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WO1997031411A1 - Stabilisation d'un laser pulse - Google Patents

Stabilisation d'un laser pulse Download PDF

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Publication number
WO1997031411A1
WO1997031411A1 PCT/SE1997/000165 SE9700165W WO9731411A1 WO 1997031411 A1 WO1997031411 A1 WO 1997031411A1 SE 9700165 W SE9700165 W SE 9700165W WO 9731411 A1 WO9731411 A1 WO 9731411A1
Authority
WO
WIPO (PCT)
Prior art keywords
pump
laser
pulse
switched
control circuit
Prior art date
Application number
PCT/SE1997/000165
Other languages
English (en)
Inventor
Magnus Arvidsson
Björn HANSSON
Carsten LINDSTRÖM
Original Assignee
Geotronics Ab
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from SE9600628A external-priority patent/SE9600628D0/xx
Application filed by Geotronics Ab filed Critical Geotronics Ab
Publication of WO1997031411A1 publication Critical patent/WO1997031411A1/fr

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
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/113—Q-switching using intracavity saturable absorbers
    • 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
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094076—Pulsed or modulated pumping

Definitions

  • This invention relates to the stabilization of a pulsed laser of the kind apparent from the introductory part of claim 1, and to the stabilization of for instance a passively Q- switched micro-chip laser.
  • Diode pumped solid-state lasers are a rapidly growing field.
  • Passively Q-switched micro-chip lasers are particularly interesting as they are able to provide short pulses ( ⁇ Ins) with high peak power (KW) for moderate pump powers, from, for instance, a laser diode or a Ti:Saphire laser or the like, using an extremely simple configuration.
  • a disadvantage with this kind of Q-switched laser has been that a passively Q-switched laser has a considerable pulse repetition frequency jitter accompanied by pulse-to-pulse amplitude fluctuation.
  • Actively Q-switched lasers i.e. Q-switched lasers in which the control of the Q-switching is done directly at the Q- switch crystal, for instance by changing its polarization, are larger than passive Q-switched lasers and they also need fast high voltage switching power supplies to work.
  • a passively Q-switched micro-chip laser for producing high- peak-power pulses of light of extremely short duration is described in US-A-5,394,413.
  • a saturable absorber prevents the onset of lasing until the average inversion density within the cavity of the Q-switched laser reaches a predeter ⁇ mined value.
  • the configuration of the laser is then such that, at the onset of lasing, a Q-switched output pulse having an extremely short length and a high peak power is generated.
  • This kind of extremely short duration, high-peak-power laser pulses could be useful in many applications, such as in electronic distance measuring devices (EDM).
  • EDM electronic distance measuring devices
  • An object of the invention is to provide stabilization of the output from a passively Q-switched laser, for instance a Q- switched micro-chip laser.
  • Another object of the invention is to provide stabilization of a Q-switched laser in such a way that a train of narrow pulses can be provided having as little jitter as possible between the output pulses.
  • Still another object of the invention is to provide stabiliz ⁇ ation of a passively Q-switched laser so that the time of the output of each laser pulse is exactly determinable.
  • the invention relates to a stabilization method and device for a passively Q-switched laser, which is pumped by at least one pump laser source.
  • the pump power of the pump laser source is modulated between a pump level lower than and a pump level above the lasing threshold for the Q-switched laser at frequencies, which are always lower than a self- pulsation frequency of the Q-switched laser.
