EP2792034A1 - Procédé et appareil utilisable dans la commutation du facteur de qualité passive - Google Patents

Procédé et appareil utilisable dans la commutation du facteur de qualité passive

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Publication number
EP2792034A1
EP2792034A1 EP12810412.2A EP12810412A EP2792034A1 EP 2792034 A1 EP2792034 A1 EP 2792034A1 EP 12810412 A EP12810412 A EP 12810412A EP 2792034 A1 EP2792034 A1 EP 2792034A1
Authority
EP
European Patent Office
Prior art keywords
switched
emission
laser apparatus
pump
optical pulse
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.)
Withdrawn
Application number
EP12810412.2A
Other languages
German (de)
English (en)
Inventor
Trevor Cook
Stephen Lee
William Alexander
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales Holdings UK PLC
Original Assignee
Thales Holdings UK PLC
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
Application filed by Thales Holdings UK PLC filed Critical Thales Holdings UK PLC
Publication of EP2792034A1 publication Critical patent/EP2792034A1/fr
Withdrawn legal-status Critical Current

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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
    • H01S3/0014—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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/0912—Electronics or drivers for the pump source, i.e. details of drivers or circuitry specific for laser 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
    • H01S3/10—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
    • 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
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • 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
    • H01S3/10038—Amplitude control
    • H01S3/10046—Pulse repetition rate control
    • 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
    • H01S3/1305—Feedback control systems
    • 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
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1611—Solid materials characterised by an active (lasing) ion rare earth neodymium
    • 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
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/163—Solid materials characterised by a crystal matrix
    • H01S3/164—Solid materials characterised by a crystal matrix garnet
    • H01S3/1643—YAG

