JP3014593B2 - Pulse laser oscillation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse laser oscillation device, and more particularly, to an improvement for improving the efficiency and output of pulse laser oscillation.

[0002]

2. Description of the Related Art FIG. 15 shows, for example, Japanese Patent Publication No. 63-64065.
Excimer laser (XeCl, KrF,
FIG. 1 is a schematic block diagram showing a conventional pulse laser oscillation device such as an ArF or the like, a TEACO ₂ laser, an N ₂ laser or the like. In the figure, reference numeral 1 denotes a case in which a laser gas is sealed; A first main electrode for generating a discharge,
Reference numeral 3 denotes a second main electrode facing the first main electrode, 4 denotes a laser medium exciting portion generated by electric discharge between the first main electrode 2 and the second main electrode 3, and 5 denotes a first main electrode 2 and a second main electrode. A discharge excitation circuit for applying a voltage between the two main electrodes 3 to start a discharge and supplying excitation energy to form a laser medium excitation section 4; 6, a laser gas is sealed in the housing 1; And a laser light transmission window for extracting laser light, 7 and 8 are total reflection mirrors and partial reflection mirrors each constituting a resonator for amplifying the laser light, and 9 is laser light extracted from the resonator.
Is an effective gain length representing a substantial discharge length contributing to amplifying the laser light, and Lc is a resonator length representing a distance between the total reflection mirror 7 and the partial reflection mirror 8.

[0003] Next, a typical excimer laser, XeC
The operation in the case of 1 laser will be described. Xe, which is a source of a laser medium forming an upper level in the housing 1,
A laser gas composed of HCl and Ne as a buffer gas is sealed at a high pressure of about 2 to 6 atm. First, the first main electrode 2 and the second main electrode 3 are operated by the operation of the discharge excitation circuit 5.
During this time, a voltage is applied. When this voltage reaches the discharge starting voltage, breakage occurs between the main electrodes 2 and 3, and an excitation discharge is formed by energy injected from the discharge excitation circuit 5. In order for this excitation discharge to be performed uniformly between the main electrodes 2 and 3,
It is necessary that the laser gas be pre-ionized over the entire region at an electron density of 10 ⁵ to 10 ⁸ / cm ³ . Means for performing preionization include arc discharge,
Alternatively, a method of irradiating ultraviolet rays generated from corona discharge to a region between the main electrodes or a method of irradiating X-rays is generally used. By the way, in the homogeneously formed excitation discharge, XeCl * (where * represents an excited state; the same applies hereinafter), which is a laser medium, is efficiently generated at a higher level, and the so-called inversion occurs. The laser medium excitation section 4 in the distribution state is formed. Then, XeCl * falls to the lower level due to the interaction (stimulated emission) with the light field, and XeCl *
In the process of dissociation into e and Cl, light is emitted in phase with the light field. This light is reflected by a total reflection mirror 7 and a partial reflection mirror 8 provided outside the housing 1 through a laser light transmission window 6 and is amplified by repeatedly passing through the laser medium excitation unit 4. A strong laser beam 9 of MW / cm ² or more is taken out from the partial reflecting mirror 8.

FIG. 16 shows a discharge excitation circuit 5 applied to a XeCl laser.
The document “Laser Research, Vol. 20, No. 38 (1992)
) Is applied to the pre-pulse / PFN circuit shown in FIG. The pre-pulse / PFN circuit separates a first discharge circuit 12 (pre-pulse circuit) for starting discharge between the first and second main electrodes and a second discharge circuit 13 (PFN circuit) for injecting energy. Circuit. Here, the first discharge circuit 12 includes a high-voltage circuit necessary for starting discharge, and supplies the minimum energy required for causing uniform discharge in terms of energy. On the other hand, the second discharge circuit 13 has the same internal impedance as the discharge resistance between the main electrodes (approximately several ohms) which drops extremely after the start of the excitation discharge, and is large by impedance matching. The excitation energy is efficiently input to the discharge field. As a result, there is a feature that the population inversion can be efficiently formed by combining the two discharge circuits separated in function.

FIG. 17 shows the stored energy Eexc at the upper level of 1 in the pre-pulse / PFN circuit device.
An example is shown in which a small signal gain per unit length that is generated when 3.4 × 10 ⁻³ J of energy is applied per cm ³ is calculated. From the population inversion (that is, the generated gain) formed in the laser medium excitation section 4, the laser light 9 is efficiently emitted.
In order to extract the effective gain length, the effective gain length L and the resonator conditions (specifications such as the curvature and reflectance of the total reflection mirror and the partial reflection mirror, and the resonator length Lc) are important. Now, from the viewpoint of increasing the output per pulse of the laser beam, the effective gain length L
Is sequentially increased to 1 m, 2 m, and 3 m. At this time, it is assumed that the length of each resonator is 1.5 m, 3.0 m, and 4.5 m, which is 1.5 times the effective gain length L, for the sake of manufacturing the device. It is assumed that the reflectance of the total reflection mirror is 100%, and the reflectance R of the partial reflection mirror is 30%, 10%, and 5%, which are almost optimum values for the effective gain length L, respectively.

