JP2671268B2 - Backward stimulated Raman pulse amplifier - Google Patents

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, primary Stokes light having a higher intensity than 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]

Means for Solving the Problems The present onset bright according to claim 1
Is a backward stimulated Raman pulse amplifier equipped with a pumping light and a means for injecting the amplified first-order Stokes light into the Raman medium.
A reflection mirror that reflects the amplified primary Stokes light emitted from the Raman medium and re-enters the Raman medium to obtain an output from the other end; and controls the amplified primary Stokes light Of the Stokes light and pumping light in the forward path and
The temporal synchronization relationship between the return path and the return path is that the pump light is the Raman of each path.
Stokes light enters and re-enters when passing through the medium
The Stokes light path is adjusted so that
It is .

Moreover, this onset bright according to claim 2, in the Raman medium, a backward stimulated Raman pulse amplifier that includes a means for inputting excitation light and the amplified first Stokes light,
A reflection mirror that reflects the excitation light emitted from the Raman medium and re-enters it into the Raman medium, and a wavelength selection mirror that controls the excitation light, and an odor provided with a polarization plane control element.
The excitation light and Stokes light in the forward and backward paths.
The synchronization relationship is that Stokes light enters and re-enters from the other end.
When the excitation light is adjusted so that it passes through the Raman medium
It has an optical path of light .

[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]

FIG. 1 is a schematic diagram showing one 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, as with 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. In addition, in FIG. 3B, the amplified first-order Stokes light 3 amplified to the left side and having a large amplitude is shown. On the right side, the residual pumping light 2 whose intensity gradually decreased due to the increase in the Raman conversion amount accompanying the amplification of the amplified primary Stokes light 3 was incident on the return path. It is shown. Further , the pump light 2 on the outward path at the same time is shown, and a considerable amount is also attenuated due to Raman conversion. Further, in FIG. 3 (c), the object to be amplified is amplified by the backward path 1
Next Stokes light 3 is shown after being Raman conversion with backward path, the excitation light 2 going emitted to the outside 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 / 4 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 excitation 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 a factor of 7 to 0.7 J / cm ^2.
cm ² . The amplification of the primary Stokes light in the forward and backward passes is 700 times, and the Raman conversion efficiency from the pump light to the primary 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]

According to claim 1 as described above the present invention exhibits, in the Raman medium, a backward stimulated Raman pulse amplifier that includes a means for inputting excitation light and the amplified first Stokes light, Amplified 1 emitted from the Raman medium
A reflection mirror that reflects the next Stokes light and re-enters it in the Raman medium, a wavelength selection mirror that controls the amplified first Stokes light, and a polarization plane control element, and obtain an output from the other end . , Stokes light and excitation light
The temporal synchronization relationship between the return path and the return path is that the pump light is
Stokes light enters and re-enters when passing through a Raman medium
Since the configuration has the optical path of the Stokes light adjusted so that even if the intensity of the amplified primary Stokes light incident on the outward path is low, the amplified primary Stokes light incident on the return path is amplified on the outward path and has a high intensity. Therefore, there is an advantage that a high conversion efficiency can be obtained on the return path.

[0017] The invention according to claim 2, in the Raman medium, a backward stimulated Raman pulse amplifier that includes a means for inputting excitation light and the amplified first Stokes light, emitted from the Raman medium that reflects the excitation light, the reflecting mirror to be incident again into the Raman medium, and the wavelength selective mirror that controls the excitation light, those provided polarization plane control element smell
The excitation light and Stokes light in the forward and backward paths.
The synchronization relationship is that Stokes light enters and re-enters from the other end.
When the excitation light is adjusted so that it passes through the Raman medium
Since the configuration has the optical path of the light, the conversion efficiency of the excitation light 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 the drawings]

FIG. 1 is a schematic configuration diagram showing one 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)

(57) [Claims] To 1. A in the Raman medium, a backward stimulated Raman pulse amplifier that includes a means for inputting excitation light and the amplified first Stokes light, to be amplified first Stokes light emitted from the Raman medium reflected by the reflecting mirror to obtain the output from the other end forces the light re-enter into the Raman medium, and the wavelength selection mirror for controlling the amplification first Stokes light, the way after having a polarization plane control element stimulated Raman pulse amplifier At
Temporal forward and return of Stokes light and pump light
The synchronization relation is that when the excitation light passes through the Raman medium of each optical path
Strokes adjusted so that the Stokes light enters and re-enters
Rear guide llama characterized by having a light path
Pulse amplifier . To 2. During the Raman medium, a pump light means and the rear stimulated Raman pulse amplifier having a to be incident to be amplified first Stokes light, and reflects the excitation light emitted from the Raman medium, reflecting mirror for re-enters into the Raman medium, and the wavelength selective mirror that controls the excitation light, in the way stimulated Raman pulse amplifier after having a polarization plane control element,
Excitation and Stokes light forward and backward synchronization
The relation is that when Stokes light enters and re-enters from the other end
Of the excitation light adjusted so that the excitation light passes through the Raman medium
Backward stimulated Raman pulse enhancement characterized by having an optical path
Breadth .