CA1056937A - Gas discharge laser - Google Patents
Gas discharge laserInfo
- Publication number
- CA1056937A CA1056937A CA255,953A CA255953A CA1056937A CA 1056937 A CA1056937 A CA 1056937A CA 255953 A CA255953 A CA 255953A CA 1056937 A CA1056937 A CA 1056937A
- Authority
- CA
- Canada
- Prior art keywords
- laser
- reflectors
- magnetic field
- gas discharge
- anisotropy
- 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
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/08059—Constructional details of the reflector, e.g. shape
-
- 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
- H01S3/02—Constructional details
- H01S3/03—Constructional details of gas laser discharge tubes
- H01S3/034—Optical devices within, or forming part of, the tube, e.g. windows, mirrors
-
- 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
- H01S3/10061—Polarization control
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optics & Photonics (AREA)
- Lasers (AREA)
Abstract
ABSTRACT:
A gas discharge laser in which the light beam emanating from said laser is linearly polarised by applying a transverse magnetic field in which reflectors are used which are more or less aniso-tropic and the anisotropy axes of which have a precise orientation relative to the magnetic field so that a high degree of polarisation is obtained.
A gas discharge laser in which the light beam emanating from said laser is linearly polarised by applying a transverse magnetic field in which reflectors are used which are more or less aniso-tropic and the anisotropy axes of which have a precise orientation relative to the magnetic field so that a high degree of polarisation is obtained.
Description
- P~l~ 8~
~L/ WJ/~UYS.
1976.02-13, ~i937 . ~
I "Gas discharge laser".
_ _ _ _ ¦ The invention relates to a gas discharge I laser having reflectors (laser mirrors) connected near :~ the two ends of the part of the discharge tube ~orming I the laser tube, in which the light beam emanating from J 5 the gas discharge laser is linearly polarized by apply-ing a transverse magnetic field the direction of which is substantially normal to the axis of the laser tube, -;
~: - said magnetic field being generated by a magnet placed near the laser tube.
1~ Such a gas discharge laser is known from Review of Scientific Instruments 40, May 1969, pp.
727-8, in which the said transverse magnetic field has a strength of 500 to 1000 Gauss along 3 to 6 cm of the discharge. The magnetic field was obtained by arrang-t5 ing a permanent magnet near the laser tube. In this case a good linear polarisation of the light emanating from the laser was obtained in which the orientation and position of the magnetic field proved not to be critical. Our investigations have proved that in these previous experiments very good isotropic reflectors must have been used, since otherwise variations, and sometimes drastic ones, occur in the linearity of the polarisation which (with a varying orientation of the magnetic field in a plane normal to the axis of the `
I -2- ~
PHN. 80~11 1976.02-13.
laser tube,) i9 then poor on average. Such isotropic reflectors are difficult to manufacture and hence ex-J - pensive and consequently not attractive for use.on a j large scale.
It is also known that lasers having a good linear polarisation can be obtained by using instead of a magnetic field one or more Brewster windows in the laser. In this case, mirror anisotropies, if any, hardly co~stitute a drawback. A problem in the con-struction of such a laser, however, is that stringent requirements have to be imposed upon the optical quality of the Brewster windows and furthermore the ~ efficiency will nevertheless always be smaller as a ¦ result of extra losses.
It i9 the object of the invention to pro-vide a laser construction in which a good linear pola-risation of the laser light in a direction which can ¦ be previously predicted is obtained by means of a ¦ transverse magnetic field, without stringent require-, 20 ments being imposed upon the isotropy of the reflectors.
, According to the invention, a gas discharge ;~ laser of the above type is charac~erized in that two phase-anisotropic (double refràcti-ve) reflectors are used, the directions of the anisotropy axes of the two reflectors substantially coinciding or being substantial-ly at right angles to each other, the direction of the magnetic field substantially coinciding with one of the ` ~os6937 PHN. 8064.
I 1976.02-13.
: i I anisotripy axes of the reflectors.
! The invention is based on the recognition j of the fact that the unfavourable influence of the phase-1 anisotropy of the mirrors on the linear polarisation ¦ 5 of the laser beam is considerably reduced when the anisotropy axes of the laser mirrors coincide with (or are at right angles to) the direction of the (po-larising) transverse magnetic field. The anisotropy axes of the laser mirrors are to be understood to mean the axes between which the difference in optical path ; length in the laser tube in the direction of the axis of the laser tube i9 a maximum. In the conventional ' vapour-deposition processes the anisotropy of the re-flectors i9 caused by during the incomplete isotropic 1 15 vapour-deposition of the multilayer coating used in said reflectors. Such a multilayer coating is manufact-ured by the alternate vapour-deposition of dielectric layers having a high and a low index-refraction. The ~ anisotropy axes are directly associated with the va-;i 20 pour-deposition geometry (e.g. the direction of vapour ~ deposition) and can be fixed in a reproduceable man-¦ ner~ for example by providing marks on the reflectors.
