Laser arrangement and start-up method

Abstract

The invention relates to a laser arrangement for producing laser light, having a laser resonator for stimulating two laser modes between a first resonator mirror and a second resonator mirror spaced apart from one another by a resonator length. The second resonator mirror is configured and provided to output couple the two laser modes from the laser resonator and has a first frequency-dependent attenuation profile for laser light. The laser arrangement also has a laser medium arranged between the resonator mirrors, a measuring device configured and provided to measure at least one parameter of the two output coupled laser modes and / or at least one ambient condition of the laser arrangement, and a control device configured and provided to adapt the resonator length and the first attenuation profile on the basis of the at least one parameter and / or the at least one ambient condition. The laser medium has a second frequency-dependent attenuation profile, and the control device is configured and provided to modify the first attenuation profile and the second attenuation profile, in particular to match these to one another.

Description

[0001] Laser arrangement and commissioning procedure

[0002] Description

[0003] The invention relates to a laser arrangement for generating laser light according to the preamble of claim 1 and a method for commissioning a laser arrangement according to claim 15.

[0004] Such a laser arrangement can be used for industrial applications, particularly when diode-pumped and with external resonant frequency doubling. Wavelengths in the ultraviolet range are particularly in demand for industrial applications, especially in the semiconductor industry. Solid-state lasers that generate wavelengths in the red or infrared spectral range are often used. The wavelength of the solid-state laser can be frequency-converted to generate the desired wavelength in the ultraviolet range. Nonlinear crystals can be used for the conversion.

[0005] Frequency conversion can occur inside or outside a laser resonator.

[0006] Frequency conversion in the laser resonator (“intracavity frequency conversion”) can have the disadvantage that strong amplitude noise can arise due to nonlinear coupling of several laser modes in the nonlinear crystal (“Green problem”; see e.g. T.Bear, J. Opt. Soc. Am. B, Vol.3, No. 9, September 1986, p.1175-1180).

[0007] Several methods are known for avoiding the Green problem. For example, the length of the laser resonator can be chosen so that a particularly large number of longitudinal laser modes are excited within the resonator (see US Pat. No. 5,638,388). Another method is to operate with a single laser mode, which necessarily excludes the coupling of multiple laser modes, as in ring lasers, twisted-mode lasers, or microchip lasers.

[0008] The two methods mentioned above require complex laser arrays that are fragile and require high operational costs. Furthermore, frequency-selective elements in the laser resonator may be required, limiting the achievable power to unattractively low values.

[0009] In another method, a laser resonator is designed so that exactly two laser modes that are adjacent in frequency, in particular longitudinal modes, are excited. With this method, the frequency conversion can be performed outside the laser resonator. An external resonator can be provided for the conversion outside the laser resonator. Nonlinear coupling of the laser modes within the laser resonator can then no longer occur. Operation with two longitudinal modes is described, for example, in the publications C. Zimmermann et al., "Design for a compact tunable Ti:Sapphire Laser", Optics Letters, Vol. 20, No. 3, 1995, pages 297-299, and A. Hohla et al., "Bichromatic frequency conversion in potassium niobate", Optics Letters, Vol. 23, No. 6, 1998, pages 436-438.

[0010] DE 10 339 210 B4 describes a laser arrangement for generating laser light with two laser modes.

[0011] The object of the present invention is to provide a laser arrangement that enables more stable operation. This object is achieved according to a first aspect of the invention by a laser arrangement according to claim 1.

[0012] Such a laser arrangement comprises a laser resonator for oscillating two laser modes between a first and a second resonator mirror. The resonator mirrors are spaced apart by a resonator length, with the second resonator mirror configured and provided to couple the two laser modes out of the laser resonator. The second resonator mirror has a first frequency-dependent attenuation profile for laser light. The second resonator mirror can be configured as an output mirror. It can serve as a frequency-selective element.

[0013] The laser resonator can be a linear resonator. In a linear resonator, standing waves form, leading to zones of high field strength (antinodes) and zones of low field strength (nodes). The zones of different field strengths spatially modulate the population inversion in the laser medium (“hole-burning effect”). If the laser medium is arranged in the optical center of the resonator, neighboring longitudinal modes are phase-shifted by 90°, so that these neighboring laser modes draw their energy from different zones. Figuratively speaking, a first laser mode has a node at a zone in which a second laser mode adjacent to the first has an antinode. The oscillation of exactly two neighboring laser modes may be preferable to avoid the hole-burning effect.

[0014] Such a formation of exactly two laser modes leads on the one hand to an efficient use of the population inversion in the laser medium, and on the other hand, the energetic coupling of different laser modes in the resonator is prevented.

[0015] The second resonator mirror, with its frequency-selective property, can ensure that two specific laser modes exhibit particularly low losses and therefore oscillate preferentially. The laser arrangement further comprises a laser medium arranged between the resonator mirrors. In particular, the laser medium can be arranged at an optical center between the resonator mirrors. The laser medium can comprise, for example, an Nd:YVO4 crystal.

[0016] By using exactly three optical elements, resonator mirror and laser medium, the resonator can be realized in a particularly compact and mechanically stable manner.

[0017] External influences can particularly disrupt operation with exactly two longitudinal modes. However, for low-noise operation, it is desirable that exactly two longitudinal modes (and no more) are active in the laser resonator.

[0018] As soon as a third laser mode is added, noise frequencies in the MHz range can arise, for example when using an external resonator, due to "mode beating" and also due to dispersion in the laser resonator, which are undesirable in applications, particularly in the semiconductor industry. A third laser mode can be caused by changes in ambient conditions such as temperature and air pressure, as well as long-term effects such as mechanical relaxation, thermal misalignment and aging of materials. Such conditions and effects can affect the geometry, in particular the length, of the laser resonator and thus the mode spectrum. For example, resonant frequencies of the laser resonator can shift compared to frequencies for which the second resonator mirror is set up and intended if the resonator length, in particular the optical length, changes. In this case, three modes can oscillate simultaneously.When three modes are active, differential frequencies of the mode spacings can occur in the frequency-converted laser beam, which differ slightly due to dispersion in the laser resonator. These differential frequencies are in the range of a few MHz. Therefore, it is desirable to keep the resonator length as constant as possible. The laser arrangement further comprises a measuring device configured and intended to measure at least one parameter of the at least one coupled-out laser mode and / or an ambient condition of the laser arrangement.

[0019] In addition, the laser arrangement comprises a control device which is configured and provided to adapt the resonator length and the first attenuation profile on the basis of the at least one parameter and / or the at least one environmental condition.

