JPH01181485A - Dye laser device - Google Patents

Abstract

PURPOSE:To synchronize the sweep frequency of a narrow band element and the sweep frequency of a laser resonator longitudinal mode, and to enable sweep by changing the cavity length of a laser resonator by a cavity-length changing means while following up pressure change in an airtight vessel. CONSTITUTION:A dye laser device has a cavity-length changing means composed of an output mirror drive 13 for moving an output mirror 2 in the direction of the optical path of a dye laser beam 6 and an output-mirror position controller 14 for operating the output mirror drive 13 on the basis of a pressure change signal from a pressure controller 9 controlling the pressure of a scanning gas filled in an airtight vessel 8. When pressure in the airtight vessel 8 changes, the position of the output mirror 2 varies while following up the pressure change, and the cavity length of a laser resonator is changed. Accordingly, the sweep frequency of an air space etalon and the sweep frequency of a laser resonator longitudinal mode are synchronized, thus allowing sweep.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention is directed to a single longitudinal mode oscillation dye laser device.

In particular, the present invention relates to a dye laser device capable of oscillating dye laser light of an arbitrary frequency with a narrow band.

(Prior Art) A dye laser device has conventionally been used as one of the laser oscillators. This dye laser device supplies a dye solution at high speed into a dye cell placed in a laser resonator, and in this state, excitation laser light of a certain wavelength is irradiated onto the dye solution flowing in one dye cell to dye the dye. By exciting the solution, dye laser light is oscillated by the action of a laser resonator. Dye laser devices are characterized in that their oscillation frequency is variable over a wide range and that they can be easily narrowed down. Among them, single longitudinal mode oscillation dye laser devices are noteworthy light sources in that they can provide extremely monochromatic laser oscillation with a frequency width of IGHz.

By the way, band narrowing elements such as etalons and gratings are usually used to narrow the band of a dye laser device.

Technical points for frequency sweeping of a narrowband dye laser device include "sweeping with good linearity" and "synchronization between each narrowband element." Sweep methods can be roughly divided into mechanical sweep methods and pressure sweep methods. In the former, for example, the oscillation frequency is swept by mechanically changing the angle of the etalon or grating, and the linearity of the sweep and the synchronization between each band narrowing element are realized by computer control via a feedback loop.

In single longitudinal mode oscillation dye laser devices, the mechanical sweep method is exclusively used because it is necessary to synchronize not only between each band narrowing element but also with the longitudinal mode of the resonator.

On the other hand, in the latter case, the frequency sweep is performed by changing the pressure within the laser resonator, and the above two points can be satisfied without intervening a complicated feedback loop, and the speed can be easily increased.

As described above, the pressure sweep method has advantages over the mechanical sweep method, and if this simple frequency sweep method can be applied to a single longitudinal mode oscillation dye laser device, it can become an extremely effective monochromatic light source.

Here, we will consider the case where the conventional pressure sweep method is applied to a single longitudinal mode oscillation dye laser device.

FIG. 3 is a block diagram showing an example of this type of single longitudinal mode oscillation dye laser device. In FIG. 3, a dye cell 3 is arranged inside a laser resonator consisting of a grating 1 that also serves as a reflection mirror and an output mirror 2, and a dye solution is supplied into the flow path of this dye cell 3. ing. Further, excitation laser light 4 oscillated from an excitation laser oscillator (not shown) is condensed by a condenser lens 5 and irradiated onto the dye solution in the dye cell 3. In this way, the dye solution is excited and converted into optical energy, and dye laser light 6 is oscillated by the action of the laser resonator.

On the other hand, 7 is an air space etalon which constitutes a band narrowing element together with the grating 1, and the grating 1 and the air space etalon 7 are installed in an airtight container 8. Further, this airtight container 8 is connected to a gas cylinder 10 via a pressure controller 9, and is filled with a sweep gas such as nitrogen gas. Thus, by changing the pressure within the airtight container 8 using the pressure controller 9, the pressure sweep of the oscillation frequency of the dye laser beam 6 is performed.

In addition, in FIG. 3, a prism beam expander 11 is installed inside the laser resonator.

This prism beam expander 11 is used to increase the diameter of the beam, for example, for the purpose of increasing the resolution of the band narrowing element. Further, the airtight container 8 is provided with a window 12 as shown in the figure.

Now, in the single longitudinal mode oscillation dye laser device as described above, when sweeping the oscillation frequency of the dye laser device, the sweep frequency of the band narrowing element and the sweep frequency of the laser resonator longitudinal mode are synchronized. Sweeping is a necessary condition. Now, consider a case where a grating 1 and an air space etalon 7 are used as band narrowing elements as shown in the figure. That is, in the case of pressure sweeping, the grating 1 and the air space etalon 7 are swept in synchrony. Therefore, we will focus on the air space etalon 7 and the laser resonator longitudinal mode.

