JPS5838954B2 - Excitation light focusing device for dye laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for condensing excitation light from a dye laser.

For excitation of the continuous wave dye laser, light from other continuous wave lasers, such as an argon ion laser, has so far been used.

In order to enable oscillation of the dye laser, the power density of the excitation light in the excitation region is normally required to be about 100 KW/cyiY.

In order to obtain this level of power density using a pumping laser with an output of several W (watts) and to achieve dye laser oscillation, the diameter of the pumping light beam must be several microns (microns) to several tens of microns.
Therefore, a suitable excitation light beam condensing device is required, and for this purpose one or more lenses are often used as this device.

On the other hand, a medium containing dye molecules, which is the active medium of a dye laser,
Alternatively, the surface of the dye cell (hereinafter simply referred to as dye solution) consisting of a transparent plate that defines the outer shape of this medium is designed to prevent the dye laser beam from being reflected at this surface. The angle of incidence is Bre
Along with this, the angle of incidence of the excitation light beam on the dye solution is also set to form the Brewster angle or an angle close to it for the purpose of increasing excitation efficiency. be.

FIG. 1 is an explanatory diagram of the function of an excitation light condensing device for a dye laser, which is comprised of lenses related to the arrangement of the dye solution and excitation light beam described above.

The excitation light beam 2 is focused by the lens 1, and enters the dye solution 3 at the Zobrusta angle to excite the dye molecules.

As a result, optical amplification occurs within the resonator constituted by the laser reflecting mirrors 4at4b and 4c, and as a result, the dye laser is oscillated and a dye laser beam 5 appears.

The dye laser beam 5 enters or exits the dye solution 3 at a Brewster angle between the laser reflector 4a and the laser reflector 4b.

In this figure, it is assumed that the excitation light beam 2 and the dye laser beam 5 are within the plane of the paper, and that the surface of the dye solution is perpendicular to the plane of the paper.

Now, the area where light amplification takes place in the dye solution 3 is
This is a region in the dye solution 3 that is shared by the dye laser beam 5 corresponding to the eigenstructure of the cavity and the excitation light beam 2. However, in order to increase the efficiency of the dye laser, the diameter of the dye laser beam 5 must be adjusted to match the dye solution 3. In 3, excitation light beam 2 in the same solution
It needs to be as small as the diameter of.

For this reason, the lens 1 must be Adjustments that involve slight movement of the position of are required.

Obviously, this movement of the lens 1 is preferably such that the area on which the excitation light beam 2 is focused can be moved to any position within a certain range.

This is realized by making such a movable lens 1 movable along three different directions.

It is desirable that two of these three directions be parallel to the surface of the dye solution 3.

This is because, if the positions of the excitation light beam 2 and the dye solution 3 entering the condenser are fixed, only by choosing the two directions as described above will the excitation light beam 2 in the dye solution 3 This is because it becomes possible to move the focused area in any direction parallel to the surface of the dye solution 3, and as a result, it is easy to match the area to an appropriate area where light amplification is performed.

For the arrangement shown in FIG. 1, it is possible to define the two directions more clearly by considering the convenience of adjustment.

These directions include, first, one is the normal line to the surface of the dye solution that passes through the region in the dye solution 3 where light amplification is performed, and the plane that includes both the dye laser beam 5 that passes through the same region (i.e., the direction toward the dye solution 3). The other direction is parallel to the line of intersection between the incident plane of the dye laser beam 5) and the surface of the dye solution, and the other direction is the direction parallel to the
The direction is perpendicular to the direction of and parallel to the surface of the dye solution.

The selection of these directions is determined by the excitation light beam 2 in FIG.
It is clear that the spatial arrangement between the dye solution 3 and the dye laser beam 5 is the one that best matches the resulting symmetry, so that adjustments involving movement of the lens 1 are made easier. .

For example, the direction of the excitation light beam 2 could be chosen as the remaining direction.

This is because by moving the lens 1 in the direction of the excitation light beam 2, the area where the excitation light beam 2 is focused can be located within the dye solution 3.

