JPS6175579A - Laser amplifier - Google Patents

Abstract

PURPOSE:To obtain a laser amplifier suppressed in a parasitic oscillation by inclining the air contacting surface of a clad glass with respect to the surface of a laser glass at a certain critical angle from a vertical direction. CONSTITUTION:One of a light beam of a bulk parasitic oscillation mode incident to the surface of a laser glass, i.e., the light beam of a range surrounded by L41, L42 is, for example, is smaller than the total reflecting angle at the incident angle in the reflection of the air contacting surface 12 of the clad glass. Accord ingly, the reflectivity is small to 0.04-0.05. The light beam of the row, i.e., the light beam of the range surrounded by L43, L44 is fully reflected in the reflection on the surface 31 of the laser glass and the air contacting surface 13 of the glad class, but is not fully reflected on the surface 22 of the other laser glass,and the reflectivity becomes approx. 0.04-0.05. Therefore,the bulk parasitic oscillation mode is dampaged at an amplifying light path, resulting in a difficulty in the oscillation. Since the surface parasitic oscillation mode is not in parallel at the air contacting surface of the clad glasses opposed through the laser glass, the reflectivity is equivalently near 0, and does not oscillate.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a laser amplifier, and more particularly to a disk-type laser amplifier in which a laser medium is a laser glass having a disk shape that is thinner than the aperture through which laser light passes.

(Prior Art) Conventionally, a disk-type laser glass used in a disk-type laser amplifier has a shape as shown in FIGS. 1 and 2. That is, as shown in Fig. 1, which shows the front view, the outside is an elliptical parallel plane plate, and its arrangement with respect to the laser beam is such that the incident angle is the so-called Brewster's angle, as shown in Fig. 2, which shows the side view. It is arranged so that it forms. As is well known, this angle is given by tan' (the refractive index of glass), and light having a polarization component parallel to the normal plane of incidence is not reflected when it is incident at this angle. FIG. 3 shows a cross section of a conventional disk-shaped laser glass.

The surface and interior of the laser glass that is irradiated with excitation light by a light source such as a flash lamp has a laser amplification gain. At this time, Figure 3 L31゜L32 and L33
Oscillation as shown by the arrow occurs. L31, L
The form of oscillation shown at L32 is called the bulk parasitic oscillation mode, and the form of oscillation shown at L33 is called the surface parasitic oscillation mode. In order to prevent as much as possible these parasitic oscillation modes that adversely affect the normal laser amplification function, it is possible to attach a glass 1 containing ions that absorb the oscillated laser light around the laser glass 2, as shown in FIG. It has been implemented. This absorbing glass is called clad glass.

In order to suppress the bulk mode, the average gain coefficient αa of the laser glass, the long axis length of the ellipse, and the absorption coefficient α of the cladding glass are required. , same thickness d, reflectance α between air and clad glass
. The following relational expression must be satisfied between ' and the incident angle θ.

fi, c' exp(-2acd/sin O)・e
xp (α6L/5ine)〈1・・・・・・・・・・・・
(1) That is, 2αc11>α, L-1-sinO・In Re' −
−・−(If we talk about the range of 210, as shown in Fig. 3, for the range larger than the total reflection angle Oc, R+e'=
For a range 1° smaller, Rc' = 9.04~0.
It becomes 05.

As is well known, θ. is given by sin"-' (reciprocal of the refractive index of glass). When phosphate glass is used as the laser glass, the wavelength used is 1.05
Since the refractive index is 1.51 in μm, it is 6 c ” 41.
It becomes 5°.

In order to suppress the surface mode, the following relational expression must be satisfied as in the case of the bulk mode.

Reexp(-2acd)*expd
wL<1...-(3) That is, 2αCd>dwL + jn Re...
-.-(41 Here, α1 is the gain of the laser glass surface, and Rc represents the reflectance between air and clad glass when θ=06, which is 0.0413.

In order to suppress these parasitic oscillation modes, it is sufficient to increase the left side of equations (2) and (4), that is, to use a clad glass with a high absorption coefficient and a large thickness. - There are limitations due to thermal stress between the laser glasses, inefficiency of excitation of the KUSHIRADO glass part, etc. Therefore, it is necessary to keep the right-hand side as small as possible.