By providing the mirrors with the anisotropy axes in the desired direction on the laser tube, a laser is obtained, as has been proved experimentally, which has a good linearity of the polarisation in a previ-ously fixed direction.
- 4 _ !
.... ~ ..
.. .... .....
PHN. ~o64 - EL/Sp/DUYS
~; 1976 .01 .07 1~ i ., , The invention will now be described in greater detail with reference to the drawing, in which:-' Figure 1 shows various possible orientations ; of the anisotropy axes relative to the applied trans-verse magnetic field and, Figure 2 shows how the polarisation of the laser light depends on the angle which the transverse magnetic field makes with the anisotropy axes of the l reflectors.
I .
i 10 Figure 1 shows diagrammatically a laser.
Reflectors 2 and 3 having reflective multilayer coating ¦ 6 and 7!~ are directly secured by means of a sealing j cement8to the preferably cylindrical part of the gas ! discharge tube which forms the laser tube 1. A trans-verse magnetic field B is applied normal to the axis of the laser tube 1. The anisotropy axes 4 and 5 are shown diagrammatically on the reflectors. The various orientations of the anisotropy axes and the magnetic field which can be used according to the invention are denoted in figures 1a, b and c and d. The laser may ~' be of the coaxial type or of the side arm type.
, In the case of a He-Ne laser wi~h a strong transverse magnetic field B of approximately 1000 Gauss, all the laser modes are polarised in the direct ion of said magnetic field. Such a laser may, for example, have the following laser parameters:
.~.
length of laser tubr ~pproximately 250 mm ~i ` .
: ~ .
.
..
PHN. 8064.
. 105~93~ 1976,02-13, ! length of active discharge approximately 205 mm current through the discharge 6.4 mA
, inside diameter of laser tube approximately 1.8 mm ¦ Gas filling 15% He .i 5 85% He gas pressure 2.3 torr resonator configuration nearly hemi-spherical .; , .
output power 1-2 mWatt at 6328 A.
One of the laser mirrors, the output mirror, has a transmission of approximately 1%. A homogeneous transverse magnetic field can be obtained by means of two magnetic pole shoes present on opposite sides of the laser tube.
¦ . . It will be obvious that the invention is not .~ restricted to the above-described He-Ne laser and to transverse magnetic fields of approximately 1000 Gauss.
The gist of the invention is to obtain a gas discharge . laser having a very good linearity of the polarisation : in a well defined direction by causing the directions ' of anisotropy of the laser mirrors to coincide with the direction of the transverse magnetic field.
Figure 2 shows how the polarisation of the .
lOS6937 PHN. 8064.
1976.02-t3.
laser light depends on the angle which the transverse magnetic field makes with the anisotropy axes of the reflectors. The ratio of the maximum intensity ImaX
to the minimum intensity Imin of the laser beam originating from the laser after passing through a po-lariser is plotted vertically. The measurements shown were made with a He-Ne laser with a transverse magnetic ... .
field of approximately 1000 Gauss active throughout the length (20 cm) of the active (laser) discharge. In this case shown in Figure 2 the corresponding anisotropy axes of the reflectors extended substantially parallel to one another. The phase anisotropy of the mirrors~
¦ which may be expressed as the optical path length dif-ference along the two anisotropy axes is in this case ! 15 of the order of 1 A.
In the situations in which the corresponding anisotropy axes of the reflectors extend substantially parallel (Figures 1a and c)~ a very good linear polarisation (ratio ImaX : Imin better than 2000 : 1) is obtained near ~=0 and ~ =~r/2, that is with the mag-netic field parallel to one of the anisotropy axes.
It has even been found that the anisotropy axes may be at a small angle to each other without this degrading the good linearity of the polarisation. This Z5 angle depends on the magnitude of the mirror anisotropies and on the desired linearity of the polarisation (even with an angle to 10, the ratio ImaX Imin is in many ~ 7 -, .
I I PHN. 8064.
~ 1~5~937 1976.02-13.
l cases better than 500 : 1). As a result of this, the .:1 provision of the reflectors is comparatively easy and ~: the fixing of the anisotropy directions during the manufacture i9 not very critical.
When the corresponding anisotropy axes of the reflectors are substantially at right angles to each . other (Figures lb and d) it appears that on average the ` j linearity of the polarisation is better than in the case : mentioned in the previous paragraph. A drawback of this situation, corresponding to Figures lb and d, is, how- .
: ever~ that the angles at which the ratio ImaX : Imin i9 ¦ a maximum can differ considerably from ~=0 or ~ /2 .:~ if the anisotropy axes are not very accurately at right . angles to each other.
:~ 15 The invention enables the simple and cheap .' manufacture of gas discharge lasers having a very good linear polarisation of the laser light in a well-defined :
direction by using the fixed anisotropy directions of the laser mirrors.
:'`'`
`1 -I
. . .
. . . ~ . .
~L/ WJ/~UYS.
1976.02-13, ~i937 . ~
I "Gas discharge laser".
_ _ _ _ ¦ The invention relates to a gas discharge I laser having reflectors (laser mirrors) connected near :~ the two ends of the part of the discharge tube ~orming I the laser tube, in which the light beam emanating from J 5 the gas discharge laser is linearly polarized by apply-ing a transverse magnetic field the direction of which is substantially normal to the axis of the laser tube, -;
~: - said magnetic field being generated by a magnet placed near the laser tube.
1~ Such a gas discharge laser is known from Review of Scientific Instruments 40, May 1969, pp.
727-8, in which the said transverse magnetic field has a strength of 500 to 1000 Gauss along 3 to 6 cm of the discharge. The magnetic field was obtained by arrang-t5 ing a permanent magnet near the laser tube. In this case a good linear polarisation of the light emanating from the laser was obtained in which the orientation and position of the magnetic field proved not to be critical. Our investigations have proved that in these previous experiments very good isotropic reflectors must have been used, since otherwise variations, and sometimes drastic ones, occur in the linearity of the polarisation which (with a varying orientation of the magnetic field in a plane normal to the axis of the `
I -2- ~
PHN. 80~11 1976.02-13.
laser tube,) i9 then poor on average. Such isotropic reflectors are difficult to manufacture and hence ex-J - pensive and consequently not attractive for use.on a j large scale.
It is also known that lasers having a good linear polarisation can be obtained by using instead of a magnetic field one or more Brewster windows in the laser. In this case, mirror anisotropies, if any, hardly co~stitute a drawback. A problem in the con-struction of such a laser, however, is that stringent requirements have to be imposed upon the optical quality of the Brewster windows and furthermore the ~ efficiency will nevertheless always be smaller as a ¦ result of extra losses.
It i9 the object of the invention to pro-vide a laser construction in which a good linear pola-risation of the laser light in a direction which can ¦ be previously predicted is obtained by means of a ¦ transverse magnetic field, without stringent require-, 20 ments being imposed upon the isotropy of the reflectors.
, According to the invention, a gas discharge ;~ laser of the above type is charac~erized in that two phase-anisotropic (double refràcti-ve) reflectors are used, the directions of the anisotropy axes of the two reflectors substantially coinciding or being substantial-ly at right angles to each other, the direction of the magnetic field substantially coinciding with one of the ` ~os6937 PHN. 8064.
I 1976.02-13.
: i I anisotripy axes of the reflectors.
! The invention is based on the recognition j of the fact that the unfavourable influence of the phase-1 anisotropy of the mirrors on the linear polarisation ¦ 5 of the laser beam is considerably reduced when the anisotropy axes of the laser mirrors coincide with (or are at right angles to) the direction of the (po-larising) transverse magnetic field. The anisotropy axes of the laser mirrors are to be understood to mean the axes between which the difference in optical path ; length in the laser tube in the direction of the axis of the laser tube i9 a maximum. In the conventional ' vapour-deposition processes the anisotropy of the re-flectors i9 caused by during the incomplete isotropic 1 15 vapour-deposition of the multilayer coating used in said reflectors. Such a multilayer coating is manufact-ured by the alternate vapour-deposition of dielectric layers having a high and a low index-refraction. The ~ anisotropy axes are directly associated with the va-;i 20 pour-deposition geometry (e.g. the direction of vapour ~ deposition) and can be fixed in a reproduceable man-¦ ner~ for example by providing marks on the reflectors.