Now, in the method described above, by moving the lens 1 in a direction parallel to the surface of the dye solution 3, the incident height of the excitation light beam 2 to the lens 1, that is, the central axis of the lens 1 and the excitation light beam 2 changes, and as a result, the width direction of the excitation light beam 2 after passing through the lens 1 also changes.
This will happen.

In other words, by moving the lens 1 in a direction parallel to the surface of the dye solution 3, the angle of incidence of the excitation light beam 2 on the dye solution 3 changes.

The above-mentioned special lens 1 in two directions orthogonal to each other
If we compare the rate of change in the angle of incidence of the excitation light 2 on the dye solution 3 with respect to the movement of movement to results in a larger rate of change of the angle of incidence.

This is because a movement of the lens 1 in this direction changes the angle of incidence of the incident light beam 2 onto the dye solution 3 in the plane of incidence.

Let us now show, with a numerical example, the changes in the angle of incidence and refraction angle of the incident light beam 2 on the dye solution 3 that occur as the lens 1 moves in this direction.

It is assumed that the excitation light beam 2 is a diffraction-limited parallel beam, the beam radius is wl, and the wavelength of the excitation light is λ.

The focal length f of the lens 1 required to condense this excitation light beam 2 with the lens 1 and make the beam radius in the condensed area w2 is determined by the following equation.

Let us assume that the values of each parameter in equation (1) are roughly as follows in accordance with the actual situation of currently realized continuous wave dye lasers.

That is, Wl "" o, 5 vtm, W2-O,O
1mrn(=10p), λ=5×10-'
mrn (=5000 A).

At this time, the value of f is approximately 301n7IL from equation (1).

Now, it is assumed that the excitation light beam 2 is incident on the dye solution 3 at a Zobrusta angle.

Assuming that this dye solution 3 has a refractive index of 1.5, the Brewster angle θB is approximately 56 degrees.

Therefore, if the lens 1 is moved by L in the direction in question, the change in the incident height of the excitation light beam 2 to the lens 1 becomes h = L cos θB,
The change Δθ1 in the angle of incidence of the excitation light beam 2 onto the dye solution 3 has a magnitude expressed by the following equation.

It has a size expressed by .

Now let L = 1 mm, and for f and θB t n (using the values mentioned above, from equation (2), △θ,
+: 1.9 x 10-2 radian -1.1 degree,
Also, from equation (3), △θ2=8.3X10-3 radian=
It becomes 0.48 degrees.

Furthermore, let us assume here that the thickness of the dye solution 3 is 1 vtm, which is a typical value employed in continuous wave dye lasers.

Then, when the excitation light beam 2 is incident at the Brewster angle, the length through which the excitation light beam 2 passes through the dye solution 3 is approximately L2mrn.

Therefore, by moving the lens 1 by 1 mm in the predetermined direction (therefore, the condensing region of the excitation light beam 2 in the dye solution 3 does not simply move by 11n1rL, but by moving the lens 1 by 1 mm).
In addition to mk, due to the change in refraction angle Δθ2, the maximum value is 1.
2△θ2f: Excitation light beam 2 between 0.01 and about -10μ
[the deviation of] is brought about.

It should be noted that the magnitude of this maximum deviation is also as large as the diameter of the dye laser beam 5 within the dye solution 3.

Furthermore, it should be noted that both the excitation light beam 2 and the dye laser beam 5 are focused in the dye solution 3, but this focused area is extremely narrow and narrow.
Its length is of the order of the length that the excitation light beam 2 mentioned above passes through the dye solution.

This becomes clear when the magnitude of the confocal parameter b, which is well known as a parameter expressing the length of the focused region, is determined.

That is, the surface hole of b is given by, but here again W2 =
o, 01 mi! If Lyλ=5X10” then b
'F1.3.

Considering these facts (・Thus, clearly express the rotation brought about by the change in the angle of incidence of the excitation light beam 2 on the dye solution 3 caused by moving the lens 1 in the above-mentioned predetermined direction. becomes possible.

