CA1303709C - Laser device - Google Patents
Laser deviceInfo
- Publication number
- CA1303709C CA1303709C CA000593254A CA593254A CA1303709C CA 1303709 C CA1303709 C CA 1303709C CA 000593254 A CA000593254 A CA 000593254A CA 593254 A CA593254 A CA 593254A CA 1303709 C CA1303709 C CA 1303709C
- Authority
- CA
- Canada
- Prior art keywords
- wavelength
- fabry
- laser
- gas
- perot etalon
- 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.)
- Expired - Fee Related
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Abstract
ABSTRACT OF THE DISCLOSURE
A laser device comprises a Fabry-Perot etalon for selecting a wavelength of laser oscillation, a wavelength monitoring device for monitoring a laser beam emitted from an oscillation wavelength changing type laser oscillator and a pressure adjuster for adjusting a pressure of gas in a gap in the Fabry-Perot etalon by the output signal of the wavelength monitoring device. The Fabry-Perot etalon is received in a sealed container filled with gas.
A laser device comprises a Fabry-Perot etalon for selecting a wavelength of laser oscillation, a wavelength monitoring device for monitoring a laser beam emitted from an oscillation wavelength changing type laser oscillator and a pressure adjuster for adjusting a pressure of gas in a gap in the Fabry-Perot etalon by the output signal of the wavelength monitoring device. The Fabry-Perot etalon is received in a sealed container filled with gas.
Description
LASER DEVICE
The present invention relates to a laser device for stabilizing the wavelength of the laser beam.
In the appended drawings:
Figure 1 is a diagram showing a conventional laser device;
lQ Figure 2 is a structural diagram showing an embodiment of the laser device according to the present invention;
Figure 3 is a diagram showing an intensity distribution of a fringe on an image pickup element 22;
Figure 4, is a diagram showing another embodiment of the present invention; and Figure 5 is a diagram showing a still another embodiment of the present invention.
Figure 1 is a diagram showing a conventional wavelength tuning type laser device disclosed, for instance, in "Applied Optics", July 1974, vol. 13, No. 7, pages 1625-1628. In Fiyure 1, a reference numeral 1 designates a laser oscillator, e.g., a dye laser in this case, a numeral 2 designates a partial reflection mirror, a numeral 3 designates a gap type Fabry-Perot etalon (hereinbelow, referred to as an FP), a numeral 4 designates a sealed container filled with gas and containing therein the FP 3, a numeral 5 designates a laser beam, a numeral 6 designates a pressure gauge to measure a gas pressure in the sealed container 4~ a symbol G designates a gas bomb, numerals 7 and 8 designate valves and a numeral 9 designates a grating.
~303709 The operation of the conventional laser device will be described. A wavelength of a laser emitted from the laser oscillator 1 is selected by means of various elements in the oscillator. In an example in the conventional device, the width of the oscillation wavelength is narrowed by inserting spectroscopic elements such as the grating 9 and the FP into a resonator. By adjusting the spectroscopic elements, the wavelength can be determined to be a desired wavelength within the width of the originally existing oscillation wavelength. In the conventional laser device, the selection of the wavelength is performed by changing an angle of inclination of the grating 9, or by changing the refraction index of gas between a gap in the FP 3, the refraction index being changed by changing a pressure of gas in the sealed container 4. The wavelength can be roughly adjusted by changing the angle of inclination of the grating 9. On the other hand, the wavelength can be finely adjusted by adjusting the pressure of gas between a gap in the FP 3. The adjustment of the gas pressure can be performed by measuring a pressure of gas by means of the pressure gauge 6 and by opening/closing operations the valves 7 and 8 as a result of the measurement.
In the conventional laser device having the construction described above, there was the problem that a pressure gauge capable of indicating a value of smaller than 0.1% in the full scale was needed in order to precisely tune the wavelength, with an accuracy of, for instance +0.01 nm.
It is an object of the present invention to provide a laser device capable of tuning accurately the wavelength and of stabilizing the wavelength.
~3~)3709 The foregoing and other objects of the present invention have been attained by providing a laser device which comprises a Fabry-Perot etalon for selecting a wavelength of laser oscillation, a wavelength monitoring means for monitoring a laser beam emitted from an oscillation wavelength changing type laser oscillator and means for adjusting a pressure of gas in a gap in the Fabry-Perot etalon by the output signal of the wavelength monitoring means.
Preferred embodiments of the laser device according --` 1303709 to the present invention will be described.
In Figure 2, reference numerals 1 through 4 designate the same elements as in Figure 1. However, the wavelength tuning type Fabry-Perot etalon (FP) 3 is received in the sealed container 4. A total reflection mirror 10 is disposed opposite the partial reflection mirror 2 with respect to the FP 3. A volume adj~stable Carn~q~ n/cat~
means 11 which may be a bellows is comminuo~tcd with the sealed container 4. A driving means 12 is connected to the volume adjustahle means 11 so that it can expand and contract the volume of the volume adjustable means 11.
A numeral 13 designates a laser beam generated fro~
an oscillation means, which comprises the laser oscillator 1, the total reflection mirror 10, the partial reflection mirror 2 and the FP 3. A mirror 14 is disposed in a path for laser beam 13 to take out a part of the laser beam 13.
A numeral 15 designates a wavelength monitoring means which has a spectroscopic function for the laser beam taken out through the beam separating mirror 140 The wavelength monitoring means 15 is constituted by an interference filter 16 which permits only the laser beam 13 to pass therethrough, a light strength adjusting filter 17, an integrator 18 for defusing the laser beam 13, a monitoring FP 19 having a gap, a sealed container 20 which sealingly receives the FP 19 and a lens 21.
A numeral 22 designates an image pickup element for observing fringes produced by the FP 19. The image pickup element 19 may be a first-dimensional image sensor. A numeral 23 designates a light shielding box which receives the above-mentioned elements 16-22 and shields light from the outside, and in which the interference filter 16 is disposed to allow the laser beam from the beam separating mirror 1~ to enter into the box 23. A numeral 24 designates a temperature adjusting means which keeps the temperature of the FP 19 to be constant, and a numeral 25 designates a picture image processing means whcih analyzes the fringes and outputs a signal to the driving means 12.
The operation of the above-mentioned embodiment of the present invention will be described.
The wavelength of the laser beam emitted from the laser oscillator 1 is selected by the various elements in the oscillator. In case of an excimer laser, the width of the wavelength can be narrower than that of the originally produced wavelength, i.e. a width of several angstrom, by installing the spectroscopic elements such as a prism, a grating, an FP and so fourth in the resonator. Further, by adjusting the spectroscopic elements, the wavelength can be determined to be a desired wavelength within the width of the originally exsisting wavelength.
A part of the thus obtained laser beam 13 is 130:~709 introduced in the wavelength monitoring means 15 which utilizes the FP 19 to determine the wavelength.
In this embodiment, circular fringes which appear when the light is transmitted through the FP 19 is utilized. The diameters o~ the fringes are related to a value ~ in the following equation (1), and a wavelength ~m can be obtained from the equation (1) by obtaining the value ~. The FP is so constructed that two mirrors having a high degree of flatness face with a gap, and the wavelength at the center of the light which passes through the mirrors at an angle of ~ gives a specified wavelength which can be expressed by:
2nd cos ~
~m = . .. (1) m where n is a refraction index of the gap and m is an integer.
The intensity of the light having ~m in the distribution of the wavelength of the oscillated laser beam is obtainable by using an FP having a high resolution. Since a laser beam generally has an angle of divergence, only a component of the laser beam which satisfies the above-mentioned equation transmits and forms ring-like interference fringes around the center of the optical axis of the laser beam.
The wavelength monitoring means 15 has the integrator 18 which weakens or diffuses the laser beam, the FP 19 and the lens 21. Of divergence components produced by the integrator 18, only the light having ~
which satisfies the above-mentioned equation reaches the lens 21 through the FP 19. When the focal distance of the lens is represented by f, the light having the component of ~ is focussed on the point apart from the axis of the lens by f~. Then, the value ~ is obtainable by measuring the light focussing point by means of the image pickup element 22; thus the value A can be calculated.