Definitions

  • the present invention relates to a passively Q-switched laser apparatus and a method for use in controlling such a laser apparatus in particular, though not exclusively, for laser target designation.
  • the present invention also concerns a controller and a program for a controller for implementation of the method.
  • Q-switching is a well known method for generating high-energy, short-duration laser pulses. Q-switching typically occurs as a consequence of the presence of variable attenuation within a laser cavity.
  • Active Q-switches are commonly used to control attenuation within a laser cavity for the production of reliable laser pulses. Although it is known to use mechanical devices for active Q-switching such as shutters, chopper wheels, spinning mirrors/prisms and the like inside a laser cavity, it is more common to use an intra- cavity modulator such as an intra-cavity acousto-optic or an electro-optic modulator. However, such active Q-switches may be relatively expensive, complex and large, and may require relatively high driving voltages and relatively fast switching of the driving voltages.
  • Passive Q-switches are inherently cheaper, simpler and smaller than active Q- switches and require no control or drive requirements.
  • known passive Q- switching methods produce more pulse-to-pulse timing jitter than active Q-switching methods.
  • the pulse-to-pulse timing jitter of known passively Q-switched lasers may be at least partially attributable to the type of pump used for excitation of a laser gain medium.
  • many known passively Q-switched lasers utilise flashlamp pumps. Such pumps are, however, prone to random intensity fluctuations which result in variations in pump-rate and, ultimately, in laser pulse-to-pulse timing jitter.
  • timing jitter may also contribute to the timing jitter.
  • changes in ambient temperature can translate into variations in laser efficiency through misalignment of laser optical components due to differential thermal expansion.
  • Any change in thermal loading while the laser is firing can couple into laser efficiency variations, for example, via thermal lensing effects or through misalignment of components.
  • Thermal loading may, in particular, vary according to time elapsed from start-up of the laser from a cold condition or as a result of varying a laser pulse repetition rate in response to a varying user requirement. Any such changes in laser efficiency may couple into timing jitter.
  • a method for use in controlling a passively Q-switched laser apparatus comprising: triggering pumping of a passively Q-switched laser apparatus at a pump trigger time;
  • the method may comprise triggering pumping of the laser apparatus at the further pump trigger time for emission of the further Q-switched optical pulse.
  • Such a method may permit the emission of the further Q-switched optical pulse from the laser apparatus substantially at or around the target emission time. This may result in improved timing of emission of the further Q-switched opticalinstalle relative to known passive Q-switching methods.
  • the method may, in particular, facilitate the use of passive Q-switching in applications where pulse-to-pulse timing is critical and where, traditionally, active Q-switching has previously been deemed necessary. Compared with active Q-switching, the method may enable the use of a simpler, more compact and lower cost Q-switched laser apparatus for such applications.
  • Such a passively Q- switched laser apparatus may also have higher reliability than a known actively Q- switched laser apparatus.
  • Pumping of the passively Q-switched laser apparatus may comprise pumping a gain medium of the laser apparatus.
  • the measured emission delay for the Q-switched optical pulse from the laser apparatus may be used as an estimate of the emission delay for the further Q-switched optical pulse.
  • the method may comprise determining the further pump trigger time by subtracting the measured emission delay from the target emission time.
  • the method may comprise determining the target emission time for the further Q-switched optical pulse based on a desired pulse-to-pulse repetition rate.
  • the further Q-switched optical pulse may be the Q-switched optical pulse emitted by the laser apparatus which immediately follows the Q-switched optical pulse.
  • the laser apparatus may emit at least one intervening Q-switched optical pulse between the Q-switched optical pulse and the further Q-switched optical pulse.
  • the method may comprise:
  • the method may comprise determining the further pump trigger time by subtracting an average of the measured emission delays from the target emission time.
  • the average of the measured emission delays may be less susceptible to any random intensity noise appearing on the individual Q-switched optical pulses and/or may be less susceptible to any measurement inaccuracies.
  • the method may comprise:
  • the method may comprise determining the emission time of the Q-switched optical pulse from the timing of a feature of the Q-switched optical pulse.
  • the particular feature of the Q-switched optical pulse used for determining the emission time may be selected according to the convenience with which the timing of the feature may be determined.
  • the method may comprise determining the emission time of the Q-switched optical pulse from the timing of a leading edge of the Q-switched optical pulse.
  • the method may comprise determining the emission time of the Q-switched optica! pulse as a time when an optical power of the Q-switched optical pulse rises through a predetermined threshold optical power level.
  • the predetermined threshold optical power level may be defined as a proportion of a peak optical power of the Q-switched optical pulse.
  • the predetermined threshold optical power level may be 50% of a peak optical power of the Q-switched optical pulse.
  • the method may comprise determining the emission time of the Q-switched optical pulse as a time corresponding to the maximum rate of increase of optical power of the Q-switched optical pulse.
  • the method may comprise determining the emission time of the Q-switched optical pulse from the timing of a trailing edge of the Q-switched optical pulse.
  • the method may comprise determining the emission time of the Q-switched optical pulse as a time when an optical power of the Q-switched optical pulse falls through a predetermined threshold optical power level.
  • the predetermined threshold optical power level may be defined as a proportion of a peak optical power of the Q-switched optical pulse.
  • the predetermined threshold optical power level may be 50% of a peak optical power of the Q-switched optical pulse.
  • the method may comprise determining the emission time of the Q-switched optical pulse as a time corresponding to the maximum rate of decrease of optical power of the Q-switched optical pulse.
  • the method may comprise determining the emission time of the Q-switched optical pulse as a time corresponding to a peak in the optical power of the Q-switched optical pulse.
  • the method may comprise:
  • the emission time of the Q-switched optical pulse may be more easily determined from the timing of a feature of such an electrical pulse.
  • the method may comprise using an electronic timing method to measure the emission delay between triggering pumping and the timing of the feature of the electrical pulse.
  • the method may comprise optically pumping the laser apparatus.
  • the method may comprise coupling light from an optical pump into a gain medium of the laser apparatus for excitation of the gain medium.
  • the method may comprise using a diode pump to pump the laser apparatus.
  • the method may comprise using at least one of a laser diode, a light emitting diode or a super-luminescent light emitting diode to pump the laser apparatus.
  • the method may comprise electrically pumping the laser apparatus.
  • the method may comprise electrically pumping a gain medium of the laser apparatus for excitation of the gain medium.
  • the method may comprise using an electrical current source to pump the laser apparatus.
  • a controller for use in controlling a passively Q-switched laser apparatus, the laser apparatus comprising a pump for pumping the laser apparatus and an optical detector for detecting emission of a Q-switched optical pulse, and the controller being configured for communication with the pump and the optical detector and being configured so as to:
  • a programmable controller for use in controlling a passively Q-switched laser apparatus, the laser apparatus comprising a pump for pumping the laser apparatus and an optica! detector for detecting emission of a Q-switched optical pulse, and the controller being configured for communication with the pump and the optical detector and being programmed so as to: trigger the pump at a pump trigger time;
  • a program for a programmable controller for use in controlling a passively Q-switched laser apparatus, the laser apparatus comprising a pump for pumping the laser apparatus and an optical detector for detecting emission of a Q-switched optical pulse, and the controller being configured for communication with the pump and the optica! detector, wherein, when executed by the controller, the program causes the controller to:
  • a data carrier comprising a program according fourth aspect.
  • a passively Q-switched laser apparatus comprising:
  • a pump configured for pumping a passively Q-switched laser apparatus
  • an optical detector for detecting emission of a Q-switched optical pulse; and a controller configured for communication with the pump and the optical detector, the controller being configured to:
  • the controller may be configured to trigger operation of the pump at the further pump trigger time for emission of the further Q-switched optical pulse.
  • the laser apparatus may comprise a gain medium.
  • the pump may be configured to pump the gain medium.
  • the pump may comprise an optical source.
  • the pump may comprise an optical diode source.
  • the pump may comprise at least one of a laser diode, a light emitting diode or a super-luminescent light emitting diode.
  • the pump may comprise an electrical pump.
  • the pump may comprise a current source.
  • the apparatus may comprise an optical arrangement configured to divert at least a portion of the optical power of the Q-switched optical pulse from a location inside and/or outside a cavity of the laser apparatus onto the optical detector.
  • Figure 1 is a schematic of a prior art passively Q-switched laser apparatus
  • Figure 2 is a schematic of a passively Q-switched laser apparatus constituting an embodiment of the present invention
  • Figure 3 is a schematic of the temporal variation of pump current and the corresponding optical pump power, laser output power and photodetector electrical signal of the passively Q-switched laser apparatus of Figure 2.
  • a known passively Q- switched laser apparatus generally designated 10 comprising an optica! cavity 20 defined between a high reflector 22 and an output coupler 24, the optical cavity 20 including an optical gain medium 26 and a passive Q-switch 28.
  • the gain medium 26 is optically pumped by a flashlamp 30.
  • the flashlamp 30 is driven by an electrical driver 32.
  • the optical cavity 20 emits a passively Q-switched output beam 33 from the output coupler 24 according to variations in optical cavity gain and optical cavity loss as will now be described in more detail below.
  • the electrical driver 32 drives the flashlamp 30 with a pulsed electrical signal represented by dotted line 34 in Figure 1 and the flashlamp 30 generates an optical pump pulse represented by solid line 36 in Figure 1.
  • the optical pump pulse 36 is coupled to the gain medium 26 so as to create a population inversion in the gain medium 26.
  • the population inversion provides the optical cavity 20 with a gain which grows during the optical pump pulse 36 until the optical cavity gain exceeds the optical cavity loss such that the optical cavity 20 reaches threshold and emits stimulated radiation.
  • the stimulated radiation saturates the passive Q-switch 28 causing a rapid fall in optical cavity loss.
  • the population inversion in the gain medium 26 falls during stimulated emission until the optical cavity gain falls below the optica! cavity loss once again thereby resulting in cessation of stimulated radiation.
  • Such variations in the optical cavity gain and the optical cavity loss during a single optical pump pulse 36 result in the emission of a passively Q- switched optical output pulse at the output coupler 24.
  • FIG 2 shows an embodiment of a passively Q-switched laser apparatus generally designated 110 comprising an optical cavity 120 defined between a high reflector 122 and an output coupler 124, the optical cavity 120 including an optical gain medium 126 and a passive Q-switch 128.
  • the gain medium 126 is optically pumped by a pulsed laser diode pump 30.
  • the laser diode pump 130 is driven by an electrical diode driver 132.
  • the laser apparatus 1 10 of Figure 2 is configured to generate a stream of passively Q-switched laser pulses having a desired repetition rate with a reduced or insignificant level of pulse-to-pulse timing jitter compared with the pulse-to-pulse timing jitter associated with the prior art laser apparatus 10 of Figure 1.
  • the desired repetition rate will depend on the application and may be predetermined or user defined.
  • One skilled in the art will also appreciate that the present invention is not limited to any particular choice of gain medium 126 or passive Q-switch 128.
  • a suitable material for the gain medium 126 may be Nd:YAG
  • a suitable material for the passive Q-switch 128 may be Cr:YAG.
  • different materials may be used for the gain medium 126 and the passive Q-switch 128.
  • the laser apparatus 110 further comprises a controller 140, an optical detector 44 and a partially reflecting mirror 146.
  • the partially reflecting mirror 146 diverts a portion 147 of the light 133 emitted by the output coupler 124 onto the optical detector 144.
  • the optical detector 144 is configured to provide an electrical signal 148 which is generally proportional to the optical power of portion 147.
  • the optical detector 144 provides the electrical signal 148 to the controller 140.
  • the controller 140 is configured to control the electrical diode driver 32 according to the electrical signal 148.