[0020] The control device can, for example, comprise an (electronic) closed-loop control for controlling an optical length of the laser resonator and the first attenuation profile. The measuring device can be configured to generate a power signal dependent on the power of the two laser modes, which serves as an input signal for the closed-loop control. The closed-loop control can be directed to maintaining low-noise, stable dual-mode operation.

[0021] The control system can compensate for external influences such as ambient conditions and long-term effects to ensure continuous, low-noise operation, especially with exactly two laser modes. The compensation can take advantage of the fact that the power of frequency-converted radiation generated from exactly two coupled laser modes reaches a maximum when the two laser modes have the same intensity in the laser resonator. The frequency-converted radiation can be generated in an external resonator.

[0022] The measuring device can have a photodetector with which the converted power P can be detected. The photodetector can, for example, provide an electronic input signal for the control of the control device. The control device can be controlled via a temperature T rof the laser resonator, change the resonator length so that the converted power P is as large as possible. Maximum power can be equivalent to operation with exactly two laser modes with symmetrical power distribution between the two laser modes.

[0023] The laser medium has a second frequency-dependent attenuation profile, and the control device is configured and provided to modify the first and second attenuation profiles, in particular to match them to one another. In particular, the second attenuation profile can be modified independently of the laser resonator and the second resonator mirror.

[0024] This can, for example, reduce undesirable long-term effects caused by mechanical relaxation or thermal misalignment, which inevitably occur during operation of the laser assembly. Mechanical relaxation can result from creep deformation of stressed materials, such as metal parts, from which the laser resonator is constructed. Thermal misalignment can arise from different expansion coefficients when bonding different materials. These different expansion coefficients can lead to relative movement during temperature changes, which can occur when laser systems are switched on and off. This can be irreversible due to changing friction coefficients.Repeated switching on and off can therefore lead to a progressive misalignment of a laser system, which can manifest itself, among other things, in the formation of unwanted additional laser modes and thus additional noise.

[0025] A laser arrangement according to the invention can counteract this and, through the controlled variation of the attenuation profiles, enable trouble-free operation for over 20,000 hours, so that, for example, failures in semiconductor production can be avoided.

[0026] In one embodiment, the laser resonator and the second resonator mirror are configured and provided so that exactly two laser modes, in particular longitudinal modes, that are adjacent in frequency, can be coupled out. When operating the laser arrangement as a two-mode laser, the effort required to maintain the two laser modes with low noise and frequency conversion can be significantly lower than, for example, is the case with a single-mode laser, where only exactly one laser mode is available.

[0027] In one embodiment, the laser arrangement comprises at least one external, in particular passive, resonator, which is configured and provided to receive the two laser modes from the laser resonator and to convert the frequency of the two laser modes. For the conversion, the at least one external resonator can comprise a nonlinear crystal. During the frequency conversion, the frequency of the two laser modes can be shifted. For example, the frequency can be increased from the red or infrared to the ultraviolet range. The conversion can be performed stepwise, starting from the frequency of the two laser modes.For example, the frequency of the two laser modes, for example from infrared, can be converted in a first step with a first external resonator to a first frequency, for example into a green frequency range, and in a second step with a second external resonator to a second frequency, for example into the ultraviolet.

[0028] In one embodiment, the measuring device is configured and provided to measure the at least one parameter of the frequency-converted laser beam. The measuring device can, in principle, measure the at least one parameter at any point after the two laser modes have been coupled out of the laser resonator. Performing the measurement along a propagation direction of the laser beam after the at least one external resonator can have the advantage, among other things, that the laser light ultimately provided by the laser arrangement can be measured.

[0029] In one embodiment, the control device is configured and provided to change the first and second attenuation profiles such that minima of the attenuation profiles match in frequency. The attenuation profiles can describe how strongly a specific laser light frequency is attenuated by the laser medium or the second resonator mirror. In principle, the strength of the attenuation oscillates as a function of frequency, so that there are attenuation maxima and minima. Changing the attenuation profiles can comprise tuning the attenuation profiles. The changing can be used, for example, to shift the minima of the attenuation profiles relative to one another. Preferably, each of the attenuation profiles is changed such that a minimum of the attenuation profiles matches a minimum of the respective other attenuation profile (i.e., is arranged at the same frequency).

[0030] In one embodiment, the laser medium has two parallel surfaces, each provided with a partially reflective (PR) coating and whose normals are arranged at an angle between 1° and 6° obliquely to a propagation direction of the two laser modes. A reflectivity of the coating can be between 0.2% and 2.0%, in particular between 0.4% and 0.8%, most particularly between 0.5% and 0.7%. A surface normal of the two parallel surfaces can enclose an angle other than zero with the propagation direction of the two laser modes, in particular 1° to 6°. By providing an (optical) coating with a predetermined reflectivity on two parallel (optical) surfaces of the laser medium and tilting them against the propagation direction, the frequency-dependent second attenuation profile of the laser medium can be generated.In particular, the coating of the laser medium makes it possible to create a defined and adjustable (second) attenuation profile, which allows stable dual-mode operation to be maintained. This is because such a coated and tilted laser medium forms a desirable and controllable etalon effect. A partially reflective coating can, on the one hand, keep losses in the laser resonator low and, on the other hand, create desirable etalon effects. One suitable method for producing the coating is ion beam sputtering (IBS). This allows a coating (even in mass production) to be produced with a reflectivity reliably above 0.2%, particularly above 0.5%. With IBS, the reflectivity accuracy can be within a tolerance range of 0.1%.In general, changes in humidity can lead to changes in the properties of optical elements, particularly the reflectivity of the coating. Changes in the reflectivity of the coating, in turn, can have different effects on the losses of the various laser modes and thus on the intensity distribution across the laser modes.

[0031] The uncontrolled emergence or disappearance of etalon effects in the laser medium can interfere with the desired frequency-selective behavior of the second resonator mirror and undesirably counteract it. Changes in the relative humidity in the laser resonator can change the reflectivity of the coating to such an extent that dual-mode operation is no longer guaranteed, resulting in unacceptable noise.

[0032] Changes in ambient humidity can be caused, for example, by purging with purge gas. The relative humidity of the purge gas can change over time. The change can occur abruptly when the gas purge system is serviced or replaced, or it can occur gradually as the performance of a laser assembly's drying system deteriorates over time.

