LiDAR sensor system with increased range

Abstract

The invention is entitled "LiDAR sensor system with increased range." According to a method for operating a LiDAR sensor system (2), an initial laser pulse (7) is generated by means of a laser light source (4), and the initial laser pulse (7) is negatively chirped by means of a chirping unit (5) depending on a predetermined maximum range. The negatively chirped laser pulse (8) is emitted into the surroundings of the LiDAR sensor system (2).

Description

Technical Field

[0001] The invention relates to a method for operating a lidar sensor system, in which an initial laser pulse is generated by means of a laser light source, as well as to a lidar sensor system and a motor vehicle having a lidar sensor system. Background Art

[0002] For automated or partially automated driving functions, the safest possible perception of the surroundings in motor vehicles is crucial. For this purpose, the vehicle's surroundings are detected using sensors such as radar sensors, lidar sensors, and / or cameras. It is particularly important to capture the surroundings in a holistic and, if possible, three-dimensional manner so that all relevant static and dynamic objects are recorded. Lidar sensors are particularly important in this regard, as they use the corresponding sensor data to measure exact distances and can also perform object classification.

[0003] Modern lidar sensor systems are based, for example, on time-of-flight measurement, also known as time-of-flight measurement (ToF measurement). Here, the time of flight of a light pulse emitted by the lidar system, reflected by the surrounding environment, and then detected again by the lidar system is measured to determine the distance between the light pulses. The maximum range is related to the number of detected photons and, therefore, the number of photons reflected by the surfaces of objects in the surrounding environment. The more photons reflected and detected, the higher the probability or accuracy of object detection.

[0004] Because the number of emitted photons per laser pulse scales linearly with the emitted power, the range can be increased by increasing the power of the emitted pulses. However, this has the disadvantage that the damaging effects of the concentrated laser radiation, and in particular the risk of eye damage to passersby, increase with the increased emitted power. To counteract this, the beam diameter of the emitted laser beam can be increased, which, however, reduces and thus also impairs the spatial awareness capabilities of the system.

[0005] US 2019 / 0137611 A1 describes a lidar-like system with multiple VCSEL light sources on a first base layer and a beam-forming element for each VCSEL on a second base layer (which is arranged on the first base layer). The beam-forming element can include a chirped gitter. This allows beam forming and beam steering to be achieved without the scanner mirrors typically used in laser scanners. Summary of the Invention

[0006] Against this background, the object of the present invention is to specify an improved concept for a lidar sensor system, by which the maximum range can be increased without compromising the eye safety or the spatial resolution of the system.

[0007] This object is achieved by the respective subject matter of the independent claims. Advantageous developments and preferred embodiments are the subject matter of the dependent claims.

[0008] The improved concept is based on the idea of ​​negatively chirping the initially generated laser pulse using a chirping unit according to a preset maximum range, thereby exploiting the effects of normal air divergence during laser pulse propagation for targeted pulse compression.

[0009] According to an improved embodiment, a method for operating a lidar sensor system is provided, wherein an initial laser pulse is generated by means of a laser light source of the lidar sensor system. The initial laser pulse is negatively chirped by means of a chirping unit of the lidar sensor system, depending on a predetermined maximum range. The chirped laser pulse, specifically the chirped initial laser pulse, is emitted into the surroundings of the lidar sensor system.

[0010] Depending on the design of the laser light source, the initial laser pulse can have a peak wavelength, also referred to as peak wavelength, in the visible, ultraviolet, or infrared spectral range. Preferably, in particular for applications in the automotive sector, the initial laser pulse has a peak wavelength in the infrared spectral range, in particular in the range between 700 nm and 1800 nm, for example in the range between 1050 nm and 1500 nm.

[0011] The chirp ("chirp" in English) of a laser pulse can be understood as a modification of the temporal distribution of the individual spectral components of a laser pulse within its envelope. In other words, the frequency or wavelength of a chirped pulse varies over time. While an unchirped laser pulse (e.g., a Fourier-limited laser pulse) has the same spectral composition at every point in time during the laser pulse, in a positively chirped pulse, the spectral components with longer wavelengths precede those with shorter wavelengths, while in a negatively chirped pulse, the spectral components with shorter wavelengths precede those with longer wavelengths. This results, in particular, in the fact that both positively and negatively chirped pulses are temporally stretched, i.e., have a longer pulse duration, compared to Fourier-limited pulses of the same bandwidth.

[0012] In the case of the method according to the improved embodiment, the chirped laser pulses also have a longer pulse duration than the initial laser pulse, ie are stretched in time relative to the initial laser pulse. Since the peak intensity I is indirectly proportional to the pulse duration T, in particular

[0013] (1)

[0014] where EP corresponds to the pulse energy, Corresponding to constant envelope parameters, and w corresponding to the beam diameter, the corresponding peak intensity of the negatively chirped laser pulse is also lower than the peak intensity of the initial laser pulse. Therefore, the output power emitted is It is possible to achieve this without increasing the peak intensity I or peak energy density of the negatively chirped laser pulse. where f corresponds to the pulse repetition rate.

[0015] As an emitted negatively chirped laser pulse propagates through the ambient air, it is compressed due to the normal spectral divergence of the air, and the correction of the spectral distribution by the negative chirp is at least partially compensated. The pulse duration is therefore reduced during propagation through the air. Thus, when the effects of the negative chirp are fully compensated, the peak intensity of the negatively chirped laser pulse at a constant beam diameter reaches a maximum value during propagation through the air, particularly approximately within a predetermined maximum range. However, since the peak intensity also decreases inversely with the beam diameter, and negatively chirped laser pulses must be emitted with a limited beam divergence, the peak intensity of the emitted laser pulse during propagation does not increase relative to the peak intensity immediately after the emission of the negatively chirped pulse, despite the increased output power. Consequently, eye safety is ensured, particularly during the entire propagation of the emitted laser pulse, without having to increase the beam diameter or divergence.

[0016] The method according to the improved embodiment maximizes the energy density of the emitted negatively chirped laser pulse after propagating over a distance corresponding to the maximum range, without increasing the energy density at shorter distances. The negative chirp and its compensation due to propagation through air effectively modulate the pulse duration as a function of the propagation length.

[0017] The emitted laser pulses can be at least partially reflected by objects in the surroundings of the lidar sensor system, and the reflected parts can return to the lidar sensor system, where they strike, for example, one or more optical detectors of the lidar sensor system, such as one or more photodiodes or avalanche photodiodes. The at least one optical detector then generates at least one corresponding detection signal based on the respective reflection and the detected part. By means of a computing unit, which can, for example, correspond to a control unit and which can include or be included by the control unit, the at least one detection signal is evaluated and / or processed, in particular based on the principle of light time-of-flight measurement, in order to determine the radial distance of the reflecting object from the lidar sensor system.

[0018] The chirp unit may, for example, contain one or more gratings or diffraction gratings, one or more diffraction prisms or one or more chirped mirrors.

[0019] By means of these optical elements, the anomalous divergence that induces negative chirp can be effectively achieved. Alternatively, the chirp unit can also comprise a material with an anomalous spectral divergence, through which the initial laser pulse z is guided to induce negative chirp.

[0020] The chirped unit can also be partially or completely integrated in the light source, for example in the form of a chirped Bragg mirror. For example, the light source and the chirped unit can be implemented as a photonic integrated circuit.

[0021] According to at least one embodiment of the method according to the development, the initial laser pulse is temporally stretched by negative chirping.

[0022] Temporal stretching is synonymous with increasing the pulse duration. In other words, the pulse duration of the negatively chirped pulse is greater than the pulse duration of the initial laser pulse, i.e., the initial laser pulse is generated as an unchirped or essentially unchirped laser pulse. This anomalous dispersion of the surrounding medium, particularly air, has the desired effect of compressing the emitted laser pulse, i.e., shortening the pulse duration during propagation.

[0023] According to at least one embodiment, the intensity of the chirp is set, in particular by means of a control unit and a chirp unit, as a function of the maximum range, such that the temporal stretching achieved by the negative chirp is at least approximately compensated by the propagation of the negatively chirped laser pulse in the surrounding medium, in particular air, over a distance corresponding to the maximum range.

[0024] In other words, the temporal stretch is restored or approximately restored by propagation through the surrounding medium. After the emitted laser pulse has thus propagated over a distance corresponding to the maximum range, the pulse duration is again at least approximately equal to the pulse duration of the initial laser pulse. In particular, the control unit can control the chirp unit to adjust the intensity of the chirp accordingly. This can be achieved, for example, by modifying the beam guidance within the lidar sensor system or by modifying individual components of the chirp unit.

[0025] By at least approximately compensating for the temporal extension, it is achieved that in the maximum range the shortest possible pulse duration and, accordingly, the highest possible peak energy density exist, without the peak energy density being exceeded immediately after the emission of the negatively chirped laser pulse.

[0026] According to at least one embodiment, the position and / or orientation of at least one component of the chirp unit is changed, in particular by means of a control unit, in order to adjust the intensity of the chirp.

[0027] In particular, the orientation and / or position of two or more components of a chirp unit (e.g., a prism, a grating, and / or a mirror) can be varied relative to one another in order to adjust the intensity of the chirp. By varying the position and / or orientation of at least one component, the optical path length for spectral components with shorter wavelengths can be specifically increased compared to the optical path length for spectral components with longer wavelengths, and this difference in optical path lengths can be adjusted and controlled.

[0028] According to at least one embodiment, the position and / or orientation of the laser light source, in particular relative to the chirp unit and / or at least one component of the chirp unit, is varied, in particular by means of a control unit, in order to adjust the intensity of the chirp.

[0029] In particular, by changing the position and / or orientation of the laser light source, the number of reflections of the laser pulses between the various components of the chirp unit can be modified, for example by correspondingly changing the angle of incidence. Thus, the optical path lengths of the spectral components or their differences can also be effectively controlled.

[0030] According to at least one embodiment, the dwell time of the laser pulse in the resonator of the chirp unit is adjusted, in particular by means of a control unit, in order to adjust the intensity of the chirp.

[0031] Thus, for example, it is possible to adjust the number of reflections to which the photons of a laser pulse are subjected in the resonator before they are coupled out of the resonator.

[0032] According to at least one embodiment, in particular with the aid of a control unit and a chirp unit, the intensity of the chirp is adjusted depending on the beam divergence of the negatively chirped laser pulse in such a way that the maximum energy density of the chirped laser pulse after propagation over a distance corresponding to the maximum effective range is less than or equal to the maximum energy density of the negatively chirped laser pulse after it is emitted directly from the housing of the lidar sensor system.

[0033] Since the maximum or peak energy density is inversely proportional to the square of the beam diameter and inversely proportional to the pulse duration, it is achieved that the peak energy density or maximum energy density is not increased by pulse compression during propagation.

[0034] In accordance with at least one embodiment, the initial laser pulse is generated as a Fourier-limited laser pulse or as an approximately Fourier-limited laser pulse.

[0035] In particular, the phase of the initial laser pulse as a function of the frequency or wavelength is approximately constant for the entire frequency band in which the initial laser pulse is based. Thus, an initial laser pulse is generated which, in particular, has a pulse duration that is as short as possible.

[0036] According to an improved embodiment, a lidar sensor system is provided that includes a laser light source and a control unit. The control unit is configured to control the laser light source to generate an initial laser pulse. The lidar sensor system includes a chirp unit that is configured and arranged, in particular to be controlled by the control unit, to negatively chirp the initial laser pulse according to a predetermined maximum range. The beam guidance of the lidar sensor system is designed such that the negatively chirped laser pulse can be emitted or directed into the surroundings of the lidar sensor system.

[0037] For example, beam steering may be achieved by one or more optical elements of a lidar sensor system, such as lenses, mirrors, beam expanders, and the like.

[0038] Further embodiments of the lidar sensor system according to the improved concept may be directly derived from different embodiments of the method according to the improved concept, and vice versa. In particular, the lidar sensor system according to the improved concept may be configured to carry out the method according to the improved concept, or the lidar sensor system may carry out such a method.

[0039] According to an improvement, a motor vehicle is also specified, which comprises an embodiment of the lidar sensor system according to the improvement.

[0040] The invention also includes combinations of features of the described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The following describes an embodiment of the present invention. In the drawings, elements with the same function are respectively provided with the same reference numerals. In the drawings:

[0042] Figure 1 is a schematic illustration of a motor vehicle with an exemplary embodiment of a lidar sensor system according to an improved concept;

[0043] Figure 2 is a schematic diagram of another exemplary embodiment of a lidar sensor system according to an improved solution;

[0044] Figure 3 is a schematic diagram of beam divergence in another exemplary embodiment of a lidar sensor system according to an improved solution;

[0045] Figures 4a-4d is a schematic diagram of the characteristics of the simulated laser pulse at the first time point;

[0046] Figures 5a-5d is a schematic diagram of the characteristics of the simulated laser pulse at the second time point;

[0047] Figures 6a-6d is a schematic diagram of characteristics of a simulated laser pulse at a third time point; and

[0048] Figures 7a-7d is a schematic diagram of the characteristics of the simulated laser pulse at the fourth time point. DETAILED DESCRIPTION

[0049] The exemplary embodiments described below relate to preferred exemplary embodiments of the present invention. The components described in the exemplary embodiments each represent individual, mutually independent features considered in the present invention, which also improve the present invention independently of one another and can therefore also be considered as components of the present invention, either individually or in combinations other than those shown. Furthermore, the described exemplary embodiments can also be supplemented by further, already described features of the present invention.

[0050] Figure 1 A motor vehicle 1 is schematically shown with an exemplary embodiment of a lidar sensor system 2 according to an improved concept. Figure 2 A schematic diagram of a lidar sensor system 2 is shown.

[0051] LiDAR sensor system 2 includes a laser light source 4 (particularly an infrared laser source) configured to emit (its pulsed laser radiation 6) which can be reflected or partially reflected, for example, by an object 3 in the surroundings of motor vehicle 1. A reflected portion 6' of laser radiation 6 can be detected by a detector unit (not shown) of LiDAR sensor system 2. LiDAR sensor system 2 also includes a control unit 16, which is coupled to laser light source 4 in order to control it to emit initial laser pulse 7. LiDAR sensor system 2 also includes a chirp unit 5, which can also be coupled to control unit 16.

[0052] For example, the maximum range of the lidar sensor system 2 , which can also be considered a target range, can be stored in a memory unit of the control unit 16 . The control unit 16 is configured to control the laser light source 4 and / or the chirping unit 5 such that the initial laser pulse 7 is negatively chirped by the chirping unit 5 , thereby generating a negatively chirped laser pulse 8 , which can be emitted from a housing (not shown) of the lidar sensor system 2 into the surroundings of the lidar sensor system 2 and, thus, the motor vehicle 1 . The initial laser pulse 7 can be generated, for example, as a Fourier-limited or nearly Fourier-limited laser pulse, in which, in particular, all spectral components have approximately the same phase. The negative chirping delays the spectral components with longer wavelengths relative to the spectral components with shorter wavelengths, thereby causing pulse stretching, which increases the pulse duration, and causing the spectral components with shorter wavelengths to precede the spectral components with longer wavelengths in the chirped laser pulse 8 .

[0053] As the chirped laser pulse 8 propagates through the surroundings (particularly through air), it is compressed due to the normal spectral dispersion of air, compensating for the advance of the spectral components with shorter wavelengths. The intensity of the negative chirp generated by the chirping unit 5 is specifically set so that, after the negatively chirped laser pulse 8 has propagated over the maximum range, the pulse stretching is approximately restored or compensated by the negative chirp. The resulting laser pulse 9 is thus compensated at the maximum range and has a shorter pulse duration than the chirped laser pulse 8 immediately after emission. The pulse duration of the resulting laser pulse 9 can, in particular, be approximately equal to the pulse duration of the initial laser pulse 7.

[0054] If the object 3 is thus located at a position corresponding to the maximum range of action, the resulting laser pulse 9 strikes the object 3 with the shortest possible pulse duration, i.e., with the highest possible peak energy density of the resulting laser pulse 9. However, due to the beam expansion of the laser radiation 6 during propagation, the peak energy density does not increase compared to the situation immediately after emission.

[0055] exist Figure 3 The beam expansion during propagation is schematically shown in FIG. At a relatively small distance from the laser light source 4 or from the lidar sensor system 2 , the laser radiation 6 has a first beam diameter W1 that is significantly smaller than the beam diameter W2 at the maximum range.

[0056] The peak intensity of the laser light source 4 is given by the relationship of equation (1) above. Taking into account the pulse repetition rate f, the peak energy density is obtained according to the following equation:

[0057] (2)

[0058] LiDAR sensor systems 2 used in an automotive environment, in particular for autonomous driving functions, are typically operated close to the maximum optical power permitted by legal regulations (e.g., for eye safety) in order to achieve the highest possible range. Therefore, the range cannot usually be further increased by increasing the emitted power. The divergence of the laser radiation 6 determines the spatial resolution of the LiDAR sensor system 2, so it is desirable to keep it as low as possible. Therefore, compensating for a potentially higher output power by increasing the beam diameter is also unsuitable. Furthermore, according to the aforementioned equation (1), the peak intensity decreases with increasing distance, which is inversely proportional to the beam diameter, resulting in a lower energy density and fewer photons emitted per unit area, which in turn reduces the object detection capability.

[0059] However, Equation (2) also shows that the increase in output power can be compensated by a longer pulse duration, since I ~ (P / T) applies, and thus the peak intensity can remain constant. However, simply extending the pulse duration also reduces the number of photons at long distances, which reduces the probability of detection for long propagation distances. To maximize the energy density at the maximum distance while still remaining below the critical limit for the emitted power at shorter distances, a modified approach modulates the pulse duration as a function of the propagation length. For shorter distances, the pulse duration is longer, and the laser pulse compresses itself as the propagation increases. This is achieved by negatively chirping the temporal distribution of the individual spectral components below the envelope.

[0060] Due to the negative chirp of the initial laser pulse 7, it can be stretched, which also reduces the peak intensity. If the chirped laser pulse 8 now propagates through a normally diverging medium (such as air), the high-frequency spectral components experience a greater time delay than the low-frequency spectral components. Due to the increased propagation in the medium, the chirped laser pulse 8 is thus compressed in time. With a correspondingly coordinated selection of the negative divergence imposed by the negative chirp, the low-frequency spectral components catch up with the high-frequency spectral components within the desired distance given by the maximum range, and the chirped laser pulse 8 reaches a pulse duration close to the Fourier limit. Since the laser radiation 6 diverges simultaneously and the peak intensity therefore decreases inversely quadratically as a function of the propagation duration or distance, the limit values ​​relevant to eye safety are not exceeded.

[0061] exist Figure 2 The lower part of the diagram schematically illustrates an exemplary variant for designing a chirp unit 5 based on two light grids 12 and 14. This should not be understood as restrictive in any way; rather, it refers to any device that can negatively chirp laser pulses in an influencing manner and is suitable for installation in a lidar sensor system. In particular, negative chirping can also be achieved using chirped mirrors, prism combinations, and the like.

[0062] exist Figure 2 In the variant shown in , the initial laser pulse 7 is deflected, for example, via a beam splitter 10 onto a mirror 11, which deflects the initial laser pulse 7 onto a first grid 12, which is oriented in such a way that a fan-out of the spectrum occurs. With the aid of an optical lens system 13, the fanned-out beam can be parallelized and refocused so that it impinges on a second grid 14. This is in particular not oriented parallel to the first grid 12, so that the convergent fan-out spectral parts are parallelized again. The resulting beam is already negatively chirped and can be used directly. Figure 2 In the device, a further mirror 15 is provided, which inverts the already partially chirped light beam so that it again strikes the second grid 14, is deflected via the optical lens system 13 onto the first grid 12 and can be coupled out as a negatively chirped laser pulse 8 via the first mirror 11 and, if necessary, the beam splitter 10.

[0063] Between the two grids 12, 14, the high-frequency spectral part travels along a longer optical path than the low-frequency part. By spacing the grids 12, 14 apart and / or modifying the orientation of the grids 12, 14 relative to each other, the intensity of the negative chirp can be modified, for example, by the control unit 16.

[0064] Figures 4a to 7d The results of simulating the pulse duration by applying negative chirp are shown schematically in . Figure 4a 、 Figure 5a 、 Figure 6a and Figure 7a In FIG, the laser pulses are schematically shown as a function of time, such as, for example, the electric field strength as a function of time. Figure 4b 、 Figure 5b 、 Figure 6b and Figure 7b , the envelope of the laser pulse is schematically shown, also as a function of time.

[0065] exist Figure 4c 、 Figure 5c 、 Figure 6c and Figure 7c In each case, the current group delay of the laser pulse, also called group delay, ie essentially the first derivative of the phase with respect to frequency, is shown as a function of the wavelength in nm. Figure 4d 、 Figure 5d 、 Figure 6d and Figure 7d In FIG, the variation of the associated group delay time, also called group delay spread, ie essentially the second derivative of the phase with respect to frequency, is shown as a function of the wavelength in nm.

[0066] exist Figures 4a to 4d Here, the initial laser pulse 7 is shown. Figure 4b As shown in , the pulse duration, which can be given by the half-value width of the envelope, for example, is approximately equal to 10 fs. The initial laser pulse 7 is simulated here as a Fourier-limited laser pulse, so that the group delay and group delay divergence are always zero. Figures 5a to 5d In FIG, a negatively chirped laser pulse 8 is shown directly after leaving the chirping unit 5. Due to the negative chirp, the pulse duration is increased by a factor of approximately 60 compared to the initial laser pulse 7. Figure 4c 、 Figure 5c 、 Figure 6c 、 Figure 7c as well as Figure 4d 、 Figure 5d 、 Figure 6d and Figure 7d The frequency dependence of the phase can be clearly seen in .

[0067] exist Figures 6a to 6d In FIG. 8 , a laser pulse 8′ is shown after propagating 10 m through air with a temperature of 20° C. and a humidity of 50%. Figures 5a to 5d Compared to the laser pulse 8, the laser pulse has been compressed and the pulse duration is only about 55 times the original pulse duration of the initial laser pulse 7. Figures 7a to 7dIn FIG, the resulting laser pulse 9 is maximally compressed after a propagation of 150 m, so that the pulse duration corresponds approximately to the pulse duration of the initial laser pulse 7. If pulse 9 continues to propagate, the high-frequency spectral part is exceeded by the low-frequency spectral part, so that the laser pulse is stretched again in time and the peak intensity drops again.

[0068] With the help of these examples, it can be seen that in this specific example, the output power emitted can be increased by a factor of 60 without compromising eye safety, because the peak intensity decreases inversely with the beam diameter. Compared to conventional lidar systems, 60 times this number of photons is available for detection, resulting in an increased maximum range.

[0069] In further embodiments, the negative chirp can be adaptively adapted, for example, by means of an LCD-based pulse shaper or by adapting the number of reflections on a chirped mirror of the chirp unit, in order to control the maximum range or the peak intensity for different ranges.