FIGS. 18 (a), 18 (b) and 18 (c) show calculation results of a gain waveform and a laser output waveform during laser oscillation at each effective gain length L based on the small signal gain shown in FIG. Each is shown. As is clear from the figure, after a gain occurs in the pulse laser, laser oscillation starts with a certain delay.
This is the time it takes for the gain value to reach the oscillation threshold,
Even after the threshold value is reached, the light intensity at which the seed light generated by spontaneous emission is efficiently extracted from the population inversion state by stimulated emission (that is, the saturation intensity required to saturate the gain, MW / cm ^{2 for} excimer laser) Of the order). In addition, since the gain waveform is always fluctuating even after the laser light rises, the gain is not fixed to a value completely determined by the resonator loss unlike a continuous wave laser, and the gain converges to that value. , But always maintains a higher value.
The gain during these oscillations is not taken out of the resonator as laser light, but becomes a loss energy in the form of collision in a laser gas or spontaneous emission.

FIG. 19 shows a calculation result in which the gain waveform g (t) at the time of laser oscillation at each effective gain length L is shown on the same figure. Further, FIG. 11 also shows the result obtained by integrating the gain waveform over time according to the following equation and expressing the result as an average loss energy E _LOSS per unit volume (1 cm ³ ).

E _LOSS = (∫g (t) dt) × Is (1)

Here, Is is the saturation intensity of the XeCl laser. As can be seen from the relationship between the laser output waveforms shown in FIG.
It is in the range of 03 ns to 111 ns, and the longer the effective gain length L tends to be, the smaller the difference is. This is because the gain hardly saturates until the laser light rises, so that the laser light increases exponentially by propagating in the laser medium pumping section 4, whereas the effect of increasing the effective gain length is This is because only the effect of increasing the initial light intensity by that amount (that is, when the effective gain length is tripled, the initial seed light intensity triples) appears. For this reason, the loss of the gain that cannot be taken out until the start of laser oscillation is almost constant per unit effective gain length, and is substantially proportional to the effective gain length in total.

On the other hand, the loss after the start of laser oscillation is determined by the oscillation threshold L per unit effective gain length determined by the resonator configuration.
og (R) ^-1/2 / L is reduced as the effective gain length is increased. From the above results, in the same discharge section, the effective gain length is increased from 1 m to 3 m under a constant power density.
When the effective gain length is longer, the loss energy per unit length is reduced as the effective gain length is longer, and the total oscillation efficiency is increased. In the example shown here, a laser output of 0.158 J / cm ² is obtained at an effective gain length of 1 m, whereas it is 0.507 J / c at an effective gain length of 3 m.
An output of m ² is obtained. This means that considering that the input energy density is constant, increasing the input three times resulted in a 3.2 times higher laser output, that is, 1.07 times the efficiency. This means that it has increased.

However, it is a problem that the loss energy until the start of laser oscillation increases almost in proportion to the effective gain length. If this relationship can be improved, higher output and efficiency can be obtained by increasing the effective gain length. You can do it. In addition, the loss energy until the start of laser oscillation increases more remarkably when the ratio of the resonator length Lc to the effective gain length L is increased for convenience in manufacturing the device. In the case of an excimer laser using the pre-pulse / PFN circuit shown here, a constant energy is applied to a long pulse (generally, 100 pulses).
(ns or more) and injected into the laser medium pumping section, the average gain is lower than in the case of conventional short pulse (pulse length of less than 100 ns) pumping, and the rise time until oscillation becomes longer. There is a problem that the loss greatly affects the laser output.

When the effective gain length L is long and the loss energy until the start of oscillation is large, as a method of reducing this, the laser medium pumping section is divided into two or more parts, and one is taken out as an oscillator and the other as an amplifier. Has been done. FIG. 20 shows an example in which the pumping section is divided into a first oscillating stage and a second oscillating stage, and the former is an oscillator and the latter is an amplifier to extract laser light. The housing, the second oscillation stage housing, 2a, 2b are the first oscillation stage first main electrode, the second oscillation stage first main electrode, 3a, 3b are the first oscillation stage second main electrode, the second oscillation, respectively. The second stage main electrodes, 4a and 4b, respectively, are the first oscillation stage laser medium excitation section, the second oscillation stage laser medium excitation section, 5a, 5b are the first oscillation stage discharge excitation circuit, the second oscillation stage discharge excitation circuit, respectively. L1 and L2 denote a first oscillation stage effective gain length, a second oscillation stage effective gain length, 14 denotes a delay pulse generator, 15 denotes a first oscillation stage operation pulse, and 16 denotes a second oscillation stage operation pulse.

Next, the operation will be described. The first oscillation stage operation pulse 15 is sent from the delay pulse generator 14 to the first oscillation stage. Based on this, the first oscillation stage is operated by the same process as that of the above-described conventional example (FIG. 15), and the first oscillation stage laser medium excitation section 4a is started. As a result, the second oscillation stage laser medium pumping section 4b rises when the laser beam 9 from the first oscillation stage rises and forms a population inversion. The second oscillation stage operation pulse 16 is sent to operate the second oscillation stage. The operation pulse of the second oscillation stage is the same as that of the conventional example. When the laser beam 9 is sent from the first oscillation stage in the process of rising the laser medium pumping section 4b of the second oscillation stage, this light is transmitted to the second oscillation stage. The gain of the stage is saturated, the intensity is increased, and the amplified laser light 17 is extracted from the second oscillation stage.

When the laser light is extracted in such a configuration, there is an advantage that the laser light can be extracted from the rising portion of the gain of the second oscillation stage by optimizing the setting of ΔT. On the other hand, when the first oscillation stage and the second oscillation stage are excited from a discharge excitation circuit having the same circuit constant, as is clear from the relationship between the gain waveform and the laser output shown in FIG. Since the oscillation duration of the laser output extracted from the first oscillation stage is always shorter than the gain waveform, there is a problem that the gain of the second oscillation stage cannot be extracted after the laser output from the first oscillation stage is completed. Further, the gain g (t) at a certain time and the light intensity I (t) existing at the place are as follows.