[0033] In a further embodiment, the coating is therefore designed and provided to provide a reflectivity that is independent of the ambient conditions, in particular the moisture content of a gas surrounding the coating. This can ensure that the reflectivity is independent of changes in the ambient humidity, for example. Such coatings can be produced using the "ion beam sputtering" (IBS) process, for example. They can be characterized by having a lower surface roughness, in particular fewer depressions in which moisture can settle, than coatings produced using other processes (e.g. "e-beam").

[0034] In one embodiment, the control device is configured and provided to adjust a temperature of the laser resonator via a first adjusting element and / or a temperature of the laser medium via a second adjusting element in order to change the first and second attenuation profiles, in particular to coordinate them with one another. To change the attenuation profiles, the geometric and / or optical properties of the laser resonator and / or the laser medium can therefore be changed. This can be achieved by heating or cooling. A thermally insulating element can be provided between the laser resonator and the laser medium to improve the independent adjustment of the temperature. The element can form a non-metallic barrier that interrupts a heat propagation path between the laser resonator and the laser medium. In general, thermal bridges between the laser resonator and the laser medium can be avoided.

[0035] The first and second actuating elements may comprise Peltier elements, which may be thermally connected to a common heat sink.

[0036] In one embodiment, the laser medium comprises a doped laser crystal whose doping level is determined such that the ratio of an optical length of the resonator to an optical length of the laser medium is greater than or equal to ten. The accuracy with which the doping level is specified can be within (and including) the limits of ± 0.05%. With a larger scatter in the doping level, the ratio of the optical length of the resonator to the optical length of the laser medium may not be guaranteed, so that, for example, a tolerance range for dual-mode operation of the laser arrangement is too narrow. Furthermore, greater scatter can lead to high self-absorption and thus to low output power.

[0037] Configuring the laser medium as an etalon and specifying the doping level more precisely can result in a mean tolerance range for the temperature of the laser resonator at values ​​greater than or equal to 1 K, which can significantly increase the stability of dual-mode operation. In principle, the temperature range of the resonator in which dual-mode operation occurs can be at least 0.5 K. In one embodiment, the at least one parameter comprises noise and / or a power of the converted laser beam. For example, the measuring device can measure a first parameter relating to the noise of the converted laser beam and / or a second parameter relating to the power. The noise can, in particular, be (optical) amplitude noise. The measuring device can have a noise detector for measuring the noise. The noise can be measured up to frequencies of at least 10 MHz.The noise detector can provide a noise signal proportional to the noise, which can optionally be used, in addition to a power signal from a photodetector, as an input signal for a closed-loop control of the control device. The control device can, for example, use the closed-loop control to control the resonator length in such a way that the noise signal is reduced and the power signal is increased.

[0038] In one embodiment, the at least one parameter comprises a weighted difference between a noise level and a power level of the converted laser beam. The weighted difference can serve as an input signal for the control device, in particular for regulating the control device.

[0039] In principle, a weighted difference between any two parameters can be used for the control device as a combined input signal Ui. The combined input signal in the form of a weighted difference can be represented as

[0040] Ui = Wp ■ Up Wpjp ■ U jp where U p can represent a voltage signal proportional to the measured power P, and UHF can represent a voltage signal proportional to the measured noise R. The combined input signal can be used in place of any of the other voltage input signals. The signals can be provided by a power detector, such as a photodetector, or a noise detector, respectively. The noise detector can be an RF noise detector.

[0041] The factors WP and WHF can be weighting factors. The influence of the RF signal UHF on the control behavior of the control device can be controlled via the weighting factor WHF. One advantage of the combined input signal can be that, in the event of rapid changes in ambient conditions, the control device can control the laser resonator in such a way that the laser resonator is quickly tuned to restore dual-mode operation. Rapid changes in ambient conditions can cause oscillations of additional laser modes to occur, which can endanger stable dual-mode operation in particular because they can lead to unacceptable noise values ​​>R cr it can lead.

[0042] In one embodiment, the control device is configured and provided to adapt the resonator length and the first attenuation profile based on a direction of change in the at least one ambient condition if the at least one parameter has exceeded a predetermined value. For example, an impermissible noise value Rent can be caused by changing air pressure. The resonator length and the first attenuation profile can then be adjusted based on whether the air pressure has increased or decreased.

[0043] In one embodiment, the at least one environmental condition comprises an amplitude of vibrations to which the laser arrangement is exposed and / or an ambient air pressure. For example, the measuring device can measure a first environmental condition relating to an amplitude of vibrations and / or a second environmental condition relating to an ambient air pressure.

[0044] Ambient air pressure can change by up to 100 mbar in a short period of time, for example, due to extreme weather phenomena. The laser resonator may be linked to the ambient air pressure. Therefore, in such cases, the (optical) resonator length changes along with the ambient air pressure. After the change, the laser resonator may deviate from an optimal setting for dual-mode operation. In particular, additional modes may oscillate, leading to unwanted noise.

[0045] If the ambient air pressure changes at a moderate rate, the control system can compensate for the change by adjusting the laser array accordingly. However, if the pressure change occurs too quickly, the control system may not be able to follow quickly enough, and the frequency-converted laser beam may begin to produce noise.

[0046] In general, strong vibrations can be a cause of stability problems. Strong vibrations can occur particularly during transport of the laser array, during installation, or during maintenance of the laser array. Such vibrations can slightly change the position of optical elements, particularly the resonator mirrors and the laser medium, within the laser cavity, thus altering the cavity length or the relative tuning of the elements to each other, which can lead to the occurrence of unwanted side modes and thus additional noise.

[0047] Shocks and vibrations can also occur for a limited period of time during operation of the laser system, for example if maintenance, repair, or modification work is taking place in the system's vicinity. This can lead to at least one parameter, in particular an input signal of the control device, being overlaid by interference. This interference is generally interpreted by the control device as a deviation that needs to be eliminated and leads to undesired reactions that may take the laser resonator out of a predetermined operating state, in particular dual-mode operation, and ultimately lead to permanent noise that may be difficult for the control device to eliminate even after the vibrations have been switched off. Vibrations can primarily increase noise in the frequency-converted laser beam and / or reduce power. Vibrations are generally only temporary.The amplitude of vibrations can be measured, for example, using an acceleration sensor of the measuring device. The control device can be configured and provided to suspend the adjustment of the resonator length and the first attenuation profile when the amplitude of vibrations exceeds a predetermined value in order to prevent undesired adjustment. By suspending the adjustment while vibrations are acting on the laser arrangement, control malfunctions caused by vibrations can be avoided.

[0048] In one embodiment, the control device is configured and provided to determine, when the laser arrangement is switched on, initial values ​​for control variables for adjusting the resonator length, the first attenuation profile, and / or the second attenuation profile, depending on the ambient air pressure. The measuring device can comprise an air pressure sensor for measuring the ambient air pressure.

[0049] The initial values ​​can be specified in such a way that the control device is able to operate the laser resonator with exactly two longitudinal modes and to maintain this state permanently.

[0050] By specifying initial values ​​depending on the ambient air pressure, it is possible, for example, to compensate for the air pressure difference between the laser's manufacturing location, where the initial values ​​are predetermined, and a different location where it is used. If, for example, a first location for operation is approximately at sea level and a second location for operation is 3,000 m above sea level, the air pressure difference will be more than 300 mbar. The settings of the laser arrangement, in particular of the laser resonator, which are optimized for sea level at the first location, may then no longer be optimal at the second location. Under certain circumstances, the settings may be so far removed from optimal values ​​that the control device is not able to achieve optimal operation, in particular dual-mode operation, on this basis. It can therefore be advantageous to specify the initial values ​​depending on the ambient air pressure.

[0051] The object is achieved according to a second aspect of the invention by a method for commissioning a laser arrangement according to claim 15.

[0052] The method comprises the following steps: switching on the laser arrangement, measuring an ambient air pressure, determining a difference between the measured ambient air pressure and a stored ambient air pressure, varying the temperature of a laser resonator of the laser arrangement over a predetermined temperature range if the difference is greater than a predetermined value, recording the parameters of a noise and a power of the converted laser beam over the temperature range, selecting a set of temperature intervals with a predetermined minimum width within the temperature range in which the noise is below a predetermined value, selecting a temperature interval from the set of temperature intervals that meets at least one criterion concerning a position of a maximum value of the power in the temperature interval,and setting an initial value of the temperature of the laser resonator to the position of the maximum value of the power in the selected temperature interval.,

[0053] The method can enable the starting of a laser arrangement with an air pressure sensor even at such an unfavorable initial temperature value (for the ambient air pressure) that a control device of the laser arrangement (possibly with electronic control) is not able to achieve low-noise dual-mode operation.

[0054] The unfavorable initial temperature values ​​can be reset by the method when the system is started, so that the control device only has to maintain low-noise operation. When the laser assembly is started, the control device can evaluate the ambient air pressure determined by the air pressure sensor and compare the value with the stored air pressure value. The control device can have a memory for a series of stored ambient air pressure values ​​and, if applicable, associated temperature values ​​for a laser resonator temperature. For example, an ambient air pressure that prevailed during an adjustment of the laser assembly can be stored. The difference can, for example, be greater than a predetermined value of approximately 100 mbar.

[0055] In such a case, that the difference is greater than a predetermined value, the control device performs a temperature scan of the laser resonator. Control based on the at least one parameter or the at least one ambient condition generally does not take place (switched off control). The resonator temperature can be changed (scanned) over a temperature range in increments of approximately 0.1 to 0.2 K. For each step, an input signal of a measured converted power (i.e., in the propagation direction behind the at least one external resonator) and a noise, in particular an input signal of a measured amplitude noise (in the propagation direction behind the at least one external resonator) can be recorded.

[0056] From the recorded power and noise, the controller can determine an optimal initial value for the resonator temperature as follows.

[0057] First, temperature ranges can be determined in which the noise is consistently below a specified value. From these, those temperature ranges can be selected whose temperature width lies above a specified minimum width.

[0058] These temperature ranges can be noted as possible operating ranges in a function matrix as the first column. Measured values ​​of the converted power can then be evaluated for each of these temperature ranges. For this purpose, a) a signal swing (maximum value minus minimum value) of the power, and / or b) a distance of the maximum power value (in temperature) to the edges of the temperature range (center temperature) can be calculated. From the ratio of the distance to the width of the temperature range in which the maximum value was analyzed, a center deviation of the maximum value can be calculated as a measure of the symmetry of a power signal curve. The calculated values, especially the center signal swing and center deviation, can be noted for each temperature range as additional columns in the function matrix. Defined threshold values ​​can be specified for the center deviation and the signal swing, which must be reached or maintained.If several temperature ranges meet several criteria to a comparable extent, weighting factors for the signal swing, the center deviation and the center temperature can be used for an evaluation in order to select a preferred operating range from the matrix and thus a starting value for the temperature of the laser resonator.

[0059] After determining the optimal initial value for the resonator temperature, the electronic control system, which may have been switched off for the execution of the process steps, can be switched on again by the control device in order to ensure permanently stable operation, in particular dual-mode operation.

[0060] The concept underlying the invention will be explained in more detail below with reference to the exemplary embodiments illustrated in the figures. They show:

[0061] Fig. 1 is a schematic view of a laser arrangement;

[0062] Fig. 2 is a schematic view of a frequency dependence of various elements of a laser array;

[0063] Fig. 3 is a schematic view of power and mode structure versus temperature for an embodiment of Fig. 1;

[0064] Fig. 4 is a schematic view of a laser arrangement with a coated and tilted laser medium;

[0065] Fig. 5 is a schematic view of coordinated attenuation profiles of a laser array; Fig. 6 is a schematic view of uncoordinated attenuation profiles of a laser array;

[0066] Fig. 7 is a schematic view of power and mode structure versus temperature for an embodiment of Fig. 4;

[0067] Fig. 8 is a schematic view of a laser arrangement with a

[0068] noise detector;

[0069] Fig. 9 is a schematic view of a laser arrangement with a

[0070] air pressure sensor and an acceleration sensor;

[0071] Fig. 10 is a schematic view of power and amplitude noise curves versus resonator temperature; and

[0072] Fig. 11 is a schematic view of population inversion curves versus a propagation path of laser modes.

[0073] Fig. 1 shows a schematic view of a laser arrangement with a dual-mode laser and an external resonator 9. The dual-mode laser 7 comprises a laser diode 1 as a pump light source emitting a pump light beam, an optional focusing optics 2, which is shown as a single lens by way of example, and a laser resonator 6 with a laser medium 5 arranged approximately centrally therein, an input mirror 3 for coupling in the pump light beam and an output mirror 4 for coupling out laser light, in particular of two laser modes.

[0074] The generation of a primary laser beam 12 by coupling the two laser modes out of the laser resonator 6 by the output mirror 4 and the generation of a frequency-doubled secondary laser beam 13 by the external resonator 9 with its optical elements 9a, 9b, 9c has already been described in DE 103 39 210 B4 in paragraphs 69 to 71, which are incorporated herein by reference. Furthermore, the laser arrangement comprises a control device 36 and a power detector 19 coupled to the control device 36. The control device 36 may, for example, comprise an electronic control system. The power detector detects a power P of the secondary laser beam 13.

