GB2331177A - Wavelength stabilisation of a laser device - Google Patents
Wavelength stabilisation of a laser device Download PDFInfo
- Publication number
- GB2331177A GB2331177A GB9823523A GB9823523A GB2331177A GB 2331177 A GB2331177 A GB 2331177A GB 9823523 A GB9823523 A GB 9823523A GB 9823523 A GB9823523 A GB 9823523A GB 2331177 A GB2331177 A GB 2331177A
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- GB
- United Kingdom
- Prior art keywords
- laser
- laser oscillator
- resonator
- temperature
- detecting
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/139—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/131—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
- H01S3/1317—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation by controlling the temperature
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/131—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
- H01S3/134—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation in gas lasers
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optics & Photonics (AREA)
- Lasers (AREA)
Abstract
A wavelength stabilizing device of a laser device such as a helium-neon laser 11 detects a constant thermal equilibrium of the laser oscillator 11a, making it possible to realize laser beam wavelength stabilization with high reproducibility. Thermal equilibrium of the laser oscillator is detected by photoelectric detectors 24a, 24b and fluctuation period detector 32 from the extension speed of the laser oscillator. When the fluctuation period becomes sufficiently great, feedback control of heaters 12 via a comparator 26 is started to stabilise the wavelength. A covering cylinder 42 and heater 43 surrounding the outer periphery of the laser are controlled and maintained at a set value by another feedback loop 41 including temperature sensors 44 and an ambient temperature setting device.
Description
WAVELENGTH STABILIZING DEVICE OF LASER DEVICE
The present invention relates to a wavelength stabilizing device of a laser device. More specifically, the present invention relates to a wavelength stabilizing device in a helium-neon (He-Ne) laser device wherein the length of the resonator is maintained as constant as possible independently of changes in the external environmental temperature, etc. to thereby facilitate the stabilization of the laser beam.
Examples of conventionally well-known methods for stabilizing the wavelength of the output laser beam in He
Ne laser (hereinafter simply referred to as "laser") include the so-called Lamb dip method, the 2-mode method, and the Zeeman method.
As the means for controlling such methods, a method based on PZT tuning, heater tuning, etc. or a method for controlling a fan, discharge current, etc. are generally used. At present, instead of mechanical control methods, a thermal tuning method which is more effective in various respects, that is, a wavelength stabilizing method in which the resonator length is maintained as constant as possible by heat-controlling the laser oscillator of the laser is mainly used.
In the case of thermal tuning for stabilizing the wavelength of a laser output, it is necessary to control the heating of the laser oscillator at a temperature higher than the thermally equilibrium state of the laser oscillator to constantly maintain the length of the resonator, which constitutes the laser light source unit, constant or substantially constant.
That is, in the above-mentioned thermal tuning, with the lighting operation of the laser device, the control for maintaining the resonator length constant, including the offset heating for wavelength stabilizing control, is started when it is detected that the laser oscillator is in a thermally equilibrium state.
For the detection of the thermally equilibrium state in the laser oscillator, the heating time for the laser oscillator or the duct wall temperature thereof, etc. is usually utilized. However, in the laser oscillator, the time it takes the thermally equilibrium state to achieve is influenced by the ambient temperature at the time of lighting and varies, so that it is not constant. Further, even if the duct wall temperature of the laser oscillator is in equilibrium and stable, the entire laser oscillator is not necessarily thermally in equilibrium.
Fig. 3 shows an example of the result of measurement of the duct temperature of a laser oscillator and the extension amount of the resonator of the laser oscillator as measured from the lighting of the laser device. The setting time for the duct wall temperature of the laser oscillator is compared with that for the extension amount of the resonator. As is apparent from this Fig. 3, the requisite time for the laser oscillator to achieve a thermal equilibrium is approximately 40 minutes in terms of the duct wall temperature and approximately 48 minutes in terms of the extension amount. Thus, if heating control is started when it is detected that the duct wall temperature of the laser oscillator has reached equilibrium, the laser oscillator it self will continue to gradually extend even afterwards, so that it is necessary to restrain the control amount and the heating amount.