G (t) = g0 (t) / (1 + I (t) / Is) (2) (where g0 is a small signal gain)

The relationship is as follows. In order to efficiently extract laser light from the laser medium in the population inversion state by stimulated emission, a strong light intensity I that is three to four times or more the saturation intensity Is with respect to the small signal gain g0 (t) generated by the discharge. To give the gain g (t) from g0 (t) / 4 to g0 (t) /
It must be saturated to 5 or more. However, when the intensity of the laser beam 9 sent from the first oscillation stage is low, the gain generated in the second oscillation stage laser medium pumping section 4b cannot be sufficiently saturated, and the laser beam cannot be efficiently extracted. However, there is a problem that is reduced. Further, there is a problem that the laser output greatly depends on ΔT, and the jitter in the delay operation time ΔT must be kept small (for example, on the order of ns) in order to stabilize the laser output.

As means for improving the output characteristics in a long discharge length and a long resonator length, a discharge excitation unit is provided in a resonator comprising a set of a total reflection mirror and a partial reflection mirror in a first oscillation stage and a second oscillation stage. For example, when the discharge excitation unit of the first oscillation stage is started, and then the second discharge excitation unit is started after the delay time ΔT, compared to the case where the two units are started simultaneously. Increasing laser output is due to the 40th Annual Meeting of the Japan Society of Applied Physics, 30p-Z-8, 98
1 (1993). FIG. 21 is a diagram showing this basic configuration. Compared with the configuration in the case of the amplification shown in FIG. 20, the installation position of the partial reflecting mirror 8 is not between the first oscillation stage and the second oscillation stage, but in the second oscillation stage. The difference is that it is installed outside. The operation process is basically the same as that of the case of the amplification described above, except that the laser light is not always started by the first oscillation stage, and therefore the gain of the second oscillation stage is also reduced. Used for launching.

FIG. 22 shows the results of evaluation by calculation of the relationship between the laser output and the delay operation time in the configuration shown in FIG. Here, it is assumed that the effective gain length L1 of the first oscillation stage is 1 m, the effective gain length L2 of the second oscillation stage is 2 m, and the resonator length Lc is 5.2 m. As is clear from this, in the case where the delay operation time ΔT is increased in one resonator configuration, the result is that the laser output monotonously decreases. FIG. 23 shows the results of the same calculation to evaluate the average gain waveform per unit effective gain length and the temporal change of the laser output when the delay operation time is 0 ns, 125 ns, and 200 ns. It can be seen that the increase in the delay operation time delays the time until the start of laser oscillation, and the increase in the oscillation pulse width also increases the loss energy during laser oscillation and monotonically decreases the laser output. Therefore, even if the delay operation is performed in the configuration shown in FIG. 21, it cannot be concluded that the laser output increases simply from the relationship between the gain and the laser output. As pointed out in the previous proceedings, it is necessary to consider other models such as the second oscillation stage being preionized due to the presence of the first oscillation stage and stabilization of discharge. In any case, in this case, there is no improvement measure for extracting the loss energy until the start of oscillation.

[0019]

Since the conventional pulse laser oscillation device is configured as described above, if an attempt is made to increase the output due to an increase in the effective gain length, the loss energy generated before the start of oscillation will be reduced to resonance. There was a problem that the length increased almost in proportion to the increase in the vessel length. This loss increases greatly when the ratio of the resonator length to the effective gain length is increased. On the other hand, the loss up to the start of oscillation has a particularly large effect when excitation is performed with a long pulse and low gain using a pre-pulse / PFN circuit. Also, when light is to be extracted by amplification by dividing the effective gain length, when the oscillation stage having the same configuration is used, a part of the gain of the amplification stage cannot be extracted, and the efficiency is reduced. Was. Further, there is a problem that the delay operation time ΔT has a large dependence on the laser output, and the system jitter in the delay operation must be reduced. Further, there is a problem that light cannot be efficiently extracted when the intensity of light entering the amplification stage is low. Furthermore, in the case where the discharge section is simply divided and the delay operation is performed on one of the discharge excitation sections, there is a problem that there is essentially no effect of reducing the loss energy until the start of oscillation.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and effectively extracts the generated gain in a system in which the effective gain length of a pulse laser is extended.
It is an object of the present invention to provide a high-efficiency and high-output pulse laser device.

[0021]

According to a first aspect of the present invention, there is provided a pulsed laser oscillation device comprising: a laser medium excitation section having a population inversion required for laser oscillation; In a pulse laser oscillation device provided with a total reflection mirror and a partial reflection mirror arranged, the laser medium exciting unit is divided into two or more regions,
At least one or more internal mirrors are provided between the laser medium excitation sections divided into two or more, and the total reflection mirror and the internal mirror are provided.
The laser medium excitation section in the region sandwiched by the mirror
In the area between the internal mirror and the partial reflecting mirror.
Laser medium excitation section as the second oscillation stage,
Before and after the laser beam rises to saturation intensity
So that the laser excitation medium part of the second oscillation stage excites
By operating the second oscillation stage with a delay for a predetermined time, the laser medium excitation section in the region sandwiched by the internal mirror and the partial reflection mirror is excited by the laser medium excitation in the region sandwiched by the internal mirror and the total reflection mirror. And means for forming a population inversion state with a delay of a certain time as compared with the section. That is, in the pulse laser oscillation device according to the present invention, at least the laser medium excitation unit has at least two laser resonators in comparison with a normal resonator configuration including a total reflection mirror and a partial reflection mirror opposed to each other with the laser medium excitation unit interposed therebetween.
An internal mirror that is divided into at least one region and has a fixed ratio of transmission of at least one or more laser beams between the divided laser medium excitation sections, and is partially reflected by the internal mirror. The laser medium excitation section in the region surrounded by the mirror is operated at least after a certain operation delay time ΔT with respect to the laser medium excitation section surrounded by the total reflection mirror and the internal mirror.

