DE10205310B4 - A method for generating the effect of a broadband incoherent LED-like light source and use of such a method in a gas measuring device and in a lighting device - Google Patents

Abstract

A method for generating the effect of a broadband incoherent LED-like light source by pulsed operation of a quantum cascade laser (7) without mode-selective structuring, in which the quantum cascade laser (7) operates with pulse packets (38) of individual very short pulses in the range of 1 ns to 200 ns with the pulse packets (38) being switched on and off at frequencies in the range of 1 Hz to 100 kHz.

Description

The The present invention relates to a method for producing the effect a broadband incoherent LED-like Light source, the use of such a method in a gas measuring device and the use of such a method in a lighting device.

The US 5 901 168 A describes quantum cascade lasers operating in multimode and pulsed mode. In the context of a quantum cascade laser with a distributed feed back structuring, a current ramp with a duration of 250 ms, pulses with a pulse width of 5 ms, a repetition rate of 500 Hz and a modulation signal are described. The resulting current ramp with the superimposed pulses and a sine wave is applied to the laser.

The DE 100 15 615 A1 shows a gas measuring system with an open optical measuring section for the spectroscopic measurement of at least one component of a gas sample with a laser source.

CAPASSO, F. u. a .: New Frontiers in Quantum Cascade Lasers and Applications, in: IEEE Journal of Selected Topics in Quantum Electronics, Vol. 6, no. 6, 2000, pp. 931-947, describes quantum cascade lasers and their applications. The described lasers be z. For example chemical determinations or used in spectroscopic applications.

laser devices with a quantum cascade laser are well known in the art known. In the market for infrared optical gas measuring instruments At present, mainly non-dispersive devices are offered. Usually broadband, thermal emitters used as infrared light sources. Radiation detection is preferably done with thermal detectors such as thermopiles, Pyrodetectors or with photoacoustic detection methods. The NDIR method (non-dispersed IR absorption) is general a spectral filtering of radiation necessary with interference filters, with micromechanical Fabry-Perot resonators or with gas filters can be realized. Limited to the performance data of these meters works On the one hand, the low modulating work of the thermal radiators out, so generally only with frequencies in the 10 to 100 Hz range can be modulated. Above all, the devices are physically but through the given, too low spectral power density of a Planck radiator limited.

With large spotlights you would though higher Achieve achievements, but these are not good on small Imaged detection elements.

One Another disadvantage of thermal radiators is that their radiation can be collimated only under significant performance losses and thus measurements over size Routes are feasible only with considerable effort.

at the cost-consuming, dispersive devices In general, thermal light sources are also used that many of the aforementioned disadvantages persist.

Laserspectroscopic Measuring methods are generally only for special applications and for highly sensitive Laboratory measurements used. This is partly due to the high Component prices and the highly sensitive and often maintenance-intensive measurement technology conditionally.

These Need procedure Lasers that only emit in one fashion. This type of lasers is but generally only through elaborate selection or additional To obtain structuring of the laser, such as by a "distributed feedback (DFB) -Structuring ". Thereby the cost of such a laser is increased.

Other compact light sources, such as IR LEDs or other non-thermal incoherent sources in the long-wave mid-infrared range (MIR) are not available.

The Development of new gas and liquid measuring instruments is currently ongoing towards the use of non-thermal light sources. Especially called quantum cascade lasers (QCL) used at room temperature operated a pulse-shaped Represent laser source with high power density.

The Development of new lighting devices, for example for motor vehicles, Ships or airplanes passes currently in the direction of the application of infrared light sources. infrared Light penetrates much better fog, leaving one with infrared sight and infrared lights equipped Motor vehicle, ship or plane in the fog much safer can be controlled, as with the usual equipment. meanwhile become passive infrared sensors and infrared camera systems in the automotive sector for collision avoidance with humans and animals on the roadway used. By an additional Infrared lighting would the security increases become.

The invention is therefore based on the object of specifying a method for generating the effect of a broadband incoherent LED-like light source, in which the average power spectral density is increased compared to previous methods. Furthermore, the use of a procedural be specified in a gas measuring device, so that faster and more sensitive measurements are possible with the gas measuring device. In addition, the use of a method in a lighting device should be specified so that the visibility in poor weather conditions, such. B. fog is increased.

These Task is with regard to the method for generating the effect a broadbandign incoherent LED-like Light source according to the invention solved by a method with the features of claim 1.