This might be coped with, for example, by widely setting the heater temperature control range with respect to the laser oscillator. However, it would be then necessary to accordingly set the offset heating temperature of the heater for the wavelength stabilizing control high, with the result that more than necessary heater power is required.
On the other hand, it is by no means desirable, in terms of the service life of the laser oscillator, to use the laser oscillator at a high temperature. Further, as stated above, since the relationship between the duct wall temperature of the laser oscillator and the extension amount of the resonator of the laser oscillator depends upon the influence of the ambient temperature at the time of lighting the laser oscillator, the condition of the laser oscillator, the resonator length, etc. in wavelength stabilization vary, with the result that a difference is generated in the wavelength stabilizing performance of the laser device.
In view of the above problems in the conventional laser device, it is an object of the present invention to provide a wavelength stabilizing device of a laser device which always detects a constant thermal equilibrium of a laser oscillator and makes it possible to realize a wavelength stabilization of a laser beam that has a high level of reproducibility independently of changes in ambient temperature, the condition of the laser oscillator, etc.
To achieve the above object, in the wavelength stabilizing device of a laser device of the present invention, the thermal equilibrium of the laser oscillator is detected from the extension speed of the resonator of the laser oscillator, and the resonator length is controlled. Further, with the resonator length control by the extension speed of the resonator of the laser oscillator, the ambient temperature in the laser oscillator is controlled so as to be maintained at a predetermined value, whereby the thermal influence on the laser oscillator due to changes in the ambient temperature is removed, and the output wavelength of the laser beam is constantly stabilized and maintained at a constant level.
In accordance with the present invention, there is provided a wavelength stabilizing device of a laser device, comprising a laser light source unit using a laser oscillator, heating means for varying the resonator length of the laser oscillator, detecting means for detecting the extension speed of the resonator of the laser oscillator on the basis of a laser beam output from the laser light source unit, and control means for controlling the heating means to maintain the resonator length constant when the extension speed of the resonator of the laser oscillator as detected by the detecting means has reached a predetermined value.
In the above-described construction, the detection of thermal equilibrium to start the control for maintaining the resonator length by controlling the heating means is conducted at the extension speed of the resonator of the laser resonator, so that, as compared with the conventional case in which the heating time for the laser oscillator, the duct wall temperature of the laser oscillator, etc. are utilized, the control start time can be detected in a more stable manner, and the same control condition can always be reproduced. Further, the control amount for the heating means may be small, and the laser oscillator temperature can be controlled at a low level, so that it is possible to improve the service life of the laser oscillator.
In accordance with the present invention, there is further provided a wavelength stabilizing device of a laser device, comprising, a laser light source unit using a laser oscillator, first heating means for varying the resonator length of the laser oscillator, first detecting means for detecting the extension speed of the resonator of the laser oscillator on the basis of a laser beam output from the laser light source unit, first control means for controlling the first heating means to maintain the resonator length constant when the extension speed of the resonator of the laser oscillator as detected by the first detecting means has reached a predetermined value, a covering cylinder for surrounding the outer periphery of the laser oscillator to cover it, second heating means for varying the inner temperature of the covering cylinder corresponding to the ambient temperature of the laser oscillator, second detecting means for detecting the inner temperature, and second control means for controlling the second heating means by the detection temperature value of the second detecting means to maintain the inner temperature at a set value.
In the above construction, the thermal equilibrium of the laser oscillator is detected from the extension speed of the resonator of the laser oscillator with the ambient temperature with respect to the laser oscillator being maintained at a predetermined set value, and the first heating means is controlled to maintain the resonator length constant, so that it is always possible to perform control with the same resonator length independently of changes in the ambient temperature, the condition of the laser oscillator, etc.
In the above construction, the first detecting means preferably comprises an optical element for extracting polarization output of the laser beam from the laser oscillator, a photoelectric conversion element for converting the polarization output extracted by the optical element to an electric signal, and a fluctuation period detecting means for detecting the fluctuation period of the signal obtained through conversion by the photoelectric conversion element.
When the optical element and the photoelectric conversion element are accommodated in the covering cylinder, they are little affected by changes in the ambient temperature, whereby a more stable control is possible.