First, the cavity length of the laser cavity is L −La + Lg +Ld = l
Suppose that it is expressed as i). Here, La is the length of the part occupied by the sweep gas in the laser resonator, Lg is the length of the part occupied by glass such as a prism, and Ld is the length of the part occupied by the dye solution.

It is assumed that the air space etalon 7 and the laser resonator longitudinal mode have been tuned in advance at V-Vo (V represents the oscillation frequency of the laser).

At this time, if the pressure inside the airtight container 8 is changed and the refractive index of the sweep gas becomes na-+na+Δna, the sweep frequency Δve of the air space etalon 7 and the sweep frequency ΔVe of the laser resonator longitudinal mode are respectively as follows. It becomes like this.

Δve−−ΔnaV□ /na
...(2)ΔVC−−ΔnBLaV, )/(ngLg
+ ndLd+ naLa) +++ (3). Here, ng is the refractive index of the glass, and nd is the refractive index of the dye solution.

From equations (2) and (3), if Lg −Ld −0, then Δ
Ve-ΔVc, the air space etalon 7 and the laser resonator longitudinal mode are swept in synchronization, and in principle it is possible to sweep the frequency infinitely. However, since there are actually restrictions on Lg and Ld, the pressure sweep width of the oscillation frequency in single longitudinal mode oscillation is limited. That is, when a certain limit is exceeded, a longitudinal mode hop occurs during the pressure sweep.

Next, to find this limit, we find the mode hop conditions.

Now, 1ΔVe−ΔVc l is the longitudinal mode interval C/2
Assuming that a mode hop occurs when the value becomes equal to (ng Lg +nd Ld +na La), the conditions for the mode hop are as follows.

C/2 (ng Lg +nd Ld +na La
) ■ΔnaVo/na ” (ngLg+ ndLd)
/(ngLg+ndLd+naLa)...(4) Therefore, Δna/nal wax-λ0/2 (ng L
g +nd Ld ) −(5) From formula (5), Δ
na/na1max is Lg.

If Ld is made smaller, it can be made larger, but these cannot be made much smaller. For example, Lg-10 Dragon, n
g-1,46 (refractive index of quartz).

Even when Ld = 10 mm and nd-1.36 (refractive index of ethyl alcohol), Δna/namax l-1,06X10'
...(6). If this is replaced with the sweep frequency, from equation (2), ΔV e −5,3(GHz) −
(7) becomes. In other words, even if Lg and Ld are made as small as possible, the pressure sweep in single longitudinal mode oscillation is 5.3
This means that frequency sweeping is possible only in an extremely narrow range (GHz), and it is impossible to perform a frequency sweep over a wide range (several tens to hundreds of GHz).

(Problems to be Solved by the Invention) As described above, the conventional single longitudinal mode oscillation dye laser device has a problem in that it is impossible to sweep the oscillation frequency over a wide range by pressure sweeping.

An object of the present invention is to provide a dye laser device capable of sweeping the oscillation frequency over a wide range by pressure sweeping while maintaining single longitudinal mode oscillation.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention irradiates excitation laser light to a dye solution supplied in a dye cell arranged in a laser resonator. This is a single longitudinal mode oscillation dye laser device that oscillates a dye laser beam by exciting a dye solution using a single longitudinal mode. The oscillation frequency of the dye laser beam is pressure-swept by changing the frequency, and the device includes a resonator length changing means that changes the resonator length of the laser resonator in accordance with pressure changes within the airtight container. .

(Function) Accordingly, in the present invention, by adopting the above means, the resonator length of the laser resonator is changed by the resonator length changing means in accordance with the pressure change in the airtight container, and thereby the band narrowing element is It becomes possible to synchronize the sweep frequency of the laser resonator with the sweep frequency of the longitudinal mode of the laser resonator.

(Example) The present invention will be described below with reference to an example shown in the drawings.

FIG. 1 is a diagram showing an example of the configuration of a single longitudinal mode oscillation dye laser device according to the present invention. The same parts as in FIG. state

That is, in addition to the dye laser device in FIG. 3, FIG.
Based on pressure change signals from an output mirror drive device 13 for moving the output mirror 2 along the optical path direction of the dye laser beam 6 and a pressure controller 9 for controlling the pressure of the sweep gas filled in the airtight container 8. Output mirror drive device 1
3 and an output mirror position control device 14 for operating the resonator length changing means. Here, the output mirror position control device 14 changes the position of the output mirror 2 via the output mirror drive device 13 in synchronization with a pressure change signal (pressure change rate and pressure absolute fit) from the pressure controller 9. Accordingly, the resonator length of the laser resonator is changed.