  • Each pump pulse having a pump level above the laser threshold is present at least until an output pulse from the Q-switched laser has been emitted.
  • the pulse length of each pump pulse is controlled by the output pulse from the Q-switched laser.
  • the modulation of the pump laser source could comprise only ac power components. However, the modulation of the pump laser source could also comprise an ac modulation signal superimposed on a dc level.
  • the modulation of the pump laser source could also be controlled to have a varying frequency during an operation period.
  • FIG. 1 shows schematically a first embodiment of the Q- switched laser according to the invention
  • FIG. 2A and 2B shows schematically a first embodiment of a timing diagram for providing the stabilization according to the invention
  • FIG. 3 shows schematically the jitter varying with changing duty cycle
  • FIG. 4 shows schematically the jitter varying with changing frequency
  • FIG. 5A and 5B shows schematically a second embodiment of a timing diagram for providing the stabilization according to the invention
  • FIG. 6 shows schematically a second embodiment of the Q- switched laser according to the invention
  • FIG. 7A and 7B shows schematically a timing diagram which can be produced by the embodiment of the invention illu ⁇ strated in FIG. 6.
  • FIG. 1 shows a passively Q-switched laser 1, such as a solid- state Q-switched laser having a cavity comprising an active medium 2 of, for instance, Nd:YV0 4 crystal having a mirror 3 at one end and as the Q-switch crystal a saturable absorber 4 of, for instance, Cr* * :YAG or Cr + :YSGG or the like at its other end.
  • a second mirror 5 is placed at the output end of the Q-switched laser near to the saturable absorber 4. In the embodiment shown the mirror 5 is planoconcave and has a high reflectance.
  • the Q-switched laser 1 could be a micro-chip laser.
  • the Q-switched laser is pumped by at least one laser diode 6 (and 6' ), which has a wavelength matched to the absorption band of the active material, through a lens system 7 or other optical means leading the light from the pump laser diode 6 to the gain medium 2 through the mirror 3.
  • the pump wavelength is about 808 nm. It is also possible to use more than one laser diode.
  • the laser diode 6 (or diodes 6, 6') has power supplied by a pulse control device 8.
  • the control device controls the pulses and can be adjusted so that the pulse length is adapted to the output of the solid-state laser pulses either by an operator or, preferably, a sensor 9 sensing the Q- switched laser output and connected to the control device 8 which turns off the control pulse to the laser diode as soon as the Q-switched laser output has been produced.
  • Some other kind of pump light source could be used instead of a laser diode, for instance a Ti:Saphire laser, which can be modulated by an acousto-optical modulator.
  • time stabilization of the Q- switched laser output is provided by modulating the pumping and locking the frequency of the Q-switched laser to the pumping modulation.
  • the pump power is momentarily increased a predetermined time before a desired Q-switched laser output pulse. If the energy in each pump pulse is adjusted such that the Q-switched laser only generates one pulse per pump pulse then frequency locking is achieved.
  • the rest inversion in the laser cavity will decay during the time between the pump pulses, and thus the conditions in the laser cavity could be the same at the beginning of each pump pulse if the pause between pulses is long enough. It is thus possible to get a very stable repetition rate, and also a stable amplitude, from a Q-switched laser stabilized in this way.
  • a stable Q-switched pulse train having adjustable pulse rate can be provided for frequences under the self- pulsation frequency f ⁇ f provided from a constantly pumped Q- switch laser, i.e. without any pump modulation.
  • the frequency region to be used for the pump power modulation is between 0 to f sf for the Q-switched laser in question.
  • the diagram shown in FIGs 2A and 2B illustrates the preferred way to pump the Q-switched laser according to the invention.
  • the control circuit 8 in this embodiment comprises a pulse oscillator and, as is apparant from FIG 2A, supplies pulses having a peak power and a duration providing an energy large enough for building up the critical value for providing the onset of the Q-switched laser pulse.
  • the Q-switched laser pulse is generated just before the end of each pump pulse.
  • the cavity was pumped with 390 mW CW input power, giving a self pulsing frequency of 13 kHz and a pulse length 20 ns.
  • the self-pulsing jitter was measured and found to be 60 ns.
  • a jitter of 33 ps was produced at a frequency of 11.7 kHz. A 100% modulation was then used, i.e. going from zero effect up to full effect.
  • the jitter varied as the duty cycle is changed, as is apparent from FIG 3.
  • the current to the laser diode was adjusted so that the Q-switched laser was locked onto the pumping frequency while the pulse length was varied.
  • the jitter from the Q-switched laser then varied from 33 ps at a 40% duty cycle to 200 ps at 80% duty cycle.
  • a duty cycle as large as 55% there is still a jitter as low as 70 ps.
  • the repetition rate of the Q-switched pulse train can be adjusted while still retaining a small jitter, as is apparent from FIG 4.
  • the pump frequency was changed while the pulse width was kept constant at 43 ⁇ s.
  • the period could be adjusted from 84 ⁇ s to 190 ⁇ s producing a jitter of from 35ps to 120ps.
  • the experiment also showed that the amplitude jitter between the Q-switched laser pulses was negligable.
  • the principle according to the invention is not limited to that.
  • This kind of control is shown in FIG 5A, showing modulation pulses superimposed on a constant power level. This could for instance be achieved by having two laser diodes, one being supplied with a constant current and the other with a pulsed current.
  • the time of the modulat- ion pulses are essentially shorter than in a case with 100% modulation. A stable pulse train can be obtained but the time jitter between the pulses is increased in relation to 100% modulation.
  • the laser frequency could be increased up to the self-pulsation frequency without having to change the shape of the pump pulse.
  • the frequency could be varied within a Q-switched pulse train as long as it does not exceed the self-pulsation frequency and this means that it is possible to control the emittance of each Q-switched pulse in the train individually.
  • a Q-switched pulse is emitted to a target and reflected back to a pulse receiver 10.
  • the receiv ⁇ er 10 controls a control circuit 11 which after a predeter ⁇ mined delay activates the laser diode 12.
  • the Q-switched laser pulse is sensed by the sensor 13 connected to a reset input of the control circuit 11 which then inactivates the laser diode 12.
  • the control circuit 11 also comprises means to make an extra delay of the control pulse to the diode 12 if the pulse received by the receiver should come so early that the momentary frequency should happen to coincide with or be above the self-pulsation frequency.
  • FIGs 7A and 7B A timing diagram of the same kind as illustrated in the FIGs 2A and 2B but related to the embodiment shown in FIG. 6 is presented in FIGs 7A and 7B. It is apparent here that it is possible to have quite different pulse pauses between the individual pump pulses.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

Méthode et dispositif de stabilisation d'un laser à impulsions géantes déclenchés passivement, pour lequel le pompage est effectué par au moins un laser source de pompage (6, 6'; 12). L'énergie de pompage du laser source de pompage (6, 6'; 12) est modulée entre un niveau de pompage inférieur et un niveau de pompage supérieur au seuil d'émission laser du laser déclenché à des fréquences qui sont toujours inférieures à la fréquence d'auto-impulsion de ce laser.
PCT/SE1997/000165 1996-02-20 1997-02-04 Stabilisation d'un laser pulse WO1997031411A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
SE9600628A SE9600628D0 (sv) 1996-02-20 1996-02-20 Laser
SE9600628-3 1996-02-20
SE9603288-3 1996-09-10
SE9603288A SE9603288L (sv) 1996-02-20 1996-09-10 Stabilisering av en pumpad lasesr

Publications (1)

Publication Number Publication Date
WO1997031411A1 true WO1997031411A1 (fr) 1997-08-28

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1997/000165 WO1997031411A1 (fr) 1996-02-20 1997-02-04 Stabilisation d'un laser pulse

Country Status (2)

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SE (1) SE9603288L (fr)
WO (1) WO1997031411A1 (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998056088A1 (fr) * 1997-06-06 1998-12-10 Spectra Precision Ab Laser
WO2000016122A1 (fr) * 1998-09-17 2000-03-23 Spectra Precision Ab Dispositif de mesure electronique des distances
WO2003007438A1 (fr) * 2001-07-12 2003-01-23 Agency For Science, Technology And Research Laser declenche
EP1696522A2 (fr) 2005-02-04 2006-08-30 JDS Uniphase Corporation Laser à Q-switch passif avec taux de répétition ajustable
WO2009027144A1 (fr) * 2007-08-31 2009-03-05 Robert Bosch Gmbh Procédé pour faire fonctionner un dispositif laser
WO2009127490A1 (fr) * 2008-04-17 2009-10-22 Robert Bosch Gmbh Système laser et procédé pour sa conduite
EP1488481B1 (fr) * 2002-03-19 2011-01-05 Lightwave Electronics Commande de boucle a phase asservie de lasers a declenchement passif
WO2016181488A1 (fr) * 2015-05-12 2016-11-17 株式会社島津製作所 Laser déclenché passif et procédé d'optimisation de son action

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4930901A (en) * 1988-12-23 1990-06-05 Electro Scientific Industries, Inc. Method of and apparatus for modulating a laser beam
US5291505A (en) * 1993-01-21 1994-03-01 Hughes Aircraft Company Active energy control for diode pumped laser systems using pulsewidth modulation
US5394413A (en) * 1994-02-08 1995-02-28 Massachusetts Institute Of Technology Passively Q-switched picosecond microlaser

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4930901A (en) * 1988-12-23 1990-06-05 Electro Scientific Industries, Inc. Method of and apparatus for modulating a laser beam
US5291505A (en) * 1993-01-21 1994-03-01 Hughes Aircraft Company Active energy control for diode pumped laser systems using pulsewidth modulation
US5394413A (en) * 1994-02-08 1995-02-28 Massachusetts Institute Of Technology Passively Q-switched picosecond microlaser

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998056088A1 (fr) * 1997-06-06 1998-12-10 Spectra Precision Ab Laser
US6263004B1 (en) 1997-06-06 2001-07-17 Spectra Precision Ab Laser
WO2000016122A1 (fr) * 1998-09-17 2000-03-23 Spectra Precision Ab Dispositif de mesure electronique des distances
US6545749B1 (en) 1998-09-17 2003-04-08 Spectra Precision Ab Electronic distance measuring device
WO2003007438A1 (fr) * 2001-07-12 2003-01-23 Agency For Science, Technology And Research Laser declenche
EP1488481B1 (fr) * 2002-03-19 2011-01-05 Lightwave Electronics Commande de boucle a phase asservie de lasers a declenchement passif
US7843978B2 (en) 2005-02-04 2010-11-30 Jds Uniphase Corporation Passively Q-switched laser with adjustable pulse repetition rate
EP1696522A3 (fr) * 2005-02-04 2009-10-07 JDS Uniphase Corporation Laser à Q-switch passif avec taux de répétition ajustable
EP1696522A2 (fr) 2005-02-04 2006-08-30 JDS Uniphase Corporation Laser à Q-switch passif avec taux de répétition ajustable
WO2009027144A1 (fr) * 2007-08-31 2009-03-05 Robert Bosch Gmbh Procédé pour faire fonctionner un dispositif laser
WO2009127490A1 (fr) * 2008-04-17 2009-10-22 Robert Bosch Gmbh Système laser et procédé pour sa conduite
US8656879B2 (en) 2008-04-17 2014-02-25 Robert Bosch Gmbh Laser device and operating method for it
WO2016181488A1 (fr) * 2015-05-12 2016-11-17 株式会社島津製作所 Laser déclenché passif et procédé d'optimisation de son action
JPWO2016181488A1 (ja) * 2015-05-12 2017-12-14 株式会社島津製作所 受動ｑスイッチレーザ及びその動作最適化方法
US10153607B2 (en) 2015-05-12 2018-12-11 Shimadzu Corporation Passive Q-switch laser and method for optimizing action of the same

Also Published As

Publication number Publication date
SE9603288D0 (sv) 1996-09-10
SE9603288L (sv) 1997-08-21

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