The light intensity distribution on the image pickup element 22 is as shown in Figure 3, wherein the ordinate represents a distance x from the center of the fringes.
Each peak corresponds to the number of power of the FP.
The space between adjacent peaks is called a free spectrum range, and the wavelength can be primarily determined in this range. Since the free spectrum range can be determined when an FP is designed, it is so determined as to be broader than a value in estimation of a shift of wavelength.
Each of the peaks has a light intensity distribution corresponding to the wavelength distribution of a laser beam. Accordingly, the picture image processing means 25 is needed to obtain the value ~ by processing the light intensity distribution. Further, in this embodiment, the wavelength A at present is calculated and then, the volume adjustable means 11 is actuated by the driving 13~3~
means 12 depending on a result of the calculation of the wavelength A, whereby the wavelength of the oscillator i~
adjusted by adjusting a pressure in the sealed container 4.
In the above-mentioned embodiment, description has been made as to the wavelength monitoring means in which the fringes of the FP are measured by the image pickup element. However, the same effect can be attained by using another type of wavelength monitoring means.
Figure 4 is a diagram showing another embodiment of the laser device according to the present invention. In Figure 4, the same reference numerals as in Figure 2 designate the same elements. A numeral 26 designates a gas bomb for supplying clean gas in the sealed container 4, numerals 27 and 28 respectively designate adjusting valves provided at the inlet and the outlet of the sealed container 4 respectively to adjust a flow rate of gas, numerals 29 and 30 respectively designate stop valves, and a numeral 31 designates a control device which receives an output signal from the wavelength monitoring means 101 to thereby control the adjusting valve 27.
The control device 31 is such that it receives the output of the picture image processing means 25 to obtain the wavelength of the laser beam 13 at present, and it controls the adjusting valve 27 for adjusting a flow rate of gas so that a ~as pressure around the FP 3 is adjusted, whereby the wavelength of the laser beam 13 has a predetermined value. The adjusting valve 27 is manually adjusted at the initial step of adjustmentO
The function of selecting the wavelength by the FP is the same as that of the FP 19 for monitoring the wavelength.
In this embodiment, the adjusting valve 27 at the inlet side of the sealed container 4 is controlled by the control device 31. ~owever, it is possible that only the adjusting valve 28 at the outlet side of the sealed container 4 is controlled. Orl the both adjusting valves 27, 28 may be controlled to thereby adjust a gas pressure in the sealed container 4. The adjusting valves 27, 28 may be replaced by orifices or a mass-flow controller or the like to thereby control a flow rate of gas, hence a gas pressure.
Figure 5 is a diagram showing another embodiment of the laser device according to the present inventionc The construction of this embodiment is the same as that as shown in Figure 4 provided that a pressure sensor 32 and a control device 33 for keeping a pressure constant are added. Namely, the pressure sensor 32 is provided at the sealed container 4 so that the output signal of the pressure sensor 32 and an output signal having information of the wavelength which is generated from the control device 20 are inputted in the control device 33 "`" 1303709 for keeping the pressure to be constant, whereby the adjusting valve 27 for adjusting a flow rate of the gas can be controlled through the device 33. Thus, a gas pressure in the sealed container 4 can be easily adjusted.
In the above-mentioned embodiments, the FP 19 for monitoring the wavelength is not provided in the atmosphere where the clean gas is supplied, in the same manner as the FP 3 for selecting the wavelength. It is because the FP 19 is so constructed that only small part of the laser beam 13 enters in the FP 19. However, further excellent result is obtainable when the FP 19 is disposed in the atmosphere in which clean gas is supplied.
In this embodiment, description has been made as to the wavelength monitoring means 101 in which the fringes resulted by the light transmitted through the FP 19 are measured by the image pickup element 22. However, the wavelength may be measured by another method.
The present invention i5 useful for stabilizing the exC ~n~r wavelength of a laser device such as an oximor laser device.
The present invention relates to a laser device for stabilizing the wavelength of the laser beam.
In the appended drawings:
Figure 1 is a diagram showing a conventional laser device;
lQ Figure 2 is a structural diagram showing an embodiment of the laser device according to the present invention;
Figure 3 is a diagram showing an intensity distribution of a fringe on an image pickup element 22;
Figure 4, is a diagram showing another embodiment of the present invention; and Figure 5 is a diagram showing a still another embodiment of the present invention.
Figure 1 is a diagram showing a conventional wavelength tuning type laser device disclosed, for instance, in "Applied Optics", July 1974, vol. 13, No. 7, pages 1625-1628. In Fiyure 1, a reference numeral 1 designates a laser oscillator, e.g., a dye laser in this case, a numeral 2 designates a partial reflection mirror, a numeral 3 designates a gap type Fabry-Perot etalon (hereinbelow, referred to as an FP), a numeral 4 designates a sealed container filled with gas and containing therein the FP 3, a numeral 5 designates a laser beam, a numeral 6 designates a pressure gauge to measure a gas pressure in the sealed container 4~ a symbol G designates a gas bomb, numerals 7 and 8 designate valves and a numeral 9 designates a grating.
~303709 The operation of the conventional laser device will be described. A wavelength of a laser emitted from the laser oscillator 1 is selected by means of various elements in the oscillator. In an example in the conventional device, the width of the oscillation wavelength is narrowed by inserting spectroscopic elements such as the grating 9 and the FP into a resonator. By adjusting the spectroscopic elements, the wavelength can be determined to be a desired wavelength within the width of the originally existing oscillation wavelength. In the conventional laser device, the selection of the wavelength is performed by changing an angle of inclination of the grating 9, or by changing the refraction index of gas between a gap in the FP 3, the refraction index being changed by changing a pressure of gas in the sealed container 4. The wavelength can be roughly adjusted by changing the angle of inclination of the grating 9. On the other hand, the wavelength can be finely adjusted by adjusting the pressure of gas between a gap in the FP 3. The adjustment of the gas pressure can be performed by measuring a pressure of gas by means of the pressure gauge 6 and by opening/closing operations the valves 7 and 8 as a result of the measurement.
In the conventional laser device having the construction described above, there was the problem that a pressure gauge capable of indicating a value of smaller than 0.1% in the full scale was needed in order to precisely tune the wavelength, with an accuracy of, for instance +0.01 nm.
It is an object of the present invention to provide a laser device capable of tuning accurately the wavelength and of stabilizing the wavelength.
~3~)3709 The foregoing and other objects of the present invention have been attained by providing a laser device which comprises a Fabry-Perot etalon for selecting a wavelength of laser oscillation, a wavelength monitoring means for monitoring a laser beam emitted from an oscillation wavelength changing type laser oscillator and means for adjusting a pressure of gas in a gap in the Fabry-Perot etalon by the output signal of the wavelength monitoring means.
Preferred embodiments of the laser device according --` 1303709 to the present invention will be described.
In Figure 2, reference numerals 1 through 4 designate the same elements as in Figure 1. However, the wavelength tuning type Fabry-Perot etalon (FP) 3 is received in the sealed container 4. A total reflection mirror 10 is disposed opposite the partial reflection mirror 2 with respect to the FP 3. A volume adj~stable Carn~q~ n/cat~
means 11 which may be a bellows is comminuo~tcd with the sealed container 4. A driving means 12 is connected to the volume adjustahle means 11 so that it can expand and contract the volume of the volume adjustable means 11.
A numeral 13 designates a laser beam generated fro~
an oscillation means, which comprises the laser oscillator 1, the total reflection mirror 10, the partial reflection mirror 2 and the FP 3. A mirror 14 is disposed in a path for laser beam 13 to take out a part of the laser beam 13.
A numeral 15 designates a wavelength monitoring means which has a spectroscopic function for the laser beam taken out through the beam separating mirror 140 The wavelength monitoring means 15 is constituted by an interference filter 16 which permits only the laser beam 13 to pass therethrough, a light strength adjusting filter 17, an integrator 18 for defusing the laser beam 13, a monitoring FP 19 having a gap, a sealed container 20 which sealingly receives the FP 19 and a lens 21.