In the accompanying drawings:
Fig. 1 is a schematic diagram showing a helium-neon laser device to which a wavelength stabilizing device according to an embodiment of the present invention is applied;
Fig. 2 is a graph showing the results of measurement of the relationship between the extension amount of the resonator of the laser oscillator and the variation amount of the laser power in the laser light source unit of the above device; and
Fig. 3 is a graph showing the results of measurement of the duct wall temperature of the laser oscillator and the extension amount of the resonator of the laser oscillator as measured from the lighting in an ordinary laser device.
A preferable embodiment of the present invention will now be described in detail with reference to Figs. 1 and 2.
Fig. 1 is a schematic diagram showing an He-Ne laser device to which a wavelength stabilizing device according to this embodiment is applied.
Referring to Fig. 1, this laser device comprises a laser light source unit 11 using a laser oscillator lla, a pair of heaters 12 as first heating means wound around the peripheral surfaces of the end portions of the laser oscillator lla to control the resonator length of the laser oscillator lla, detecting means 31 as a first detecting means for detecting the extension speed of the resonator of the laser oscillator 11a on the basis of the laser output beam from the laser light source unit 11, control means 21 as a first control means for controlling the heaters 12 to maintain the resonator length constant when the extension speed of the resonator lla as detected by the detecting means 31 reaches a predetermined value, and a peripheral temperature setting device 41 for maintaining the set peripheral temperature of the laser oscillator ila constant. In the drawing, numeral 13 indicates a laser drive power source.
The control means 21 comprises a polarization beam splitter 22 for separating the laser output beam from the laser oscillator lla, a beam splitter 23 for separating one of the beams obtained through separation by the polarization beam splitter 22 into two beams, photoelectric conversion elements 24a and 24b for converting the other beam obtained through separation by the polarization beam splitter 22 and one beam of the beam splitter 23 to electric signals, amplifiers 25a and 25b for amplifying the outputs of the photoelectric conversion elements, a comparator 26 for comparing the outputs of the amplifiers 25a and 25b, and a control unit 27 for controlling the heating power supplied to the heaters 12 through a driver 28 such that the ratio of the outputs of the comparator 26, that is, the ratio of the outputs of the amplifiers 25a and 25b, is constant. In the drawing, numeral 29 indicates an offset voltage source for supplying offset voltage to the heaters 12 of the laser oscillator lia.
The detecting means 31 comprises the beam splitter 23, the photoelectric conversion element 24b, the amplifier 25b and a fluctuation period detector 32 for detecting the fluctuation period of the output signal from the amplifier 25b. When the fluctuation period of the output signal from the amplifier 25b exceeds a preset value, the fluctuation period detector 32 turns on a switch 33 to start control by the control means 21. That is, in this embodiment, the extension speed of the resonator of the laser oscillator lla is detected by the period of the power variation of the polarization output from the laser light source unit 11, and, when this period exceeds a preset value, it is determined that the laser oscillator ila is in thermal equilibrium.
Fig. 2 shows the results of measurement of the relationship between the extension amount A of the resonator of the laser oscillator lia and the variation amount B of the laser beam output power in the laser light source unit 11. As is apparent from the measurement results shown in Fig. 2, in the case of this laser oscillator lla, it was determined that it was in a thermal equilibrium when the period of the power variation of the laser beam had exceeded three minutes, whereby it was ascertained that the extension amount A of the laser oscillator lla afterwards is substantially within the range of ix (543 nm). Thus, in this case, the heaters 12 for controlling the resonator length have only to possess a control capacity of approximately +X. Thus, the control amount of the heaters 12 may be small, and the laser oscillator temperature can be controlled at a low level, so that the service life of the laser oscillator lia can be improved.