[0075] An adjusting element 17 is provided for regulating the temperature of the laser resonator 6. The adjusting element 17 can be controlled by the control device 36. The control device 36 is configured and provided to adjust the resonator length by changing the temperature based on the power P.

[0076] The control device 36 can compensate for external influences such as changing ambient conditions in order to ensure continuous, low-noise dual-mode operation. The control device 36 utilizes the fact that the power of the frequency-converted radiation 13 generated in the external resonator 9 reaches a maximum when two laser modes, in particular longitudinal modes, have oscillated in the laser resonator 6 and have the same intensity. The power detector 19 detects the power P and supplies an electronic input signal, for example a voltage signal Up, to the control device 36. The control device changes the power P via a temperature T r of the laser resonator a length of the laser resonator such that the power P of the secondary laser beam 13 is as large as possible, which is equivalent to dual-mode operation with symmetrical distribution of the power between the two modes.

[0077] Fig. 2 schematically shows the frequency dependence of the various elements in the laser resonator 6 over the frequency v. The top curve shows a gain profile of the laser medium (active medium) 5. The upper middle curve shows a reflectivity of an outcoupling etalon 4 (outcoupling mirror), and the lower curve shows resonances of the laser resonator 6. The preferred frequencies of the outcoupling etalon 4 are those frequencies at which the reflectivity of the outcoupling etalon 4 is maximum and thus the resonator losses are minimum. To achieve dual-mode operation, a preferred frequency of the outcoupling etalon 4 must approximately match a center frequency vo of the gain profile of the laser medium 5, and the frequencies of two adjacent laser modes according to the lower middle curve must be approximately symmetrical to vo.If the preferred frequency of the output coupling etalon 4 deviates too greatly from the center frequency vo of the gain profile, additional laser modes will oscillate, which is illustrated in the lower curve, which shows three laser modes at three different frequencies. Thus, if the optical length of the laser resonator 5 changes, the resonant frequencies of the laser resonator 5 shift relative to the frequencies favored by the output coupling mirror 4, allowing three laser modes to oscillate simultaneously. The frequency separation between adjacent laser modes is indicated as Av.

[0078] Fig. 3 shows a power P, a noise R and a mode structure of the secondary laser beam 13 over the temperature T rof the laser resonator 5. When two laser modes in the laser resonator have the same intensity, the power P of the frequency-converted secondary laser beam 13 generated in the external resonator 9 reaches a maximum. Outside the range in which two laser modes are oscillating in the laser resonator 5 (dual-mode operation), an additional third mode is oscillating. A difference in power between a center and an edge of the dual-mode operation range is indicated as θP. The amplitude noise R of the secondary laser beam increases sharply outside of dual-mode operation. Outside of dual-mode operation, the fluctuations of the power signal P also increase. A predetermined, critical value for the noise Rent, which should not be exceeded, is reached shortly after leaving dual-mode operation.The control device should therefore prevent, if possible, the dual-mode operation from being abandoned in order to achieve low noise and high power. In other words, it is desirable for the control device to ensure that the laser arrangement is operated with exactly two laser modes. Fig. 4 shows a schematic view of a laser arrangement with a laser medium 5 having two parallel surfaces 51, 52, each provided with a coating whose reflectivity is between 0.2% and 2.0%, in particular between 0.4% and 0.8%, and whose normals are arranged at an angle 6 oblique to a propagation direction of the two laser modes. The angle 6 is between 1° and 6°. Basic components of the laser arrangement correspond to the components of the laser arrangement described in connection with Fig. 1 and are provided with identical reference numerals.

[0079] The coatings on surfaces 51, 52 ensure a specific minimum reflectivity Rmin and maximum reflectivity Rmax at the fundamental frequency of the two laser modes, regardless of the ambient humidity. Such coatings can be applied to surfaces 51, 52 using an ion beam sputtering (IBS) process. A preferred reflectivity range is, for example, between (and including) Rmin = 0.4% and Rmax = 0.8%.

[0080] The laser medium 5 is also tilted by an angle 6 (1° < 5 < 6°) against a propagation direction of the two laser modes. This corresponds to a tilt relative to an axis of the laser resonator 6. This tilt prevents the formation of sub-resonators between the optical surfaces of the laser medium and the resonator mirrors 3, 4. Such sub-resonators can lead to disturbances in the dual-mode operation. The laser medium is thus designed and intended to enable frequency-dependent modulation of intra-resonator losses, which is equivalent to the effect of a so-called "tilted etalon."

[0081] Fig. 5 shows a comparison of several curves 41, 42, 43, and 44 plotted against a frequency of the two laser modes. The curves are explained individually below.

[0082] Curve 41 describes the relative losses V (in percent of the total power of the two laser modes) as a function of the frequency generated by the output mirror 4. Thus, curve 41 represents an example of an attenuation profile of the second resonator mirror (first attenuation profile). A frequency spacing of the minima of curve 41 Av a is transmitted over an optical length n a *L a of the output mirror 4 is determined as follows:

[0083] Curve 42 describes the relative losses V (in percent of the total power of the two laser modes) as a function of the frequency of the two laser modes, a so-called fundamental frequency, which the laser medium 5 generates in the laser resonator 6. Thus, curve 42 represents an example of an attenuation profile of the laser medium (second attenuation profile). A frequency spacing Av x the minima of curve 42 is determined by an optical length n x *Lx of the laser medium is determined as follows: cv x = — T~ 2n x L x

[0084] There is n x the refractive index, L x a length of the laser medium 5, and c the speed of light. Maximum loss in the maxima is determined by the reflectivity of the (optical) surfaces of the laser medium. Increased reflectivity provided by the coatings reduces the power of the two laser modes on the one hand, but increases the frequency-selective effect of the laser medium 5 on the other.

[0085] Curve 43 describes the relative losses V generated by the laser medium 5 and the output mirror 4. The lower the value of the sum of curves 41, 42 in curve 43, the higher the power that the two laser modes can achieve.

[0086] With a favorable choice of the length ratios of L x and L aand the reflectivity of the surfaces 51, 52 of the laser medium, the frequency selectivity of the total loss curve 43 is increased without noticeably reducing the power of the two modes. In the example shown, and the reflectivity R = 0.6%. The minima of the relative losses at the output mirror 4 therefore have a frequency spacing Av that is many times larger. a to each other as the minima of the relative losses at the laser medium 5 with their frequency spacing Av x .