In a conventional disk-shaped laser glass having a cross-sectional shape as shown in FIG. Since it is perpendicular to the two parallel surfaces 21 and 22, there is a drawback that two parasitic oscillation modes, a bulk mode and a surface mode, tend to oscillate. That is, regarding the light ray between the light ray L31 that is incident at the total reflection angle on the surface 21 of the laser glass and the light ray L32 that is incident at the same total reflection angle on the cladding glass air contact surface, Rc'=t for each reflection. Tona 9,
Furthermore, since the subsequent reflection becomes total reflection, a bulk parasitic oscillation mode is stably generated. Furthermore, since the air-contacting surfaces of two KUSHIRADO glasses face each other in parallel with the laser glass in between, a surface parasitic oscillation mode occurs.

(Objective of the Invention) An object of the present invention is to provide a laser amplifier that eliminates the −F defect and suppresses the occurrence of parasitic oscillation.

(Structure of the Invention) That is, the present invention provides a structure in which the shape of the surface in contact with air of the clad glass for absorbing laser light, which is attached to the side surface that surrounds the two surfaces on which the laser light enters and exits, is in contact with the air. This is a laser amplifier using a disk-shaped laser glass as a laser medium, which is inclined with respect to a vertical line at an angle greater than or equal to 90 degrees minus an angle twice the total reflection angle.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 4 shows an embodiment of the present invention.

In the figure, in this example, the inclination of the air-contacting surface of the clad glass is 0 or more than a certain angle α perpendicular to the laser glass surface. Indicates the angle obtained by subtracting twice the angle.

For example, when one of the bulk parasitic oscillation mode light rays incident on the laser glass surface, that is, the light ray in the area surrounded by L41 and L42, is reflected by the clad glass air contact surface 12, the incident angle is already equal to the total reflection angle '. Since it is small, the reflectance is as low as 0.04 to 0.05.

Furthermore, the light rays in the column, that is, the light rays in the area surrounded by L43 and L44, undergo total internal reflection when reflected at the surface 21 of the laser glass and the air-contacting surface 13 of the clad glass, but at the surface 22 of the other laser glass. does not result in total reflection and has a reflectance of about 0.04 to 0.05. Therefore, in the bulk parasitic oscillation mode, oscillation becomes difficult due to loss in the amplification optical path.

Regarding the surface parasitic oscillation mode, the air-contacting surfaces of the clad glass that face the laser glass through the glass are parallel and large, so the reflectance is isometrically close to O, so there is no oscillation and there is no oscillation. . Further, in this embodiment, the air-contacting surface of the clad glass is separated into two surfaces, and the cross-sectional shape is linear, but it goes without saying that the number and shape of the surfaces are not limited to these.

(The germ of the invention) As mentioned above, by tilting the air-contacting surface of the clad glass to the laser gas surface on a critical angle plate that is perpendicular to the surface, a large amount of loss is caused in the optical path of parasitic oscillation. It is possible to obtain the effect of making it impossible to form a beam or an optical path itself. That is, according to the present invention, it is possible to obtain a laser amplifier in which parasitic oscillation is suppressed.

[Brief explanation of the drawing]

Figure 1 is a front view of the disc-shaped laser glass, Figure 2 is a side view showing the arrangement of the disc-shaped laser glass with respect to the laser beam, Figure 3 is a cross-sectional view of the conventional disc-shaped laser glass, and Figure 4 is the book. FIG. 1 is a cross-sectional view of a disk-shaped laser glass showing an embodiment of the invention. 1... Clad glass, 2... Laser glass, 11
゜12.13...Surface of clad glass in contact with air,
That is, air contact surface, 21.22... surface of laser glass, L31. L32. L41. L42. L43. L44
...Light ray indicating bulk parasitic oscillation mode, L33...
Ray showing surface parasitic oscillation mode. Agent: Susumu Uchihara, patent attorney. -8-,,,,+,,' Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] The shape of the surface in contact with the air of the clad glass for laser light absorption attached to the side surface surrounding the two surfaces where the laser light enters and exits is relative to a line perpendicular to the surface.
A laser amplifier using a disk-shaped laser glass as a laser medium, which is tilted at an angle greater than 90 degrees minus twice the angle of the total reflection surface.