By providing the mirrors with the anisotropy axes in the desired direction on the laser tube, a laser is obtained, as has been proved experimentally, which has a good linearity of the polarisation in a previ-ously fixed direction.
- 4 _ !
.... ~ ..
.. .... .....
PHN. ~o64 - EL/Sp/DUYS
~; 1976 .01 .07 1~ i ., , The invention will now be described in greater detail with reference to the drawing, in which:-' Figure 1 shows various possible orientations ; of the anisotropy axes relative to the applied trans-verse magnetic field and, Figure 2 shows how the polarisation of the laser light depends on the angle which the transverse magnetic field makes with the anisotropy axes of the l reflectors.
I .
i 10 Figure 1 shows diagrammatically a laser.
Reflectors 2 and 3 having reflective multilayer coating ¦ 6 and 7!~ are directly secured by means of a sealing j cement8to the preferably cylindrical part of the gas ! discharge tube which forms the laser tube 1. A trans-verse magnetic field B is applied normal to the axis of the laser tube 1. The anisotropy axes 4 and 5 are shown diagrammatically on the reflectors. The various orientations of the anisotropy axes and the magnetic field which can be used according to the invention are denoted in figures 1a, b and c and d. The laser may ~' be of the coaxial type or of the side arm type.
, In the case of a He-Ne laser wi~h a strong transverse magnetic field B of approximately 1000 Gauss, all the laser modes are polarised in the direct ion of said magnetic field. Such a laser may, for example, have the following laser parameters:
.~.
length of laser tubr ~pproximately 250 mm ~i ` .
: ~ .
.
..
PHN. 8064.
. 105~93~ 1976,02-13, ! length of active discharge approximately 205 mm current through the discharge 6.4 mA
, inside diameter of laser tube approximately 1.8 mm ¦ Gas filling 15% He .i 5 85% He gas pressure 2.3 torr resonator configuration nearly hemi-spherical .; , .
output power 1-2 mWatt at 6328 A.
One of the laser mirrors, the output mirror, has a transmission of approximately 1%. A homogeneous transverse magnetic field can be obtained by means of two magnetic pole shoes present on opposite sides of the laser tube.
¦ . . It will be obvious that the invention is not .~ restricted to the above-described He-Ne laser and to transverse magnetic fields of approximately 1000 Gauss.
The gist of the invention is to obtain a gas discharge . laser having a very good linearity of the polarisation : in a well defined direction by causing the directions ' of anisotropy of the laser mirrors to coincide with the direction of the transverse magnetic field.
Figure 2 shows how the polarisation of the .
lOS6937 PHN. 8064.
1976.02-t3.
laser light depends on the angle which the transverse magnetic field makes with the anisotropy axes of the reflectors. The ratio of the maximum intensity ImaX
to the minimum intensity Imin of the laser beam originating from the laser after passing through a po-lariser is plotted vertically. The measurements shown were made with a He-Ne laser with a transverse magnetic ... .
field of approximately 1000 Gauss active throughout the length (20 cm) of the active (laser) discharge. In this case shown in Figure 2 the corresponding anisotropy axes of the reflectors extended substantially parallel to one another. The phase anisotropy of the mirrors~
¦ which may be expressed as the optical path length dif-ference along the two anisotropy axes is in this case ! 15 of the order of 1 A.
In the situations in which the corresponding anisotropy axes of the reflectors extend substantially parallel (Figures 1a and c)~ a very good linear polarisation (ratio ImaX : Imin better than 2000 : 1) is obtained near ~=0 and ~ =~r/2, that is with the mag-netic field parallel to one of the anisotropy axes.
It has even been found that the anisotropy axes may be at a small angle to each other without this degrading the good linearity of the polarisation. This Z5 angle depends on the magnitude of the mirror anisotropies and on the desired linearity of the polarisation (even with an angle to 10, the ratio ImaX Imin is in many ~ 7 -, .
I I PHN. 8064.
~ 1~5~937 1976.02-13.
l cases better than 500 : 1). As a result of this, the .:1 provision of the reflectors is comparatively easy and ~: the fixing of the anisotropy directions during the manufacture i9 not very critical.
When the corresponding anisotropy axes of the reflectors are substantially at right angles to each . other (Figures lb and d) it appears that on average the ` j linearity of the polarisation is better than in the case : mentioned in the previous paragraph. A drawback of this situation, corresponding to Figures lb and d, is, how- .
: ever~ that the angles at which the ratio ImaX : Imin i9 ¦ a maximum can differ considerably from ~=0 or ~ /2 .:~ if the anisotropy axes are not very accurately at right . angles to each other.