The peripheral temperature setting device 41 comprises a covering cylinder 42 surrounding the outer periphery of the laser oscillator lia to cover it, a heater 43 as a second heating means for varying the inner temperature of the covering cylinder 42 corresponding to the ambient temperature of the laser oscillator lla, temperature sensors 44 as a second detecting means consisting of a pair of thermistors or the like for detecting this inner temperature, a temperature comparator 45 for comparing the average value of the temperature detection values of these temperature sensors 44 with an external temperature setting signal Tref set to a predetermined temperature in advance, and a driver 46 for controlling the heating of the heater 43 by the comparison output of this temperature comparator 45. Further, the temperature comparator 45 and the driver 46 form a second control means 47 for controlling the heater 43 to maintain the inner temperature of the covering cylinder 42 constant.
The covering cylinder 42 has an outer peripheral portion surrounding the entire periphery of the laser oscillator lla equipped with the heaters 12. In the case of this embodiment, it is long enough to surround the entire periphery where the beam splitters 22 and 23 and the photoelectric conversion elements 24a and 24b are arranged.
That is, the beam splitters 22 and 23 and the photoelectric conversion elements 24a and 24b are accommodated in the interior of the covering cylinder 42. The temperature sensors 44 are arranged at positions corresponding to the axial ends of the laser oscillator lla.
Thus, the detection signal of the inner atmospheric temperature of the covering cylinder 42 detected by the temperature sensors 44, in other words, the temperature detection signal that is the average value of the ambient temperature of the laser oscillator 11a in the laser light source unit 11, is input to the temperature comparator 45 and compared with the external temperature setting signal
Tref set to a predetermined temperature in advance, and then the heater 43 is controlled by the comparison output through the driver 46. Due to this arrangement, the ambient temperature of the laser oscillator Ila is controlled and maintained at a preset value, so that it is possible to effectively remove the thermal influence on the laser oscillator lia due to changes in the ambient temperature.
In an example of experiment of this heating control of the heater 43, the temperature variation range corresponding to the interior of the covering cylinder 42 could be reduced to approximately 1/50 as compared with the conventional case, in which the covering cylinder 42 is not used. That is, when the external temperature is varied within the temperature range of 10 to 300C with the experimental device being accommodated in an electric furnace, it has been ascertained that the extension amount of the laser oscillator lla is 0.027 Zm/ C. This means that, when the external temperature changes by 10C, the temperature in the covering cylinder only changes by 0.020C. Further, as described above, by arranging the optical elements, the photoelectric conversion elements 24a and 24b, etc. including the laser oscillator lla, it is possible to satisfactorily mitigate the thermal influence due to the external temperature.
Thus, as described above, regarding the detection of the thermal equilibrium of the laser oscillator lla to start the wavelength stabilization control of the laser beam output in the laser device, it is conducted in correspondence with the extension speed of the resonator of the laser oscillator lia with the thermal influence on the laser oscillator lla due to changes in the ambient temperature being satisfactorily removed, whereby it is always possible to easily detect the stable control start time. As a result, it is possible to execute the resonator length control under the same conditions and, further, the intended wavelength stabilization control, effectively and with satisfactory reproducibility.
As described above, in the wavelength stabilizing device of a laser device of the present invention, the heating means is controlled and the detection of the thermal equilibrium to start the control for maintaining the resonator length constant is executed by the extension speed of the resonator of the laser oscillator, so that, as compared with the conventional case, in which the heating time for the laser oscillator, the duct wall temperature of the laser oscillator, etc. are utilized, a more stable control start time can be detected and it is always possible to reproduce the same control state. Further, since the control amount of the heating means may be small and the laser oscillator temperature can be controlled at a low level, it is possible to improve the service life of the laser oscillator.
Further, since the thermal equilibrium of the laser oscillator is detected from the extension speed of the resonator of the laser oscillator with the ambient temperature for the laser oscillator being controlled and maintained at a predetermined set value, and the heating means is controlled to maintain the resonator length constant, it is always possible to perform control with the same resonator length independently of changes in the ambient temperature, the condition of the laser oscillator, etc.
Claims (5)
1. A wavelength stabilizing device of a laser device, comprising a laser light source unit using a laser oscillator, heating means for varying the resonator length of the laser oscillator, detecting means for detecting the extension speed of the resonator of the laser oscillator on the basis of a laser beam output from the laser light source unit, and control means for controlling the heating means to maintain the resonator length constant when the extension speed of the resonator of the laser oscillator as detected by the detecting means has reached a predetermined value.