A numeral 22 designates an image pickup element for observing fringes produced by the FP 19. The image pickup element 19 may be a first-dimensional image sensor. A numeral 23 designates a light shielding box which receives the above-mentioned elements 16-22 and shields light from the outside, and in which the interference filter 16 is disposed to allow the laser beam from the beam separating mirror 1~ to enter into the box 23. A numeral 24 designates a temperature adjusting means which keeps the temperature of the FP 19 to be constant, and a numeral 25 designates a picture image processing means whcih analyzes the fringes and outputs a signal to the driving means 12.
The operation of the above-mentioned embodiment of the present invention will be described.
The wavelength of the laser beam emitted from the laser oscillator 1 is selected by the various elements in the oscillator. In case of an excimer laser, the width of the wavelength can be narrower than that of the originally produced wavelength, i.e. a width of several angstrom, by installing the spectroscopic elements such as a prism, a grating, an FP and so fourth in the resonator. Further, by adjusting the spectroscopic elements, the wavelength can be determined to be a desired wavelength within the width of the originally exsisting wavelength.
A part of the thus obtained laser beam 13 is 130:~709 introduced in the wavelength monitoring means 15 which utilizes the FP 19 to determine the wavelength.
In this embodiment, circular fringes which appear when the light is transmitted through the FP 19 is utilized. The diameters o~ the fringes are related to a value ~ in the following equation (1), and a wavelength ~m can be obtained from the equation (1) by obtaining the value ~. The FP is so constructed that two mirrors having a high degree of flatness face with a gap, and the wavelength at the center of the light which passes through the mirrors at an angle of ~ gives a specified wavelength which can be expressed by:
2nd cos ~
~m = . .. (1) m where n is a refraction index of the gap and m is an integer.
The intensity of the light having ~m in the distribution of the wavelength of the oscillated laser beam is obtainable by using an FP having a high resolution. Since a laser beam generally has an angle of divergence, only a component of the laser beam which satisfies the above-mentioned equation transmits and forms ring-like interference fringes around the center of the optical axis of the laser beam.
The wavelength monitoring means 15 has the integrator 18 which weakens or diffuses the laser beam, the FP 19 and the lens 21. Of divergence components produced by the integrator 18, only the light having ~
which satisfies the above-mentioned equation reaches the lens 21 through the FP 19. When the focal distance of the lens is represented by f, the light having the component of ~ is focussed on the point apart from the axis of the lens by f~. Then, the value ~ is obtainable by measuring the light focussing point by means of the image pickup element 22; thus the value A can be calculated.
The light intensity distribution on the image pickup element 22 is as shown in Figure 3, wherein the ordinate represents a distance x from the center of the fringes.
Each peak corresponds to the number of power of the FP.
The space between adjacent peaks is called a free spectrum range, and the wavelength can be primarily determined in this range. Since the free spectrum range can be determined when an FP is designed, it is so determined as to be broader than a value in estimation of a shift of wavelength.
Each of the peaks has a light intensity distribution corresponding to the wavelength distribution of a laser beam. Accordingly, the picture image processing means 25 is needed to obtain the value ~ by processing the light intensity distribution. Further, in this embodiment, the wavelength A at present is calculated and then, the volume adjustable means 11 is actuated by the driving 13~3~
means 12 depending on a result of the calculation of the wavelength A, whereby the wavelength of the oscillator i~
adjusted by adjusting a pressure in the sealed container 4.
In the above-mentioned embodiment, description has been made as to the wavelength monitoring means in which the fringes of the FP are measured by the image pickup element. However, the same effect can be attained by using another type of wavelength monitoring means.
Figure 4 is a diagram showing another embodiment of the laser device according to the present invention. In Figure 4, the same reference numerals as in Figure 2 designate the same elements. A numeral 26 designates a gas bomb for supplying clean gas in the sealed container 4, numerals 27 and 28 respectively designate adjusting valves provided at the inlet and the outlet of the sealed container 4 respectively to adjust a flow rate of gas, numerals 29 and 30 respectively designate stop valves, and a numeral 31 designates a control device which receives an output signal from the wavelength monitoring means 101 to thereby control the adjusting valve 27.
