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
  • H01S3/115—Q-switching using intracavity electro-optic devices
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
  • G02F1/0327—Operation of the cell; Circuit arrangements
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
• • 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
  • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
  • H01S3/107—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using electro-optic devices, e.g. exhibiting Pockels or Kerr effect

Definitions

• the present invention relates to a method for exciting a crystal of a Pockels cell with (high) voltage pulses, in particular for providing a time-limited optically stable polarization window. Furthermore, the invention relates to an amplification unit, in particular a regenerative amplification unit.
• the activation of a Pockels cell for the polarization adjustment of electromagnetic radiation, in particular laser radiation, is effected by a fast switching of high-voltage applied to the crystal of the Pockels cell.
• the applied high voltage causes via the electro-optical effect an electrical polarization in the crystal, which leads for example to a desired birefringence of the crystal.
• the birefringence can be used, for example, to adjust the polarization state of laser radiation guided through the crystal of the Pockels cell.
• Pockels cell drive circuit An example of a Pockels cell drive circuit is described in EP 1 801 635 AI.
• Exemplary drive circuits are based on so-called “double-push-pull" switching processes which allow voltage rise times in the range of a few nanoseconds., It is also known that such fast voltage circuits can be accompanied by mechanical oscillations of the crystal which occur due to a piezoelectric energy occurring simultaneously with the electro-optical effect Effect are caused.
• a mechanical damping of such resonances is effected for example by appropriate use of damping films and by attachment of the crystals by soldering or gluing to special brackets.
• DE 10 2013 012 966 A1 discloses damping mechanical vibrations by integrally bonding the crystal to the electrodes.
• EP 2 800 212 A1 discloses regarding the so-called “accoustic ringing" of an electro-optical modulator to tune a modulation pulse width approximately to an integer multiple of the period of the mechanical oscillation of the "acoustic ringing".
• One aspect of this disclosure is based on the object of providing a useful time window of a Pockels cell which is as uninfluenced by mechanical vibrations as possible. At least one of these objects is achieved by a method for exciting a crystal of a Pockels cell according to claim 1 and by a, in particular regenerative, amplifying unit according to claim 14. Further developments are specified in the subclaims.
• a method for exciting a crystal of a Pockels cell with high voltage pulses for polarization adjustment of the electromagnetic radiation passing through the crystal, in particular laser radiation comprises the steps of: applying a sequence of useful voltage pulses to the crystal, each having a useful Have period and a Nutz -Pulsumble and for inducing a birefringence of the crystal via an electrical polarization in the crystal for the polarization of the electromagnetic radiation, in particular laser radiation, are formed, and applying a sequence of compensation pulses to the crystal, each having a voltage profile, wherein the sequence of compensation pulses is superimposed in time with the sequence of useful voltage pulses in such a way that the voltage curves of the compensation pulses of an excitation of a mechanical oscillation in the crystal of the Pockels cell by the Nutz-Spannungsp counteract.
• the invention relates to an amplification unit, in particular a regenerative amplification unit, with a gain medium, an optical switch unit with a Pockels cell and with a polarization beam splitter for forming an optical switch and a control unit for driving the Pockels cell according to the above method and the disclosed herein further developments of the method.
• the invention relates to a method for exciting a Pockels cell with a pulsed high voltage, wherein the pulsed high voltage repetitive useful pulses having a useful period and a useful pulse width and is adapted to the optical properties of Pockels- Modify the cell to induce birefringence in the Pockels cell.
• the excitation further comprises brake pulses, which each follow a useful pulse, and are designed so that a stimulated by the useful pulse mechanical vibration (acoustic shock wave) is attenuated in the Pockels cell.
• switching edges of the voltage profiles of the compensation pulses can be designed as mechanically effective portions of the voltage waveforms of the compensation pulses such that their time course and their temporal position relative to the Nutz voltage pulses are designed so that they induce acoustic events in the crystal, with acoustic Events in the crystal caused by the utility voltage pulses interfere destructively.
• the time profile can be determined in particular by a rise time or a fall time of a switching edge.
• the useful voltage pulses may each have a first voltage switching operation for setting a useful voltage and a second voltage switching operation for terminating the presence of the useful voltage, and at least one of the switching operations may be suitable for mechanical vibration of the crystal of the Pockels Cell, and in particular to cause an acoustic shock wave.