[0070] Reference Signs List

[0071] 1 Motor Vehicle

[0072] 2 LiDAR Sensor System

[0073] 3 objects

[0074] 4 Laser light source

[0075] 5 Chirp Unit

[0076] 6 Laser radiation

[0077] 6' reflected part

[0078] 7 Initial laser pulse

[0079] 8 Negatively chirped laser pulses

[0080] 9 Generated laser pulses

[0081] 10 beam splitters

[0082] 11 Mirror

[0083] 12 light grid

[0084] 13 Lens system

[0085] 14 light grid

[0086] 15 Mirror

[0087] 16 control unit.

Claims

1. A method for operating a lidar sensor system (2), wherein: generating an initial laser pulse (7) by means of a laser light source (4), It is characterized in that - the initial laser pulse (7) is negatively chirped by means of a chirping unit (5) depending on a predetermined maximum range; - Negatively chirped laser pulses (8) are emitted into the surroundings of the lidar sensor system (2); - receiving, by an optical detector of the lidar sensor system, the emitted laser pulses at least partially reflected by objects in the surrounding environment, and generating at least one corresponding detection signal based on the corresponding reflected and detected laser pulse portions; The initial laser pulse (7) is stretched in time by the negative chirp; The intensity of the negative chirp is adjusted as a function of the maximum range in such a way that the temporal extension caused by the propagation of the negatively chirped laser pulses (8, 9) in the surrounding medium is at least approximately compensated for over a distance corresponding to the maximum range; and The intensity of the negative chirp is adjusted depending on the beam divergence of the negatively chirped laser pulse (8) so that the maximum energy density of the negatively chirped laser pulse after propagation over a distance corresponding to the maximum effective range is less than or equal to the maximum energy density of the negatively chirped laser pulse (8) after being directly emitted from the housing of the lidar sensor system (2).

2. The method according to claim 1, It is characterized in that The position and / or orientation of at least one component of the chirp unit (5) is changed in order to adjust the intensity of the negative chirp.

3. The method according to claim 1, It is characterized in that The position and / or orientation of the laser light source (4) is changed to adjust the intensity of the negative chirp.

4. The method according to claim 1, It is characterized in that The dwell time in the resonator of the chirp unit (5) is adjusted to adjust the intensity of the negative chirp.

5. The method according to any one of the preceding claims 1 to 4, It is characterized in that The initial laser pulse (7) is generated as a Fourier-limited laser pulse or as an approximately Fourier-limited laser pulse.

6. A laser radar sensor system comprising a laser light source (4) and a control unit (16), wherein the control unit (16) is configured to control the laser light source (4) to generate an initial laser pulse (7). It is characterized in that The lidar sensor system (2) has a chirping unit (5), which is designed and arranged to negatively chirp the initial laser pulse (7) as a function of a predetermined maximum range; - the beam guidance of the lidar sensor system (2) is designed such that negatively chirped laser pulses can be emitted into the surroundings of the lidar sensor system; as well as - the lidar sensor system further comprises an optical detector, which is configured to receive the emitted laser pulses at least partially reflected by objects in the surroundings and to generate at least one corresponding detection signal based on the respective reflected and detected laser pulse parts; The lidar sensor system is set up such that: - the initial laser pulse (7) is stretched in time by the negative chirp; - adjusting the intensity of the negative chirp as a function of the maximum range in such a way that the temporal stretching caused by the propagation of the negatively chirped laser pulses (8, 9) in the surrounding medium over a distance corresponding to the maximum range is at least approximately compensated; and - adjusting the intensity of the negative chirp as a function of the beam divergence of the negatively chirped laser pulse (8) such that the maximum energy density of the negatively chirped laser pulse after propagation over a distance corresponding to the maximum range is less than or equal to the maximum energy density of the negatively chirped laser pulse (8) after it is emitted directly from the housing of the lidar sensor system (2).

7. A motor vehicle having a lidar sensor system (2) according to claim 6.

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