The control device 31 is such that it receives the output of the picture image processing means 25 to obtain the wavelength of the laser beam 13 at present, and it controls the adjusting valve 27 for adjusting a flow rate of gas so that a ~as pressure around the FP 3 is adjusted, whereby the wavelength of the laser beam 13 has a predetermined value. The adjusting valve 27 is manually adjusted at the initial step of adjustmentO
The function of selecting the wavelength by the FP is the same as that of the FP 19 for monitoring the wavelength.
In this embodiment, the adjusting valve 27 at the inlet side of the sealed container 4 is controlled by the control device 31. ~owever, it is possible that only the adjusting valve 28 at the outlet side of the sealed container 4 is controlled. Orl the both adjusting valves 27, 28 may be controlled to thereby adjust a gas pressure in the sealed container 4. The adjusting valves 27, 28 may be replaced by orifices or a mass-flow controller or the like to thereby control a flow rate of gas, hence a gas pressure.
Figure 5 is a diagram showing another embodiment of the laser device according to the present inventionc The construction of this embodiment is the same as that as shown in Figure 4 provided that a pressure sensor 32 and a control device 33 for keeping a pressure constant are added. Namely, the pressure sensor 32 is provided at the sealed container 4 so that the output signal of the pressure sensor 32 and an output signal having information of the wavelength which is generated from the control device 20 are inputted in the control device 33 "`" 1303709 for keeping the pressure to be constant, whereby the adjusting valve 27 for adjusting a flow rate of the gas can be controlled through the device 33. Thus, a gas pressure in the sealed container 4 can be easily adjusted.
In the above-mentioned embodiments, the FP 19 for monitoring the wavelength is not provided in the atmosphere where the clean gas is supplied, in the same manner as the FP 3 for selecting the wavelength. It is because the FP 19 is so constructed that only small part of the laser beam 13 enters in the FP 19. However, further excellent result is obtainable when the FP 19 is disposed in the atmosphere in which clean gas is supplied.
In this embodiment, description has been made as to the wavelength monitoring means 101 in which the fringes resulted by the light transmitted through the FP 19 are measured by the image pickup element 22. However, the wavelength may be measured by another method.
The present invention i5 useful for stabilizing the exC ~n~r wavelength of a laser device such as an oximor laser device.
Claims (3)
1. A laser device which comprises a Fabry-Perot etalon for selecting a wavelength of laser oscillation, a wavelength monitoring means for monitoring a laser beam emitted from an oscillation wavelength changing type laser oscillator and means for adjusting a pressure of gas in a gap in said Fabry-Perot etalon by said output signal of said wavelength monitoring means.
2. The laser device according to Claim 1, wherein said means for adjusting a pressure of gas in said Fabry-Perot etalon is constituted by a sealed container which receives therein said Fabry-Perot etalon, a volume adjustable means capable of increasing and decreasing its volume which is communicated with said sealed container and a driving means capable of receiving said output signal of said wavelength monitoring means to thereby actuate said volume adjustable means.
3. The laser device according to Claim 1, wherein said means for adjusting a pressure of gas in a gap in said Fabry-Perot etalon is constituted by a sealed container which receives therein said Fabry-Perot etalon and means for adjusting an amount of gas flowing to said sealed container on the basis of the output signal of said wavelength monitoring means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31893/1988 | 1988-03-10 | ||
| JP3189388U JPH01135756U (en) | 1988-03-10 | 1988-03-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1303709C true CA1303709C (en) | 1992-06-16 |
Family
ID=12343698
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000593254A Expired - Fee Related CA1303709C (en) | 1988-03-10 | 1989-03-09 | Laser device |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH01135756U (en) |
| CA (1) | CA1303709C (en) |
-
1988
- 1988-03-10 JP JP3189388U patent/JPH01135756U/ja active Pending
-
1989
- 1989-03-09 CA CA000593254A patent/CA1303709C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH01135756U (en) | 1989-09-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |