JPH0715067A - Apparatus for amplifying pulse laser light to produce short pulse - Google Patents

Abstract

PURPOSE:To provide an apparatus which can conduct amplification of pulse laser light and production of short pulse simultaneously. CONSTITUTION:The apparatus for amplifying pulse laser light L to produce a short pulse comprises a section 4 for pumping a laser medium, a reflector 5 having a plurality of reflective faces 6a, 6b shifted from each other with respect to the optical axis of pulse laser light introduced to the laser pumping section and reflecting a pulse laser light, incident across the reflective faces, substantially in same direction, and a phase plate 8 for imparting a predetermined phase difference between respective pulse laser lights reflected on the respective reflective faces before they are superposed with a time difference corresponding to the positional shift of the reflective face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for amplifying pulse laser light and for shortening the pulse width of the pulse laser light.

[0002]

2. Description of the Related Art Recently, in the field of measurement, it is required to measure, for example, a biological reaction, a chemical reaction, a behavior of a charged particle of a semiconductor, etc., and it is under study to perform the measurement with a laser beam. By the way, the reaction time is
Since it is a very short time of nsec or less, the laser light for measuring the phenomenon is theoretically shorter than the reaction time of the phenomenon by 1 to 2 digits or more, and the time pulse width is 10 ^-9 sec.
The following short pulses are required.

Moreover, in order to measure various phenomena with high accuracy, not only the pulse width is very short as described above, but also the short pulse laser light has an output (energy) higher than a predetermined level. Required.

Conventionally, there is known a device capable of oscillating and outputting laser light of a short pulse by a pulse compression method or the like. Then, by amplifying the laser light short-pulsed by such a device by the excited laser medium, it becomes possible to obtain the short-pulse laser light of a desired output.

However, when the pulse compression method is used, a portion for compressing the pulse width, a portion for converting the wavelength of the pulse laser light, and a portion for amplifying the compressed pulse laser light are separately provided. Since it is necessary to provide the device in the above, the entire device may become large and complicated.

[0006]

As described above, in the past, in order to obtain a short pulse laser beam having a high output, the size and complexity of the apparatus have been sometimes brought about. The present invention has been made based on the above circumstances. An object of the present invention is to provide a pulse laser capable of obtaining a pulse laser beam having a high output and a short pulse width with a relatively simple and small device. An object is to provide a device that amplifies and shortens light.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an apparatus for amplifying and shortening pulse laser light, in which a laser medium is excited.
A laser excitation section and a plurality of reflection surfaces provided at different positions with respect to the optical axis direction of the pulse laser light introduced into the laser excitation section, and the light is incident over each reflection surface. A reflector that reflects the pulsed laser light in substantially the same direction, and each pulsed laser light reflected by each of the above-mentioned reflecting surfaces is overlapped with each pulsed laser light before they overlap with each other with a time difference according to the displacement of each reflecting surface. And a phase control means for providing a predetermined phase difference.

[0008]

According to the above construction, the pulse laser beams reflected by the respective reflecting surfaces are overlapped with each other with their phases being shifted by a predetermined time difference, so that the overlapped portions cancel each other out, and only the portion shifted due to the time difference is taken out as an output. Therefore, the pulse width can be made to correspond to the time difference, and further, amplification can be performed by the laser excitation unit.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The apparatus of the present invention shown in FIG. 1 is provided with a laser oscillator 1 capable of oscillating and outputting a pulse laser light L having a pulse width of ps (picosecond) unit such as a dye laser. The pulsed laser light L oscillated and output from the laser oscillator 1 is incident on the beam splitter 2 arranged at an inclination angle of about 45 degrees. In the optical axis direction of the laser light L reflected by the beam splitter 2, a reflector 5 is arranged facing the beam splitter 2 at a predetermined distance.

A laser excitation unit 4 is provided between the beam splitter 2 and the reflector 5. The laser excitation unit 4 is composed of a gas laser medium such as CO ₂ gas and an electrode that excites the gas laser medium for discharge, and the pulse laser is excited in the excited gas laser medium. As the laser light L passes, the laser light L is amplified.

The reflector 5 has a disk shape, and the surface facing the beam splitter 2 is divided into a semi-circular first reflecting surface 6a and a second reflecting surface 6b. First
The reflecting surface 6a and the second reflecting surface 6b of the
A difference is provided in the position (height) along the optical axis of the light L,
Further, the reflectance is different. In this embodiment, the step difference, which is the difference in position between the first reflecting surface 6a and the second reflecting surface 6b, is set to 15 μm, and the reflectance is 99% for the first reflecting surface 6a and the second The reflection surface 6b is set to 90%.

At the portion of the laser excitation section 4 on the reflector 5 side, the pulse laser is incident on and reflected by the first reflecting surface 6a and the second reflecting surface 6b of the reflector 5. A separation plate 7 for separating the laser light L is provided over a length of about one-third of the laser excitation section 4.

The pulse laser light L reflected by the beam splitter 2 and the reflector 5 has its beam diameter expanded by diffraction. Thereby, the respective reflected lights (the first reflected light L1 and the second reflected light 6b) of the reflector 5 are reflected by the first reflecting surface 6a and the second reflecting surface 6b and separated by the separating plate 7.
Is reflected light L2. ) Passes through the beam splitter 2 after being partially overlapped with each other after passing through the separating plate 7.

In the optical path of the second reflected light L2, the second reflected light L2 is 90 degrees relative to the first reflected light L1.
A phase plate 8 that provides a phase difference of degrees is provided. Since the second reflected light L2 enters the reflector 5 and is reflected by the second reflector, the second reflected light L2 passes through the phase plate 8 twice, thereby having a phase difference of 180 degrees with respect to the first reflected light L1. Become.

