JPS58176989A - Stabilized frequency laser - Google Patents

Abstract

PURPOSE:To set operable condition within a short period with a heat generated from a laser tube without generation of mode hopping by sufficient forced expansion of supporting means through a heater. CONSTITUTION:A supporting rod 5 used as a supporting means is set in the forced heating condition with a heater 6 in the preceding stage where the feedback mechnism is operated for laser oscillation or stabilization. At this time, a heating temperature is set to a temperature which is further higher than the temperature to which the supporting rod 5, expanded up to a degree not allowing skip of vertical mode, reaches. Thereby, heat is not led to the supporting rod 5 from the laser tube 2 dueing laser oscillation and a thermal influence is hardly generated from the laser tube 2. Accordingly, the time required by the supporting rod 5 to be heated up to the specified temperature with a heater 6 is becomes the stand-by time required for obtaining stabilized frequency as the laser. Such time differs in accordance with a room temperature but it is very short period and the stand-by time required by a laser apparatus can be drasticaly curtailed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single frequency stabilized laser, which stabilizes the frequency in a short time at the beginning of use, and prevents mode hopping (order skipping) in one cycle. The aim is to minimize the

As is well known, for example, in a cass laser, there is one or more oscillation lines of the same wave number selected by the optical resonator within the Doppler width, and in the case of multiple oscillation lines, an etalon is placed inside the optical resonator. It is possible to make only one of them fully oscillate (single frequency).

And this frequency ν is between the resonator length and the length.

- Knee L The relational expression holds true. Here, C corresponds to the speed of light, 2 m, and the order of the longitudinal mode.

However, since the length of the crab resonator generally changes depending on external conditions such as environmental temperature and external force, the oscillation frequency also changes with this change. Therefore, in order to stabilize this frequency completely, the length of the resonator must be kept constant. It is necessary to maintain the value.

A typical structure of a resonator is that a pair of resonator reflecting mirrors are integrally arranged at both ends of a laser tube, and the reflecting mirrors are connected via a support, and the length of the resonator is connected to the support. It is influenced by the expansion and contraction caused by changes in external conditions.

Therefore, conventionally, at the connection part between the support and the reflection mirror,
The length of the resonator was kept constant by arranging a piezo element, an electrostrictive element, etc., detecting a change in frequency, and applying a voltage corresponding to the change to the element.

1) A structure in which a pipe for circulating water whose temperature is controlled with high precision is arranged near the support is considered to be complicated, and there are drawbacks and dissatisfaction such as the fact that it cannot be easily added to a conventional device. It existed.

Furthermore, in the conventional configuration, when the laser starts to oscillate, the heat generated by the laser tube flows into the support, the temperature of the support gradually rises, and the accompanying expansion of the support causes the longitudinal mode to disappear. jumps to larger orders one after another (mode hopping χ This jump in longitudinal modes occurs continuously over a long period of time, gradually increasing the pitch from an initially very short pitch until the support reaches a certain temperature) Therefore, the characteristic time required to obtain frequency stability sufficient to withstand use was unavoidable.And even if measures were taken to stabilize the frequency by arranging piezo elements as described above, However, if the elongation of the piezo element caused by the voltage application is not sufficient, the elongation of the support due to this heat generation cannot be absorbed by the contraction of the element, so it is necessary to wait for a long time until mode hopping does not occur. This is particularly noticeable when the resonator length is long.

Incidentally, for example, in some racers, the above-mentioned waiting time may extend to several hours, and the jump pitch in the longitudinal mode that is acceptable for use is about 30 minutes.

The present invention was devised in view of the above-mentioned drawbacks and inconveniences of the prior art, and includes a heater arranged on a support,
This heater is designed to be fully operated under predetermined conditions, and one embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a principle diagram of the present invention, in which reference numeral 1 denotes an external mirror type gas laser resonator, in which a pair of resonator m reflecting mirrors 3, spaced apart at a predetermined interval at both ends of a laser tube 2, 3 are placed opposite each other.

Each of the reflecting mirrors 3, 3 is attached to a holding plate 4, 4, respectively, to form a single reflecting mirror, and one holding plate 4.4 is supported by three supporting rods 5...all valves. connected.

Each of the support rods 5 is equipped with one heating heater 6 (as shown in the figure), or is placed in close contact with the heating heater 6. The heating heater 6 is connected to a controller 7, respectively. ing.

The heater 6 may be a nichrome wire as shown in the figure, or an infrared heater, etc. In the latter case, it may be placed near the rod 5 for irradiation.

Therefore, since the resonator 1 is connected to a pair of holding plates 4 holding the nine reflecting mirrors 3 by the rod 5, the distance between the holding plates 40, which is the length of the resonator, is the external force applied to the supporting rod 5. Although it depends on the conditions of interest,
Since the support rod 5 is provided with a power heater 6, the expansion and contraction of the support rod 5 can be controlled by adjusting the power via the controller 7. Therefore, when the frequency of the oscillated laser beam B slightly changes due to the expansion and contraction of the support rod 5, the heating heater 6 is activated to detect the change and, for example, when the support rod 5 is expanded, to contract it to a predetermined value. Just adjust the power.