According to a second aspect of the present invention, there is provided a pulse laser oscillation apparatus according to the first aspect, wherein
The effective gain length in the laser oscillation optical axis direction of the laser medium pumping section interposed between the internal mirror and the partial reflection mirror is smaller than the effective gain length of the laser medium pumping section interposed between the internal mirror and the total reflection mirror. They are almost equidistant or long.

According to a third aspect of the present invention, in the pulse laser oscillator of the first or second aspect, the reflectance of the partial mirror is equal to the reflectance of the inner mirror, or It is small.

According to a fourth aspect of the present invention, there is provided a pulse laser oscillation apparatus according to any one of the first to third aspects, wherein the first and second main electrodes opposed to each other in the pulse laser gas. A discharge excitation circuit for initiating a discharge between the main electrodes and supplying discharge energy, wherein the laser medium excitation section is formed by the discharge generated between the main electrodes.

According to a fifth aspect of the present invention, there is provided a pulse laser oscillation apparatus according to the fourth aspect, wherein
The discharge excitation circuit comprises a first discharge excitation circuit for starting discharge and a second discharge excitation circuit for supplying energy.

[0026]

In the pulse laser oscillator according to any one of the first to fifth aspects of the present invention, a laser beam is first started in a laser medium excitation section sandwiched between a total reflection mirror and an internal mirror.
At the timing before and after the rise of the laser light, the laser medium excitation section in the region sandwiched between the internal mirror and the partial reflection mirror is activated. As a result, in the latter region, the laser light can be effectively extracted from the rising portion of the gain, and at the same time, a part of the light going out of the resonator is returned to the resonator and amplified by the partial reflecting mirror. Therefore, even in the case of weak input light, the gain in the latter region is completely saturated, and oscillation can be continued as long as pumping is performed, so that the laser light can be efficiently emitted from the population inversion formed in the laser medium pumping section. Can be taken out.

[0027]

【Example】

Embodiment 1 FIG. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 18 denotes an internal mirror partially transmitting laser light.

Next, the operation of this embodiment will be described.
In this embodiment, the opposing first main electrodes 2 shown in FIG.
And the second main electrode 3 are divided into two, a first oscillation stage main electrode pair 2a, 3a and a second oscillation stage main electrode pair 2b, 3b, as shown in FIG. 1a, and is installed in the laser gas in the second oscillation stage housing 1b. Here, the cross-sectional shape of the main electrode pair has substantially the same dimension in the first oscillation stage and the second oscillation stage. The first oscillation stage operation pulse 15 is sent from the delay pulse generator 14 to the first oscillation stage. With this pulse, the laser medium excitation section 4a rises in the first oscillation stage by the process described in the conventional example, and a population inversion is formed. The light converted into laser light by stimulated emission reciprocates mainly between the total reflection mirror and the internal mirror and grows into laser light exceeding the saturation intensity Is. Before and after the laser light from the first oscillation stage rises until reaching the saturation intensity, the second oscillation stage laser medium excitation section 4
The second oscillation stage operation pulse 14 is sent with a delay of a predetermined time ΔT with respect to the second oscillation stage so that b starts discharging, and the second oscillation stage is started up in the same process as the first oscillation stage. . In the second oscillation stage, light exceeding the saturation intensity is sent from the first oscillation stage to the second oscillation stage from the time when the laser medium excitation section 4b starts to rise, so that the population inversion (that is, the gain) that rises in the second oscillation stage. Can be efficiently extracted from the beginning as a laser beam. The process up to this point is similar to the amplification shown in the conventional example, but in the case of amplification, the light passes through the second oscillation stage in one pass as it is. However, in the present invention, a part thereof is further returned to the second oscillation stage and the first oscillation stage by the partial reflecting mirror 8. Thereby, even when the laser beam sent from the first oscillation stage is weak to some extent, the gain in the second oscillation stage can be sufficiently saturated. Further, even when the laser beam sent from the first oscillation stage is terminated while the gain of the second oscillation stage is being generated, the total reflection 7, the internal mirror 18, and the partial reflection mirror 8
Oscillation is continued to the end by the composite resonator formed between the two, and the gain generated in the second oscillation stage is efficiently extracted. As a result, the energy loss before the oscillation starts can be suppressed to a value corresponding to that in the first oscillation stage, and other gains can be almost converted to laser light except for the resonator loss energy determined by the resonator. .

FIG. 2 shows the result of calculating the laser output with respect to the delay operation time in the configuration of this embodiment.
Here, the waveform shown in FIG. 17 is given as the small signal gain per unit length. The effective gain length L1 of the first oscillation stage is 1 m, the effective gain length L2 of the second oscillation stage is 2 m, the resonator length Lc is 5.2 m, and the reflectance R2 of the internal mirror 18 is 30.
%, And the reflectance R of the partial reflecting mirror 8 is 5%. FIG. 11 also shows the result of performing a delay operation on the conventional resonance configuration shown in FIG. As is clear from the figure,
There is an optimal value of 125 ns for the delay operation time, but 1
The results show that the output dependence is small in the range of 00 ns to 150 ns. This characteristic means that the jitter of the first oscillation stage and the second oscillation stage does not need to be extremely small as in the conventional device in order to stabilize the laser output. The benefits. The reason why the output dependency on the delay operation time is small in this embodiment is that the resonator is basically formed also in the second oscillation stage, and after the light rises, the laser light from the first oscillation stage is not affected. This is because the gain of the second oscillation stage region can be drawn out even if there is no temporal overlap. In this embodiment, the laser output is increased by about 10% with respect to the conventional resonator configuration without the internal mirror. The degree of improvement of the output characteristics becomes remarkable in a system in which the resonator length is long and the loss energy until the start of oscillation is large.

