JPH0643507A - Rear induction raman pulse amplifier - Google Patents

Abstract

PURPOSE:To obtain high conversion efficiency even on a return path by providing a reflecting mirror which reflects primary Stokes' light to be amplified which is projected from a Raman medium and makes it incident on the Raman medium again. CONSTITUTION:Exciting light 2 which is not Raman-converted on a going way is reflected by a wavelength selecting mirror 5, circularly polarized by a polarization plane control element 8, and then reflected by the reflecting mirror 6. Then, the light is polarized into reversely circular polarized light, which passes thorugh a polarization plane control element 8 to become linear polarized light having its plane of polarization rotated by 90 deg.; and the light is propagated again through the return path in the direction of the axis of the Raman medium container 1 from a window 1b to excite the Raman medium again. When the exciting light 2 on the going path reaches a window 1b, the primary Stakes' light 3 to be amplified which is made incident on the Raman medium container 1 is propagated reversely as exciting light 2 and amplified. Further, the primary Stokes' light 3 to be amplified is propagated in the same linear polarized light direction with the exciting light 2 on the going path by a polarization plane control element 9 and a reflecting mirror 7, and then propagated in the Raman medium container 1 in the reverse direction again and amplified, and the light is transmitted through the wavelength selecting mirror 5, and separated by a polarizing plate 10 and outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backward stimulated Raman pulse amplifier which highly efficiently compresses a laser pulse width and multiplies peak power.

[0002]

2. Description of the Related Art FIG. 4 is a schematic diagram showing an example of a conventional backward stimulated Raman pulse amplifier. In this figure, pumping light 2 is input from the window 1a of the Raman medium container 1, and amplified primary Stokes light 3 is input in opposite directions from the window 1a on the opposite side of the window 1a. It is Hellaman conversion. That is, when the excitation light 2 propagates through the Raman medium container 1 and reaches the exit side window 1b, the window 1b
The amplified first Stokes light 3 is incident from the
By making the pulse width of the amplified primary Stokes light 3 shorter than the pulse width of the pumping light 2, the primary Stokes light having an intensity higher than that of the pumping light 2 and a short pulse width is obtained. Reference numerals 4 and 5 are wavelength selective mirrors.

[0003]

However, in the conventional backward stimulated Raman pulse amplifier shown in FIG. 4, the intensity of the input Stokes light is small until it is gradually amplified by the pumping light 2, and therefore the first half of the pumping light 2 is used. The Raman conversion efficiency (that is, immediately after the incident primary amplified Stokes light 3) was kept low. In order to improve this, it is conceivable to increase the intensity of the pumping light 2 to increase the conversion efficiency, but there is a problem that the loss accompanying the generation of spontaneous Stokes light by the pumping light 2 itself increases. Further, it is possible to increase the intensity of the incident amplified primary Stokes light 3, but there is a problem that the intensity ratio of the input and output Stokes light becomes small.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a backward stimulated Raman pulse amplifier having a small size and high conversion efficiency.

[0005]

A backward stimulated Raman pulse amplifier according to the present invention is a backward stimulated Raman pulse amplifier provided with a pumping light and a means for injecting a first-order Stokes light to be amplified into a Raman medium. It is provided with a reflecting mirror that reflects the amplified primary Stokes light emitted from the medium, re-enters the Raman medium, and obtains an output from the other end.

Further, the backward stimulated Raman pulse amplifier according to the present invention is a backward stimulated Raman pulse amplifier provided with a means for causing the pumping light and the amplified first-order Stokes light to enter the Raman medium, and the light is emitted from the Raman medium. It is provided with a reflecting mirror that reflects the excitation light to be re-incident in the Raman medium.

[0007]

In the present invention, the first-order Stokes light amplified on the outward path is reflected by the reflecting mirror and Raman-converted on the return path by the unconverted excitation light that has not been Raman-converted on the outward path. The efficiency of conversion into Stokes light is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic block diagram showing an embodiment of the present invention. In this figure, the same symbols as those in FIG. 4 indicate the same components. Reference numerals 6 and 7 are reflection mirrors, respectively, pumping light 2, amplified 1
The next Stokes light 3 is reflected. 8 and 9 are, for example, λ / 4
The polarization plane control elements 10, 11 made of plates and the like are polarizing plates made of, for example, polarization beam splitters. 2 (a) and 2 (b) show the excitation light 2 in the embodiment of FIG.
FIG. 4 is a configuration diagram showing in more detail the optical system for each of the amplified first-order Stokes light 3, and FIG.
(B), (c) is a figure which shows the state in each process.
In FIG. 2, reference numerals 12 and 13 denote polarizing plates, and 14 and 15
Is a reduction lens system for controlling the beam diameter.

Next, the operation will be described. In FIG. 1, after being selectively transmitted by the polarizing plate 11, the excitation light 2 reflected by the wavelength selection mirror 4 and incident from the window 1a propagates in the axial direction of the Raman medium container 1 and excites the Raman medium. Reach the window 1b. At this time, the polarizing plate 1 is opened from the window 1b.
0, the amplified first-order Stokes light 3 enters through the wavelength selection mirror 5 (FIG. 3A), but the pumping light 2 that has not been Raman-converted in the outward path is transmitted through the wavelength selection mirror 5. After being reflected and circularly polarized by the polarization plane control element 8, the reflecting mirror 6
Will be reflected at. After that, the excitation light 2 which is reflected by the reflecting mirror 6 and is made into the circularly polarized light in the reverse direction passes through the polarization plane control element 8 to become linearly polarized light with its polarization plane rotated by 90 °, and again from the window 1b to the Raman medium. The Raman medium is re-excited by propagating in the return path in the direction opposite to the first direction in the axial direction of the container 1. On the other hand, when the forward excitation light 2 reaches the window 1b of the Raman medium container 1, the amplified primary Stokes light 3 incident on the Raman medium container 1 propagates in the opposite direction to the excitation light 2 and is amplified. The amplified primary Stokes light 3 that has been amplified on the outward path (FIG. 3B) has the same linear polarization direction as the excitation light 2 on the return path due to the polarization plane control element 9 and the reflecting mirror 7, similarly to the excitation light 2. Then, the Raman medium container 1 propagates in the opposite direction to the window 1b again and is amplified (FIG. 3C). Then, after this, the light passes through the wavelength selection mirror 5, is separated by the polarizing plate 10, and is output.

That is, in the backward stimulated Raman pulse amplifier of the present invention, the amplified first-order Stokes light 3 amplified and output in the Raman medium having the population inversion is continuously formed by the pumping light 2. It is possible to obtain a sufficiently amplified output from the initial state by adopting a configuration in which the output is obtained by reciprocating in the Raman medium. In addition, unconverted excitation light 2 which has not been used before
By performing Raman conversion to the amplified first-order Stokes light 3 again in the return path, the conversion efficiency from the pump light 2 to the output first-order Stokes light can be improved.

The states of FIGS. 3 (a), 3 (b) and 3 (c) will be described in more detail.
The Raman medium is being excited by the excitation light 2 and the amplified first-order Stokes light 3 is about to enter the Raman medium. Further, in FIG. 3B, the amplified first-order Stokes light 3 that has been amplified and has a large amplitude is shown on the lower left side. Amplified 1 on the right
It is shown that the residual pumping light 2 whose intensity gradually decreased due to the increase in the Raman conversion amount accompanying the amplification of the next Stokes light 3 was incident on the return path. Further, the pump light 2 on the outward path at the same time is shown in the upper stage, and is also considerably attenuated due to Raman conversion. Further, in FIG. 3C, the amplified first-order Stokes light 3 amplified on the outward path is shown in the upper stage, and the excitation light 2 that is emitted to the outside after Raman conversion on the return route is shown on the lower stage. It is shown.

Next, the structure shown in FIGS. 2A and 2B will be described. In each of these configurations, a reduction lens 14 for controlling a beam diameter for increasing the intensity by converging the excitation light 2 whose intensity is reduced by Raman conversion in the outward path, and a beam diameter of the excitation light 2 in the outward path. Amplification on return path 1
A reduction lens 15 for controlling the beam diameter for adjusting the beam diameter of the next Stokes light 3 is provided.

The polarization plane control elements 8 and 9 made of a λ / 2 plate are used to control the polarization directions of the forward and backward pumping light 2 and the amplified primary Stokes light 3. The specific conditions in this implementation are listed below.

Input excitation light wavelength 249 nm intensity 1 J / cm ² pulse width 100 ns (krypton fluorine excimer laser light) Input first-order Stokes light wavelength 268 nm intensity 1 mJ / cm ² pulse width 20 ns Raman medium methane gas 3 atmospheric pressure medium container length 15 m wavelength Selective mirror Specified wavelength is obtained by a mirror with a thin film with a thickness of 1/4 of the wavelength of two types of dielectrics (magnesium, silicon, aluminum, etc. oxides and fluorides) having high and low refractive indices, deposited in a multilayer structure. Reflects the light. For example, 49
At an incident angle of 90 degrees, S-polarized light of 249 nm reflects 98% or more, P-polarized light of 249 nm reflects 85% or more, and S-polarized light and P-polarized light of 268 nm transmits 90% or more.

In such a structure, the input first-order Stokes light is amplified 100 times in the forward path, and the intensity is 1 mJ / c.
the 0.1J / cm ² from m ^2. Excitation light intensity is 1
Attenuated from J / cm ² to 0.9 J / cm ^2. When the intensity of the pumping light on the return path is reduced to 1 J / cm ² by the reduction lens system, the first-order Stokes light on the return path is amplified by 7 times to 0.7 J / cm ^2.
It becomes cm ² . The amplification of the first-order Stokes light in both the forward and backward passes is 700 times, and the Raman conversion efficiency from the pump light to the first-order Stokes light is 70%. The input excitation light intensity per unit time is 10 ⁷ W / cm ² because the pulse width is 100 ns, but the output first-order Stokes light intensity is 3.5 × 10 5 because the pulse width is 20 ns.
^It becomes ⁷ W / cm ² , and the output primary Stokes light intensity per unit time becomes 3.5 times as large as the input excitation light intensity.

[0016]

As described above, the present invention provides a backward stimulated Raman pulse amplifier including a pumping light and a means for injecting the amplified first-order Stokes light into the Raman medium.
The amplified primary Stokes light emitted from the Raman medium is reflected and re-incident in the Raman medium, and an output is obtained from the other end. Even if the intensity of the Stokes light is low, the amplified primary Stokes light that enters the return path is amplified in the forward path and becomes high in intensity, which has the advantage that high conversion efficiency in the return path can be obtained.

Further, in the Raman medium, the pumping light and the amplified light 1
In the backward stimulated Raman pulse amplifier having means for making the next Stokes light incident, by providing a reflecting mirror that reflects the excitation light emitted from the Raman medium and makes it incident again in the Raman medium, The conversion efficiency can be further increased, the intensity of the excitation light can be reduced, and the generation of spontaneous Stokes light can be suppressed as much as possible.

As a result, the input / output intensity ratio of the first-order Stokes light can be increased, and the high-output pumping light can be shortened by the backward stimulated Raman pulse amplifier having a small number of stages.
In addition, since the round-trip optical paths of the excitation light and the first-order Stokes light coincide with the axis of the Raman medium container, the number of Raman medium containers, the length, and the aperture do not increase, so that the efficiency is high. This has the effect of rapidly expanding the application range of small backward-induction Raman pulse amplifiers in industry.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing details of FIG.

FIG. 3 is a diagram showing a temporal synchronization relationship between pump light and first-order Stokes light.

FIG. 4 is a schematic configuration diagram showing an example of a conventional backward stimulated Raman pulse amplifier.

[Explanation of symbols]

 1 Raman medium container 2 Excitation light 3 Amplified primary Stokes light 4 Wavelength selection mirror 5 Wavelength selection mirror 6 Reflection mirror 7 Reflection mirror 8 Polarization plane control element 9 Polarization plane control element 10 Polarizing plate 11 Polarizing plate 12 Polarizing plate 13 Polarizing plate 14 Reduction lens system for controlling beam diameter 15 Reduction lens system for controlling beam diameter

Claims (2)

[Claims] 1. A backward stimulated Raman pulse amplifier, comprising: a Raman medium; and means for making pumping light and amplified first-order Stokes light incident on the Raman medium, and reflects the amplified first-order Stokes light emitted from the Raman medium. A backward stimulated Raman pulse amplifier, characterized in that the Raman medium is provided with a reflecting mirror that re-enters the Raman medium to obtain an output from the other end. 2. A backward stimulated Raman pulse amplifier comprising a pumping light and a means for allowing the amplified first-order Stokes light to enter the Raman medium, and reflects the pumping light emitted from the Raman medium to produce the Raman medium. A backward stimulated Raman pulse amplifier having a reflecting mirror for re-incident light.