In the single longitudinal mode oscillation dye laser device having such a configuration, when the pressure inside the airtight container 8 changes, the position of the output mirror 2 changes to follow this pressure change, and the resonator length of the laser resonator changes. This makes it possible to synchronize and sweep the sweep frequency of the air space etalon 2 and the sweep frequency of the laser resonator longitudinal mode.

That is, what changes in this case is La in the above-mentioned equation (1). Assume that the pressure inside the airtight container 8 is changed so that the refractive index of the sweep gas becomes na-+na+Δna, and the resonator length of the laser resonator changes in synchronization with this. At this time, the sweep frequency ΔV of the air space etalon 7
e, the sweep frequency ΔVc of the laser resonator longitudinal mode is
(2) above.

Based on formula (3), ΔVe−−Δn 1VO/na
−(8)ΔVc −−(ΔnaLa+nHΔLa)/(
ngLg+ndLd+naLa>...(9). Here, if ΔVe - ΔVc, the air space etalon 7 and the laser resonator longitudinal mode are swept in synchronization. From equations (8) and (9), this condition is Δna/na−(ΔnaLa+naΔLa)/(ngL
g+ndLd+naLa)...(10) Therefore, ΔLa --(ngLg+ndLd)/na・Δa/n
a - (11).

Further, the pressure change ΔP and the refractive index change Δna have a proportional relationship, which is expressed by the following equation.

Δna! ΔP-2'rNmaΔP/RT
-(12) where Nll1 is Avogadro's number, R is the gas constant, α is the average polarizability of the swept gas molecules (or atoms), and T is the absolute temperature.

Substituting equation (12) into equation (11), ΔLa = −
(ng Lg +nd Ld) KΔP/na 2-
(13). Therefore, ΔLa = −(ng Lg +nd Ld) ・2
πNm aΔP/RT (14).

Therefore, the type of sweep gas is adjusted so that equation (14) is satisfied.
What is necessary is to determine the temperature, the amount of pressure change, the amount of change in output mirror position, and the laser resonator configuration (ng Lg , nd Ld ).

For example, the sweep gas is nitrogen gas, the temperature is T-300°, Lg-50mm, ng-1,47 (quartz glass),
When Ld = 10 mm, nd-1.36 (less ethyl alcohol), ΔLa is ΔLa −−32,7(n m/Torr) −( for unit pressure change (/Torr)
15). That is, in this case, by controlling the position of the output mirror 4 to move at a rate of change expressed by equation (15) in response to a change in the pressure inside the airtight container 8,
It is possible to sweep the pressure of the oscillation frequency while maintaining single longitudinal mode oscillation.

For example, assume that a piezoelectric element is used as the output mirror drive device 13. Assume that the stroke of the piezoelectric element is 5 μm at the maximum applied voltage IKv.

Assuming that the piezoelectric element exhibits a linear response to the applied voltage, the applied voltage change amount ΔV is ΔV −−8,2 (v/Toor) = i1
．． 6). Also, the frequency sweep band Δv m
For ax, the sweep frequency when using nitrogen gas is ~188 (
MHz /Toor), ΔVmax
=28. 7 (GHz) - (17) Howl.

As described above, in the single longitudinal mode oscillation dye laser device of this embodiment, the position of the output mirror 2 of the laser resonator is changed in accordance with the pressure change in the airtight container 8 filled with the sweep gas. Since the resonator length of the laser resonator is changed by changing the resonator length of the laser resonator, it is possible to synchronize the sweep frequency of the air space etalon 7 that constitutes the band narrowing element with the sweep frequency of the longitudinal mode of the laser resonator. can.

Therefore, when applying the frequency pressure sweep method to a single longitudinal mode oscillation dye laser device, conventionally the sweep width was at most several GHz.
The oscillation frequency can be pressure-swept over a high range while maintaining single longitudinal mode oscillation. Furthermore, the single longitudinal mode oscillation dye laser device of this embodiment is extremely superior to conventional mechanical sweep type dye laser devices in that it is easy to sweep a high frequency band and it is easy to increase the speed. It becomes possible to use it as a useful monochromatic light source.

Next, other embodiments of the present invention will be described.

FIG. 2 is a diagram showing another configuration example of the single longitudinal mode oscillation dye laser device according to the present invention. The same parts as in FIG. I will only talk about.

That is, FIG. 2 shows the output mirror drive device 13 and output mirror position control device 1 in the dye laser device of FIG.
4 is omitted, and instead of these, one glass plate 15 is rotatably provided on the optical path of the dye laser beam 6 in the laser resonator, and the pressure of the sweep gas filled in the airtight container 8 is controlled. A glass plate angle control device 16 that operates the glass plate 15 based on a pressure change signal from a pressure controller 9°.
The structure includes a resonator length changing means consisting of the following.

Here, the glass plate angle control device 16 changes the inclination angle of the glass plate 15 in synchronization with the pressure change signal (pressure change rate and pressure absolute value) from the pressure controller 9 in the same manner as described above. The resonator length of the resonator is changed.