• the voltage curve of the compensation pulses can have at least one compensation switching operation for exciting one of the oscillations which counteract the mechanical oscillation which can be excited by the useful voltage pulses.
• the counteracting oscillation may be out of phase with the mechanical vibration that can be excited by the useful voltage pulses, in particular with a phase shift in the range of 135 ° to 225 °.
• the phase shift can lead to a destructive interference with the stimulated by the useful voltage pulses mechanical vibration, optionally the phase position is selected to optimize damping and damped vibrations to reduce overcompensation and in particular to prevent.
• the crystal may have at least one acoustic resonant frequency, particularly by dimensions such as the amount of crystal between electrodes for voltage application, crystal type, crystal shape, crystal cut, an adjacent E field vector, and / or originally unexcited Spatial axes is determined.
• the sequence of useful voltage pulses may, due to the useful period, in principle be suitable for exciting resonances of the crystal with the at least one acoustic resonant frequency, and the sequence of compensating pulses may be designed to reduce the excitations of resonances in the crystal, in particular prevent.
• the voltage waveform of the compensation pulses may each include a first compensation voltage switching operation and a second compensation voltage switching operation.
• the first compensation voltage switching operation may, in particular, substantially, simultaneously or with a time delay corresponding, in particular, substantially, a period or a multiple of the period of a resonant frequency of the crystal, after the voltage switching operation to be compensated.
• the second compensation voltage switching operation may be performed with a time delay corresponding, in particular, substantially, a period or an integer multiple of the period of a resonant frequency of the crystal, to the voltage switching operation to be compensated and subsequent to the associated first compensation voltage switching operation.
• the time delay between one of the useful voltage pulses and the compensation pulse directly following this useful voltage pulse can, in particular essentially, be zero, so that the voltage switching operations at the end of the useful pulse and at the beginning of the compensation pulse, in particular substantially, at the same time done so that compensate for the associated vibration excitations.
• voltage switching operations can be used which have a voltage gradient which is inverse to the useful switching operation to be compensated.
• the sequence of compensation pulses may comprise a plurality of compensation pulses for a useful voltage pulse, the beginning of at least one of the subsequent compensation pulses may be delayed by an integer multiple of the resonance period with respect to the beginning of the first compensation pulse.
• the voltage waveform of one of the compensation pulses may include a compensation voltage switching operation having a time offset of at most 12.5% of the resonant period of the crystal, for example, a maximum of 5% to 10%, and more preferably a minimum of 1% of the resonant period of the crystal, Example from 2% to 5%, done after the second voltage switching operation.
• the voltage waveform of one of the compensation pulses may include a compensation voltage switching operation having a time offset of at most 12.5% of the resonant period of the crystal, for example, a maximum of 5% to 10%, and a minimum of 1% of the resonant period of the crystal, for example, 2%. up to 5%, with respect to an integer multiple of the resonance period.
• the compensation pulses may form polarization windows that start at a maximum time offset of 12.5% of the useful period relative to a delay of an integer multiple of the resonant period with respect to the second voltage switch of the payload window and their end at an integer multiple of the resonant period regarding the beginning of the user window is.
• At least one of the voltage switching operations of the utility voltage pulses and the compensation pulses may include an erratic voltage change, particularly in the range of a few hundred volts to a few kilovolts.
• the voltage change of one of the compensation voltage switching operations may be in the order of magnitude of the voltage change of the voltage switching operations of the useful voltage pulse, in particular comparable or a fraction thereof.
• the voltage change of the compensation voltage switching operations of a compensation pulse can be reduced compared to the voltage change of the first Nutzthesesschaltvorgangs and / or the second Nutzthesesschaltvorgangs, and the compensation can optionally be supplemented with at least one, another compensation pulse forming, compensation voltage switching operation.
• the reduction in the voltage change of the compensation voltage switching operations compared to the voltage change of the first voltage switching operation and / or the second voltage switching operation may be at least so large that the reduced voltage change between the compensation voltage switching operations, in particular in a resonator-internal application of Pockels- Cell, for example in a regenerative amplification unit, causing (laser radiation loss in the optical beam path (eg of a laser system), in particular, the target operation of the laser system.)
• a plurality of resonance frequencies may be provided by providing a plurality and / or of time in the course of the sequence
• compensation pulses may randomly generate the sequence of compensation pulses for a set of known resonant frequencies
• it is possible to amplify the excitation of the resonances by completely To prevent poor compensation pulses, ie to destroy the periodicity by additional "noise".
• electromagnetic radiation in particular laser radiation
• the implementation of the concepts proposed herein is principally independent of the crystal geometry.
• the implementation of the concepts proposed herein can take place with little or no manufacturing effort, since these can be implemented as a method implemented in the control software for suitable HV switches.
• the concepts disclosed herein for excitation of a crystal of a Pockels cell with (high) voltage pulses can also be used in other polarization adjusting applications of the Pockels effect.
• the concepts described herein relate in particular to the coupling of amplified electromagnetic radiation, in particular of laser pulses, and the decoupling of amplified laser pulses, in particular in Q-switched lasers, cavity dumping or regenerative amplification. and polarization modulation outside a cavity, eg when controlling a pulse picker
• Other applications include CW lasers, expander with upstream pulse picker and Q switch.
• FIG. 1 shows a schematic representation of a laser amplifier system with at least one Pockels cell
• FIG. 2 shows an exemplary schematic double-push-pull circuit for excitation of a crystal of a Pockels cell with (high) voltage pulses
• FIGS. 3A and 3B schematically show constructions for the use of Pockels cells in the formation of switchable wave plates
• FIGS. 4A to 4C are graphs illustrating the influence of excited resonances on the polarization state
• FIGS. 5A to 5C are graphs illustrating the influence of the concepts disclosed herein on the excitation of resonances
• Figures 6A to 6C are graphs showing the influence of the concepts disclosed herein on polarization states provided by voltage pulses for three pulse durations and
• FIGS. 7A to 7C show exemplary schematic sequences of combined useful voltage pulses and compensation voltage pulses according to the open-ended concepts for excitation of a crystal of a Pockels cell for a polarization adjustment.
• aspects described herein are based, in part, on the recognition that the optical crystals used in Pockels cells (e.g., BBO or KTP crystals) have more or less pronounced piezoelectric properties. These can cause electrical switching pulses made to produce acoustic shockwaves in the Pockels cell.
• the dimensions, geometry and speed of sound of the particular crystal may generally provide the crystals with one or more resonant frequencies that may be individually or collectively excited upon excitation with sequences of voltage pulses.
• operation near a resonant frequency (or associated subharmonic) can result in unstable switching behavior, e.g. lead to an unstable coupling or decoupling behavior in a regenerative amplifier. Further, such operation may result in mechanical damage to the crystal or its attachment.
• the vibrational behavior of the crystal can be influenced by means of secondary compensation pulses.
• compensation pulses can be arranged temporally in the sequence of Nutz pulses such that mechanical vibrations do not occur at all (or at least only reduced), since they destructively "disturb” interfering due to oscillation superposition
• Such a stimulation of a crystal of a Pockels cell can avoid the disadvantages of the mentioned unstable switching behavior and / or the mechanical destruction of the crystal.
• the high-voltage excitation proposed herein is possible, in particular, even at a plurality of resonant frequencies, as is often the case with Pockels cells in the case of excitation without compensation pulses.
• the choice of the time interval in which the Pockels cell is activated to provide a useful window may be less (if compared to uncompensated operation) or not at all to be disabled.
• this goal can be supported with additional measures such as a reduction in the pulse rate coupled into a regenerative amplification unit with, for example, an upstream pulse picker.
• additional measures such as a reduction in the pulse rate coupled into a regenerative amplification unit with, for example, an upstream pulse picker.
• resonant oscillation can be effectively prevented or reduced to the extent required using the concepts disclosed herein.
• Pockels cells can be used for the rapid switching of electromagnetic radiation, in particular laser beams, in which a birefringence is induced by applying a high voltage (possibly useful voltages up to and greater than 10 KV) to a suitable optical crystal ,
• the switchable birefringence allows a temporally adjustable change of the polarization state of the light passing through the crystal.
• the quality of a laser resonator can be switched in this way. This is used eg in Q-switched lasers, cavity dumping and in regenerative amplifiers.
• Switching the Pockels cell between two voltage states usually takes place very rapidly (eg within a few nanoseconds), whereby a voltage state is maintained for an adjustable duration of the polarization window (eg for a few microseconds). herald). This makes it possible, for example, to select individual (laser pulses of a pulse train.)
• the power loss in the electrical switches can also be kept as low as possible Fig.
• At least one of the gain units 3A, 3B comprises, for example, a Pockels cell 5 with a crystal 5A arranged between contact electrodes 7 for providing a gain (time) window by means of an electro-optical effect, the polarization of in the respective
• Amplifier unit 3A, 3B present laser radiation (for example, circulating ultrashort laser pulses) influenced. Furthermore, the laser system 1 comprises a control unit 9 and optionally a pulse picker 11 upstream of the amplification unit 3A.
• a primary laser beam 13 of the seed laser 2 is split with a beam splitter 15A into two (coherent) partial beams, which are the first in FIG Seed laser beam 13A and second seed laser beam 13B are marked.
• Each sub-beam is supplied to the associated amplifying unit 3A, 3B for generating a first amplified laser beam 17A based on the first seed laser beam portion 13A and a second amplified laser beam 17B based on the second seed laser beam 13B, respectively.
• the amplified laser beams 17A, 17B are collinearly superposed to form a sum laser beam 19.
• FIG. 1 also shows deflecting mirrors 21 and lambda-half waveplates 23 for changing the polarization states of the laser beams (indicated schematically by arrows / dots in FIG. 1).
• the Pockels cell 5 sets a desired polarization state in a gain window.
• the influencing of the polarization of the laser radiation passing through the Pockels cell 5 during the amplification window should be as constant as possible and constant over time, whereby the beginning and end of the amplification window should take place with temporally steep flanks.
• FIG. 2 shows an exemplary double-push-pull circuit 25 that can provide high voltage levels with rise times of a few nanoseconds.
• the double-push-pull circuit 25 is an example of a known fast high-voltage circuit (see also Fig. 1 of the manual "Splitter Box Model BME SP05", revision
• HV generally represents the high voltage applied to the high voltage inputs 27.
• the control unit 9 triggers the switching operations via four control inputs 29 assigned to the switches A, B (On A, Off A, On B, Of B).
• the double-push-pull circuit 25 shown as an example is designed for the most flexible possible control of the Pockels cell and represents a HV switch according to Bergmann's double-push-pull principle, in which the individual control inputs 29 (FIG. On A, Off A, On B, Off B) can be controlled with a freely programmable trigger generator.
• "On A” and “Off B” or “Off A” and “On B” are switched simultaneously, so that the voltage is switched between + 2HV and -2HV. These voltages can cause a delay of +/- ⁇ / 8, for example, in the constructions explained below in connection with FIGS. 3A and 3B.
• Alternative circuits and drive patterns for exciting a crystal of a Pockels cell, in particular a pulse picker, with (high) voltage pulses include e.g. Overlapped switching operations such as On A - On B - Off B - Off A.
• the latter switching pattern is particularly suitable for very short switching window.
• this may require a high voltage HV twice that for the same birefringence (assuming identical crystal properties).
• control unit 9 configured to implement the switching concepts disclosed herein and to enable or disable the various switches (eg, high voltage switches A, B in FIG. 2). to provide the desired sequences of payload and compensation (voltage) pulses on the 5 A crystal.
• switches eg, high voltage switches A, B in FIG. 2
• the optical property can be influenced (disadvantageously) not only by the electro-optical effect but also by piezoelectric effects in connection with varying pressure oscillations in the crystal.
• the piezoelectric effect mechanical vibrations induce electrical voltages, which in turn have an electro-optical effect.
• the concepts of using compensation pulses disclosed herein are aimed at improving the optical quality of the polarization window provided by a Pockels cell (eg in the case of FIG. 1 of the gain window provided by the Pockels cell 5 during the amplification process).
• the compensation pulses are arranged temporally in the sequence of the useful pulses determining the polarization window such that they counteract a mechanical oscillation in the crystal of the Pockels cell excited by the useful pulses.
