JP2500363B2 - Short pulse light generator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short pulse light generator capable of shortening the pulse width of laser light.

[0002]

2. Description of the Related Art FIG. 2 is a schematic diagram showing an example of a conventional short pulse generator. In the figure, L1 is a pulsed incident laser beam having a waveform such as LA , 4 is a polarizing plate for making the incident laser beam L1 linearly polarized, 5 is a Pockel cell switch for rotating the polarization direction, and 6 is a short It is a polarizing plate for cutting out pulsed light. When the high-voltage pulse 7 is applied while the horizontally polarized laser light is incident on the Pockel cell switch 5, the polarization direction of the laser light is rotated and becomes the vertical direction only when the high-voltage pulse 7 is applied. When the laser light emitted from the Pockel cell switch 5 enters the polarizing plate 6, the horizontally polarized portion LE of the laser light pulse passes through the polarizing plate 6 (laser light L
3) , the vertically polarized part LF is reflected (laser
Light L2) . The pulse width of the laser beam L2 reflected by the polarizing plate 6 is determined by the pulse width of the high voltage pulse 7. In this manner, short pulse light can be generated by cutting out a part of the laser light pulse having a long pulse width.

[0003]

In the conventional short pulse generator shown in FIG. 2, the time synchronization relationship between the high voltage pulse 7 and the laser light pulse applied to the Pockel cell switch 5 and the pulse width of the high voltage pulse 7 are given. There is a problem in that the time until the short pulse light is cut out from the rising time of the incident laser light L1 as a starting point and the pulse width of the short pulse light are not constant due to fluctuations in each repeated operation.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a short pulse light whose pulse width can be easily controlled without fluctuation in each repeated operation.

[0005]

In the short pulse light generating device according to the present invention, it is desired to change the pulse width as the stimulated scattering medium in order to generate the Stokes light by injecting the laser light into the stimulated scattering medium. Two types of media are used: a stimulated scattering medium that generates Stokes light, and a stimulated scattering medium that has a different transient response time. The gain of stimulated scattering of the stimulated scattering medium is controlled by adjusting the particle density (pressure or concentration) of the two kinds of media, and the pulse width of the Stokes light from the former stimulated scattering medium is changed.

[0006]

In the present invention, two types of stimulated scattering medium A having a short transient response time and stimulated scattering medium B having a long transient response time are used.
And are used. Note that the mediums A and B will be simply referred to below. A and B of FIG. 3 show temporal changes in the gain of stimulated scattering of the two kinds of media A and B. The horizontal axis represents the time starting from the rise time of the excitation light, and the vertical axis represents the stimulated scattering gain in the transient response time. ta1 and tb1 indicate times at which the Stokes light of the media A and B starts to be generated, respectively. ta2 and tb2 are
The time at which the stimulated scattering gains of the media A and B reach the steady-state value is shown. GS represents the minimum gain necessary for Stokes generation, GA represents the steady-state gain of the medium A, and GB represents the steady-state gain of the medium B. The steady state stimulated scattering gain GB of the medium B is set larger than the stimulated scattering gain GA of the medium A. Since the stimulated scattering gain of the medium B up to the transient response time tb2 is suppressed to be lower than the set stimulated scattering gain of the steady state, the stimulated scattering gain of the medium A is opposite to the set stimulated scattering gain of the medium B. A time (gain reversal time) TG that becomes larger than the gain can be obtained. Therefore, the Stokes light is generated by the medium A only during the time TA when the gain is inverted from the time when the Stokes light from the medium A starts to be generated, and in the steady state, most of the excitation is performed by the medium B having a large set induced scattering gain. Light is converted to Stokes light. The pulse width TA of the Stokes light from the medium A can be controlled by adjusting the gain GA or GB in the steady state of each medium by the particle density of the medium A or the medium B and changing the gain reversal time TG.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a schematic view showing an embodiment of the present invention. The medium container 1 is filled with methane gas and hydrogen gas which are stimulated Raman scattering media as the media A and B. Two
Is a convex lens for increasing the intensity of the excitation light Le in the medium container 1. The output Stokes light and the transmitted excitation light are separated by the prism 3. The Stokes light LsA from the methane gas as the medium A is shown by a solid line, and the Stokes light LsB from the hydrogen gas as the medium B is shown by a broken line. Note that L
eO represents transmitted excitation light, and Lsa represents anti-Stokes light. FIG. 1B shows the waveform LA of the incident excitation light Le and the transmitted excitation light Le.
A waveform LB of O, a waveform LC of Stokes light LsA from methane gas, and a waveform LD of Stokes light waveform LsB from hydrogen gas are shown. As an example, the excitation light has a pulse width of 20.
The pulse width of the Stokes light from methane gas at 4.5 atm was controlled by adjusting the pressure of hydrogen gas in the range of 0.7 to 3.5 atm by using a krypton fluorine excimer laser beam of ns.

The specific conditions of this embodiment will be listed below. Excitation light Le wavelength 249 nm Excitation light energy 100 mJ Excitation light pulse width 20 ns Focal length of convex lens 2 for collecting excitation light 170 cm Container length 300 cm Induction scattering medium (A) Methane gas pressure 4.5 atm Stokes light wavelength 268 nm Steady-state stimulated scattering gain GA 30 Transient response time ta2 840 ps Time from pumping light rise time to Stokes light generation ta1 140 ps Stimulated scattering medium (B) Hydrogen gas gas pressure 0.7 to 3.5 atm Stokes light Wavelength 278 nm Steady-state induced scattering gain GB 40 to 200 Transient response time ta2 40 to 220 ns Time until the same gain as that of medium A TG 10 to 1.3 ns Due to the transient response, the induced scattering gain of methane gas is hydrogen. Gain reversal becomes larger than gas gain TG, corresponding to stimulated scattering gain 40-70 steady state hydrogen gas, 10
~ 1.3 ns. Time from rising of excitation light of methane gas to generation of Stokes light ta1 = 140 ps
Is negligible because it is sufficiently smaller than the above gain reversal time TG = 10 to 1.3 ns, and by adjusting the particle density of hydrogen gas by gas pressure (0.7 to 3.5 atm), Stokes due to methane gas The light has a pulse width of 10 ns to 1.3 ns.

As the induction scattering medium other than the above-mentioned hydrogen and methane gas, as the gas, sulfur hexafluoride gas, nitrogen gas, germanium hydride gas, as the liquid,
Examples of methanol, acetone, toluene, and benzene solids include quartz, calcite, silicon, and diamond.

In the above embodiment, attention is paid to Stokes light from methane gas, but Stokes light from hydrogen can be controlled as the pulse width by adjusting the pressures of methane gas and hydrogen gas, and is therefore useful as a short pulse light. is there.

Further, since the anti-Stokes light is generated by the energy exchange between the wave motion of the same medium as the Stokes light and the incident laser light, the anti-Stokes light can be shortened in the same manner as the Stokes light. Can be used.

[0012]

As described above, in the short pulse light generator according to the present invention, the medium container is filled with two types of media having different transient response times, and the transient response time is long.
The gain of one medium in the steady state has a shorter transient response time.
By setting the gain larger than the steady-state gain of the medium, it is possible to control the pulse width of Stokes light with high efficiency, which was impossible in the past. It is possible to realize an ideal short pulse Stokes light generator. In addition, since the time from the rise time of the excitation laser light to the generation of the short-pulse Stokes light and the pulse width of the Stokes light are determined by the particle density of the stimulated scattering medium, there is no fluctuation in each repetitive operation and high reproducibility. There is an effect that the range of application of the short pulse light generator using the method in the industry can be rapidly expanded.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention and a waveform diagram of excitation light and Stokes light in an embodiment .

FIG. 2 is a schematic configuration diagram showing an example of a conventional short pulse light generation device.

FIG. 3 is an explanatory diagram showing the principle of the present invention.

[Explanation of symbols]

1 medium container 2 convex lens 3 prism 4 polarizing plate 5 Pockel cell switch 6 polarizing plate 7 high-voltage pulse Le excitation laser light LeO transmission excitation light Ls Stokes light LsA Stokes light from stimulated scattering medium A LsB Stokes light from stimulated scattering medium B Lsa Anti-Stokes light L1 Incident laser light pulse L2 Horizontally polarized portion of laser light pulse L3 Vertically polarized portion of laser light pulse ta1 Time at which Stokes light from medium A starts to be generated ta2 Medium A The time at which the stimulated scattering gain reaches a steady state tb1 The time at which the Stokes light from the medium B begins to be generated tb2 The time at which the stimulated scattering gain of the medium B reaches a steady state GS The gain required to generate the Stokes light GA The steady state of the medium A Stimulated Scattering Gain at GB GB Stimulated Scattering Gain at steady state of Medium B TG Gain reversal time TA Time when Stokes light of medium A is generated

Claims (1)

(57) [Claims] 1. In a short pulse light generator for generating a Stokes light having a wavelength different from that of the excitation light by injecting the excitation laser light into a medium container filled with the stimulated scattering medium, a wave of the induction scattering medium generating the Stokes light is generated. Two kinds of stimulated scattering media having different transient response times, which are the time required to grow to a steady state, are filled in the medium container, and the transient response time is set.
The steady-state gain of the longer medium is
Set larger than steady-state gain of shorter medium
As a result, a short pulse light generator characterized by being able to generate Stokes light with a shortened pulse width.