  • the controller 140 controls the electrical diode driver 132 so as to provide passively Q-switched pulses having the desired pulse repetition rate whilst suppressing or, at least reducing, pulse-to-pulse timing jitter.
  • the controller 140 uses feedback from measurements performed during the emission of a passively Q-switched pulse to control the timing of the emission of a subsequent passively Q-switched pulse as will now be described with reference to Figure 3.
  • Figure 3 is only intended to provide a schematic illustration of the temporal variation of pump current 34 and the corresponding temporal variation in optical pump power 136, optical power output 133 from the passively Q-switched laser apparatus 110 of Figure 2 and the electrical signal 148 provided by the optical detector 144, and that the actual temporal variations observed in practice may differ from those shown schematically in Figure 3.
  • the controller 140 sends an i th electrical trigger signal to the diode driver 132, where i represents an integer index value.
  • the diode driver 132 initiates an i th current pulse 134' to the laser diode pump 130.
  • the i th optical pump pulse 136' is coupled to the gain medium 126 which causes the gain of the gain medium 26 to increase until an i th passively Q-switched pulse 133' is emitted from the optical cavity 120.
  • the optical detector 144 generates an i th electrical pulse 148' signal having an instantaneous value which is generally proportional to the power of the i th passively Q- switched pulse 133'.
  • the controller 140 processes the i th electrical pulse 148 1 received from the optical detector 144 and determines a time of emission for the i th passively
  • Q-switched pulse 133' may be defined as the time corresponding to the leading edge of the i t!l electrical pulse 148' according to a predetermined definition of q .
  • T q may, for example, be defined as the time when the i lh electrical pulse 148' rises through a predetermined reference level.
  • T q ' is used. It should also be understood that the i th passively Q-switched pulse 133' is subject to pulse-to-pulse timing jitter and that the emission time of the i ih passively
  • Q-switched pulse 133 ! is shown in Figure 3 as being offset relative to the ideal or target time of emission of the i th passively Q-switched pulse 133' (i.e. the time of emission of the i th passively Q-switched pulse 133' corresponding to zero pulse-to-pulse timing jitter) given by: y(> ' ) _ ⁇ (0)
  • Equation 1 where , is a target time of emission for the 0 th passively Q-switched pulse (not shown) and AT q is a desired pulse-to-pulse temporal separation or period corresponding to a desired pulse repetition rate of 1/ ⁇ ? .
  • the controller 140 determines an emission delay AT lq for the i th passively Q- switched pulse 133' defined as the time elapsed between emission of the i th electrical trigger signal at t and the emission time T q for the i th passively Q-switched pulse 133' according to the relation:
  • the controller 140 determines a time for triggering the diode driver 132 for the initiation of the emission process for the (i+1 ) th passively Q-switched pulse 133 (l+1 ) according to the relation: + ⁇ ) 1)
  • the controller 140 sends an electrical trigger signal to the diode driver 132 at time to initiate the (i+1) th current pulse 134 (i+ ) .
  • the (i+1) th current pulse 134 (i+1 ⁇ results in the output of an (i+1 ) th optical pump pulse 136 (i+1) from the laser diode pump 130.
  • the (i+1 ) ih optical pump pulse 136 ⁇ i+1 ) is coupled to the gain medium 126 which causes the output of an (i+1) th passively Q- switched pulse 133 (l+1 ) from the optical cavity 120 at or close to the target emission time ⁇ q rget required to provide the desired pulse repetition rate of .
  • the controller 140 may, for example, comprise a comparator, a timer and a processor.
  • the comparator may be configured to receive the electrical signal 148 from the photodetector 144 and to compare the electrical signal 148 to a reference level input.
  • the timer may be configured to receive a trigger signal from the processor and an output signal from the comparator.
  • the processor may simultaneously send an i th electrical trigger signal to the diode driver 132 and to the timer to initiate an elapsed time measurement.
  • the comparator may receive the i th electrical pulse 148' and compare it to the reference level input.
  • the comparator output signal may cause the timer to finish the elapsed time measurement. Subsequently, the timer may provide the measured elapsed time to the processor which treats the elapsed time as the emission delay AT ⁇ and calculates the time for triggering the diode driver
  • an alternative optical pump source may be used such as a light emitting diode (LED), a superiumtnescent light emitting diode (SLED), a flashlamp, or the like.
  • the gain medium 126 may be electrically pumped. In such electrically pumped embodiments, the gain medium 126 may, for example, be electrically pumped directly by an electrical driver.
  • a fraction of the optical power may be diverted or tapped from the laser cavity 120 and detected using a further photodetector (not shown) configured for communication with the controller 140.
  • the controller 140 may determine the emission delay A tq between triggering the diode driver 132 and any feature of the electrical pulse 148' received from the optical detector 144. For example, the controller 140 may determine the emission delay AT between triggering the diode driver 132 and a peak or a failing edge of the electrical pulse 148'.
  • the controller 140 may estimate the emission delay (e.g. ⁇ ) for the (i+1 ) th passively Q-switched pulse using an emission delay ... of an earlier passively Q-switched pulse and determine the time ⁇ ' + ⁇ for triggering the diode driver 132 for initiation of the emission process for the (i+1 ) th passively Q-switched pulse 133 (!+1 ) from any one of the relations:
  • the controller 140 may estimate the emission delay T ⁇ +f> for the (i+1 ) th passively Q-switched pulse from a function / of the emission delays ... of a pluraiity of preceding passively Q-switched pulses and determine the time T ⁇ for triggering the diode driver 132 for the initiation of the emission process for the (i+1 ) th passively Q-switched pulse 133 (l+1) from:
  • Equation 6 ⁇ ⁇ may, for example, be an average of the emission delays ⁇ and
  • the laser apparatus 1 10 of Figure 2 with reference to Figure 3 only refers to the emission of a single passively Q-switched laser pulse per optical pump pulse, it will be appreciated that, depending on the duration and/or the intensity of the optical pump pulse, the laser apparatus 1 10 may be operated so that more than one passively Q-switched laser pulse may be emitted per optical pump pulse.
  • the photodetector 144 of the laser apparatus 110 of Figure 2 generates electrical pulses 148', 148 (l+1) which are generally proportional to the power of the corresponding passively Q-switched pulses 133', 133 (l+1> .
  • the electrical pulses 148', 148 (l+1) may not be exactly proportional to the optical power of the passively Q-switched pulses 133', 133 (l+1) , but may be delayed or may be of a different shape to the passively Q-switched pulses 133', 133 (l+1> . This does not, however, affect the passive Q-switching method described above.

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

Abstract

Le procédé selon l'invention utilisable dans le contrôle d'un appareil laser à commutation du facteur de qualité passive (110) consiste à déclencher le pompage d'un appareil laser à commutation du facteur de qualité passive à un instant de déclenchement de pompe, à mesurer un retard d'émission entre l'instant de déclenchement de pompe et un instant d'émission d'une impulsion optique à commutation du facteur de qualité de l'appareil laser. Le procédé consiste en outre à utiliser le retard d'émission mesuré et un instant cible pour l'émission d'une autre impulsion optique à commutation du facteur de qualité de l'appareil laser pour déterminer un autre instant de déclenchement de pompe. Le procédé peut être utilisé afin d'améliorer la synchronisation d'émission d'impulsions optiques à commutation du facteur de qualité et peut, en particulier, servir à supprimer le scintillement de synchronisation d'impulsion à impulsion en particulier, mais pas exclusivement, pour la désignation de cible laser. Le laser comprend un miroir d'extrémité (122), un support de gain actif (126), un commutateur du facteur de qualité passif (128), un coupleur de sortie (124), un diviseur de faisceau (146), un photodétecteur (144), dont le signal électrique (148) est évalué par un contrôleur (140). Le contrôleur fournit des informations au pilote de diode laser (132) qui pilote la diode laser (130) émettant de la lumière (136) permettant de pomper le gain actif (126). Le scintillement dans le taux de répétition du laser à commutation de facteur de qualité passive peut être réduit par le contrôle de puissance de pompe.
EP12810412.2A 2011-12-12 2012-12-12 Procédé et appareil utilisable dans la commutation du facteur de qualité passive Withdrawn EP2792034A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1121379.0A GB2497549A (en) 2011-12-12 2011-12-12 Method and apparatus for use in passive q-switching
PCT/GB2012/053103 WO2013088139A1 (fr) 2011-12-12 2012-12-12 Procédé et appareil utilisable dans la commutation du facteur de qualité passive

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EP2792034A1 true EP2792034A1 (fr) 2014-10-22

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CN104466654A (zh) * 2014-12-29 2015-03-25 中国科学院半导体研究所 脉冲泵浦被动调q输出单脉冲的激光器
FR3034578B1 (fr) 2015-03-30 2018-04-27 Horiba Abx Sas Procede et dispositif de declenchement de sources lumineuses impulsionnelles
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US10483714B2 (en) 2016-03-30 2019-11-19 Saab Ab Q-switched laser with stabilized output energy
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GB2497549A (en) 2013-06-19
GB201121379D0 (en) 2012-01-25

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