FIG. 3 shows output characteristics with respect to delay operation time when an experiment was conducted under the conditions of the effective gain length and the resonator length. However, the reflectance R2 of the inner mirror is 40%, the reflectance R of the partial reflector is 4%, and the cross-sectional area of the discharge is approximately 8 cm.
² In the experimental results, a peak output is obtained from approximately 75 ns to 175 ns, which is a result substantially reflecting the calculation result.

FIG. 4 shows that the delay operation time ΔT is 0 ns,
The figure shows the gain waveform during oscillation (results averaged over the entire effective gain length) and the laser output waveform for 5 ns and 200 ns. FIG. 5 shows the relationship between the gain waveform during oscillation and the loss energy obtained by integrating the waveform during each delay operation time. When the delay operation time ΔT is 0 ns, as in the case of FIG. 19 shown in the conventional example, the maximum gain of about 2% / cm generated up to about 100 ns at which oscillation starts is discarded. On the other hand, when the delay operation time is 125 ns, the oscillation start time is delayed by 160 ns. However, the average gain during that period is almost equivalent to the effective gain length of 1 m. 1 /
3, and as a result, the energy loss until oscillation starts is reduced. After the start of the oscillation, the oscillation is continued until the given gain becomes equal to or less than the loss determined by the resonator loss, as in the case where the delay operation time is 0 ns despite the fact that the total excitation pulse width is extended by 125 ns. Is confirmed. Delay operation time of 200
In the case of ns, since the laser light is started up at the gain of the first oscillation stage, the energy loss until the start of oscillation is not so much different from the case of 125 ns, but the total excitation pulse width is consequently reduced. , The loss energy during laser oscillation increases, and the laser output conversely decreases.

FIG. 6 shows the output characteristics according to this embodiment and FIG.
0 shows the output characteristics (that is, the output characteristics when the partial reflection mirror 8 is not mounted on the laser beam extraction side of the second oscillation stage), and the experimental results, due to the amplification configuration shown in FIG. Here, the horizontal axis represents the input light through which the laser light emitted from the first oscillation stage passes through the second oscillation stage, and the vertical axis represents the laser output after passing through the second oscillation stage, and the output taken out of the second oscillation stage (second output). (Output obtained by subtracting the transmitted input light from the laser output after passing through the oscillation stage.)
It is. Here, the small signal gain in the second oscillation stage is almost the same as that shown in FIG. 17, and is constant. According to the experimental results in this embodiment, the reflectance R2 of the internal mirror is set to 30%, and the reflectance R of the partial reflecting mirror 8 is set to 10%. On the other hand, in the case of amplification, the reflectance between the first oscillation stage and the second oscillation stage is 30%.
Is installed. From the figure, it can be seen that the output according to this embodiment is always higher than the output due to amplification regardless of the energy of the transmitted input light. The difference is remarkable when the energy of the transmitted input light is small, and when the energy of the transmitted input light is increased, the output in the case of amplification tends to converge to the output according to this embodiment. This characteristic is
Considering the output taken out from the oscillation stage, the output taken out of the second oscillation stage is saturated at a relatively low transmitted input light energy in the configuration according to this embodiment, while the output in the case of amplification is obtained. Tend to gradually saturate according to the magnitude of the transmitted input light energy. This is because, in the configuration of FIG. 1, a part of the light extracted by the partial reflecting mirror 8 is returned to the resonator, and due to the effect of re-amplification, the efficiency of the second oscillation stage is improved even for relatively low transmitted input light energy. This means that laser light can be extracted well. In this embodiment, in practice, the first oscillation stage and the second oscillation stage are provided as one oscillating device to give substantially the same gain per unit length (that is, the input densities to the discharges are made substantially the same). The operating point of the laser is operated with the input light indicated by the solid line. The output difference ΔP from the amplified case at this time
Out is about 7%.

This embodiment considers how to reduce the loss energy until the start of oscillation under the condition that the power density in each stage is of the same order to some extent.
Effective gain length L1 of oscillation stage and effective gain length L2 of second oscillation stage
In the relation (1), it is usually more efficient to select the length of L2 longer than L1 or at least to the same length. Ie

L1 ≦ L2 (3)