[0087] Curve 44 describes the quality factor (Q) of laser resonator 6 as a function of frequency, without taking into account the variability of resonator losses. It is clear that only discrete laser modes spaced apart from one another can be oscillated in the laser resonator. The oscillatable laser modes are located at the resonant frequencies of the laser resonator.

[0088] Distances AVR of the resonance frequencies of the individual laser modes are given by where Lpopt is the optical length of the laser resonator 6, which consists of the following parts: where LR is the laser resonator length, ie the distance from the input coupling mirror to the output coupling mirror, and HL is a refractive index of an interior of the laser resonator 6, which is determined, for example, by a gas mixture located therein or by the air present.

[0089] The laser resonator length LR is usually significantly larger than the other components, so that LR has the greatest influence on the frequency of the possible laser modes.

[0090] The laser modes marked by arrows are active laser modes, which are preferentially oscillated in the exemplary curve 44. This is because they are closest to the minimum of the total loss curve. The other possible laser modes of the laser resonator suffer greater losses than the two oscillatable laser modes. Once two laser modes in the laser resonator have oscillated, no gain remains for other laser modes. This creates a self-stabilizing regime of two laser modes.

[0091] The position of the minima of the relative losses V generated by the laser medium 5 and the output mirror 4 in curves 41 and 42 in relation to one another and to the possible laser modes of the laser resonator depends sensitively on the length of various frequency-selective elements of the laser resonator and, above all, on the length of the output mirror 4 and the laser medium 5. In order for the frequency selectivity of the overall loss curve 43 to be optimal for the desired two adjacent laser modes that are active (arrows on curve 44), the curves 41, 42, and 44 must be synchronized with one another. Synchronization of the curves 41, 42, and 44 includes, in particular, adjusting the length of the laser resonator 6 (effect on curve 44), the length of the output mirror 4 (effect on curve 41), and the length of the laser medium 5 (effect on curve 42).

[0092] To adjust the three lengths mentioned, the laser arrangement according to the embodiment shown in Fig. 4 comprises a control device 36 which is designed and provided to control a temperature T r of the laser resonator 6 via a first adjusting element 17 and / or a temperature T x of the laser medium 5 via a second adjusting element 29 in order to change the first and second attenuation profiles, in particular to match them to one another. The temperature T x of the laser medium 5 is independent of the temperature T r of the laser resonator 6. A temperature sensor 27 is connected to the laser resonator 6 for measuring the temperature T r provided and coupled to the control device 36. In addition, a temperature sensor 28 is provided on the laser medium 5 for measuring the temperature T xprovided and coupled to the control device 36. The temperature control of the laser medium 5 is designed and intended to operate largely independently of the temperature control of the laser resonator 6. This is achieved by avoiding thermal bridges between the laser resonator 6 and the laser medium 5. Peltier elements, which are thermally connected to a common heat sink 30, are preferably used for the control elements 17 and 29.

[0093] When the resonator temperature T changes r the oscillatable laser modes shift in frequency, ie, the maxima of the resonator modes in curve 44 change, since the resonator length changes due to the temperature expansion. The output mirror 4 is thermally connected to the laser resonator 6. Therefore, with T ralso the minima of curve 41 , which is assigned to the output mirror 4. However, the displacement has a much lower rate than the displacement of the oscillatable laser modes. A displacement rate of curve 41 is not only determined by a thickness L a (ie a length along the propagation direction of the laser mode) of the output mirror 4, but also by a temperature coefficient of the refractive index n a of the material from which the output mirror 4 is made.

[0094] By changing the resonator temperature T r So curve 44 and curve

[0095] 41 are shifted relative to each other so that the minimum of curve 41 is symmetrical to two selected oscillatable laser modes of the laser resonator 6. By changing the temperature T x of the laser medium 5, essentially only the curve 42 shifts. By appropriate adjustment of the temperature T xTherefore, curve 42 can be synchronized with curves 44 and 41. Synchronization involves adjusting the second attenuation profile (curve 42) to the first attenuation profile (curve 41).

[0096] In Fig. 5, the temperatures of the laser resonator 6 and the laser medium 5 are optimally matched to each other, so that a minimum of the curves 41 and

[0097] 42 are located one above the other and symmetrically to two oscillatable laser modes that were selected for oscillation. Fig. 6 shows a case where the temperatures are not matched. In this case, laser modes spaced apart from each other by at least one oscillatable laser mode can be oscillated, so that stable dual-mode operation is not possible (see the two vertical arrows pointing to two laser modes spaced apart by three oscillatable laser modes in curve 44).

[0098] Fig. 7 shows the power P of the frequency-converted secondary laser beam 13 generated in the external resonator 9 of the embodiment according to Fig. 4. The diagram largely corresponds to the diagram in Fig. 3. However, in contrast to the curve in Fig. 3, the maximum power P is significantly more pronounced. The difference in power between a center and an edge of the dual-mode operation region 6P is significantly larger. The greater variation in power P over the resonator temperature T r is due to the coating and the inclination of the laser medium 5. The resulting etalon effect enables higher frequency selectivity.

[0099] The difference 6P of the power P between the center and the edge of the dual-mode region is approximately 10 times greater in the embodiment according to Fig. 4 than in Fig. 3. As a result, the signal-to-noise ratio of the input signal for the control device 36 in Fig. 4 is improved by approximately a factor of 10, whereby the control can react more reliably and quickly to rapid changes in the ambient conditions.

[0100] In the laser arrangement according to Fig. 4, the laser medium 5 is doped. The accuracy with which the doping level is specified can be within (including) the limits of plus / minus 0.05%. By designing the laser medium 5 as an etalon and the more precise specification of the doping level, the mean tolerance range of the resonator temperature T r to values ​​greater than or equal to 1 K, which significantly increased the stability of the two-mode operation.

[0101] Fig. 8 shows a further embodiment. The illustration largely corresponds to the illustration in Fig. 4, with identical components having the same reference numerals. In contrast to the embodiment according to Fig. 4, the embodiment according to Fig. 8 additionally includes a noise detector 31. The noise detector 31 provides the control device 36 with a second input signal 33 in addition to a first input signal 32 from the power detector 19.

[0102] The noise detector is designed and configured to measure noise amplitudes of the secondary laser beam 13 at frequencies up to at least 10 MHz, preferably up to 100 MHz or more, and to output a UHF DC voltage signal proportional to the noise amplitude. This can be achieved, for example, using a fast photodiode and a subsequent true-RMS RF detector. Such true-RMS RF detectors are available as integrated components.

[0103] The control device can have an extended control strategy that takes into account not only the first input signal 32 of the power detector 19 but also the second input signal 33 of the noise detector. The control device is designed and provided to achieve a low noise amplitude by slowly changing the resonator temperature T r the power P of the secondary laser beam 13. The control variable T r modulated with a very low frequency (<0.1 Hz) and the resulting changes in the power P of the secondary laser beam 13 are detected in a phase-sensitive manner. From this, a direction (plus / minus) and an amount of correction for the control variable T r The control parameters are set so that no oscillations occur and the ever-present signal noise does not cause abrupt changes in the manipulated variable.

[0104] Outside the dual-mode range, the measured power 32 becomes less meaningful because it is subject to increasing fluctuations. At the same time, however, the RF noise amplitude steadily increases. The control behavior in this range is increasingly determined by the noise amplitude.

[0105] Fig. 9 shows a further embodiment. The illustration largely corresponds to the illustration in Fig. 8, with identical components having the same reference numerals. In contrast to the embodiment according to Fig. 8, the embodiment according to Fig. 9 additionally includes an air pressure sensor 34 and an acceleration sensor 35. The air pressure sensor 34 and the acceleration sensor 35 provide input signals which, like the input signals of the power detector 19 and the noise detector 31, are forwarded to the control device 36, which is preferably implemented as a microprocessor controller. The actuating elements 17 and 29 for regulating the resonator temperature and the temperature of the laser medium 5, respectively, are controlled by the control device 36.

[0106] The air pressure sensor 34 is intended to prevent the laser arrangement from starting operation with such an unfavorable initial setting with regard to the resonator temperature and the temperature of the laser medium that the control device with an electronic control based on the first and second input signals 32, 33 is not able to establish low-noise dual-mode operation.

[0107] When the laser assembly starts up, the control device 36 reads the air pressure sensor 34 and compares the value with the stored air pressure value that prevailed during the laser assembly adjustment. If the difference is greater than a critical value of approximately 100 mbar, the control device first performs a scan of the resonator temperature. The resonator temperature is changed in increments of approximately 0.1 to 0.2 K over a specified range, and the first and second input signals 32, 33 are recorded.

[0108] Fig. 10 shows a schematic representation of the signals recorded during such a scan. The upper curve shows the power of the secondary laser beam 13 versus the resonator temperature T r The lower curve shows the noise of the secondary laser beam 13 versus the resonator temperature T r From these recorded signals, the control unit determines the best starting value for the resonator temperature. The best starting value for the resonator temperature lies in the range AT given as an example. r In this region, the power is locally maximum and the noise is below a given critical value Rent.

[0109] The acceleration sensor 35 of the embodiment shown in Fig. 9 is used to detect shocks and vibrations that act externally on the laser arrangement during operation. If these influences exceed a predetermined critical value, they can disrupt the input signals for the electronic control of the resonator temperature or the temperature of the laser medium to such an extent that the control is no longer able to maintain dual-mode operation. The control device is programmed such that the control is suspended for the duration of the vibrations. It then keeps the control element variables constant, thereby maintaining the existing state. If the intensity of the vibrations falls below the critical value again, the control continues operating from the state before the disturbance.This prevents temporary disturbances caused by vibrations from taking the laser array out of dual-mode operation and thus leading to increased noise.

[0110] A laser arrangement according to an alternative embodiment to the embodiment shown in Fig. 9 has a control device 36 that uses exclusively the input signals of the noise sensor 31 and the air pressure sensor 34 for control. The signal of the power detector 19 is not used for control.

[0111] For control via air pressure and noise, the direction of the air pressure change is first determined from the temporal progression of the input signal of the air pressure sensor 34 over a suitable period of time. If the input signal 33 of the noise sensor 31 exceeds a critical threshold, the resonator temperature T rThe control device changes the signal level by a predetermined value, with the direction (increase or decrease) depending on the direction of the air pressure change. This process can be repeated until the input signal 33 of the noise sensor 31 is below the critical threshold, meaning the laser arrangement operates with low noise again.

[0112] Fig. 11 shows curves illustrating the spatial modulation of the population inversion by zones of different field strengths in the laser medium 5 (“hole-burning effect”) for one laser mode and for two laser modes. The curves are the results of a simulation calculation for a population inversion AN in a laser crystal versus the propagation distance of a laser mode Z. The entrance side into the laser medium 5 for the pump radiation is located at Z=0. The upper curve shows the population inversion for the case where only one longitudinal mode is active, and the lower part for the case where two longitudinal modes are active. Due to the formation of a standing wave, a strong modulation of the population inversion, i.e., a strong hole-burning effect, can be seen in the case of only one longitudinal mode. In the case of two longitudinal modes, the modulation of the population inversion is greatly reduced and disappears completely at the point Z=L. C , where L cis the point in the crystal that is in the optical center of the resonator.

[0113] Complete suppression of the hole-burning effect by the 90° phase shift of neighboring laser modes, especially neighboring longitudinal modes, is therefore only possible at one point in the laser resonator 6, namely at the optical center. The hole-burning effect increases with increasing distance from the optical center. Since the laser medium has a finite extension, an increasing hole-burning effect occurs with increasing extension of the laser medium 6 and thus increasing distance from the optical center. This ensures an increasing amplification of unwanted longitudinal modes with distance from the optical center. As the length of the laser medium in the propagation direction of the laser modes increases, the risk of oscillating secondary modes, which lead to unwanted noise, therefore increases.

[0114] For a diode-pumped Nd:YVÜ4 laser crystal as the laser medium, an absorption length L a of the laser medium is determined by an absorption coefficient a of the laser medium at the pump wavelength. This, in turn, depends on the doping level of the crystal with neodymium atoms. If the length of the laser crystal L x greater than the absorption length L a the length of the laser medium can be approximately equal to the absorption length L a =1 / a, since the amplification no longer makes a significant contribution after this absorption distance. For the stability of the dual-mode operation, the ratio r| of the optical length of the resonator LR Op t to the optical length of the laser medium n x -L a relevant:

[0115] The smaller this ratio, the smaller the tolerance range for the optical resonator length or the temperature of the resonator for which dual-mode operation is possible. For good laser stability, a tolerance range for the resonator temperature of at least 0.5 K is required. The ratio r| can be approximately: j] > 13 During the manufacture of laser crystals, variations in the doping level occasionally occur, which can lead to this value being exceeded. An insufficiently doped laser crystal can cause the absorption length of the laser medium 5 to increase so unfavorably that unstable dual-mode operation occurs. Instabilities arise, for example, when the tolerance range for the resonator temperature is reduced due to the variation in the doping level to values ​​below 0.3 K.On the other hand, the doping must not be too high, as excessive doping leads to self-absorption of laser modes in an unpumped section of the laser medium, thus reducing the output power. In general, variations in the parameters of optical components can be a source of instabilities.

