CA1139869A - Laser control apparatus - Google Patents
Laser control apparatusInfo
- Publication number
- CA1139869A CA1139869A CA000343634A CA343634A CA1139869A CA 1139869 A CA1139869 A CA 1139869A CA 000343634 A CA000343634 A CA 000343634A CA 343634 A CA343634 A CA 343634A CA 1139869 A CA1139869 A CA 1139869A
- Authority
- CA
- Canada
- Prior art keywords
- radiation
- beams
- output
- modes
- cavity
- 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
Links
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
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optics & Photonics (AREA)
- Lasers (AREA)
Abstract
ABSTRACT
A laser control system using a resonant cavity of the type producing adjacent modes of opposite polarization and with mirrors mounted by a system having a non-zero thermal expansion coefficient. A
beam splitter plate in the output beam provides two low intensity beams which are passed through film polarizers to provide beams proportional to the intensities of oppositely polarized adjacent modes. A detector is positioned in each low intensity beam and a differential amplifier is connected to the detectors. The output of the differential amplifier controls a heating coil around the resonant cavity which in turn controls the mirror spacing by varying the temperature of the mounting system. Thus, the radiation received at each detector is maintained equal and the adjacent modes stabilized. A further polarizer in the output path transmits the radiation at one of the modes.
A laser control system using a resonant cavity of the type producing adjacent modes of opposite polarization and with mirrors mounted by a system having a non-zero thermal expansion coefficient. A
beam splitter plate in the output beam provides two low intensity beams which are passed through film polarizers to provide beams proportional to the intensities of oppositely polarized adjacent modes. A detector is positioned in each low intensity beam and a differential amplifier is connected to the detectors. The output of the differential amplifier controls a heating coil around the resonant cavity which in turn controls the mirror spacing by varying the temperature of the mounting system. Thus, the radiation received at each detector is maintained equal and the adjacent modes stabilized. A further polarizer in the output path transmits the radiation at one of the modes.
Description
"` ~139869 This invention relates to a laser control system and, in particular, to one which produces a stable output at substantially a single frequency.
Because the gain-frequency distribution of a laser medium is relatively broad, it is common to find that the optical cavity is capable of resonating at several closely . .
spaced frequencies and, thus, the output does not consist of a single frequency. To achieve accuracy in spectroscopy, for example, it is desirable to use as narrow band a source as possible.
The present invention provides a laser system which has a narrow band output. Specifically, the invention relates to a laser system comprising a resonant cavity with a mirror at each end permitting oscillation at more than one frequency, adjacent modes being of different poLarization. The mirrors are mounted on a system having a non-zero thermal expansion coefficient.
Beam splitting means are positioned to receive a portion of the radiation from the cavity and to provide separate beams of different polarization. A pair of detectors is positioned one in each of the beams, with a differential amplifier having its inputs connected one to each of the detectors. Frequency control apparatus varies the temperature of the mounting system and is connected to the output of the amplifier whereby the radiation intensity received at each detector is maintained equal. A polarizer is positioned in the radiation output path of the cavity, transmitting radiation of only one polariæation.
mg/~
~139869 A preferred embodiment of the invention will now be described in conjunction with the accompanying drawing in which:
Figure 1 is a schematic diagram of the laser system of this invention; and Figure 2 is a graph showing the gain of the laser medium and two adjacent modes of oscillation.
mb/ - 2 --` 1139869 DES Rll'T [ON OF TIIE PREFERRED E~lr;ODIMENT
Figure 1 shows a gas discharge tube 10 having mirrors 11 and 12 at each end as is known, forming a conventional helium-neon laser. The gas is suitably heated by discharge electrodes or r.f. heating and one end portion of the gas discharge tube is partially transmitting to provide the output beam. The most pronounced transition in neon is that which leads to laser action at a wavelength of 6328 A. The gain of the medium at this wavelength is wide enough that oscillation can occur in the laser at a series of modes given by 1/~ = n/2L where L is the length of the optical cavity.
In Figure 2, for example, curve 21 gives the gain of the medium and curves 22 and 33 are ad;acent modes of oscillation in the optical cavity. For use in spectro-scopy, for example, it is most desirable to have laser action in only one mode.