This will be explained next.

It is now assumed that the excitation light beam 2 is focused by the lens 1 at an appropriate position within the dye solution 3, and as a result, oscillation of the dye laser is realized.

However, if for some reason the excitation light beam 2 moves within the plane of incidence on the dye solution 3 and the height of incidence on the lens 1 changes, the oscillation of the dye laser will easily stop.

Therefore, in order to realize oscillation again, it is necessary to move the lens 1 in the above-mentioned predetermined direction and return the area where the excitation light beam 2 is focused to an appropriate position.

However, even if dye laser oscillation could be realized again in this way, it would be impossible to reproduce the original oscillation characteristics of the previous dye laser (e.g., the excitation light power threshold required for oscillation, input/output characteristics, etc.). Become.

This is because the change in the refraction angle of the excitation light beam 2 due to the surface of the dye solution 3 results in a displacement of the excitation light beam 2, as already mentioned, so that the excitation light beam 2 and the dye 1 nose beam 5 are disposed within the dye solution 3. This is because the shape and volume of the area shared by the two, ie, the area where optical amplification occurs, changes.

This change is further emphasized by the fact that both the excitation light beam 2 and the dye laser beam 5 are extremely elongated within the dye solution 3 mentioned above.

One step of movement of lens 1 (this is the amount of movement required to compensate for a slight change in the height of incidence of excitation light beam 2 on lens 1 by Q, 56 mm) is shown above in this regard. Numerical example [If you study carefully, it will be easy to understand how significant the changes in the shape and volume of the region where light amplification occurs are.

This invention is intended to eliminate the above-mentioned drawbacks, and includes a means provided in front of the lens that is driven in conjunction with the movement of the lens in the predetermined direction and that keeps the height of incidence of the excitation light beam on the lens constant. By providing this, the angle of incidence of the excitation light beam on the dye solution is kept constant and adjustment of the dye laser is facilitated.

FIG. 2 is a diagram for explaining one embodiment of the present invention.

The excitation light beam 2a is formed by two reflecting mirrors 6a and Bbl placed in parallel with each other at a distance d perpendicular to the plane of the paper, and becomes a beam 2b which is within the plane of the paper and parallel to 2a, and is condensed by the lens 1 to become a beam 2c. and enters the dye solution 3.

At this time, in FIG. 2, the angle θ between the normal line of the dye solution 3 and the excitation light beam 2C is the Brewster angle of the dye solution,
The lens 1 moves within the plane of the paper in a direction parallel to the line of intersection between the plane of incidence of the excitation light beam 2c and the dye solution 3.

On the other hand, the two reflecting mirrors 5a and 6b are assumed to be coaxial while maintaining a constant distance d around an axis perpendicular to the plane of the paper.

In FIG. 2, since the incident angle of the excitation light beam 2a is α, the interval H between the excitation light beams 2a and 2b is calculated using the following formula (%).On the other hand, the lens 1 is used to determine the extension and direction of the excitation light beam 2a. There is a position f of t from the intersection A with .

That is, t and H have the following relationship.

That is, by linking a so-called sine bar (5ine Bar) with a lever with a length of 2d/cosθ to the movement of lens 1 and changing α with t, the height of incidence of excitation light beam 2b on lens 1 can be kept constant. It turns out that it is possible to maintain

In reality, the thickness of the excitation light beam 2a is finite, so α=
Since it cannot be O, a finite value of α, for example α.

This method can only be used in larger areas.

Therefore, the value of t when α=α0. must be designed to satisfy the following equation.

Letting the value of H at this time be H8, H8 is given by the following equation.

FIG. 3 is a schematic diagram showing an embodiment of the present invention.

FIG. 3 is a view of (as seen from the left side). In FIG. 3, it is assumed that the excitation light beams 2 a e 2 b and 2 c are within the plane of the paper, and the dye laser beam 5 is also within the plane of the paper.