In the single longitudinal mode oscillation dye laser device having such a configuration, when the pressure inside the airtight container 8 changes, the inclination angle of the glass plate 15 changes in accordance with this pressure change, and the resonator length of the laser resonator changes. By doing so, it becomes possible to synchronize and sweep the sweep frequency of the air space etalon 2 and the sweep frequency of the laser resonator longitudinal mode.

That is, what changes in this case is Lg in the above-mentioned equation (1). At this time, the sweep frequency ΔVe of the air space etalon 7 and the sweep frequency ΔVc of the laser resonator longitudinal mode are as described in (2) above.

Based on formula (3), Δve−−Δnl vO/na −
(18)ΔVc−−(ΔnaLa+ngΔLg)Vo/
(ngLg+ndLdtennaLa)...(19) It becomes.

Here, if Δve - ΔVc, the air space etalon 7 and the laser resonator longitudinal mode are swept synchronously, so ΔLg - (ng Lg + nd Ld ) /ng
・Δna/na −= (20) is sufficient.

Further, the thickness of the glass plate 15 is set to 1. When the tilt angle (-incident angle) is θ, the relationship between ΔLg and the change Δθ in the tilt angle θ is ΔLg−na2ng21stn(2θ)Δθ/2 (n
g2-na2sin2θ)3'2...(21)

Therefore, from equations (20) and (21), Δθ−112(ng Lg +nd Ld )(ng2
-na2sin2θ) 3. '2 /na2ng31s
tn (2・Δna/na−(22)).

Therefore, it is only necessary to change the inclination angle θ of the glass bell 15 so that equation (22) is satisfied.

For example, the thickness of the glass plate 15 is 1=3 mm, the inclination angle θ-3
If Δθ−(ngLg+
ndLd) (ng2-θ2)3''2/ng31θ・Δ
na/na...(23)

Substituting the same numerical value as when deriving equation (15) into equation (23), we get Δθ−0,141(μrad/Torr)
−(24).

That is, in this case, with respect to the pressure change inside the airtight container 8,
By controlling the tilt angle θ of the glass plate 15 to change at the rate of change expressed by equation (24), it is possible to sweep the oscillation frequency under pressure while maintaining single longitudinal mode oscillation.

In addition, in the embodiment shown in FIG. 2 above, the number of glass plates provided in the laser resonator does not necessarily have to be one.
For example, in order to suppress the positional fluctuation of the output light, two glass plates arranged in opposite directions may be provided in the laser resonator, and in this case, the inclination angle θ of the glass plate 15 is
The rate of change Δθ is 1/2 of the value shown by equation (24).

Further, in each of the above embodiments, a grating or an air space etalon is used as a band narrowing element, but other narrow band narrowing elements such as a double grating or a multi air space etalon may be used.

[Effects of the Invention] As explained above, according to the present invention, pressure changes in an airtight container equipped with a band narrowing element are followed.

Since the resonator length of the laser resonator was changed,
The sweep frequency of the band narrowing element and the sweep frequency of the laser resonator longitudinal mode can be swept in synchronization, and the oscillation frequency can be swept over a wide range by pressure sweep while maintaining single longitudinal mode oscillation. A possible dye laser device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of a dye laser device according to the present invention, FIG. 2 is a block diagram showing another embodiment of a dye laser device according to the present invention, and FIG. 3 is an example of a conventional dye laser device. FIG. 1... Grating, 2... Output mirror, 3...
- Dye cell, 4... Excitation laser beam, 5... Condensing lens, 6... Dye laser beam, 7... Air space etalon, 8... Airtight container, 9... Pressure controller, 10... Gas cylinder, 11... Prism beam expander, 12... Window, 13... Output mirror drive device, 14... Output mirror position control device,
15...Glass plate, 16...Glass plate angle control device. Applicant's agent Patent attorney Takehiko Suzue

Claims (3)

[Claims] (1) A single longitudinal mode oscillation dye that oscillates a dye laser beam by irradiating an excitation laser beam onto a dye solution supplied in a dye cell placed in a laser resonator to excite the dye solution. The laser device is equipped with a band narrowing element in an airtight container filled with a sweep gas, and pressure sweeps the oscillation frequency of the dye laser beam by changing the pressure in the airtight container, wherein the airtightness A dye laser device comprising a resonator length changing means for changing the resonator length of the laser resonator in accordance with pressure changes within the container. (2) The dye laser device according to item (1), wherein the resonator length changing means changes the position of the output mirror of the laser resonator in accordance with pressure changes within the airtight container. (3) The resonator length changing means is configured to change the inclination angle of the glass plate provided in the laser resonator in accordance with the pressure change in the airtight container. Dye laser equipment.