It has been found that adjacent modes are plane polarized at right angles to each other and this feature is employed in the present invention. The polarization is not random but is found to take two perpendicularly oriented states which are fixed relative to the cavity. Presumably, small defects in the construction of cavity cause imperfect radial symmetry which results in the fixed orientation of the polarizations.
The laser output beam 13 falls on a splitter plate 14 which reflects a small amount of the incident energy in two beams 15 and 16. Film polarizers 17 and 18 are placed in the path of beams 15 and 16 to separate mb/ - 3 -- 1~39869 the polarized eomponents. Thus, a beam of intensity proportional to one of the modes then falls on a photodetector 20 and a beam of intensity proportional to the other mode falls on a photodetector 21. The electrical signals from the photodetectors are supplied to the inputs of a differential amplifier 22. The output of amplifier 22 is used to control the current in a coil 23 around the gas discharge tube which, by heating, controls cavity length. The primary factor influencing cavity length is thermal expansion. The following methods are possible: 1) to construct a mechanism which has zero thermal expansion coefficient,
Because the gain-frequency distribution of a laser medium is relatively broad, it is common to find that the optical cavity is capable of resonating at several closely . .
spaced frequencies and, thus, the output does not consist of a single frequency. To achieve accuracy in spectroscopy, for example, it is desirable to use as narrow band a source as possible.
The present invention provides a laser system which has a narrow band output. Specifically, the invention relates to a laser system comprising a resonant cavity with a mirror at each end permitting oscillation at more than one frequency, adjacent modes being of different poLarization. The mirrors are mounted on a system having a non-zero thermal expansion coefficient.
Beam splitting means are positioned to receive a portion of the radiation from the cavity and to provide separate beams of different polarization. A pair of detectors is positioned one in each of the beams, with a differential amplifier having its inputs connected one to each of the detectors. Frequency control apparatus varies the temperature of the mounting system and is connected to the output of the amplifier whereby the radiation intensity received at each detector is maintained equal. A polarizer is positioned in the radiation output path of the cavity, transmitting radiation of only one polariæation.
mg/~
~139869 A preferred embodiment of the invention will now be described in conjunction with the accompanying drawing in which:
Figure 1 is a schematic diagram of the laser system of this invention; and Figure 2 is a graph showing the gain of the laser medium and two adjacent modes of oscillation.
mb/ - 2 --` 1139869 DES Rll'T [ON OF TIIE PREFERRED E~lr;ODIMENT
Figure 1 shows a gas discharge tube 10 having mirrors 11 and 12 at each end as is known, forming a conventional helium-neon laser. The gas is suitably heated by discharge electrodes or r.f. heating and one end portion of the gas discharge tube is partially transmitting to provide the output beam. The most pronounced transition in neon is that which leads to laser action at a wavelength of 6328 A. The gain of the medium at this wavelength is wide enough that oscillation can occur in the laser at a series of modes given by 1/~ = n/2L where L is the length of the optical cavity.
In Figure 2, for example, curve 21 gives the gain of the medium and curves 22 and 33 are ad;acent modes of oscillation in the optical cavity. For use in spectro-scopy, for example, it is most desirable to have laser action in only one mode.
It has been found that adjacent modes are plane polarized at right angles to each other and this feature is employed in the present invention. The polarization is not random but is found to take two perpendicularly oriented states which are fixed relative to the cavity. Presumably, small defects in the construction of cavity cause imperfect radial symmetry which results in the fixed orientation of the polarizations.
The laser output beam 13 falls on a splitter plate 14 which reflects a small amount of the incident energy in two beams 15 and 16. Film polarizers 17 and 18 are placed in the path of beams 15 and 16 to separate mb/ - 3 -- 1~39869 the polarized eomponents. Thus, a beam of intensity proportional to one of the modes then falls on a photodetector 20 and a beam of intensity proportional to the other mode falls on a photodetector 21. The electrical signals from the photodetectors are supplied to the inputs of a differential amplifier 22. The output of amplifier 22 is used to control the current in a coil 23 around the gas discharge tube which, by heating, controls cavity length. The primary factor influencing cavity length is thermal expansion. The following methods are possible: 1) to construct a mechanism which has zero thermal expansion coefficient,
2) to stabilize the temperature, or 3) to provide a compensating length change during temperature changes.
