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
  • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
  • H01S3/1106—Mode locking
  • H01S3/1112—Passive mode locking
  • H01S3/1115—Passive mode locking using intracavity saturable absorbers
  • H01S3/1118—Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
• • 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
• • 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
  • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
  • H01S3/1106—Mode locking
  • H01S3/1109—Active mode locking
• • 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
  • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
  • H01S3/1123—Q-switching
  • H01S3/1127—Q-switching using pulse transmission mode [PTM]
• • 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
  • H01S3/1312—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 optical pumping

Definitions

• pulsed laser operation can occur. Such a macro pulse occurs at the earliest when sufficient energy can be retrieved from the gain medium.
• mode coupling in which it is ensured that when a first of the resonator modes begins to build up, this is also the case with others.
• an element can be provided in the resonator, which absorbs or reflects to different extents depending on the strength of the incident light.
• a known element of this type is a so-called saturable semiconductor absorber mirror, cf. U. Keller, KJ Weingarten, FX Kärtner, D. Kopf, B. Braun, ID Jung, R. Fluck, C. Höninger, N. Matuschek and J.
• Switching instabilities In particular, there is a very strong fluctuation in the average laser power. Such faults can occur under certain operating conditions, e.g. at certain pump capacities.
• the fluctuation typically has frequencies in the range between 10 kHz and a few megahertz.
• the fluctuations can also occur non-periodically, but irregularly, which is particularly disturbing.
• the short-term very strong intensities in the resonator can also destroy the internal or other components of the resonator or shorten their lifespan.
• the proposed absorption processes limit the maximum achievable pulse energy:
• the absorbers are exposed to very heavy loads and the service life is limited by the strong saturation that occurs, which is associated with the deposition of large amounts of material ,
• the object of the present invention is to provide something new for commercial use.
• a laser with a coupling-out means for the emission of a laser power dependent on at least one parameter that can be influenced and a mode-coupling means for coupling a plurality of the laser-capable modes of the resonator that a detection means for detecting a laser power , in particular related to the emitted laser power, and a parameter changing means for changing the at least one parameter in response to the detected size is provided.
• the invention allows higher repetition rates than before.
• pulse energies in continuously mode-locked operation can be chosen higher than before, since the beam cross sections in the amplification medium and / or on the saturable absorber can be chosen larger without fear of undesired Q-switching.
• Stabilization of the laser power can also be achieved if instead of a counter-acting parameter change
• the parameter is changed along with feedback, can achieve a targeted destabilization. It should be mentioned that changing the parameter can also be used to bring about a mode coupling process by supplying the parameter changing means with a suitable trigger pulse.
• the latter is advantageous in particular for reinforcing Q-switch instability.
• This targeted influencing of the Q-switch instability can be used in order to emit the large pulses that can be generated by Q-switch at certain times. In this way, a stable repetition rate can be obtained with the aid of an approximately crystal-stabilized signal generator.
• the generator signals and the detected variable representative of the laser power are preferably added together. Much higher pulse energies and / or repetition rates can be achieved than usual.
• the or one of the parameters influencing the output laser power is the pump power.
• the parameter influencing, in particular of the control can be implemented particularly simply and by means of essentially purely electronic changes to conventional laser systems. This variant is therefore particularly easy to implement, in particular in the case of diode-pumped laser systems, because only the pump current fed to the laser pump diodes has to be changed here.
• loss modulation can take place, i.e. a loss modulator is provided within the resonator and its loss is changed in response to the detected quantity.
• the parameter changing means is designed to change the parameter in such a way that
• the regulation can take place in such a way that the parameter changing means equalizes the output power averaged over at least one resonator cycle time.
• the control works comparatively slowly, in particular slowly compared to the resonator cycle time, for example because a slow and thus quasi-integrating photo element is used to record the quantity related to the laser power.
• a means is then provided for integrating and / or averaging rapid variations in the size related to the laser power, the parameter changing means then being designed to change the parameter in response to the averaged and / or integrated size.
• the parameter can be changed in various ways in response to the deviation of the detected variable from a target variable.
• linear changes corresponding to the deviation are possible; alternatively, PID-proportional, integral and / or differential) behavior can be realized and / or a non-linear change can be achieved.