The lens 1 is fixed to a holder 8a, and this holder 8a has a sliding surface 1 relative to the holder 8b by rotating an adjustment screw 9a.
0a in a direction perpendicular to the plane of the paper.

The holder 8b is rotated by the adjustment screw 9b, so that the holder 8c
The dye solution 3 is moved parallel to the paper surface along the sliding surface 10b.

Accordingly, the lens 1 also moves in this direction.

Furthermore, by rotating the adjustment screw 9c, the holder 8c is moved in the left and right directions in the plane of the paper along the sliding surface 10c with respect to the holder base material 11 whose arrangement is fixed relative to the dye solution 3, that is, the excitation light beam 2a and 2b, and along with this, the lens 1 also moves in the same direction.

Reflecting mirrors 6a and 6b are parallel to each other and perpendicular to the plane of the paper (5)
, The following equation is obtained from equation (6).

It is attached to a stand 12 and rotates within the plane of the paper via a bearing 14 about a shaft 13 fixed to a holder 8d.

The holder 8d is fixed to the holder 8c.

For attachment, a lever 7a is attached to the stand 12, and a protrusion 17 is provided on this, and a lever 7b fixed to a holder 8b is in contact with this.

The surface 16 that contacts the protrusion 17 of the lever 7b is the sliding surface 10b.
The surface is perpendicular to the sliding direction of the surface, and the projection 17 is processed so that it can move smoothly on the surface.

The spring 18 is used to keep the protrusion 17 in constant contact with the lever 7b.

Here, the distance between the center of the shaft 13 and the protrusion is 2d/cos θ in order to satisfy equation (7).

The first adjustment of the apparatus is to ensure that the direction of the excitation light beam 2a is in the plane of the paper at Brewster's angle with the dye solution 3.

The excitation light beam 2b must then be adjusted to be incident on the center of the lens 1.

For this purpose, it is convenient if the protrusion 17 can be moved back and forth with respect to the lever 16, or if the length of the levers 7a and 7b in the moving direction of the holder 8b relative to the holder 8c is variable.

Other methods, such as allowing the holder 8a or 8c to move up and down within the plane of the paper, are also considered, but these are irrelevant to the essence of the present invention.

Next, the position of the excitation light beam 2c is adjusted by turning the adjustment screws 9a, 9h, and 9c so that the laser output is maximized.

At this time, even if the adjustment screw 9b is turned to move the holder 8b relative to the holder 8c, the levers 7a and 7b rotate the reflectors 6a and 6b, changing the height of the excitation light beam 2b, as described above. Since the height of incidence on the lens 1 is kept constant, the angle of incidence of the excitation light beam 2c on the dye solution does not change.

FIG. 4 is a diagram for explaining another embodiment of the invention.

Before entering the lens 1, the excitation light beam 2a passes through a parallel plate 20 having a thickness of D, emerges as an excitation beam 2b, and enters the lens 1.

The plane of incidence of the excitation light beam 2a on the parallel plate 20 is arranged so that the excitation light beams 2a, 2b and the predetermined movement direction of the lens 1 (in FIG. 2, this direction represents the amount of movement of the lens 1). (indicated by a double-headed arrow with a variable mark)).

In the figure, this plane of incidence is assumed to be within the plane of the paper.

The parallel plate 20 is rotated around a rotation axis 21 of the parallel plate perpendicular to the plane of the paper.

The position of the rotation axis 21 of this parallel flat plate may be arbitrarily selected as long as it is perpendicular to the plane of the paper.

When the excitation light beam 2a is incident on the parallel plate 20 at an incident angle ψ as shown in the figure, the excitation light beam 2b after exiting is translated by H as shown in the figure with respect to the incident excitation light beam 2a. shall be.

When the refractive index of the parallel plate 20 is n', H is calculated by the following formula. It is desirable that the angle of incidence of the excitation light beam 2b on the parallel plate 20 is at or near Brewster's angle.

Assuming that the material of the parallel plate 20 is a suitable glass, and assuming that its refractive index n' is 1.5, the Brewster angle is approximately 56.
In this case, the rate of change in the moving amount H of the excitation light beam 2b with respect to the rotation angle of the parallel plate 20 is obtained by differentiating equation (10).

Therefore, when the lens 1 is moved by L in the above-mentioned predetermined direction, the absolute value Δψ of the rotation angle of the parallel plate 6 required to keep the incident height of the excitation light beam 2b on the lens 1 unchanged is as follows.

As mentioned above, θB is about 56 degrees (12
) formula becomes further as follows.

△ψ-0,75L/D (radians) -43L/D (degrees) (12)' Now, the error caused by applying (12)' when the rotation angle of the parallel plate 6 is large is that the incident angle is 56 It depends on whether the value of dH/dψ when changing from the degree to a certain value ψ matches the value of equation (11).

The rate of change of dH/dψ with respect to ψ, that is, d2H/dψ2, is expressed as (
10) and numerically consider it, the value of ψ is at least between 50 degrees and 60 degrees (in this case, d2H/
dψ2 is constant, 2.5×1O-4D/(degree)
It can be seen that it takes a value of 2.

Therefore, let us now use numerical examples to show various characteristics assuming a fairly arbitrary value and a tolerance of 5 degrees.

First, the allowable rotation angle of the parallel plate (:20) is 0.05
1.3 x 10-2/2.5 x 10→=2.6 degrees.

Therefore, using equation (12'), within the currently assumed accuracy, the maximum value ΔL of the amount of movement of the lens 1 in the predetermined movable direction is as follows.

For example, if ΔL is required to be 1 mm, the thickness D of the parallel plate 20 may be 17 mm.

The value of △L in equation (13) is the value when the parallel plate 20 is rotated in one direction from ψ = 56 degrees, so when combined with rotation in the opposite direction, t is actually the movable range of the lens 1. is twice as large as △L.

Furthermore, when the parallel plate 20 is made of one transparent plate, within the above-mentioned allowable rotation angle, the change in loss caused by the reflection of the incident light beam 2 at both end surfaces l of the parallel plate 20 is the change in the loss of the excitation light beam 2. It is less than 0.2% of the power, which is insignificant.

Now, using the above numerical example, lens 1 is (13)
The change in the angle of incidence of the excitation light beam 2c passing through the lens 1 into the dye solution 3 when moving by ΔL given by the equation is 5% compared to the change when the parallel plate 20 is not provided. As a result, the influence on the various properties of the dye laser is significantly reduced.

FIG. 5 is a schematic diagram showing another embodiment of the present invention.

In the figure, excitation light beams 2a, 2b. 2c is t within the plane of the paper, and it is assumed that the plane of incidence of the dye laser beam 5 on the dye solution 3 coincides with the plane of the paper.

The lens 1 is fixed to a holder 8a, and this holder 8a has a sliding surface 1 relative to the holder 8b by rotating an adjustment screw 9a.
0a in a direction perpendicular to the plane of the paper.

The holder 8b is rotated by the adjustment screw 9b, so that the holder 8c
The paper is moved parallel to the surface of the paper and the surface of the dye solution 3 along the sliding surface 10b.

Accordingly, the lens 1 also moves in this direction.

Furthermore, the arrangement of the holder 8c relative to the dye solution 3 is fixed by rotation of the adjusting screw 9c.

It moves along the sliding surface 10c with respect to the holder base material 11 in the left and right directions in the plane of the paper, that is, along the direction of the excitation light beams 2a and 2b, and accordingly the lens 1 also moves in the same direction. The holder 8c is provided with a cam rotation shaft 22 perpendicular to the paper surface, and a cam 23 attached to this cam rotation shaft 22 is provided.
An elongated hole 24 is cut in a direction different from the moving direction of the holder 8ct of the holder 8b.

A pin 25 fixed to the holder 8b and extending perpendicular to the plane of the paper is inserted into this elongated hole 24, and this pin 25 is movable along the longitudinal direction of the elongated hole 24.