The pulse laser light L transmitted through the beam splitter 2, that is, the first and second reflected light L1 and L2 are shaped by the aperture 9 and then transmitted through the saturable absorber 10. The aperture 9 allows only the overlapped portion indicated by D in FIG. 1 of the first reflected light L1 and the second reflected light L2 transmitted through the beam splitter 2 to pass therethrough, and The supersaturated absorber 9 absorbs a portion where the peak intensity of the reflected light is below a certain level.

Next, the operation of the apparatus having the above configuration will be described with reference to FIG.
This will be described with reference to (a) to (f). Figure 4 (a) shows
The waveform of the pulse laser light L oscillated and output from the laser oscillator 1 and incident on the beam splitter 2 is shown.
The laser light L is amplified by passing through the laser excitation unit 4, and is incident on the reflector 5 while being separated by the separation plate 6.

The pulse laser light L incident on the reflector 5 is
Reflected by the first reflecting surface 6a and the second reflecting surface 6b,
After being partially amplified, they are again amplified through the laser excitation unit 4, and then transmitted through the beam splitter 2.

Since the first reflecting surface 6a and the second reflecting surface 6b of the reflector 5 have a step difference (optical path difference) of 15 μm, the first reflecting surface 6a shown in FIG. A time difference d occurs between the reflected first reflected light L1 and the second reflected light L2 reflected by the second reflecting surface 6b shown in FIG. 4 (c). For example, the pulse width of the pulse laser light L is 1 ps.
Then, the time difference d between the first reflected light L1 and the second reflected light L2 caused by the step of 15 μm is 100.
It becomes fs (femto second). Therefore, the two reflected lights L1 and L2 have an aperture 8 with a time difference d of 100 fs.
To reach.

The phase difference between the first reflected light L1 and the second reflected light L2 is 180 degrees due to the phase plate 8. for that reason,
The two reflected lights L1 and L2 which have reached the aperture 9 with a time difference d of 100 fs cancel each other due to the mutual interference of the overlapping portions a shown in FIG.
As indicated by the slanted lines, the part b which is displaced by the time difference d
The amplified light of only b and b ′ passes through the aperture 8 (FIG. 4 (e)).

The amplified light that has passed through the aperture 8 is absorbed by the saturable absorber 10 if its peak intensity is below a certain level. That is, in the reflector 5, the reflectance of the first reflecting surface 6a is 99%, and the reflectance of the second reflecting surface 6b is 90%. Therefore, as shown in FIG. The intensity P2 of the second reflected light L2 is lower than the intensity P1 of the light L1.
Therefore, if the peak value of the absorption of the supersaturated absorber 10 is set to be not less than the second peak value P3 shown in FIG. 4 (e) and not more than P1, the overlap shown by diagonal lines in FIG. Of the non-existing portions b and b ', the portion b'is absorbed and only the portion b passes.

As a result, the laser light emitted from the saturable absorber 10 has a wavelength width of 10 as shown in FIG. 4 (f).
The short pulse laser light L'of 0 fs is obtained. That is, the pulse laser light L oscillated and output from the laser oscillator 1 is
The excitation section 4 amplifies the intensity, and the reflector 5 and the phase plate 8 convert it into pulsed light having a short pulse width.

In the above embodiment, the reflecting surface of the reflector is 2
However, the number of reflective surfaces may be three or more,
The point is that the pulsed laser light incident on the incident surface can be divided into a plurality of reflected lights with a time difference. Further, although the laser light is divided by using the separating plate, since the reflecting surface of the reflector has a step, the laser light reflected by each reflecting surface of the reflector is separated without using the separating plate. can do.

[0023]

As described above, according to the present invention, the pulse laser light is introduced into the laser pumping section where the laser medium is pumped, and the pulsed laser light is directed in the optical axis direction. On the other hand, each pulse laser beam is made incident on a reflector having a plurality of reflection surfaces displaced from each other, and each pulse laser light reflected by each reflection surface is overlapped with a time difference corresponding to the positional deviation of each reflection surface. The light has a predetermined phase difference.

Therefore, the pulsed laser light is not only amplified to a predetermined intensity by the laser pumping section, but also the pulsed laser light from the reflecting surfaces that overlap each other with a time difference has a phase difference. Since only the portion deviated by the time difference can be taken out as the output, the pulse width of the pulse laser light can be sufficiently shortened as compared with the initial pulse width. Moreover, since the amplification of the pulse laser light and the reduction of the pulse width can be performed by one device, the device can be downsized and simplified.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a perspective view of the same reflector.

FIG. 3 is an enlarged sectional view of a part of the reflector.

FIG. 4A to FIG. 4F are explanatory views of waveforms of pulse laser light.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser oscillator, 4 ... Laser excitation part, 5 ... Reflector, 6
a, 6b ... Reflective surface, 8 ... Phase plate, 9 ... Phase plate, 10 ... Saturated absorber, L ... Pulse laser light, L1, L2 ... Reflected light.

Claims (1)

[Claims] 1. A device for amplifying and shortening a pulsed laser beam, wherein a laser medium is excited.
A laser excitation section and a plurality of reflection surfaces provided at different positions with respect to the optical axis direction of the pulse laser light introduced into the laser excitation section, and the light is incident over each reflection surface. A reflector that reflects the pulsed laser light in substantially the same direction, and each pulsed laser light reflected by each of the above-mentioned reflecting surfaces is overlapped with each pulsed laser light before they overlap with each other with a time difference according to the displacement of each reflecting surface. A device for amplifying and shortening a pulse laser beam, comprising: a phase control means for providing a predetermined phase difference.