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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
  • G01M3/24—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using infrasonic, sonic, or ultrasonic vibrations
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/38—Investigating fluid-tightness of structures by using light
• • 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
  • H01S3/0014—Monitoring arrangements not otherwise provided for
• • 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
  • H01S3/105—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
  • H01S3/1055—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length one of the reflectors being constituted by a diffraction grating

Definitions

• THIS INVENTION relates to a method of, and apparatus for, computer controlled tuning of lasers.
• lasers are used in areas such as cutting, welding, surveying and gas analysis, while in medicine, they are used as scal ⁇ pels and for welding detached retinas.
• each laser having a characteristic set of lines within its gain envelope. For example, it has not been possible to accurately tune C0 ? type lasers at all of the. characteristic lines in their- gain envelope. Generally each laser has been set to operate at a fixed wavelength. It is well known that different gases absorb light at different wavelengths in characteristic patterns which provide a "signature" for the gases. These patterns enable the existence and/or concentration of the gases to be detected e.g. for leak detection purposes in factories.
• two or more accurately tuned, highly stabilized lasers must be employed, each tuned to a particular wavelength.
• the equipment must be highly stabilized as variations in temperature and pressure can change the wavelength of the laser light. The change in wavelength may be such that the lasers operate at characteristic lines other than for which they are allegedly tuned and so false qualitative and/or quantitative measurements may be made in relation to the gas.
• the equipment necessary to maintain the stabi ⁇ lity of the lasers prevents them from being readily portable or versatile and so has restricted the range of potential industrial applications.
• the present invention resides in a method for tuning a laser of the type having a cavity, a front window, a Brewster window and a grating, the method including the steps of:
• the present invention resides in an apparatus for tuning a laser of the type comprising a cavity, a front window, a Brewster window and a grating, the apparatus including: a mounting for the grating movable to vary the angular position and the cavity length of the grating relative to the cavity; means to move the mounting; a first detector to measure the power output from the laser; a photoacoustic cell or second detector located in at least a portion of the output beam from the laser; means to measure the output from th ' e ' photo- acoustic cell or second detector; and means to control the movement of the mounting, and thereby the grating, dependent on the measurement of the output power of the laser by the first detector and the measured output of the photoacoustic cell or second detector.
• the laser grating is mounted on a turn-table.
• rotatable e.g. by a stepping motor
• the turn-table being longitudinally movable (e.g. by a piezoelectric drive) along, or parallel to the cavity axis to vary the cavity length.
• the output from the laser is measured by a first detector which registers the intensity of the beam reflected from the Brewster window in the laser tube.
• a beam chopper-splitter is provided outside the cavity, spaced from the front window, to provide a chopped output beam at the laser frequency and proportional to its power.
• the beam reflected by the chopper-splitter is reflected by a mirror onto a photoacoustic cell (containing e.g. ammonia or ethylene) to measure the laser output in step (e).
• the system is controlled by a compute /microprocessor capable of driving the stepping motor, the piezoelectric driver and registering the outputs from the detector and the photoacoustic cell.
• Suitable software is provided to control the system.
• FIG. 1 is a schematic layout of the control system
• FIG. 2 is a graph of the CO, laser gain curve
• FIG. 3 is a graph of the absorption character ⁇ istic of ammonia relative to the lines of the CO gain curve.
• the laser 10 has a cavity 11 with a front window 12 and a Brewster window 13.
• the grating 14 is mounted on a turn-table 15 which is rotatable by a micrometer driven by a stepping motor 16 to vary the grating angle and which is movable along (or parallel to) the cavity axis, to vary the cavity length, by a piezoelectric device 17.
• the laser power output is monitored by a detector 18 which registers the intensity of the beam reflected from the back of the Brewster window 13.
• a beam chopper-splitter 19 is provided in front of the front window 12 and is driven by a motor 20. The face of the chopper-splitter 19 is mirrored to reflect a chopped output beam to a mirror 21, which reflects the beam to a photoacoustic cell 22 containing e.g. ammonia or ethylene at a low partial pressure to to calibrate the frequency (or wavelength) of the parti ⁇ cular line.
• the stepping motor 16, piezoelectric device 17, detector 18 and photoacoustic cell 22 are connected to a computer or micropressor C.
• the software in the computer C causes the stepping motor 16 to drive the grating 14 to a selected angular position and then varies the cavity length (via the piezoelectric device 17).
• the grating position can beoptimised for a particular laser characteristic line.
• the output from the photoacoustic cell 22 is monitored and the steps are repeated until the gain envelope of the laser (FIG. 2) has been traversed.

Landscapes

• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• General Physics & Mathematics (AREA)
• Lasers (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=3770937

Family Applications (1)

Country Status (4)

Families Citing this family (4)

Citations (2)

Family Cites Families (3)

• 1986
  • 1986-02-04 EP EP19860901020 patent/EP0248797A4/de not_active Withdrawn
  • 1986-02-04 WO PCT/AU1986/000026 patent/WO1986004746A1/en not_active Application Discontinuation
  • 1986-02-04 JP JP50101086A patent/JPS62501947A/ja active Pending
  • 1986-02-04 GB GB08717608A patent/GB2192090B/en not_active Expired

Patent Citations (2)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events