The rotating shaft 21 of the parallel plate 20 is fixed to the holder 8c, and the parallel plate 20 held by the holder 8d can rotate around it.

When the holder 8b is moved by the rotation of the adjustment screw 9b, the cam 23 is simultaneously rotated around the cam rotation shaft 22.
As a result of rotating the holder 8d that is in contact with the cam 23 around the rotating shaft 21 of the parallel plate, the parallel plate 20 also rotates.

According to this embodiment, the region on which the excitation light beam 2c is focused is positioned in the dye solution 3 by rotating the adjusting screw 9c, and then the adjusting screw 9a is rotated (thereby moving this region into the plane of the paper). If you can position it, all you need to do is adjust the adjustment screw 9.
By only rotating b, this area is covered by the excitation light beam 2c.
While keeping the angle of incidence on the dye solution 3 almost constant, the light can be moved to the most suitable position within the dye solution where light is amplified.

Although the above description has been made with reference to an example in which the excitation light beam is continuous, the present invention is not limited to this, and can also be applied to a dye laser that uses single or intermittently incident pulsed light as the excitation light.

It can also be applied to lasers other than dye lasers that use laser light as excitation light.

At this time, the laser medium is a liquid (not limited to a gas, solid, etc.).

Furthermore, although a lens is used as the condensing device in the above embodiment, it is also possible to apply a reflective optical system such as a concave mirror or a parabolic mirror.

In addition, in the above explanation, the change in the incident height of the excitation light comb due to the movement of the lens or parallel plate in a specific direction (although only this is mentioned, other directions, such as the direction perpendicular to the plane of the paper in FIG. It goes without saying that the above invention can be applied to the following.

As described above, according to the excitation light condensing device for a dye laser according to the present invention, the lens that condenses the excitation light beam is connected to the intersection line ( The incident height of the excitation light beam on the lens can be kept constant by moving in parallel to this direction and rotating the two reflecting mirrors or parallel plane waves provided in front of this lens by moving in the same direction. As a result, it is possible to significantly reduce the change in the angle of incidence of the excitation light beam onto the dye solution, so even if the excitation light beam moves, the oscillation characteristics of the dye laser can be adjusted by adjusting the movement of the lens. This provides excellent reproducibility.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the function of the excitation light focusing device for dye laser,
Fig. 2 is an explanatory diagram of the operation of an embodiment of the present invention, Fig. 3a
yb is an equipment configuration diagram showing one embodiment of this invention, FIG. 4 is an explanatory diagram of the operation of another embodiment of this invention, and FIG. 5 is a schematic diagram of another embodiment of this invention. In the figure, 1 is a lens, 2 is an excitation light beam, 3 is a dye solution, and 4
is a laser reflector, 5 is a dye laser beam, 6 is a reflector, 7 is a lever, 8 is a holder, 9 is an adjustment screw, 10 is a sliding surface, 11 is a holder base material, 12 is a mounting base, 13 is the axis,
14 is a bearing, 16 is a surface, 17 is a protrusion, 18 is a spring, 20
21 is a parallel plate, 21 is a rotating shaft of the parallel plate, 22 is a cam rotating shaft, 23 is a cam, 24 is an elongated hole, and 25 is a pin.

Claims (1)

[Claims] 1. A lens that focuses a light beam that excites dye molecules, which is an active medium of a dye laser, and a region where the excitation light beam is focused can be moved parallel to the surface of the active medium. An excitation light condensing device for a dye laser, comprising means for keeping the incident height of the excitation light beam on the lens constant according to movement in the movable direction. 2. Claim 1, which uses two reflecting mirrors that are provided in front of the lens and rotate in accordance with the movement in the movable direction as means for keeping the height of incidence of the excitation light beam on the lens constant. The excitation light focusing device for the dye laser described above. 3. The dye according to claim 1, which uses a parallel plate that is provided in front of the lens and rotates in accordance with the movement in the movable direction as a means for keeping the height of incidence of the excitation light beam on the lens constant. Excitation light focusing device for laser.