Incidentally, the support body to which the reflection mirror unit in the external mirror type is screwed may be an optical bench.

In addition, the reflection mirror is integrated with a holding plate 4 on both ends of the laser tube 2.
Alternatively, an internal mirror type in which a tube holder is provided and a direct reflection mirror 3 is attached may be used. With this internal mirror type, the laser
The tube 2 itself also serves as the support, and in some cases it may have a double tube structure, with the inner tube serving as the laser tube 2 and the outer tube serving as the support.

Of course, if the support is an optical pliers, the heater 6 will be placed on this optical bench, or if it is an internal mirror type, the heater 6 will be wrapped directly around the laser tube 2 itself. I think I'll have to do something like that.

Various means for detecting the above-mentioned frequency change can be considered, but in the present invention, a part of the obtained laser beam B is divided, for example, through a half mirror 8,
The beam is made to pass through a frequency change detector 9 such as a split beam Ill iodine cell or a Fapry-Perot, and a photodetector 10 such as a phototransistor or photodiode, and the photodetector 10 is further connected to the controller 7.

Therefore, when the frequency of the desired laser beam B slightly changes due to the expansion and contraction of the support rod 5 due to the external conditions, the divided beam B passes through the frequency change detector 9.
The light intensity of ' changes, and the photodetector 10 detects this change in intensity and sends the signal to the controller 7 to control the power to the heater 6.

The method for detecting this frequency change will now be described in more detail.

Let's take a look at the 5145 large line of the argon laser.

For example, iodine gas has an absorption spectrum at exactly 5145λ, and in a relationship diagram with the vertical axis of transmission intensity and one frequency ν on the horizontal axis, it becomes a concave line as shown in Figure 2, and the resonator 1
By adjusting the etalon (not shown) placed inside the center so that the oscillation line is at point A, which is the shoulder of the curve, the frequency change detector 9 detects a slight change in the two frequencies. The intensity of light transmitted through a given iodine cell also varies slightly.

Therefore, in the controller 7, the photodetector 1o-y'))
Set the value of the measured transmission amount at point A, and if it exceeds the value, increase or decrease the power of the heating heater 6 or turn on or off.
If ff is activated, the support rod 5 can be expanded and contracted in response to slight frequency fluctuations of the laser beam B, thereby stabilizing the frequency.

To explain in detail how the above-mentioned device is used, first, before the feedback mechanism for laser oscillation or stabilization is activated, the support iron 5, which is a support body, is forcibly heated by the heating heater 6. This heating temperature is several to several degrees higher than the temperature reached at the time when the support rod 5 expands to the extent that a jump in the longitudinal mode does not occur unduly. Heat can flow from the laser tube 2 to the support rod 5 during one oscillation, so there is almost no thermal influence from the laser tube 2.

Therefore, the time required for the support rod 5 to reach a predetermined temperature by the heating heater 6 is the waiting time for a stable frequency that can be used as a laser, and it is extremely short, about 15 minutes, although it depends on the environment such as room temperature. This significantly reduces the waiting time required by conventional laser devices.

When the support rod 5 undergoes thermal fluctuations due to other external conditions while the use is continued in the above-mentioned state, the frequency change detector 9 and the photodetector 10 detect a slight change in frequency from the set frequency. The electric power of the heater 6 is increased/decreased via the controller 7, and the expansion state of the support rod 5 is adjusted to a desired value, thereby stabilizing the frequency.

The present invention employs one or more of the configurations and functions described above.

Therefore, since the support is forcibly expanded sufficiently in advance via a heating heater, the heat emitted from the laser tube can reach a usable state in a short period of time without causing mode-hora pink.

Then, by operating the heater using the controller, the resonator length can be kept constant at all times, and a laser beam with a desired extremely stable frequency can be obtained.

In addition, the present invention has a simple structure, can be manufactured at low cost, and can be implemented by simply adding a heater to a conventional device.The present invention exhibits excellent and effective effects.

[Brief explanation of drawings]

FIG. 1 is a principle diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing an example of the relationship between transmission intensity and frequency. Explanation of symbols 1...Resonator, 2...Laser tube, 3...
Reflection mirror, 4... Holding plate, 5... Support rod, 6
... Heater, 7... Controller, 8...
・Half mirror, 9...Frequency change detector, 10...
・Photodetector, B...laser beam.

Claims (1)

[Claims] A pair of resonator reflecting mirrors placed opposite each other at both ends of the laser tube are connected via a support, and a mirror is connected to the support in response to changes in optical output detected by a frequency change detector such as a Fabry Bellow. A frequency-lowering laser equipped with a heater whose power is controlled.