2. A wavelength stabilizing device of a laser device, comprising, a laser light source unit using a laser oscillator, first heating means for varying the resonator length of the laser oscillator, first detecting means for detecting the extension speed of the resonator of the laser oscillator on the basis of a laser beam output from the laser light source unit, first control means for controlling the first heating means to maintain the resonator length constant when the extension speed of the resonator of the laser oscillator as detected by the first detecting means has reached a predetermined value, a covering cylinder for surrounding the outer periphery of the laser oscillator to cover it, second heating means for varying the inner temperature of the covering cylinder corresponding to the ambient temperature of the laser oscillator, second detecting means for detecting the inner temperature, and second control means for controlling the second heating means by the detection temperature value of the second detecting means to maintain the inner temperature at a set value.
3. A wavelength stabilizing device of a laser device according to Claim 2, wherein the first detecting means comprises an optical element for extracting polarization output of the laser beam from the laser oscillator, a photoelectric conversion element for converting the polarization output extracted by the optical element to an electric signal, and a fluctuation period detecting means for detecting the fluctuation period of the signal obtained through conversion by the photoelectric conversion element.
4. A wavelength stabilizing device of a laser device according to Claim 3, wherein the optical element and the photoelectric conversion element are accommodated in the covering cylinder.
5. A laser device, substantially as described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30712297A JP3466441B2 (en) | 1997-11-10 | 1997-11-10 | Laser device wavelength stabilization device |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9823523D0 GB9823523D0 (en) | 1998-12-23 |
| GB2331177A true GB2331177A (en) | 1999-05-12 |
| GB2331177B GB2331177B (en) | 2002-05-15 |
Family
ID=17965304
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9823523A Expired - Lifetime GB2331177B (en) | 1997-11-10 | 1998-10-27 | Wavelength stabilizing device of laser device |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP3466441B2 (en) |
| GB (1) | GB2331177B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1775805A1 (en) * | 2005-10-14 | 2007-04-18 | Leica Geosystems AG | Frequency Stabilised Gaslaser |
| CN102545025A (en) * | 2012-01-11 | 2012-07-04 | 哈尔滨工业大学 | Double-longitudinal-mode laser preheating method based on hot adjustment of cavity length |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010109289A (en) * | 2008-10-31 | 2010-05-13 | Sunx Ltd | Excited state deciding method of laser oscillating device, laser oscillating device and laser processing device |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4908829A (en) * | 1987-11-30 | 1990-03-13 | Su "Kliment Ohridski" | Laser frequency stabilization by active resonator length regulation |
-
1997
- 1997-11-10 JP JP30712297A patent/JP3466441B2/en not_active Expired - Fee Related
-
1998
- 1998-10-27 GB GB9823523A patent/GB2331177B/en not_active Expired - Lifetime
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4908829A (en) * | 1987-11-30 | 1990-03-13 | Su "Kliment Ohridski" | Laser frequency stabilization by active resonator length regulation |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1775805A1 (en) * | 2005-10-14 | 2007-04-18 | Leica Geosystems AG | Frequency Stabilised Gaslaser |
| CH697822B1 (en) * | 2005-10-14 | 2009-02-27 | Leica Geosystems Ag | A method for the frequency stabilization of a gas laser and frequency-stabilized laser glass. |
| US7529285B2 (en) | 2005-10-14 | 2009-05-05 | Leica Geosystems Ag | Frequency stabilised gas laser |
| CN102545025A (en) * | 2012-01-11 | 2012-07-04 | 哈尔滨工业大学 | Double-longitudinal-mode laser preheating method based on hot adjustment of cavity length |
| CN102545025B (en) * | 2012-01-11 | 2013-04-24 | 哈尔滨工业大学 | Double-longitudinal-mode laser preheating method based on hot adjustment of cavity length |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH11145544A (en) | 1999-05-28 |
| GB9823523D0 (en) | 1998-12-23 |
| JP3466441B2 (en) | 2003-11-10 |
| GB2331177B (en) | 2002-05-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Expiry date: 20181026 |