This invention uses temperature stabilization to keep the tube length constant. The tube length varies approximately 3 x 10 6 cm per cm/C so the effective tube temperature must be kept constant to within 0.03 C
in order to achieve an emission line position precision of 1 part in 10 (.0016 cm at 16,000 cm 1), Thus the control loop formed by the photocells, amplifier and coil functions to maintain the amplitude of ad~acent modes equal as shown in Figure 2. The laser output is taken through a film polarizer 24.
In the preferred embodiment splitter plate 14 is formed by a 318 inch lucite plate positioned in the beam at 30 from normal.
mb/ - 4 ~
S:ince about four percent of the incident radiation is reflected at each face of the lucite plate, the two beams 15 and 16 separated by about .25 inches are provided. Polarizing films 17 and 18, with their polarization axes aligned with the two polarization azes of the laser, permit the separation of the laser polarizations for the subsequent detection and differential amplification.
mb/ - 5 -
This invention uses temperature stabilization to keep the tube length constant. The tube length varies approximately 3 x 10 6 cm per cm/C so the effective tube temperature must be kept constant to within 0.03 C
in order to achieve an emission line position precision of 1 part in 10 (.0016 cm at 16,000 cm 1), Thus the control loop formed by the photocells, amplifier and coil functions to maintain the amplitude of ad~acent modes equal as shown in Figure 2. The laser output is taken through a film polarizer 24.
In the preferred embodiment splitter plate 14 is formed by a 318 inch lucite plate positioned in the beam at 30 from normal.
mb/ - 4 ~
S:ince about four percent of the incident radiation is reflected at each face of the lucite plate, the two beams 15 and 16 separated by about .25 inches are provided. Polarizing films 17 and 18, with their polarization axes aligned with the two polarization azes of the laser, permit the separation of the laser polarizations for the subsequent detection and differential amplification.
mb/ - 5 -
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A laser system comprising a resonant cavity with a mirror at each end permitting oscillation at more than one frequency, adjacent modes being of different polarization, each mirror being mounted by a system having a non-zero thermal expansion coefficient, beam splitting means positioned to receive a portion of the radiation from the cavity and to provide separate beams of different polarization, a pair of detectors positioned one in each of the beams; a differential amplifier having its inputs connected one to each of the detectors, frequency control apparatus varying the temperature of the mounting system and connected to the output of the amplifier whereby the radiation intensity received at each detector is maintained equal and a polarizer in the radiation output path of the cavity transmitting radiation of only one polarization.
2. A laser system as claimed in claim 1 wherein said beam splitting means is a plate positioned at an angle in the radiation output path in combination with a pair of polarizing films, one in each of the beams reflected from the front and rear surfaces of the plate.
3. A laser system as claimed in claim 2 wherein said plate is formed of lucite.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000343634A CA1139869A (en) | 1980-01-14 | 1980-01-14 | Laser control apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000343634A CA1139869A (en) | 1980-01-14 | 1980-01-14 | Laser control apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1139869A true CA1139869A (en) | 1983-01-18 |
Family
ID=4116041
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000343634A Expired CA1139869A (en) | 1980-01-14 | 1980-01-14 | Laser control apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1139869A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0120310A2 (en) * | 1983-02-24 | 1984-10-03 | VEB Kombinat Feinmechanische Werke Halle | Method, device and circuit for the compensation of misalignments due to the operating and/or environmental conditions of laser resonators in a folded structure |
-
1980
- 1980-01-14 CA CA000343634A patent/CA1139869A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0120310A2 (en) * | 1983-02-24 | 1984-10-03 | VEB Kombinat Feinmechanische Werke Halle | Method, device and circuit for the compensation of misalignments due to the operating and/or environmental conditions of laser resonators in a folded structure |
| EP0120310A3 (en) * | 1983-02-24 | 1987-04-15 | Veb Kombinat Feinmechanische Werke Halle | Method, device and circuit for the compensation of misalignments due to the operating and/or environmental conditions of laser resonators in a folded structure |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |