Methods for producing a laser pulse and devices for producing a driver control signal

In methods and devices for generating a laser pulse of an excitation laser that is actuated by a driver in response to a triggering time of a trigger signal, the driver actuation signal is generated taking into account the time interval between the triggering time and a preceding triggering time.

TECHNICAL FIELD

The disclosure relates to methods for producing a laser pulse of an excitation laser in response to an actuation time of an actuation signal.

BACKGROUND

In laser systems, excitation lasers are controlled by a driver. The output signal of the excitation laser is amplified by an optical amplifier and subsequently output. Excitation lasers and optical amplifiers together constitute a laser system. Such laser systems are often operated in a pulsed manner. In some instances, however, the pulse energy of several pulses at the laser output may vary in spite of driver control signals of the same length and same strength.

SUMMARY

The current disclosure provides methods and laser systems that generate a laser having a predetermined, e.g., a substantially constant, pulse energy. The new methods include producing a laser pulse of an excitation laser in response to an actuation time of an actuation signal, wherein the excitation laser is controlled by a driver and the driver control signal is produced taking into account the time interval of the actuation time or laser pulse with respect to a previous actuation time or laser pulse. It is possible to use as an excitation laser, for example, a seed laser or a seed diode. An actuation time is also often referred to as a trigger time.

At least a portion of the oscillation of the pulse energy of a plurality of pulses at the laser output, in spite of identical driver control signals, is brought about by the time interval of the actuation time with respect to a previous actuation time or laser pulse. With pulsed lasers, the time intervals between the actuation times of the actuation signal can vary, and thus, the time intervals between the laser pulses may vary. Since the laser pulses of the excitation laser are amplified to differing degrees depending on the time interval between the pulses, the pulse energy of a plurality of pulses at the laser output can have different power levels in spite of identical driver control signals. The reason for this result is that the gain level of the optical amplifier is dependent on the pumping time between the pulses. The longer the pumping operation, the more energy is extracted.

As a result of the fact that the time interval of the actuation times or laser pulses is taken into account for the production of the driver control signal, the driver control signal can be adjusted such that laser pulses with constant pulse energy are generated at the output of the laser. It is thereby possible to adapt or scale the control of the excitation laser, which enables a compensation of the gain level in the optical amplifier. It is thereby possible for the power of the excitation laser to be adapted in accordance with the spacing of the actuation times or laser pulses.

The driver control signal can be produced taking into account the properties of an optical amplifier that is controlled by the excitation laser. From the time interval of the actuation times or laser pulses, it is possible to draw conclusions regarding the state of the optical amplifier. Conclusions can be drawn regarding the gain level of the optical amplifier. The driver control signal can accordingly be generated in such a manner that, taking into account the gain level of the optical amplifier and consequently the properties of the optical amplifier, laser pulses with a predetermined, e.g., constant, energy are produced.

The driver control signal can be produced by a digitally encoded pulse shape being compensated by a digitally encoded compensation signal. In this instance, the digitally encoded compensation signal can further be dependent on the time interval of the actuation time or laser pulse with respect to the previous actuation time or laser pulse. In this instance, the compensated digitally encoded pulse shape can further be converted into an analog signal. Normally, it is the case that, when a trigger time occurs from a pulse shape store, a digitally encoded pulse shape is read and subsequently converted into an analog signal, by which a driver is controlled. If this is done without taking into account the state of the optical amplifier, laser pulses with different energies are produced in the output of the laser. In some embodiments, before the analog signal is generated, the digitally encoded pulse shape can be modified with a digitally encoded compensation signal to produce a driver control signal. This can lead to pulses with predetermined, e.g., constant, energy being output or generated at the output of the laser. Since the state of the optical amplifier can depend on the time interval of the actuation times or laser pulses, a suitable encoded compensation signal is determined with reference to the interval of the actuation times or laser pulses.

In this instance, the digitally encoded compensation signal can be read in accordance with the time interval of the actuation time or laser pulse with respect to the or a previous actuation time or laser pulse from a compensation signal store.

Alternatively, the driver control signal can be produced by a pulse shape from a digitally encoded pulse shape by digital/analog conversion being compensated with a compensation signal. In this instance, the compensation signal can be dependent on the time interval of the actuation time or laser pulse with respect to a previous actuation time or laser pulse. In this instance, the compensation for the pulse shape or the driver control signal can be carried out in the analog range.

A time-dependent factor in the range 0<factor≤1 can be used as a compensation signal. Depending on how much time there is between the actuation times or laser pulses, the pulse shape is multiplied by a factor between 0 and 1.

The compensation signal can be reset in a time-delayed manner with respect to the actuation time. The compensation signal can be reset at the end of the produced pulse shape. Consequently, from this time, the time-dependent factor can also be reduced in a time-dependent manner from 1 to 0. The more time consequently elapses between two actuation times or laser pulses, the more powerfully the pulse shape is compensated for or corrected.

The time interval between the actuation time or laser pulse and the previous actuation time or laser pulse can be determined and, taking into account the determined time interval, a driver control signal shape determined.

In another aspect, this disclosure includes devices for producing a driver control signal for controlling a driver that controls an excitation laser, having an actuation signal input and a driver signal output. In this instance, the actuation signal input is connected to a pulse shape store and at least indirectly to a compensation signal establishment means. Furthermore, the actuation signal input is connected to a scaling device, to which the pulse shape and the compensation signal are supplied and configured to generate a driver control signal. With this arrangement, it is possible to determine a compensated driver control signal such that an excitation laser is controlled with a driver control signal and at the output of the laser pulses with a predetermined, e.g., constant, energy are always generated. The pumping time of an optical amplifier of the laser can be taken into account.

The actuation signal input can be connected via a delay member to the compensation signal establishment means. Consequently, a correction of the driver control signal can be carried out in a time-delayed manner.

The compensation signal establishment means can include a compensation signal store. Depending on the time interval between actuation times, different compensation signals can be taken from the compensation signal store and consequently a pulse shape can be compensated for or corrected. In some embodiments, only one compensation signal shape is stored in the compensation signal store. In this instance, the compensation signal can be time-dependent so that a time-dependent compensation of the pulse shape can be carried out.

The scaling device can include a multiplier. Depending on whether the compensation is carried out in the digital domain or in the analog domain, the multiplier can be a digital or an analog multiplier, respectively.

The compensation signal establishment means can include a resettable counter. Furthermore, depending on the counter, a compensation signal can be read from the compensation signal store. The resettable counter can be reset to an actuation time. From then, the counter counts upwards or downwards at a predetermined rate. In this instance, depending on the counter status, at the next actuation time a compensation signal can be read from the compensation signal store and used to compensate a pulse shape.

In another aspect, the disclosure further includes laser systems having a laser that includes an excitation laser controlled by a driver, and a device for producing a driver control signal as described herein connected to the driver.

Other features and advantages will be appreciated from the following detailed description with reference to the drawings, and from the claims. The features shown therein are not necessarily intended to be understood to be to scale and are depicted in such a manner that the specific features can be made clearly visible. The different features can be implemented individually per se or together in any combinations in variants.

DETAILED DESCRIPTION

FIG. 1shows a laser system1having a laser2that has an excitation laser3and an optical amplifier4. The excitation laser3may, for example, be a seed diode. The excitation laser3is controlled by a driver5. The output signal of the excitation laser3is amplified by an optical amplifier4, to which a pump light is also supplied, so that at the output6laser light, e.g., a laser pulse, can be output or generated.

A device7for producing a laser pulse is used to control the driver5. The device7has an actuation signal input8, at which an actuation signal is supplied. It is possible to use as an actuation signal, for example, a pulse signal, where the time of the occurrence of a rising flank can represent an actuation time. The actuation signal is supplied to a pulse shape store9that is clocked by a clock source10. When an actuation time of the actuation signal occurs, from the pulse shape store9a digitally encoded pulse shape is output at the rate of the clock source10. This is supplied to a digital/analog converter11. The digital/analog converter11converts the digitally encoded pulse shape into an analog pulse shape. The analog pulse shape is supplied to a scaling device12. If the analog pulse shape were to be used directly as a driver control signal that is supplied to the driver5, laser pulses with different energy could be generated at the output6of the laser, because the pulse shape or energy of the laser pulse can be dependent on the state of the optical amplifier4. Depending on the time intervals at which actuation times occur, the gain level of the optical amplifier4is potentially different so that different laser pulses can also be output. To prevent this result, the device7has a compensation signal establishment means13. The compensation signal establishment means13has a compensation signal store14. The compensation signal store14is timed by a clock source15. The compensation signal establishment means13can further have a digital/analog converter16.

