generation into a pulse-periodic mode inside the resonator with a duty cycle of the generator within a constant value of K = 15 while maintaining a constant value of the pulse repetition rate of laser radiation up to 200 Hz, selected from the relation:

where t _gene is the generation time,
t _CR - time interruption,
wherein t _gene + t _CR = T, where T is the period of laser radiation.

 The pulse repetition rate of laser radiation can be adjusted up to 200 Hz. The adjustment is carried out by applying a stabilized voltage to the DC motor from the generator 8, which generates a constant stabilized voltage of various sizes. As you know, when a different voltage is applied, the rotation speed on the motor shaft changes.

 To accurately set the shaft speed, a stabilized voltage is selected for any type of electric motor.

 When you turn on the block of the electronic-mechanical chopper 7 carry out alternate interruption in the optical axis of the resonator with an interruption frequency of up to 200 Hz, and the open resonator time is 15 times longer than the closed one.

 When the resonator closes with an electronic-mechanical chopper, no laser radiation is emitted through the output mirror. At the same time, ions are excited in the body of the active element and their transition to a higher energy level.

 At the moment of opening of the resonator by an electronic-mechanical chopper, the process of buildup of generation occurs. The frequency of stimulated transitions is compared with the excitation rate of the upper laser level, due to which the field intensity begins to grow like an avalanche.

 The value of the laser radiation energy at this moment reaches its maximum value.

The energy value at the chopper is: E _ave = 0,98E _n where E _n - laser energy when operating in a continuous mode. The ratio of the duration of the resonator (open) to the duration of the closed resonator is 15/1, i.e. this is 6.25% of the energy loss, if the chopper was not in the cavity, then it would be a attenuator and the attenuation was 6.25%. E _donkey = 0.9375E _n , where E _donkey is the energy of the attenuator.

Thus, E _eff = (0.98 - 0.93) E _n ~ 0.05 E _n , where E _ef is the effective energy obtained when using the chopper. From the graph (Fig. 2) it can be seen that the resonator operating in the interrupt mode with variable time parameters emits less average energy in time than in the continuous pump mode: E _n > E _pr - the value is unchanged in the entire range of laser pulse repetition frequencies radiation up to 200 Hz and is 98% of E _n .

 The emitter operates in the mode of pulsed excitation, which lasts, as a rule, for more than 1 μs and is the so-called “peak generation mode”.

From the graph shown (Fig. 1) it is seen that despite continuous excitation throughout the entire light pulse of the pump pulse with an intensity of 1 _n (1 _n is the pump current through the lamp), the laser radiation appears after some delay time and has the form of individual spikes with a characteristic duration of 1 μs and 10 μs intervals between them. The main processes responsible for the spike nature of the generation of solid-state lasers include the so-called relaxation-vibrational mode of generation of electromagnetic waves in the cavity.

 The proposed pump method, without generating large peak values of the pulse energy due to the modulation of the resonator by an electronic-mechanical chopper, makes it possible to form a series of radiation spikes that are adjustable both in duration and in frequency, which allows not to bring the temperature of the boundary layers of the fabric, which are affected by transverse modes , to the temperature of thermal destruction (carbonization) and stimulates the coagulation process.

 The experimental results were used to create a device that provides a contact method for dissecting tissues to any depth and tissues of various structures and densities with a laser beam emanating from a solid-state Nd: YAG laser. The design of the device took into account all the basic requirements for devices for this purpose: radiation wavelength - 1064 nm; power regulation range - 0 ... 100 W; radiation divergence - 3 ... 5 m rad; pulse repetition rate - 0 ... 200 Hz; frequency regulation resolution - 10 Hz.

The choice of modulation modes for various biological tissues is illustrated by the following examples:
Example 1

 The pulse repetition rate f = 70 Hz.

 The period of laser radiation is T = 14.2 μs (T = 1 / f = 1/70 = 0.0142 s or 14.2 μs).

Generation time t _gene = 14/15 x 14.2 μs = 13.25 μs.

Interruption time t _CR = 1/15 x 14.2 μs = 0.95 μs.

 Example 2

 The pulse repetition rate from f = 70 Hz to 140 Hz is the processing of medium-density tissues.

 The pulse repetition rate f = 140 Hz.

 The period of laser radiation is T = 7.1 μs (T = 1 / f = 1/140 = 0.0714 s or 7.14 μs).

Generation time t _gene = 14/15 x 7.1 μs = 6.63 μs.

The interruption time t _CR = 1/15 x 7.1 μs = 0.47 μs.

 Example 3

 The pulse repetition rate from 140 Hz to 200 Hz - soft tissue processing.

 The pulse repetition rate f = 200 Hz.

 The period of laser radiation is T = 5 μs (T = 1 / f = 1/200 = 0.005 s = 5 μs).

Generation time t _gene = 14/15 x 7.1 μs = 6.63 μs.

The interruption time t _CR = 1/15 x 7.1 μs = 0.47 μs.

 The use of laser beam exposure on the proposed device will increase the effectiveness of cancer treatment, having a strong effect on the tissue of malignant tumors and minimal on healthy tissue.

 A large range of regulation of the pulse repetition rate up to 200 Hz with a resolution of 10 Hz will significantly expand the application of various surgical procedures.

Claims (2)

1. A method of modulating laser radiation by igniting a pump lamp of a laser generator, forming an arc and applying an adjustable voltage to the lamp to obtain a pulse-variable generation mode, characterized in that the pump lamp cavity is modulated by an electronic-mechanical chopper with a pulse repetition rate of up to 200 Hz and discreteness of frequency regulation 10 Hz, while the duration of the open resonator is chosen within a constant value K = t _gene / t _CR = 15, where t _gene is the generation time, t _CR is the time interruptions, and t _gene + t _pr = T, where T is the period of laser radiation.  2. Device for modulating laser radiation, comprising a generator power supply unit connected to the ignition unit and a laser radiation generator including a quantron with a pump lamp, characterized in that between the blind mirror of the resonator and the quantron, on the same optical axis with them and an output mirror a breaker made in the form of a semicircular flat plate with a flag, the ratio of the arc length of which to the full circle is 1:15, mounted on the shaft of the DC motor with the formation of electric Ronno-mechanical switch having an input coupled to the output power supply unit of the laser radiation generator.

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