METHOD AND DEVICES FOR REDUCING MINIMUM EYE SAFETY DISTANCES IN CONNECTION WITH ILLUMINATION LASER RADIATION

Description

[0001] The present invention relates to methods and devices for reducing minimum eye safety distances during active object observation and fine tracking using laser illumination. The minimum eye safety distance is also referred to as the non-ocular hazard distance, abbreviated NOHD. It represents the distance of a person from a laser radiation source at which the laser radiation incident on the person falls below a predetermined exposure limit (ELW).

[0002] To illuminate an object in a defined environment, a minimum illumination intensity must be achieved on the object so that an optical sensor, which detects the illumination radiation reflected by the object, receives a sufficient number of photons for evaluation of the reflected illumination radiation.

[0003] In a first per se known method for operating a laser radiation device comprising an illumination laser and an active laser, the illumination laser is operated in a first operating mode of the laser radiation device, in which the active laser does not emit active laser radiation, such that its illumination laser radiation has a first illumination laser radiation power.

[0004] Such a procedure is known from US 5 837 996 A.

[0005] In a laser radiation device having a first illumination laser beam path and a second illumination laser beam path, wherein in the first illumination laser beam path propagating laser radiation emerges from a first aperture of the laser radiation device and in the second illumination laser beam path propagating laser radiation emerges from a second aperture of the laser radiation device, which is spatially separated from the first aperture, the illumination laser beam paths overlap.

[0006] In a second method known per se for adjusting the illumination laser radiation power, the distance of a target to be illuminated by the illumination laser is measured with a distance measuring device different from the illumination laser.

[0007] A third method, known per se, is used to set the parameters of an illumination laser and comprises the following steps: measuring the distance of a target to be illuminated by the illumination laser, determining parameters of the illumination laser as a function of the measured distance, emitting at least one laser radiation pulse directed at the target from the illumination laser operated with the determined parameters, checking whether laser radiation from the emitted laser radiation pulse is reflected to a detector of the illumination laser and then, if this is the case, determining the distance of the object that reflected the laser pulse as a function of the reflected and detected laser radiation.

[0008] For a variety of reasons (cross-sectional area, cleaning, signature, etc.), it is desirable for the illumination laser to have the smallest possible transmitting aperture. This can lead to high intensities, especially near the aperture, and thus to undesirably high NOHD values.

[0009] For actively observing objects in space at different distances, it is particularly desirable in urban applications to achieve low NOHD values ​​for the use of the illumination laser in order to avoid safety-related restrictions on lighting.

[0010] To achieve low NOHD values ​​in this conflicting objective, current methods use emitter apertures for illumination laser radiation that are similar in size to those of significantly higher-powered lasers. Another possibility is to limit the power emitted by an illumination laser to a minimum value that is just sufficient for the illumination function. The use of illumination laser radiation with so-called "eye-safe wavelengths," which are associated with high exposure limits (the exposure limit increases with increasing wavelength), is also known.

[0011] Limiting the illumination laser's radiation power is fundamentally disadvantageous because it directly reduces the illumination quality and thus the object recognition quality and resolution. Illumination lasers that emit so-called eye-safe illumination laser radiation are very expensive and have low efficiency.

[0012] Against this background, the object of the invention is to provide methods for operating illumination lasers with very low NOHD values, which allow the use of illumination lasers in an urban environment while complying with exposure limits, even at illumination laser wavelengths not generally considered "eye-safe". A further object is to provide a device that allows the use of illumination lasers in an urban environment while complying with exposure limits. In particular, the use should also be possible with illumination laser wavelengths that are not inherently considered "eye-safe". This object is achieved by the sum of the features of each independent claim.

[0013] The first method mentioned above is characterized according to the invention in that the illumination laser in a second operating mode of the laser radiation device, in which the active laser emits active laser radiation, is operated in such a way that its illumination laser radiation has a second illumination laser radiation power that is greater than the first illumination laser radiation power.

[0014] The above-mentioned laser radiation device, which is not according to the invention, is characterized in that an overlap of the two illumination laser beam paths only occurs at a distance from the apertures that is greater than a predetermined minimum distance for each of the two beam paths.

[0015] The second method mentioned above, which is not according to the invention, is characterized in that an illumination laser radiation power of the illumination laser is determined as a function of the measured distance and that the target is subsequently illuminated by the illumination laser, wherein the illumination laser is operated in such a way that it emits the determined illumination laser radiation power.

[0016] The third method mentioned above, which is not according to the invention, is characterized in that the distance of the object is compared with the distance of the target and that, if the distance of the object is less than the distance of the target, parameters of the illumination laser are changed so that an exposure limit at the location of the object is not exceeded by the laser radiation of the illumination laser striking that location.

[0017] A preferred embodiment of the first method is characterized in that the illumination laser is operated in the first operating mode and in the second operating mode such that it emits the illumination laser radiation in the form of illumination laser radiation pulses, wherein a repetition frequency with which the illumination laser radiation pulses are emitted is lower in the first operating mode than in the second operating mode.

[0018] A preferred operating method of the laser radiation device is characterized in that it is operated in such a way that the laser radiation propagating in the illumination laser beam paths is fed into the illumination laser beam paths in the form of illumination laser radiation pulses, wherein the illumination laser radiation pulses are fed alternately into the first illumination laser beam path and the second illumination laser beam path from illumination laser radiation pulse to illumination laser radiation pulse.

[0019] A preferred embodiment of the second method is characterized by the fact that the illumination laser radiation power is determined in such a way that it also decreases with decreasing distance.

[0020] A preferred embodiment of the third method is characterized in that the distance to the target is measured using a distance measuring device different from the illumination laser.

[0021] It is also preferred that the laser radiation striking the object is modified by reducing the average intensity of the laser radiation from the illumination laser.

[0022] It is further preferred that the average intensity of the laser radiation is changed by reducing the repetition rate of the illumination laser.

[0023] Further advantages arise from the dependent claims, the description, and the accompanying figures.

[0024] It is understood that the aforementioned features and those to be explained below can be used not only in the combination specified, but also in other combinations or on their own.

[0025] Exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. In this context, identical reference numerals in different figures denote identical or at least functionally comparable elements. The figures show, in schematic form: Figure 1 shows a laser radiation device with which the methods according to the invention can be carried out; Figure 2 shows an embodiment of a first method according to the invention with which the illumination laser is operated; Figure 3 shows an embodiment of a laser radiation device according to the invention; Figure 4 shows an embodiment of a second method, not according to the invention; and Figure 5 shows a flowchart as an embodiment of the third method, not according to the invention, for setting parameters of an illumination laser.

[0026] In detail, the Figure 1A laser radiation device 10 comprising a housing 12. The housing 12 has a first illumination laser aperture 16 through which illumination laser radiation 22 can emerge from the housing 12 in a first illumination laser beam path 52. The housing 12 also has an active laser aperture 17 through which an active laser beam can emerge from the housing 12.

[0027] The laser radiation device 10 comprises an active laser 13, a first illumination laser 14, a deflecting mirror 36 which is reflective for the wavelength of the active laser radiation 20 and transparent for the wavelength of the illumination laser radiation 22, a tip tilt mirror 24 which can be controlled with respect to its orientation in space, an active laser telescope 26, a first illumination laser telescope 28, an optical sensor 30, a control unit 32 and a distance measuring device 34.

[0028] The illumination laser radiation 22 preferably has a different wavelength than the active laser radiation 20.

[0029] The first illumination laser 14 is preferably configured to generate pulsed illumination laser radiation as illumination laser radiation 22. Alternatively, the first illumination laser 14 is configured to generate the illumination laser radiation 22 as continuous wave laser radiation.

[0030] The illumination laser radiation 22 emerges from the housing 12 through the first illumination laser aperture 16 and, if the laser radiation device 10 is correctly roughly aligned, detects a target 38.

[0031] A rough alignment is achieved, for example, by a mechanical alignment device designed to roughly align the housing 12, and thus also the laser radiation 20, 22 emerging from the housing 12, with the target 38 in azimuth and elevation. This rough alignment is controlled, for example, by a radar system, which in one embodiment also serves as a range-measuring device 34.

[0032] Illumination laser radiation 42, reflected from target 38, propagates through the effective laser radiation telescope 26 and via the tip-tilt mirror 24 to the deflecting mirror 36, which is reflective for the wavelength of the effective laser radiation 20 and transparent for the wavelength of the illumination laser radiation 22 and the reflected illumination laser radiation 42. The reflected illumination laser radiation 42 passes through the deflecting mirror 36 and is detected by the optical sensor 30. The signal generated by the optical sensor 30 is evaluated by evaluation software 44 of the control unit 32, and the result of the evaluation is used by a control unit 46 of the control unit 32 to control the tip-tilt mirror 24. The control is such that the tip-tilt mirror 24 aligns any emitted effective laser radiation 20 onto target 38. This alignment constitutes fine tracking.

[0033] The control unit 46 also controls the first illumination laser 14 and the working laser 13 and processes signals from the distance measuring device 34.

[0034] The first illumination laser 14 is controlled in such a way as to achieve the lowest possible NOHD value. For calculating the illumination laser parameters that result in the lowest possible, yet still sufficiently high, power levels of the illumination laser radiation 22, two exposure limits must be considered for pulsed illumination lasers 14: a peak exposure limit (PEL_peak, W / m²< ) for each individual illumination laser radiation pulse and an average exposure limit (PEL_average, W / m²< ) for the average power of a sequence of illumination laser radiation pulses. In general, the peak exposure limit (PEL_peak) for an illumination laser radiation pulse is significantly higher than the average exposure limit (PEL_average). This results in a low PEL_peak value for low pulse repetition frequencies.

[0035] In addition to the EGW_peak and EGW_average values, further parameters are taken into account when calculating NOHD, some of which are listed below without claiming to be exhaustive: Peak heart rate P_tip Average performance P_Mean = E_Pulse * f_rep Repetition rate f_rep (number of pulses per unit of time) Pulse energy E_Pulse (J) Divergence (radiation opening angle) (wheel) Peak Pulse Intensity (W / m²<) Intensity Pulse I_Medium (W / m²<) wavelength Lambda (m)

[0036] For active object observation and fine tracking, comparatively large areas are illuminated with illuminating laser radiation 22. Larger areas are, for example, those that appear at a viewing angle of, say, 2 mrad to 4 mrad when viewed from the aperture of the illuminating laser. Illuminating laser radiation 42 reflected from the target 38 or another object is detected by the effective laser telescope 26 and converted into electrical signals by the optical sensor 30, which is preferably a camera. These signals are then evaluated by the evaluation software 44 of the control unit 32. Overall, the laser radiation device 10 is configured to carry out a method according to the invention or to control its execution. This configuration is achieved, in particular, by appropriately programming the control unit 32.

[0037] Contrary to the representation of the Figure 1The illumination laser can also be arranged in a separate housing from the housing 12 of the working laser 13. The control unit 32 is then located, for example, in one of the two housings.

[0038] In a further embodiment, the housing 12 contains, in particular, the active laser telescope, and the active laser 13 is arranged outside the housing 12 of the active laser telescope. The active laser radiation is then preferably guided into the housing 12 by at least one optical fiber. Alternatively or additionally, illumination laser radiation is guided into the housing 12 by one or more optical fibers. It is also preferred that the illumination laser radiation and the active laser radiation are combined by an optical coupler and both propagate through the active laser telescope and are emitted through the same aperture.

[0039] Figure 2shows an embodiment of the first method according to the invention, with which the illumination laser is operated.

[0040] In this embodiment, which relates to a laser radiation device 10 comprising at least one illumination laser 14 and one working laser 13, the illumination laser 14 is operated in two different operating modes. In a first step 100, the illumination laser 14 is operated in a first operating mode of the laser radiation device 10. The first operating mode is characterized by the fact that the working laser 13 does not emit any working laser radiation. Operation is carried out with parameters of the illumination laser 14 that result in the lowest possible NOHD value while simultaneously maintaining sufficient power of the illumination laser radiation 22 for the illumination purpose.

[0041] In a second step 102, it is checked whether active laser radiation 20 is to be emitted. If this is not the case, the procedure returns to the first step 100. If, on the other hand, this is the case, the illumination laser 14 is operated in the second operating mode of the laser radiation device 10 in a third step. Active laser radiation 20 is also emitted in the second operating mode. The radiation power emitted with the active laser radiation 20 is generally so high that it significantly exceeds the exposure limits. In this case, compliance with exposure limits by the illumination laser 14 is therefore no longer relevant. Therefore, in the third step, and thus in the second operating mode, the illumination laser 14 is operated such that its illumination laser radiation 22 has a second illumination laser radiation power that is greater than the first illumination laser radiation power.With the higher illumination laser radiation power, the signal-to-noise ratio of the illumination laser radiation reflected from the object improves 42, which improves fine tracking.

[0042] The different illumination laser radiation powers in the two operating modes are preferably achieved by the illumination laser 14 emitting illumination laser radiation 22 in the form of illumination laser radiation pulses in the first operating mode and in the second operating mode, wherein the repetition frequency at which the illumination laser radiation pulses are emitted is lower in the first operating mode than in the second operating mode. The power of the individual illumination laser radiation pulses remains constant. Alternatively, the repetition frequency can also be maintained. In this case, the illumination laser operates with a lower single-pulse power in the first operating mode. Furthermore, hybrid forms are also possible in which both the single-pulse power and the repetition frequency differ from one operating mode to the other.From the third step 104, the procedure always returns to step 102, so that a cessation of the emission of active laser radiation triggers a return to the first operating mode.

[0043] Figure 3 Figure 1 shows an embodiment of another laser radiation device 50 according to the invention. The laser radiation device 50 differs from the laser radiation device 10 from Figure 10. Figure 1by an additional, second illumination laser beam path 54. In the first illumination laser beam path 52, propagating illumination laser radiation 22 emerges from a first illumination laser aperture 16 of the laser radiation device 50, and in the second illumination laser beam path 54, propagating illumination laser radiation 22 emerges from a second illumination laser aperture 56 of the laser radiation device 50, which is spatially separated from the first illumination laser aperture by a distance 58. This splits the illumination laser radiation 22.

[0044] The distance 58 between the illumination laser apertures 16, 56 is chosen such that the two illumination laser beam paths do not overlap within the minimum eye-safe distance NOHD defined by the exposure limits to be observed. The overlap of the two illumination laser beam paths only occurs at a distance from the apertures that is greater than a specified minimum distance NOHD for each of the two illumination laser beam paths 52, 54. The radiation powers propagating in the two illumination laser beam paths only add up in the overlap region 60.

[0045] The embodiment according to the Figure 3 Its device aspects are derived from the subject matter of Figure 1 by the additional second illumination laser 62 with its associated second illumination laser telescope 64. Otherwise, the description of the Figure 1 also for the Figure 3 .

[0046] In a preferred embodiment, the laser radiation device 50 is operated such that the laser radiation propagating in the illumination laser beam paths is fed into the illumination laser beam paths in the form of illumination laser radiation pulses, wherein the illumination laser radiation pulses are fed alternately into the first illumination laser beam path 52 and the second illumination laser beam path 54. The average intensities of the individual illumination laser radiations from the two illumination laser beam paths then add up on the illuminated object.

[0047] Figure 4Figure 2 shows an embodiment of a second method. This method is used to adjust the illumination laser power. In a first step 200, the distance to a target to be illuminated by the first illumination laser 14 and / or the second illumination laser 62 is measured using a distance measuring device 34 that is different from the illumination laser 14 and / or 62. The distance measuring device 34 is preferably a radar device, such as those also used for coarse tracking.

[0048] In a second step 202, the illumination laser power of the illumination laser 14 and / or 62 is determined as a function of the measured distance. Subsequently, in a third step 204, the target is illuminated by the illumination laser 14 and / or 62, which is operated such that it emits the determined illumination laser power. The procedure then returns to its first step 200. This three-step loop is continuously repeated, so that the illumination laser power is continuously adjusted to changing distances to the target 38. The illumination laser power is determined such that it decreases with decreasing distance.The illumination laser radiation power is determined in particular in such a way that the NOHD value is as small as possible while still maintaining sufficient intensity of the illumination laser radiation illuminating target 38.

[0049] Figure 5 Figure 400 shows a flowchart as an embodiment of the third method for setting the parameters of an illumination laser. In a first step 400, it is checked whether a target 38 is to be observed. If no target is to be observed, the check is repeated from time to time without any further steps of the methods described here being carried out. If, on the other hand, a target is to be observed, the distance between a target 38 to be illuminated by the illumination laser 14 and / or 62 and the illumination laser 14 and / or 62 is measured in the first step 400.

[0050] The measurement is preferably carried out with a distance measuring device 34 that differs from the illumination laser 14 and 62.. This includes, for example, a radar device.

[0051] In a second step 402, parameters of the illumination laser 14 and / or 62 are determined depending on the measured distance.

[0052] In a third step 404, at least one illumination laser radiation pulse directed towards the target 38 is emitted by the illumination laser 14 and / or 62, which is operated with the specified parameters. Based on the parameters of the illumination laser 14 and the first aperture 16, the NOHD value for this illumination laser radiation pulse with pulse energy E_Puls, or E_0, can be determined.

[0053] In a fourth step 406, a check is performed to see whether laser radiation of the emitted laser radiation pulse is reflected to the optical sensor 30 or another detector of the illumination laser 14 and / or 62.

[0054] If this is the case, in a fifth step 408 the distance of the object that reflected the laser pulse is determined as a function of the reflected and detected illumination laser radiation 42. Alternatively or additionally, the reflection is checked with an optical sensor 30, which may be designed as a camera, to see if it depicts a human face.

[0055] In a sixth step 410, the distance of the object from the illumination laser 14 and / or 62 is compared with the distance of the target 38 from the illumination laser 14 and / or 62. Then, if the distance of the object is less than the distance of the target, the parameters of the illumination laser 14 and / or 62 are changed in a seventh step 412 so that an exposure limit value (ELV) at the location of the object is not exceeded by the laser radiation from the illumination laser 14 and / or 62 incident there. The same applies if the reflection depicts a human face. The reflection with the shortest distance defines the permissible value for the NOHD for the average power P_average.

[0056] The change is achieved in one configuration by altering the average intensity of the laser radiation from the illumination laser.

[0057] This can be achieved, for example, by changing the laser radiation hitting the object by reducing the repetition rate of the illumination laser.

[0058] Given a pulse energy, the maximum permissible repetition rate for the illumination laser can now be determined according to the "Technical Rules for the Occupational Safety and Health Ordinance on Artificial Optical Radiation (TROS Laser Radiation)" (P_Mean = E_Puls * f_rep.). The procedure then returns to the third step 404.

[0059] If, however, in the sixth step 410 it is determined that no object is closer to the illumination laser 14 and / or 62 than the target 38, the procedure returns to the third step 404 without changing the illumination laser parameters.

[0060] If no reflex and therefore no target is detected in the fourth step 406, the procedure returns to the first step 400, in which it is checked whether a target 38 should be observed.

Claims

1. A method for operating a laser radiation device (10) that has an illumination laser (14) and an active laser (13), and wherein, in a first operating mode of the laser radiation device (10) in which the active laser (13) does not emit any active laser radiation (20), the illumination laser (14) is operated such that its illumination laser radiation (22) has a first illumination laser radiant flux, characterized in that, in a second operating mode of the laser radiation device (10) in which the active laser (13) emits active laser radiation (20), the illumination laser (14) is operated such that its illumination laser radiation (22) has a second illumination laser radiant flux that is greater than the first illumination laser radiant flux.

2. The method according to claim 1, wherein the illumination laser (14) is operated in the first operating mode and in the second operating mode such that it emits the illumination laser radiation (22) in the form of illumination laser radiation pulses, wherein a repetition frequency with which the illumination laser radiation pulses are emitted is less in the first operating mode than in the second operating mode.

3. The method according to any one of claims 1 or 2, wherein the laser radiation device (50) comprises a first illumination laser beam path (52) and a second illumination laser beam path (54), wherein the laser radiation device (50) is operated such that laser radiation (22) propagating in the first illumination laser beam path (52) exits from a first aperture (16) of the laser radiation device (50) and laser radiation (22) propagating in the second illumination laser beam path (54) exits from a second aperture (56) of the laser radiation device (50), which is spatially separated from the first aperture (16), and wherein the illumination laser beam paths (52, 54) overlap, wherein an overlap of the two illumination laser beam paths (52, 54) occurs only at a distance from the apertures (16, 56) that is greater than a predetermined minimum distance for each individual one of the two beam paths (52, 54).

4. The method according to claim 3, wherein the laser radiation device (50) is operated such that the laser radiation (22) propagating in the illumination laser beam paths (52, 54) is coupled into the illumination laser beam paths (52, 54) in the form of illumination laser radiation pulses, wherein the illumination laser radiation pulses are alternately coupled into the first illumination laser beam path (52) and into the second illumination laser beam path (54) from illumination laser radiation pulse to illumination laser radiation pulse.

5. A laser radiation device (10) comprising an illumination laser (14) and an active laser (13), wherein, in a first operating mode of the laser radiation device (10) in which the active laser (13) does not emit any active laser radiation (20), the illumination laser (14) is operable such that its illumination laser radiation (22) has a first illumination laser radiant flux, characterized in that in a second operating mode of the laser radiation device (10) in which the active laser (13) emits active laser radiation (20), the illumination laser (14) is operable such that its illumination laser radiation (22) has a second illumination laser radiant flux that is greater than the first illumination laser radiant flux.

6. The laser radiation device (10) according to claim 5, wherein the illumination laser (14) is operable in the first operating mode and in the second operating mode such that it emits the illumination laser radiation (22) in the form of illumination laser radiation pulses, wherein a repetition frequency with which the illumination laser radiation pulses are emitted is lower in the first operating mode than in the second operating mode.

7. The laser radiation device (50) according to claim 5 or 6, wherein the laser radiation device (50) comprises a first illumination laser beam path (52) and a second illumination laser beam path (54), wherein laser radiation (22) propagating in the first illumination laser beam path (52) exits from a first aperture (16) of the laser radiation device (50) and laser radiation (22) propagating in the second illumination laser beam path (54) exits from a second aperture (56) of the laser radiation device (50) that is spatially separated from the first aperture (16), and wherein the illumination laser beam paths (52, 54) overlap, wherein an overlap of the two illumination laser beam paths (52, 54) occurs only at a distance from the apertures (16, 56) that is greater than a predetermined minimum distance for each individual one of the two beam paths (52, 54).

8. The laser radiation device (50) according to claim 7, wherein the laser radiation device (50) is operated such that the laser radiation (22) propagating in the illumination laser beam paths (52, 54) is fed into the illumination laser beam paths (52, 54) in the form of illumination laser radiation pulses, wherein the illumination laser radiation pulses are fed alternately into the first illumination laser beam path (52) and the second illumination laser beam path (54) from one illumination laser radiation pulse to the next illumination laser radiation pulse.