• FIGS. 3A and 3B Exemplary arrangements are shown in FIGS. 3A and 3B, in which one or two Pockels cells 5 are arranged together with wave plates 31 in the beam path of a laser beam 33, for example in double passage by means of a mirror 35.
• FIGS. 3A and 3B these arrangements are shown supplemented with a beam splitter 37 and a photodiode 39 to check the properties of the polarization window, in particular its temporal quality.
• the structure according to FIG. 3A shows how an optical switch can be realized with a Pockels cell.
• the excitation of the crystal is designed such that after the double passage through the wave plate 31 (eg a ⁇ / 8 wave plate) and the crystal 5A (eg switchable as a + / 8 wave plate or ⁇ / 8 wave plate) during the Polarization window (eg, excited Pockels cell) no polarization change is made while outside of the polarization window (eg non-excited Pockels cell) is a ⁇ / 2 wave plate and the retrograde laser beam 33 is reflected at the beam splitter 37.
• the construction according to FIG. 3A was used as a test setup for the investigations described below in connection with FIGS. 6A to 6C.
• FIG. 3B has been extended by a Pockels cell (eg also switchable as a + / 8 wave plate or ⁇ / 8 wave plate) in comparison with the structure of FIG. 3A and has been used as a test structure for the following used with the Figures 4A to 4C and 5A to 5C studies described.
• the structure is designed such that after the double passage through the wave plate 31 and two crystals 5 A during of the polarization window a +3 ⁇ / 4- wave plate and outside the polarization window a ⁇ wave plate is present, so that with ideal switching behavior (in particular without influence of the piezoelectric effect and the resulting mechanical vibrations) no switching operation in the signal of the photodiode 39 visible should be.
• the optical crystals used in Pockels cells have more or less pronounced piezoelectric properties. This causes the application of an electric voltage to the crystal depending on the polarity to an expansion or contraction of the crystal. If the change in voltage occurs very rapidly (for example, within a few nanoseconds), acoustic signals are formed
• the crystal itself which is usually cuboid, represents an acoustic resonator. Depending on the dimensions, the geometry and the speed of sound of the crystal, this acoustic resonator may have several resonance frequencies.
• Piezoelectric effect is superimposed on the external electric field by the applied voltage, the birefringence of the crystal is modulated at the resonant frequency.
• a clean switching between defined polarization states is made more difficult.
• the crystals can be mechanically damaged / destroyed by strong resonances.
• the resonance resonance can be prevented by preventing the constructive interference of the shock waves in the crystal.
• shock waves are generated with the start phase shifted by 180 °, and attenuation in the crystal can be neglected.
• a HV switch according to Bergmann's double-push-pull principle was used to drive the Pockels cell in the structure according to FIG. 3B.
• the control inputs 29 "On A” and “Off B” or “Off A” and “On B” were switched simultaneously in normal operation, so that the voltage between + 2HV and -2HV is switched, with a Delay of +/- ⁇ / 8 in the two Pockels cells was effected.
• FIGS. 4A to 4C show by way of example three excited resonances of the examined Pockels cell, which were measured with the photodiode 39 in the structure of FIG. 3B.
• FIGS. 4A to 4C the activation of the control inputs 29 is shown.
• the switch-on pulse 41 and the switch-off pulse 43 are thus each assigned a useful voltage switching operation. (Generally herein, each switching pulse is associated with a voltage switching operation.)
• high-voltage pulses of, for example, 3.2 kV were used to increase the resonances.
• FIGS. 5A to 5C show, for example, a suppression with two exemplary integrated compensation pulse sequences (see in particular FIGS. 5B and 5C).
• Fig. 5A substantially corresponds to Fig.
• the useful pulse duration T N corresponds to half the period T RI of the resonant frequency f 1.
• Photodiode signal Rl with the resonant frequency fRi 147 kHz.
• a compensating pulse sequence consisting of compensation (voltage) pulses, one each between two pay pulses, is added. It can be seen correspondingly more pairs of switching pulses 47, 49 trigger the associated compensation voltage switching operations. This results in a considerably reduced photodiode signal Rl 'in its fluctuation.
• one of the pairs of switching pulses 47, 49 is highlighted by arrows 47A and 49A.
• the switching pulses 47, 49 cause the associated, one of the useful pulses subsequent, compensation pulse.
• a compensation pulse duration T K is in addition to the
• the selected instants of the switching pulses 47, 49 lead to a destructive interference of the mechanical oscillations, which correspond to the repetitive switching processes (the sequence of useful pulses and the sequence of compensation pulses). sen) are assigned. It can be seen that the resonance at 147 kHz can be effectively suppressed in this way.
• FIG. 5C shows another excitation concept that can be implemented with HV switches that allow multiple voltage levels, such as the double-push-pull circuit 25 that can switch the two electrodes separately from Pockels cells.
• a compensating pulse sequence consisting of compensation (voltage) pulses, of which two are provided between each two useful pulses, is added. It can be seen correspondingly more pairs of switching pulses 51, 53, 55, 57. It results in a likewise reduced in its fluctuation photodiode signal Rl ".
• 5C shows the first pair of (on and off) switching pulses 51, 53, which is illustrated by arrows 51A and 53A in the photodiode signal RI "and effects a first compensation pulse following the useful pulse (On) switching pulse 51 of the first compensation pulse also substantially directly (eg with a delay of 200ns) after the switch-off pulse 43, and the (off) switching pulse 53 of the first compensation pulse as in Fig. 5B with a delay, the Nutzpulsdauer T N , after the turn-off pulses 43 (or a resonance period T RI after the turn-on pulse 41).
• FIG. 5C shows the first pair of (on and off) switching pulses 51, 53, which is illustrated by arrows 51A and 53A in the photodiode signal RI "and effects a first compensation pulse following the useful pulse (On) switching pulse 51 of the first compensation pulse also substantially directly (eg with a delay of 200ns) after the switch-off pulse 43, and the (off) switching pulse 53 of the first compensation pulse as in
• the switching pulses 55, 57 cause a second compensating pulse, and the pair of switching pulses 55, 57 are delayed from the pair of switching pulses 51, 53 substantially by one resonance period T RI
• the (on) switching pulse 55 with respect to the switch-off pulse 43 may be delayed exactly by one resonance period T RI .
• the electrode B may be used for the second compensation pulse.
• the voltage change of one of the compensation voltage switching operations is of the order of a fraction of the voltage change of the voltage switching operations of the useful pulse (N) -as a function of the number of compensation pulses.
• the embodiment of the excitation according to FIG. 5C has the further advantage that when used in a regenerative amplifier no second amplification window is generated.
• the pulse picker 11 shown in FIG. 1 can specifically couple only pulses in the polarization window of the useful pulse into the amplification unit 3A.
• the compensation for an application in a regenerative amplification unit should be such that, although the resonator is only partially closed, for example, for a disk amplifier, the losses are still sufficiently large to allow for gain outside the gain window prevent.
• FIGS. 5A to 5C it can be seen that the photodiode signals R 1 'and R 1 "are substantially more uniform in comparison to the photodiode signal R 1 and are therefore closer to the ideal" flat "curve. That is, the negative effects of piezoelectrically generated Shock waves were reduced by excitation via the compensation pulse sequence. Accordingly, a more uniform effect of the Pockels cell on the laser radiation is provided during the polarization window.
• FIGS. 6A to 6C show, by way of example, for three amplification times (1 ⁇ , 4, 6 ⁇ ), the decoupled intensity of a cw laser beam in the structure of FIG.
• curve 0i illustrates the sequence of useful pulses N with pulse durations T N of 1 ⁇ and a useful period T PN .
• the useful pulses N can be recognized by the fact that the compensation window has half the amplitude with respect to the useful window. Furthermore, fluctuations in the photodiode signal, which are superimposed on the signal characteristics and which are due to the excitation of the resonance with the resonance period of 6.8 ⁇ , can be recognized. That is, the useful period Tp , N is located so that a resonant excitation of acoustic vibrations in the crystal 5A by the Nutz Pulse takes place.
• the curves 0 4 and 0 6 illustrate the sequence of useful pulses N with pulse durations T N of 4 ⁇ and 6 ⁇ , respectively.
• polarization window K which open the polarization window (herein also referred to as compensation window K) with the same polarization state as during the useful polarization window immediately after the turn-off pulse 43 and after a resonance period T RI from the turn-on 41 again close (duration T K of the compensation pulse K thus about 5.8 ⁇ ).