The actuation signal from the actuation signal input8is supplied to the compensation signal store14in a time-delayed manner brought about by the delay member17. When the delayed actuation signal arrives at the compensation signal store14, a digitally encoded compensation signal is output therefrom at the rate of the clock source15. The digitally encoded compensation signal is transferred to the digital/analog converter16. There, an analog compensation signal is produced. The analog compensation signal is supplied to the scaling device12.

In the embodiment shown, the scaling device12is a multiplier so that the pulse shape that is output by the analog/digital converter11is multiplied by the compensation signal. A time-dependent pulse shape scaling is thereby carried out. The pulse shape that is thus compensated at the output of the scaling device12or at the driver signal output18now represents a driver control signal that is supplied to the driver5. Depending on the time interval between two actuation times of the actuation signal, there is produced a compensation signal by which a pulse shape is compensated. From this, a driver control signal is generated and takes into account the state of the optical amplifier4so that at the output6laser pulses with a constant energy are always generated. The compensation signal that is stored in the compensation signal store14is advantageously selected in accordance with the properties of the optical amplifier, e.g., the gain level thereof depending on the pump time between two pulses.

FIG. 2shows an alternative embodiment of a laser system100. Elements that correspond to those ofFIG. 1are given the same reference numeral.

A device107has an actuation signal input8. An actuation signal can be supplied via the actuation signal input8to a pulse shape store9. At the rate of a clock source10, from the pulse shape store9at an actuation time of the actuation signal a digitally encoded pulse shape is produced. The digitally encoded pulse shape is supplied to a scaling device112. The actuation signal is supplied via a delay member17to a compensation signal establishment means113. The actuation signal is supplied to a counter120. The counter120is a resettable counter. This resettable counter can always be reset when an actuation time occurs and can then count upwards or downwards depending on the embodiment. According to the counter status, before resetting the counter120a digitally encoded compensation signal can be read from a compensation signal store114. This digitally encoded compensation signal is supplied to the scaling device112so that with this signal the digitally encoded pulse shape can be compensated, e.g., multiplied thereby. The digitally encoded signal produced by the scaling device112, e.g., a compensated digitally encoded pulse shape, is supplied to a digital/analog converter11. The digital/analog converter11can generate an analog signal from this. The analog signal corresponds to a driver control signal and can accordingly be supplied to the driver5via the driver signal output118.

FIG. 3shows signal shapes to explain the method. In the first line, an actuation signal is illustrated, where the actuation signal has individual pulses200,201,202. The rising flank203of the pulse201represents an actuation time. The rising flank204of the pulse200accordingly represents a previous actuation time. If the actuation times203,204,205occur, for example, pulse shapes206,207,208are produced in accordance withFIG. 1at the output of the digital/analog converter11.

In a time-offset manner with respect to the actuation times203to205, at the output of the delay member17, pulses209to211are present. The delay member17can thus be selected in such a manner that the rising flank of the pulses209to211in each case coincides with the end212to214of the pulse shapes206to208. In some embodiments, the pulses209to211can be actuated at the end212to214of the pulse shapes206to208. When the pulses209to211occur, a time-dependent compensation signal215to217is produced in each case. At an earlier time that is not shown, the compensation signal225was produced. In the embodiment shown, the compensation signals are a signal shape with a declining straight line. In the case of a rising flank of one of the pulses209to211, the compensation signal225,215,216,217is output with the value 1 and then falls in a linear manner over time.

To produce a driver control signal218to220, the compensation signals225,215,216are multiplied by the pulse shapes206to208. Since the time interval between the pulses200and201or209and210is greater than the time interval between the pulses201and202or210and211, the pulse shape207is multiplied by a lower value than the pulse shape208. This is a result of the fact that, at the beginning of the pulse shape207, the compensation signal215has fallen further than the compensation signal216has fallen at the beginning of the pulse shape208. Accordingly, the compensation signal219that has been produced from a multiplication of the pulse shape207by the compensation signal215has a lower amplitude than the driver control signal220that has been produced from a multiplication of the pulse shape208by the compensation signal216. Nonetheless, the laser pulses221to223have the same shape. The laser pulses221to223are generated at the output6(FIGS. 1, 2). As a result of the multiplication of the pulse shapes206to208by the compensation signals225,215,216, the spacing between the rising flanks of the pulses200,201,202and consequently the time-dependent state of the optical amplifier4has been taken into account. This can be carried out in such a manner that, at the output6of the laser, laser pulses with predetermined, in the present example with constant, energy are always produced.

OTHER EMBODIMENTS