• the mode coupling takes place passively, for example via a power-dependent absorbing and / or reflective element in the resonator.
• an at least partially saturable absorber can be provided, for example.
• the resonator has an internal frequency doubler and / or that a loss modulator is provided, the loss of which is the or one of the changeable parameters.
• a loss modulator can in particular be mechanically, acoustically, optically and / or electro-optically modulatable.
• the provision of a loss modulator is particularly preferred in those laser systems in which the pump power cannot be varied in a particularly simple manner.
• the laser can be a system which exhibits a "spiking behavior" without changing the at least one parameter in response to the detected variable and / or which is designed for "cavity dumping".
• 9 1 shows a laser arrangement according to the invention
• a laser 1, generally designated 1 comprises a resonator formed by mirrors 2, 3, 4 and an amplification medium 5, which is pumped by a pumping means 6.
• the laser 1 further comprises a detection means 7 for detecting a variable related to the laser power and a parameter changing means 8 for changing at least one parameter influencing the laser power as a function of the variable relating to the laser power.
• the mirror 2 is applied to the amplification medium 5 as a reflective coating which is partially transparent to the laser light with approximately 2% and transparent to the pump light from the pumping means 6 and thus serves as an output coupler, via which a portion of the light waves building up in the resonator are coupled out and their use can be supplied.
• the mirror 3 is a spherical dielectric mirror. This mirror has a reflection of about 99.9%.
• the spherical curvature of the dielectric mirror 3 is chosen so that stable resonator modes can form.
• the end mirror 4 is a saturable absorber mirror, which serves to lock the mode.
• the round trip time through the resonator is about 10ns.
• the gain medium 5 is formed by an Nd: YV04 ⁇ crystal.
• the fluorescence lifetime of the laser crystal is approximately 100 ⁇ s.
• the pumping means 6 comprises a number of (semiconductor laser
• pump diodes 6a which are designed to radiate light through a focusing lens 6b, a dichroic plate 6c and the coupling mirror 2 focused on the Nd: YV ⁇ 4 crystal forming the gain medium 5.
• the dichroic plate 6c is at an angle in the beam and is selected so that the pump light passes through and the laser light is reflected.
• a photodetector 7 is now provided as the detection means 7 for the laser power present in the resonator, onto which part of the small amount of light passing through the dielectric mirror is irradiated.
• the output signal from the photodetector 7 is fed to a signal conditioning unit via a switch 9 used for experimental purposes.
• this comprises a signal amplifier 8a, the output of which is led to a PID element 8b in order to output a parameter change signal, which is one of the signals, in response to a deviation of the signal amplified by the signal amplifier 8a from a desired variable which is also fed to the PID element 8b Deviation proportional, one that
• Integrating deviation and a proportion corresponding to a temporal change in the deviation comprises.
• the output signal from the PID element 8b is fed to an adder 8c, where it is added to a desired manipulated variable which is representative of a set pump current.
• the output signal from the adder 8c is applied to one
• the laser of the present invention operates as follows:
• a desired pump current is set and the emitted laser power is measured in the outcoupled beam. If the pump current is varied, very large variations result in certain areas of the pump current, as shown by FIG. 2 a.
• the switch 9 is closed, so that the laser light power is stabilized by changing the pump current with a closed control loop. Again, the emitted laser power is measured in the outcoupled beam.
• the curve of FIG. 2b results. In all areas this shows a substantially smaller width than the curve of FIG. 2a, which means that the emitted laser light is emitted essentially uniformly and without short-term fluctuations.
• a laser output power which is at least substantially constant over the resonator round trip time is obtained.
• Amplifier media can be used.
• Y3AI5O12 should be mentioned as another example.
• the invention thus opens up a number of new fields of application, for example in material processing, e.g. drilling
• Laser with a decoupling means for emitting a laser power dependent on at least one parameter that can be influenced and a mode coupling means for coupling a plurality of the modes of the resonator characterized in that a detection means for detecting a quantity related to the laser power and a parameter changing means for changing the at least one Parameter is provided depending on the size related to the laser power.
• the parameter changing means is designed to change the parameter so that the emitted laser power is evened out, in particular averaged over a resonator cycle time.
• the parameter changing means is designed to equalize the output power averaged over a resonator cycle time to better than 10%, preferably better than 5%.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Nanotechnology (AREA)
• Lasers (AREA)

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• 1999
  • 1999-12-22 DE DE19962047A patent/DE19962047A1/de not_active Withdrawn
• 2000
  • 2000-12-22 US US10/149,900 patent/US6819690B2/en not_active Expired - Fee Related
  • 2000-12-22 JP JP2001547704A patent/JP2004500709A/ja active Pending
  • 2000-12-22 EP EP00985237A patent/EP1243054A1/de not_active Withdrawn
  • 2000-12-22 WO PCT/EP2000/013138 patent/WO2001047075A1/de not_active Ceased

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