[0116] List of reference symbols

[0117] 1 pump light source

[0118] 2 focusing optics

[0119] 3 coupling mirrors

[0120] 4 output mirrors

[0121] 5 Laser medium

[0122] 51, 52 area

[0123] 6 laser resonator

[0124] 7 dual-mode lasers

[0125] 9 external resonator

[0126] 9a, 9b, 9c optical elements

[0127] 12 primary laser radiation

[0128] 13 secondary laser radiation

[0129] 17 Control element

[0130] 19 Power detector

[0131] 28 Temperature sensor

[0132] 29 Control element

[0133] 30 heat sink

[0134] 31 Noise detector

[0135] 32 first input signal

[0136] 33 second input signal

[0137] 34 Air pressure sensor

[0138] 35 Accelerometer

[0139] 36 Control device

[0140] 41, 42 Attenuation profile

[0141] 43 Total loss curve

[0142] 44 Quality curve

[0143] 5 angles

[0144] L c optical center

[0145] Lx length of the laser medium

[0146] AN occupation inversion

[0147] Av frequency spacing

[0148] Vo center frequency

[0149] V Frequency p Power

[0150] AP power difference R noise

[0151] Rent noise value

[0152] Q Quality

[0153] T r Resonator temperature AT r Temperature range

[0154] V relative losses

[0155] Z Propagation distance

Claims

Claims 1. Laser arrangement for generating laser light, with - a laser resonator (6) for oscillating two laser modes between a first and a second resonator mirror (3, 4) which are spaced apart from each other by a resonator length, wherein the second resonator mirror (4) is configured and provided to couple the two laser modes out of the laser resonator (6), and wherein the second resonator mirror (4) has a first frequency-dependent attenuation profile (41) for laser light, - a laser medium (5) arranged between the resonator mirrors (3, 4), - a measuring device (19, 31) which is set up and intended to measure at least one parameter (P, R) of the two coupled-out laser modes (12, 13) and / or at least one environmental condition of the laser arrangement, - a control device (36) which is configured and provided to adjust the resonator length and the first attenuation profile (41) on the basis of the at least one parameter (P, R) and / or the at least one environmental condition, characterized in that the laser medium (5) has a second frequency-dependent attenuation profile (42) and the control device (36) is configured and provided to change the first and the second attenuation profile (41, 42), in particular to match them.

2. Laser arrangement according to claim 1, characterized in that the laser resonator (6) and the second resonator mirror (4) are configured and provided to allow exactly two longitudinally adjacent laser modes to be coupled out in frequency.

3. Laser arrangement according to one of claims 1 to 3, characterized by at least one external resonator (9) which is configured and provided to receive the two laser modes (12) from the laser resonator (6) and to convert the frequency of the two laser modes (12).

4. Laser arrangement according to claim 3, characterized in that the measuring device (19, 31) is set up and provided to measure the at least one parameter (P, R) on the frequency-converted laser beam (13).

5. Laser arrangement according to one of the preceding claims, characterized in that the control device (36) is configured and provided to adjust the first and the second attenuation profile (41, 42) such that minima of the attenuation profiles coincide in frequency.

6. Laser arrangement according to one of the preceding claims, characterized in that the laser medium (5) has two parallel surfaces (51 , 52) which are each provided with a partially reflective coating, the reflectivity of which is in particular between 0.2% and 2.0%, and in particular between 0.4% and 0.8%, and whose normals are arranged at an angle (6) between 1° and 6° oblique to a propagation direction of the two laser modes.

7. Laser arrangement according to claim 6, characterized in that the coating is configured and provided to provide a reflectivity that is independent of the ambient conditions, in particular the moisture content of a gas surrounding the coating.

8. Laser arrangement according to one of the preceding claims, characterized in that the control device (36) is configured and provided to set a temperature of the laser resonator (6) via a first actuating element (17) and / or a temperature of the to adjust the laser medium (5) via a second actuating element (29) in order to change the first and second attenuation profiles (41 , 42), in particular to match them to each other.

9. Laser arrangement according to one of the preceding claims, characterized in that the laser medium (5) comprises a doped laser crystal whose degree of doping is determined such that the ratio of an optical length of the laser resonator (6) to an optical length of the laser medium (5) is greater than 10.

10. Laser arrangement according to one of the preceding claims, characterized in that the at least one parameter comprises a noise (R) and / or a power (P) of the two coupled-out laser modes (13), in particular a weighted difference of a noise (R) and a power (P) of the two coupled-out laser modes (13).

11. Laser arrangement according to one of the preceding claims, characterized in that the control device (36) is configured and provided to adapt the resonator length and the first attenuation profile (41) on the basis of a direction of change of the at least one environmental condition when the at least one parameter (P, R) has exceeded a predetermined value.

12. Laser arrangement according to one of the preceding claims, characterized in that the at least one environmental condition comprises an amplitude of vibrations to which the laser arrangement is exposed, and / or an ambient air pressure.

13. Laser arrangement according to claim 12, characterized in that the control device (36) is configured and provided to suspend the adjustment of the resonator length and the first attenuation profile (41) when the amplitude of vibrations exceeds a predetermined value in order to avoid an undesired adjustment. Laser arrangement according to one of claims 12 or 13, characterized in that the control device (36) is configured and provided to determine initial values ​​for control variables for adjusting the resonator length, the first attenuation profile (41) and / or the second attenuation profile (42) when the laser arrangement is switched on, depending on the ambient air pressure. Method for commissioning a laser arrangement, comprising the following steps: a. Switching on the laser arrangement, b. Measuring an ambient air pressure, c. Determining a difference between the measured ambient air pressure and a stored ambient air pressure, d. Varying the temperature of a laser resonator (6) of the laser arrangement over a predetermined temperature range if the difference is greater than a predetermined value, e. Recording the parameters of a noise (R) and a power (P) of two laser modes coupled out of the laser resonator (6) over the temperature range, f.g. Selecting a set of temperature intervals with a predetermined minimum width within the temperature range in which the noise (R) is below a predetermined value, g. Selecting a temperature interval from the set of temperature intervals that satisfies at least one criterion relating to a position of a maximum value of the power (P) in the temperature interval, and h. Setting an output temperature value of the laser resonator (6) to the position of the maximum value of the power (P) in the selected temperature interval.

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