It is desirable that

FIG. 7 shows the reflectivity R of the internal mirror of this embodiment when the typical small signal gain shown in FIG. 17 is given.
2. Output characteristics of the partial reflecting mirror with respect to the reflecting mirror R are shown. The effective gain length L of the first oscillation stage is 1 m, the effective gain length L2 of the second oscillation stage is 2 m, the resonator length Lc is 5.2 m, and the delay operation time of the second oscillation stage with respect to the first oscillation stage is 125 ns. . As can be seen from the figure, the laser output characteristic of the internal mirror with respect to the reflectance R2 is relatively moderate. In this case, if a value of 30% to 70% is selected, an output of 90% or more of the peak output is secured. It is understood that it is done. Further, it is necessary to set the reflectance R of the partial reflecting mirror to a value of 20% or less. FIG. 8 shows an experimental result when the reflectance of the partial mirror is set to 4% and the reflectance of the internal mirror is changed under the above-described calculation conditions. Here, V _PFN indicates the charging voltage of the PFN circuit, and changing V _PFN means changing the input density (that is, gain).
The case of 6 kV corresponds to the typical gain shown in FIG.
As is clear from the above, the experimental results show the same tendency as the calculation results, and the dependence of the output on the internal mirror varies depending on the voltage value of V _PFN , but the reflectance is relatively moderate with a peak around 40%. Dependencies are shown. This condition varies depending on the selection of the given small signal gain and the effective gain length, but generally, as described above, the effective gain length L2 of the second oscillation stage is set to the first value from the viewpoint of high efficiency. Since the effective gain length L1 of the oscillation stage is selected to be equal to or longer than the effective gain length L1, the reflectance of each part is inevitably related to the gain.

R2 ≧ R (4)

It is desirable that

Embodiment 2 FIG. FIG. 9 shows another embodiment of the present invention. In the second embodiment, the first main electrode of the second oscillation stage is 2b.
1 and 2b2, the second main electrodes of the second oscillation stage are 3b1 and 3b2
And the second oscillation stage laser medium pumping section is 4b1
And 4b2. Such a configuration is only performed because it is difficult to manufacture a long main electrode or to accurately install the main electrode in the actual manufacturing of the device, and the effective gain length L21 of each divided portion, and It can be considered that the sum of L22 is the effective gain length L2 of the second oscillation stage. As described above, the laser medium excitation section of the second oscillation stage may be divided into any number, and the inside of the first oscillation stage may be divided into any number. In the example shown here, the laser medium excitation unit 4b of the divided second oscillation stage
1 and 4b2, the same delay operation time ΔT is given. As is apparent from FIG. 2, in the present invention, near the optimum value of the delay operation time, the output dependence on the delay operation time is shown. Does not necessarily become large, so that the delay operation times of the two do not necessarily have to match.

Embodiment 3 FIG. FIG. 10 shows that the housing of the second oscillation stage is L
The configuration in the case of dividing into two, b1 and Lb2, is shown.
In this case as well, it is difficult to fabricate the second oscillation stage housing in one housing, so that the second oscillation stage housing is simply divided and the effective gain length L2
Since the sum of 1 and L22 merely becomes the effective gain length L2 of the second oscillation stage, it does not change the effect of the present invention at all. Also, in FIG.
Although an example in which the first oscillating stage is divided into three is shown, the first oscillating stage may be divided into two or more. Also, here, as described above, the delay operation times of the laser medium excitation sections divided in the second oscillation stage do not necessarily have to be the same.

Embodiment 4 FIG. FIG. 11 shows that the laser medium pumping section is divided into three regions of a first oscillation stage, a second oscillation stage, and a third oscillation stage, and a total reflection mirror and a partial reflection mirror are provided at both ends thereof. A configuration in which a first internal mirror 18a and a second internal mirror 18b are provided at both ends of two oscillation stages is shown. Here, 1c is a third oscillation stage housing, and 2c is a third oscillation stage first.
A main electrode, 3c a third oscillation stage second main electrode, 4c a third oscillation stage laser medium excitation section, 5c a third oscillation stage discharge excitation circuit,
L3 is an effective gain length of the third oscillation stage, and 19 is an operation pulse of the third oscillation stage.

Next, the operation of this embodiment will be described. Example 1 is the same as that of the first embodiment until the first oscillation stage is started by the first oscillation stage operation pulse 15 and the second oscillation stage is started after the delay operation time ΔT1. As a result, laser light is sent from the second internal mirror 18b between the first and second main electrodes 2c, 3c of the third oscillation stage. When this laser beam reaches an intensity that saturates the gain of the third oscillation stage, the third oscillation stage laser medium pumping section 4
The third oscillation stage operation pulse 19 is set to the third
The laser beam is sent to the oscillating stage, and the third oscillating stage laser exciting section 4c is started up in the same process as the first and second oscillating stages. As a result, the gain of the third oscillation stage is saturated by the laser light whose intensity has been further increased by the second oscillation stage, and extremely efficient laser light can be extracted. Further, a part of the light reflected by the partial reflecting mirror 8 is quickly returned to the third oscillation stage laser medium excitation unit 4c by the second internal mirror, and has an effect of resaturating the gain of the third oscillation stage. For example, this configuration is effective in extraction in a system in which the resonator length Lc is extremely long. In some cases, the number of divisions of the laser medium excitation section may be further increased, and third and fourth internal mirrors may be provided.

Embodiment 5 FIG. Further, in the above-described configuration, an example of a so-called external mirror type resonator in which the laser light transmission window 6 is provided for each housing has been described, but as shown in FIG. The internal mirror 18 may be configured as an internal mirror resonator installed in each housing, or one of the internal mirrors may be configured as an internal mirror resonator.

Embodiment 6 FIG. In the example described above, an example in which the present invention is applied to a so-called transverse excitation type laser is shown. On the other hand, FIG.
An example in which the present invention is applied to a coaxial pump laser used in an O ₂ laser or the like is shown. In this case, the casings 1a and 1b have the shape of a cylindrical tube, and the first main electrodes 2a and 2b and the first 2
The main electrodes 3a and 3b are provided at both ends of the cylindrical tube. The excitation discharge is generated in the tube axis direction, and forms the laser medium excitation parts 4a and 4b. It goes without saying that the present invention is also effective in such a configuration.

Embodiment 7 FIG. Although the above-described discharge excitation circuit has been described in the case where a gain of long pulse excitation by the pre-pulse / PFN circuit is given, a so-called capacity transition type circuit in which discharge initiation and energy injection are performed by the same circuit, and other discharge circuits are described. The same effect can be obtained though the effect is large or small.

Embodiment 8 FIG. In the example described above, an example in which the present invention is applied to a so-called gas laser that generates a laser medium excitation part by generating a discharge in a laser gas has been described. However, this is a YAG laser in which the laser medium excitation part is generated in a solid crystal. Or a solid laser such as a YLF laser, a titanium-sapphire laser, an alexandrite laser, or a liquid laser such as a dye laser existing in a liquid laser medium. FIG. 14 shows an example in which the present invention is applied to a solid-state laser.
Oscillation stage and second oscillation stage excitation light source circuits 22a and 22b are first oscillation stage and second oscillation stage excitation light sources such as flash lamps, semiconductor lasers and other lasers, and 23a and 23b, respectively.
Denotes pump light for the first oscillation stage and pump light for the second oscillation stage, which are emitted from the excitation light sources 22a and 22b, respectively, and 24a and 24b denote the first oscillation stage solid laser medium pumping portions made of solid laser crystals;
The second oscillation stage is a solid-state laser medium excitation section.

Next, the operation of the eighth embodiment will be described. The first oscillation stage pumping light source circuit 21a operates by the first oscillation stage operation pulse 15, and the first oscillation stage excitation light source 22a
The oscillation stage excitation light 23a is emitted. When this light is applied to the first oscillation-stage solid laser medium excitation section 24a made of a solid crystal for laser, a so-called inverted distribution state is formed there.
The second oscillation stage operation pulse 16 is sent to the second oscillation stage excitation light source circuit 21b with a delay of the delay operation time ΔT from the first oscillation stage operation pulse 15, and thereafter, the second oscillation stage is processed by the same process as the first oscillation stage. The step laser medium excitation unit 24b is activated. After the first oscillation stage laser medium excitation section 24a and the second oscillation stage laser medium excitation section 24b are formed, the laser beam 9 is extracted by exactly the same process as in the first embodiment, and the effect at this time is exactly the same. . Also, in the case of a liquid laser, the solid-state laser medium excitation units 24a and 24a
The configuration is basically the same as that of FIG. 14 except that b is changed to the medium in the liquid.

[0048]

As described above, according to the pulse laser oscillation device of the first aspect of the present invention, the laser medium excitation section of the pulse laser oscillation device is divided into two or more regions, and a normal total reflection mirror and to the resonator structure consisting of the partial reflection mirror, it is placed inside mirror between split laser medium exciting unit, and the total
Excitation of the laser medium in the region sandwiched between the reflector and the inner mirror
Section as a first oscillation stage, sandwiched between the internal mirror and the partial reflection mirror.
The laser medium excitation section in the enclosed region is used as the second oscillation stage,
Start up until laser light from one oscillation stage reaches saturation intensity
Excitation of the laser excitation medium of the second oscillation stage before and after
Operation by delaying the second oscillation stage by a certain time
And the area between the internal mirror and the partial reflecting mirror
The laser medium excitation section is sandwiched between the internal mirror and the total reflection mirror
Inversion after a certain time delay compared to the laser medium excitation section in the region
Since the cloth state is formed, the laser light can be efficiently extracted from the laser oscillation device having a long effective gain length and a long resonator length, and the effect that a high efficiency and high output pulse laser oscillation device can be realized. Play.

A pulse laser oscillation device according to a second aspect of the present invention is the pulse laser oscillation device according to the first aspect,
The effective gain length in the laser oscillation optical axis direction of the laser medium pumping section interposed between the internal mirror and the partial reflection mirror is smaller than the effective gain length of the laser medium pumping section interposed between the internal mirror and the total reflection mirror. The laser beam can be efficiently extracted from the laser oscillation device having a long effective gain length and a long resonator length, and the pulse laser oscillation with high efficiency and large output can be achieved. There is an effect that the device can be realized.

According to a third aspect of the present invention, in the pulse laser oscillator of the first or second aspect, the reflectance of the partial mirror is equal to the reflectance of the inner mirror, or Since the size is small, the laser light can be efficiently extracted from the laser oscillation device having a long effective gain length and a long resonator length similarly to the first aspect, and a pulse laser oscillation device having high efficiency and high output can be realized. To play.

According to a fourth aspect of the present invention, there is provided the pulse laser oscillation apparatus according to any one of the first to third aspects, wherein the first and second main electrodes opposed to each other in the pulse laser gas. A discharge excitation circuit for starting discharge between the main electrodes, and supplying discharge energy, so that the laser medium excitation section is formed by the discharge generated between the main electrodes,
As in the first aspect, a laser beam can be efficiently extracted from a laser oscillation device having a long effective gain length and a long resonator length, and a pulse laser oscillation device having high efficiency and high output can be realized.

A pulse laser oscillation device according to a fifth aspect of the present invention is the pulse laser oscillation device according to the fourth aspect,
Since the discharge excitation circuit includes a first discharge excitation circuit for starting discharge and a second discharge excitation circuit for supplying energy, the discharge excitation circuit has a long effective gain length and a long resonator length. The laser beam can be efficiently extracted from the laser oscillation device, and an effect of realizing a pulse laser oscillation device with high efficiency and high output can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a pulse laser oscillation device according to an embodiment of the present invention.

FIG. 2 is a diagram of a laser output characteristic (calculation result) with respect to a delay operation time according to the first embodiment.