:~ 15 The invention enables the simple and cheap .' manufacture of gas discharge lasers having a very good linear polarisation of the laser light in a well-defined :
direction by using the fixed anisotropy directions of the laser mirrors.
:'`'`
`1 -I
. . .
. . . ~ . .
Claims (2)
PROPERTY OR????????? OR PRIVILEGE IS CLAIMED ARE DEFINED
AS FOLLOWS:
CLAIMS:
1. A gas discharge laser having reflectors (laser mirrors) connected near the two ends of the part of the discharge tube forming the laser tube, in which the light beam emanating from the gas discharge laser is linearly polarised by applying a transverse magnetic field the direction of which is substantially normal to the axis of the laser tube, said magnetic field being generated by a magnet arranged near the laser tube, characterized in that two phase-anisotropic (double refractive) reflectors are used, the directions of the anisotropy axes of the two reflectors substantially coinciding or being substantially at right angles to each other, the direction of the magnetic field sub-stantially coinciding with one of the anisotropy axes of the reflectors.
2. A laser tube having reflectors for a gas discharge laser as claimed in Claim 1, characterized in that two phase-anisotropic (double refractive) reflectors are used, the directions of the anisotropy axes of the two reflectors substantially coinciding or being substantially at right angles to each other.
Eindhoven, July 1, 1975.
Eindhoven, July 1, 1975.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NL7507853A NL7507853A (en) | 1975-07-02 | 1975-07-02 | GAS DISCHARGE LASER. |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1056937A true CA1056937A (en) | 1979-06-19 |
Family
ID=19824068
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA255,953A Expired CA1056937A (en) | 1975-07-02 | 1976-06-29 | Gas discharge laser |
Country Status (10)
Country | Link |
---|---|
JP (1) | JPS526489A (en) |
AU (1) | AU502750B2 (en) |
CA (1) | CA1056937A (en) |
DE (1) | DE2627585C3 (en) |
ES (2) | ES449380A1 (en) |
FR (1) | FR2316766A1 (en) |
GB (1) | GB1552186A (en) |
IT (1) | IT1062378B (en) |
NL (1) | NL7507853A (en) |
SE (1) | SE7607381L (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
NL7802454A (en) * | 1978-03-07 | 1979-09-11 | Philips Nv | GAS DISCHARGE LASER FOR GENERATING LINEAR POLARIZED RADIATION. |
FR2544445B1 (en) * | 1983-04-14 | 1985-06-21 | Electricite De France | SAFETY DEVICE WITH MEMBRANE AND BREAKING KNIFE FOR LIMITING THE PRESSURE OF A FLUID |
-
1975
- 1975-07-02 NL NL7507853A patent/NL7507853A/en not_active Application Discontinuation
-
1976
- 1976-06-19 DE DE2627585A patent/DE2627585C3/en not_active Expired
- 1976-06-28 IT IT68598/76A patent/IT1062378B/en active
- 1976-06-29 CA CA255,953A patent/CA1056937A/en not_active Expired
- 1976-06-29 JP JP51076102A patent/JPS526489A/en active Granted
- 1976-06-29 GB GB27023/76A patent/GB1552186A/en not_active Expired
- 1976-06-29 SE SE7607381A patent/SE7607381L/en unknown
- 1976-06-30 AU AU15426/76A patent/AU502750B2/en not_active Expired
- 1976-06-30 ES ES449380A patent/ES449380A1/en not_active Expired
- 1976-07-02 FR FR7620347A patent/FR2316766A1/en active Granted
- 1976-10-16 ES ES452473A patent/ES452473A1/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
FR2316766A1 (en) | 1977-01-28 |
JPS526489A (en) | 1977-01-18 |
NL7507853A (en) | 1977-01-04 |
DE2627585B2 (en) | 1978-06-08 |
AU1542676A (en) | 1978-01-05 |
DE2627585C3 (en) | 1979-02-08 |
FR2316766B1 (en) | 1981-09-18 |
AU502750B2 (en) | 1979-08-09 |
IT1062378B (en) | 1984-10-10 |
ES452473A1 (en) | 1977-11-01 |
GB1552186A (en) | 1979-09-12 |
ES449380A1 (en) | 1977-08-01 |
DE2627585A1 (en) | 1977-01-13 |
SE7607381L (en) | 1977-01-03 |
JPS5415678B2 (en) | 1979-06-16 |
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