JP3045827B2 - Optical short pulse generator and laser device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray lithography that requires a short pulse of
The present invention relates to an optical short pulse generator suitable for use in a line microscope and the like and a laser device using the same.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional short optical pulse generator (pulse slicer, pulse selector) using a Pockels cell.
FIG.

[0003] Reference numeral 301 in the figure denotes a laser oscillator, and a polarizer 302, a Pockels cell 303, and a half-wave plate 3
04, a polarizer 305 is sequentially provided. Reference numeral 306 denotes a high-voltage pulse generator for applying a high voltage to the Pockels cell 303.

The laser beam (FIG. 3A) emitted from the laser oscillator 301 has its polarization direction accurately restricted by a polarizer 302 and enters a Pockels cell 303. In the Pockels cell 303, since the voltage from the high-voltage pulse generator 306 has not been applied yet, the polarization direction of the laser light passes through without change. Next, the laser light is transmitted through the half-wave plate 304 to rotate the polarization direction by 90 degrees, and is kicked out by the polarizer 305 in the B direction in the drawing.

At any time during which the pulsed laser beam passes through the Pockels cell 303, the Pockels cell 303
When a pulse voltage (approximately 7 kV) corresponding to a 波長 wavelength voltage is applied from the high-voltage pulse generator 306 to the Pockels cell 303, the polarization direction is rotated by 90 degrees, and
The polarization direction is rotated by 90 degrees by the half-wave plate 304, and the laser light that has been kicked out in the B direction before the pulse voltage is applied travels straight in the C direction and is output. The optical pulse waveform at this time is as shown in FIG. Thus, an optical pulse having an arbitrary time width (width shorter than the first laser light) can be generated from the optical short pulse generator.

[0006]

However, in the above-described conventional optical short pulse generator, the Pockels cell 303
Requires a high-voltage pulse generating circuit that stably generates a high-voltage pulse (approximately 7 kV) with a rising speed of several nanoseconds or less, but such a circuit is very expensive and increases the cost. There is a problem.

In addition, the life of the high-speed switching element used in the high-voltage pulse generation circuit often becomes a problem, and the pulse laser light and the high-voltage pulse generator for driving the Pockels cell 303 are also accurately synchronized. There is a problem that the apparatus is complicated and lacks reliability.

The present invention has been made in view of the above problems, and has a very simple and inexpensive configuration that does not require installation of a high-voltage pulse generating circuit or a synchronous operation, and has an optical short pulse having the same function as before. An object of the present invention is to provide a generator and a laser device using the same.

[0009]

SUMMARY OF THE INVENTION An optical pulse generator according to the present invention comprises a laser oscillator and a laser which normally transmits laser light from the laser oscillator and reflects the laser light when the energy of the laser light reaches a threshold value. First reflecting means for forming a reflected laser beam having a steep rising waveform, and usually transmitting the laser beam, blocking and reflecting the laser beam at the moment when the threshold value is reached, and steeply rising from the transmitted laser beam. And a second reflecting means for forming a laser beam having a falling waveform.

Further, the first and second reflecting means include:
It is desirable to use a substance that causes stimulated Brillouin scattering.

Further, in the laser device, the optical short pulse generator is provided with an optical amplifier for amplifying the optical short pulse generated by the optical short pulse generator.

Further, the laser device may further include the first and second reflecting means, and the optical short pulse obtained by the laser device may be further shortened.

[0013]

In the optical short pulse generator having the above construction, when the laser light from the laser oscillator enters the first reflection means, it is normally transmitted, and the first reflection occurs when the energy of the laser light reaches the threshold. The means causes a reflection action to reflect the laser light. Thereby, reflected laser light having a steep rising waveform is formed.

The reflected laser light having a steep rising waveform reflected by the first reflecting means enters the second reflecting means and passes therethrough. When the energy of the laser light reaches a threshold, the second reflected light is instantaneously obtained. The reflecting means causes a reflecting action to block and reflect the laser light. Thereby, the transmitted laser light having a steep rising waveform becomes a laser light having a steep falling waveform, and an optical pulse having a steep rising and falling waveform can be formed.

By using a substance causing stimulated Brillouin scattering as the first and second reflecting means, it is possible to efficiently form the light pulse having the steep rising and falling waveforms.

In the laser device having the above-described configuration, the optical pulse having sharp rising and falling waveforms obtained by the optical short pulse generator is amplified by the optical amplifier, so that the optical short pulse having higher energy can be obtained. Obtainable.

Further, by providing the first and second reflecting means, a short pulse of light having a large energy obtained from this laser device can be further shortened.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing a main part of an optical short pulse generator according to a first embodiment. FIG. 2 is a point A in FIG.
It is explanatory drawing which shows the waveform of a laser beam in a point and a C point.

Here, stimulated Brillouin scattering (hereinafter, referred to as
"SBS") means that when a certain threshold is reached, the laser light is suddenly almost completely reflected inside,
Moreover, it is a phenomenon in which incident laser light is reflected with the same plane of polarization, and this phenomenon itself is already well known. Hereinafter, a container containing a substance (SBS medium) that causes this phenomenon is referred to as an SBS cell.

In FIG. 1, reference numeral 1 denotes a laser oscillator, reference numeral 2 denotes a reflection SBS cell as first reflection means, and reference numeral 3 denotes a transmission SBS cell as second reflection means.

The laser oscillator 1 is a Q-switched pulse laser using a Nd: YAG crystal as a laser medium, and generates a laser beam having a pulse width of about 50 nanoseconds and an energy of 5 mJ at a repetition rate of 10 times per second.

The reflection SBS cell 2 normally transmits the pulsed laser beam from the laser oscillator 1 and reflects the pulsed laser beam at the moment when the energy of the pulsed laser beam reaches a threshold value, and has a sharp rising waveform. To form

The transmission SBS cell 3 transmits the laser light reflected by the reflection SBS cell 2 and cuts off and reflects the laser light when the threshold value is reached. The transmitted SBS cell 3 changes sharply from the transmitted laser light having a steep rising waveform. A laser beam having a gentle falling waveform is formed. The SBS cells 2 and 3 are made of glass so that a laser beam can enter and exit. In the center, carbon disulfide (CS ₂ ) well known as an SBS medium is sealed.

The laser oscillator 1 and the reflection SBS cell 2
A light guide device 11 for guiding laser light between the laser oscillator 1 and the first and second SBS cells 2 and 3 is provided between the transmission SBS cell 3 and the transmission SBS cell 3. The light guide device 11 restricts the polarization direction of the laser light from the laser oscillator 1, transmits the laser light, restricts the polarization direction, and reflects the laser light reflected by the reflection SBS cell 2 and returned by rotating the polarization direction by 90 degrees. And transmitted twice, the polarization direction is 9
Quarter-wave plate 5 that rotates 0 degrees and SB for reflecting laser light
A condenser lens 6 for condensing light on the S cell 2 and a polarizer 4
A reflecting mirror 7 for reflecting the laser beam reflected by the reflector to the transmitting SBS cell 3, and a transmitting SBS for reflecting the laser beam reflected by the reflecting mirror 7.
And a condenser lens 8 for condensing light on the BS cell 3. Outside the transmission SBS cell 3, the transmission SBS
A collimating lens 9 for collimating the laser light emitted from the cell 3 is provided.

With the above configuration, first, the laser oscillator 1
The pulsed laser light emitted from at point A in FIG.
As shown in FIG. 4A, the laser light has a smooth waveform generally called a Gaussian distribution. Next, Polarizer 4
And is condensed by the lens 6 through the quarter-wave plate 5 into the reflection SBS cell 2.

Here, the laser beam is reflected by the SBS cell 2 for reflection.
Until the energy reaches the threshold, the light passes through the reflection SBS cell 2 as it is, but the reflected light is suddenly generated at the moment when the threshold is reached. This reflected light has a very steep rising waveform of 1 nanosecond or less (FIG. 4).
(B)). Since this reflected laser beam is a phase conjugate wave characteristic of the reflection SBS cell 2, the reflection SBS cell 2
The light returns exactly in the same optical path as when it was incident on.

At this time, the reflected laser light is transmitted to the ４ wavelength plate 5.
, The polarization direction is rotated by 90 degrees, and is reflected by the polarizer 4 without being transmitted. The reflected laser light is
The light is further reflected by the reflecting mirror 7, condensed by the condenser lens 8, and enters the transmission SBS cell 3. In the transmission SBS cell 3, like the reflection SBS cell 2, the energy is transmitted as it is by the incident laser beam until the energy reaches the SBS threshold, but at the moment when the energy reaches the SBS threshold. It suddenly turns into reflection and cuts off the transmission of laser light thereafter.

As a result, the transmitted light from the transmitting SBS cell 3 becomes an optical pulse (FIG. 4C) having a very fast (1 nanosecond or less) rising waveform and falling waveform.

In this embodiment, the width (time) of the light pulse can be changed by adjusting the light amount of the laser light emitted from the laser oscillator 1 with an attenuation filter, and the light amount transmitted through the polarizer 4 is further restricted. Then, a short light pulse can be obtained. As a result of the measurement, in this embodiment, the pulse width could be continuously changed from about 1 nanosecond to about 20 nanoseconds. Alternatively, a wave plate may be placed between the laser oscillator 1 and the polarizer 4 and the amount of light transmitted through the polarizer 4 may be adjusted by rotating the wave plate. The width (time) of the light pulse can also be changed by changing the focal length of the lenses 6 and 8 (exchanging lenses or using a zoom lens). That is, if the focal length of the lens 8 is increased, the threshold value increases, and the width of the light pulse also increases. When the focal length of the lens 6 is increased, the pulse width is reduced.

As described above, the rising waveform of the light pulse is formed by the reflection SBS cell 2 and the falling waveform is formed by the transmission SBS cell 3, so that the very fast rising and falling of 1 nanosecond or less can be achieved. It is possible to easily and easily generate a light palace having the light.

Further, it is not necessary to install an expensive high-voltage pulse generating circuit or a high-level synchronizing operation, and the apparatus can be simplified to stably generate short optical pulses, thereby improving reliability and reducing costs. Can be achieved.

FIG. 5 is a schematic diagram showing a main part of a second embodiment of the optical short pulse generator according to the present invention.

In the case of this embodiment, a transmission SBS cell 503 is provided facing the laser oscillator 501.
A condensing lens 502 is provided between the light emitting device 01 and the SBS cell 503. Further, a collimating lens 504 is provided on the emission side of the transmission SBS cell 503, and a polarizer 505, a quarter-wave plate 506, and a condenser lens 507 are sequentially provided.
A cell 508 is provided.

As a result, the laser beam emitted from the laser oscillator 501 (FIG. 6A) first forms a falling waveform (FIG. 6B) in the transmission SBS cell 503, and the reflection SBS cell 508. Thus, a rising waveform (FIG. 6C) is formed. The magnitude of this waveform can be easily set by adjusting the focal length or the like. The laser beam reflected by the reflection SBS cell 508 passes through the quarter-wave plate 506 twice, whereby the polarization direction is rotated by 90 degrees, reflected by the polarizer 505, and extracted outside.

As a result, the same effects as in the first embodiment can be obtained.

FIG. 7 is a schematic configuration diagram showing a third embodiment. In this embodiment, the light guide device is simplified. That is,
Laser light emitted from the laser oscillator 701 is reflected by a half mirror 702 as a light guide device, and is reflected by a reflection SBS.
The reflected laser light entering the cell 703 and reflected by the reflection SBS cell 703 passes through the half mirror 702 and enters the transmission SBS cell 704.