FIG. 3 is a graph of laser output characteristics (experimental results) with respect to delay operation time according to the present invention and a conventional device.

FIG. 4 is a diagram of a gain waveform and a laser output waveform (calculation result) at each delay operation time according to the present invention.

FIG. 5 is a diagram of a gain waveform and a resonator loss energy integrated value (calculation result) with respect to each delay operation time according to the present invention.

FIG. 6 is a diagram of laser output characteristics (experimental results) with respect to input light transmitted through a first oscillation stage according to the present invention and a conventional method (amplification).

FIG. 7 is a diagram of laser output characteristics (calculation results) for an internal mirror according to the present invention.

FIG. 8 is a diagram of laser output characteristics (experimental results) for the internal mirror according to the present invention.

FIG. 9 is a block diagram showing a pulse laser oscillation device when a main electrode in a second oscillation stage is divided according to another embodiment of the present invention.

FIG. 10 is a block diagram showing a pulse laser oscillation device when a housing in a second oscillation stage is divided according to another embodiment of the present invention.

FIG. 11 is a block diagram showing a pulse laser oscillation device provided with a third partial reflecting mirror in addition to an internal mirror according to another embodiment of the present invention.

FIG. 12 is a block diagram showing a pulse laser oscillation device when an internal resonator according to another embodiment of the present invention is configured.

FIG. 13 is a block diagram showing a pulse laser oscillation device when applied to a coaxially pumped laser according to another embodiment of the present invention.

FIG. 14 is a block diagram showing a pulse laser oscillation device when applied to a solid-state laser or a liquid laser according to another embodiment of the present invention.

FIG. 15 is a block diagram showing a conventional pulse laser oscillation device.

FIG. 16 is a circuit diagram when a pre-pulse / PFN circuit is applied as a discharge excitation circuit of the present invention.

FIG. 17 is a diagram of a gain waveform (calculation result) used for evaluating the present invention and the conventional device.

FIG. 18 is a diagram showing a gain waveform with respect to an effective gain length and a laser output waveform (calculation result) in a conventional device.

FIG. 19 is a diagram of a gain waveform with respect to an effective gain length and an integrated value of a resonator loss energy (calculation result) in a conventional device.

FIG. 20 is a block diagram showing another conventional pulse laser oscillation device.

FIG. 21 is a block diagram showing another conventional pulse laser oscillation device.

FIG. 22 is a diagram of a laser output characteristic (calculation result) with respect to a conventional delay operation time.

FIG. 23 is a diagram of a gain waveform and a laser output waveform (calculation result) at each delay operation time by the conventional pulse laser oscillation device.

[Explanation of symbols]

2 First main electrode, 3 Second main electrode, 4 Laser medium excitation section, 5 Discharge excitation circuit, 7 Total reflection mirror, 8 Partial reflection mirror, 14 Delay pulse generator, 15 First oscillation stage operation pulse, 16 Second Oscillation stage operating pulse, 18 internal mirror.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsuo Inoue 8-1-1 Tsukaguchi Honcho, Amagasaki City Inside Central Research Laboratory Mitsubishi Electric Corporation (72) Inventor Takeo Haruta 8-1-1 Tsukaguchi Honcho Amagasaki City Mitsubishi (56) References JP-A-63-98172 (JP, A) JP-A-2-129988 (JP, A) JP-A-53-137694 (JP, A) JP-B-44 25556 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 3/08 H01S 3/097-3/0977 H01S 3/07 H01S 3/23

Claims (5)

(57) [Claims] 1. A pulse laser oscillating device comprising: a laser medium excitation section in which a population inversion necessary for laser oscillation is formed; a total reflection mirror opposed to the laser medium excitation section; and a partial reflection mirror. in the laser medium exciting unit is divided into two or more regions, wherein provided at least one internal mirror between the laser medium exciting unit that is divided two or more, and, prior to said total reflection mirror
First excitation of the laser medium excitation section in the area sandwiched by the internal mirror
A region between the internal mirror and the partial reflecting mirror
The laser medium pumping section of the above as the second oscillation stage,
Before and after the laser beam rises until it reaches the saturation intensity.
At this point, the laser excitation medium of the second oscillation stage performs excitation.
By operating the second oscillation stage with a delay for a predetermined time, the laser medium excitation section in the region sandwiched by the internal mirror and the partial reflection mirror is driven by the laser in the region sandwiched by the internal mirror and the total reflection mirror. A pulse laser oscillation device comprising: means for forming a population inversion state with a delay of a predetermined time as compared with a medium excitation unit. 2. An effective gain length in a laser oscillation optical axis direction of a laser medium pumping section sandwiched between the internal mirror and the partial reflection mirror is equal to that of the laser medium pumping section sandwiched between the internal mirror and the total reflection mirror. 2. The pulse laser oscillation device according to claim 1, wherein the pulse laser oscillation device is substantially equidistant or longer than an effective gain length. 3. The pulse laser oscillation device according to claim 1, wherein a reflectance of said partial reflecting mirror is equal to or smaller than a reflectance of said internal mirror. 4. The first, opposed laser beam in a laser gas.
A discharge excitation circuit for initiating a discharge between the second main electrode and the main electrode and supplying discharge energy, wherein the discharge generated between the main electrodes forms the laser medium excitation section. The pulse laser oscillation device according to any one of claims 1 to 3, wherein 5. A first discharge excitation circuit for starting discharge by the discharge excitation circuit and a second discharge excitation circuit for supplying energy.
5. The pulse laser oscillation device according to claim 4, comprising a discharge excitation circuit.