• a possibly disturbing influence of the compensation window can have an optical effect, in particular if the resonance period is comparable to or substantially greater than the useful duration. This influence can be reduced by several compensation pulses with reduced amplitude.
• a procedure with two compensation pulses K1, K2 is explained with reference to the curve 2i in FIG. 6A. Again, one recognizes the sequence of Nutz pulses N and a directly subsequent compensation window (compensation pulse K1). The duration of this first compensation window / the compensation pulse K1 is comparable to the duration of the compensation window of the curve. (This applies analogously for the duration of the first compensation window of the curve 1 4 and the curve 1 6 ). One recognizes again the reduced voltage change during the first compensation pulse K1.
• a second compensation window (second compensation pulse K 2) then follows, also with a reduced voltage change.
• the second polarization window is based on the switching pulses 55, 57 back. Due to the reduction of the voltage change, the compen- A polarization state, which differs from the present during the useful pulse polarization state.
• the curves 2 4 and 2 6 illustrate the sequence of useful pulses N with pulse durations T N of 4 and 6 ⁇ , in each of which a sequence of compensation pulses with two compensation pulses K 1, K 2 for each useful pulse.
• Puls N is arranged such that the compensation pulses Kl, K2, in particular their switching operations, counteract a stimulated by the useful pulse N mechanical vibration in the crystal of the Pockels cell. Due to the extended useful pulse durations, the duration of the compensation pulses Kl, K2 shortens again to approximately 2.8 or approximately 0.8 ⁇ .
• sequences of combined payload pulses and compensation voltage pulses are shown by way of example and schematically, the sequences for exciting a crystal of a Pockels cell e.g. for a polarization adjustment can be made.
• a sequence of useful voltage pulses N which are plotted in a time (t) voltage (U) diagram.
• the control is determined in terms of mechanical effectiveness by the switching edges of the voltage waveforms of the useful voltage pulses and the compensation pulses.
• the timing profile can be determined in particular by a rise time or a fall time of a switching edge.
• FIG. 7A further shows compensation pulses K following each of the useful voltage pulses which counteract resonance.
• the respective compensation pulses K 1 which are directly following one of the useful voltage pulses, are shown with reduced voltage, and in each case a second compensation follows. onspuls K2, which is applied in such a time-delayed manner that, for example, it counteracts the same resonance.
• the timing of the compensation pulses may be varied during operation. In doing so, e.g. in a group of successive enhancement windows at each individual enhancement window, the additional pairs of switching pulses are timed to combat different resonances. With sufficient damping or avoidance of the resonances in the crystal itself, u.U. several resonances are attenuated simultaneously. The resonances to be damped can then be e.g. targeted, based on measurements of the resonant properties, are selected. Moreover, by a suitable algorithm, the choice of a target resonance can be made quasi randomly during operation, so as to implement a broadband attenuation by the respective random damping of a mechanical vibration.
• FIG. 7C Such different pulse strategies are illustrated schematically in FIG. 7C.
• three compensation pulses ⁇ ', K ", K” are shown, which are reduced in voltage and counteract one or more resonant frequencies.
• the second useful pulse N shown only one compensation pulse K "" of greater length is switched, and after the third useful pulse N shown, a compensation pulse K - similar to that of FIG. 7A - is switched. It can be seen that one or more or even a broadband suppression of resonance effects can be converted to the polarization state effected by a Pockels cell circuit due to the multitude of design options.
• the switching operations are designed to effect a change in an electrical polarization in the crystal of the Pockels cell.
• the voltage switching operations referred to herein are pole reversal operations of a voltage applied to the Pockels cell, for example from + HV to -HV.
• the concepts disclosed herein are particularly relevant when the change of an electrical see polarization in the crystal of the Pockels cell via a piezoelectric effect to a change in size of the crystal, thereby leading to acoustic vibrations and resonances in the crystal.
• the provision of compensation pulses then just causes a reduction in the formation of acoustic vibrations and resonances in the crystal.
• compensating may be understood to mean both partial compensation and complete compensation.
• the compensation pulses may also have slower switching operations, such as a slower drop to a second voltage value, from which then quickly switched again.
• slower switching operations such as a slower drop to a second voltage value

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