Thus, with a simple configuration, it is possible to generate an optical pulse having a very fast rising and falling waveform by the same operation as in the first embodiment.

Further, each of the short optical pulse generators having the above-mentioned configuration has
A laser device may be configured by providing an optical amplifier (not shown) for amplifying the optical short pulse generated by the optical short pulse generator. Thus, by amplifying the optical pulse having the steep rising and falling waveforms obtained by the optical short pulse generator by the optical amplifier, it is possible to obtain an optical short pulse having higher energy.

Further, the above-mentioned laser device may be further provided with the reflection SBS cell 2 and the transmission SBS cell 3, and the light short pulse obtained by the laser device may be further shortened. This makes it possible to easily obtain a steep short pulse having the required energy.

The reflection SBS cells 2, 508,
The SBS medium used in the transmissive SBS cell 3,503 like, in CS ₂ than those listed in Example, TiCl _4,
Liquids such as SnCl ₄ and CCl ₄ , high-pressure gases such as CH ₄ and SF ₆ , and other substances that cause stimulated Brillouin scattering can be used.

[0042]

As described above, according to the present invention, the following effects can be obtained.

(1) Since a rising waveform of an optical pulse is formed by the first reflecting means and a falling waveform is formed by the second reflecting means, an optical pulse having a very fast rising and falling waveform can be easily obtained. And can be easily generated.

(2) The apparatus can be simplified to stably generate short optical pulses without the need for expensive high-voltage pulse generators or advanced synchronization operations, thereby improving reliability and reducing costs. Can be planned.

(3) An optical amplifier is provided in an optical short pulse generator to constitute a laser device, and an optical pulse having sharp rising and falling waveforms obtained by the optical short pulse generator is amplified by the optical amplifier. As a result, an optical short pulse having a higher energy can be obtained.

(4) The laser device is further provided with the first amplifier and the second reflector by providing the optical amplifier, and the optical short pulse obtained by the laser device is further shortened so that a necessary pulse is obtained. A steep short pulse with strong energy can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an optical short pulse generator according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a conventional optical short pulse generator.

FIG. 3 is an explanatory diagram showing optical pulse waveforms at points A, B, and C of the optical short pulse generator of FIG.

FIG. 4 is an explanatory diagram showing optical pulse waveforms at points A, B, and C of the optical short pulse generator of FIG.

FIG. 5 is a schematic configuration diagram showing an optical short pulse generator according to a second embodiment of the present invention.

6 is an explanatory diagram showing optical pulse waveforms at points A, B, and C of the optical short pulse generator of FIG.

FIG. 7 is a schematic configuration diagram showing an optical short pulse generator according to a third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser oscillator 2 reflection SBS cell 3 transmission SBS cell 4 polarizer 5 wavelength plate 6 focusing lens 7 reflecting mirror 8 focusing lens 9 collimating lens 501 laser oscillator 502 focusing lens 503 transmission SBS cell 504 collimating Lens 505 Polarizer 506 Quarter wave plate 507 Condensing lens 508 SBS cell for reflection

Claims (4)

(57) [Claims] 1. A laser oscillator and a laser beam which normally transmits laser light from the laser oscillator and is reflected at the moment when the energy of the laser beam reaches a threshold to form a reflected laser beam having a steep rising waveform. A first reflecting means, and a second reflecting means for transmitting laser light, usually blocking and reflecting the laser light at a moment when a threshold value is reached, and forming a laser light having a sharp falling waveform from the transmitted laser light; An optical short pulse generator comprising: 2. The optical short pulse generator according to claim 1, wherein a substance causing stimulated Brillouin scattering is used as said first and second reflection means. 3. The laser device according to claim 1, further comprising an optical amplifier for amplifying the optical short pulse generated by the optical short pulse generator. . 4. The apparatus according to claim 3, further comprising the optical short pulse generator.
3. The laser device according to claim 1, further comprising:
A laser device comprising the first and second reflecting means described above, and further shortening an optical short pulse obtained by the laser device.