Regarding the use of a method in a gas measuring device is the task according to the invention the use of a method with the features of the claim 6 solved.

The Task is relative the use of a method in a lighting device according to the invention the use of a method having the features of claims 10 and 11 solved.

At the inventive method for generating the effect of a broadband incoherent LED light source by pulsed operation of a quantum cascade laser without modem-selective structuring becomes the quantum cascade laser with pulse packets of individual very operated short pulses in the range of 1 ms to 200 ms, the pulse packets switched on and off at frequencies ranging from 1 Hz to 100 Hz become.

From Advantage may be, if with the quantum cascade laser a heat dissipation device, the heat passively derived, is connected.

One Such method is inexpensive and the quantum cascade laser and the pulse generator have a compact Construction on. Therefore, it may be in a gas measuring device or a Lighting device can be used. As QCL, preferably Fabry-Perot laser or ridge laser used without mode-selective structuring.

With Such a method can many times higher average spectral power densities can be achieved than with available IR LEDs. With these high spectral power densities are thus faster and more sensitive infrared measuring devices possible. Here, the better collimability to thermal emitters can be exploited.

The Modulability in performance is without problems over the Operating current possible and better than with thermal emitters. Furthermore, such Laser device in an existing arrangement z. B. a headlight installed and operated from the 12 V / 24 V electrical system of a motor vehicle become.

From Advantage may be, if the frequency is variable. To this Way, the frequency according to the respective Requirement selected become.

Farther is it cheap if the pulse height and / or Pulse duration of a single pulse and / or the pulse intervals of Single pulses during the Pulspaketes and / or in different Pulse packets can be varied. This is a good match different work processes possible.

In an advantageous development of the invention may be the Quantum cascade laser in a preferably standardized, standard housing with at least one for the laser radiation permeable Wall section are located. This wall section can, for example from a partially IR (infrared) -permeable polymer (eg polyethylene) be formed. This gives a compact design and that Method can also be easily used in other devices, which reduces the costs.

From Advantage may be, if the housing with a gas such. B. Nitrogen or argon filled and is sealed. As a result, the quantum cascade laser, or the Construction technique (solder joints etc.) protected, which can be sensitive to oxidizing gases.

Cheap can be it when the for the laser radiation permeable Wall section has a Fresnel lens. This can cause the radiation be shaped according to the application. For example, this Fresnel lens by hot pressing a plastic material (eg polyethylene) may be formed.

Advantageous It may be when the Fresnel lens is segmented, since it then for light scattering, z. B. in a headlight, is suitable.

From It can also be an advantage if the heat dissipation device is located in the housing, because of this an effective heat dissipation and a compact design is given.

Farther it can be cheap be when the heat dissipation device designed as a passive cooling device is because it lowers costs

Furthermore, it may be beneficial if the radiation is coupled into an infrared optical fiber. This makes it possible to redirect the radiation Lich.

moreover it can be cheap when the distance between the quantum cascade laser and the lens variable is. Thereby can various possibilities the lighting can be realized. This change in distance For example, by an integrated electromagnetic in the housing Device, such. B. a pot coil or a piezoversteller, be achieved.

From Advantage may be when to generate the pulse trains a Voltage supply with a DC / DC conversion is used. Thereby is a universal use of the method, eg. B. in motor vehicles or planes possible. It can be z. B. the power supply from a 12 V or a 24 V electrical system of a motor vehicle can be used.

By the use of the method according to the invention in a gas meter is a faster and more sensitive Infrared measurement as with usual NDIR techniques possible.

moreover it can be cheap be when the gas measuring device for detecting the radiation is a cost having thermal detector, z. Thermopile, pyrodetector, microbolometer or photoacoustic detector.

Advantageous it may be when the quantum cascade laser and the detection unit are mounted on a common substrate, since this space requirements and also the costs are reduced. For example, by doing so Optics components are saved.

By the use of the method according to the invention in a lighting device is a good scene lighting possible.

It can be cheap be if another illumination device different from the method, is provided. This allows independent operation.

From It can also be an advantage if parts of the headlight are visible and infrared light are usable. This saves components and further reduced costs.

In a method which is not the subject of the present invention is, for detecting light from a lighting device, in the inventive method is used, for detection, an infrared receiver system used. This is a further processing of the of the lighting device emitted infrared light possible.

From It may also be an advantage if the infrared receiver system has a thermal imaging device thereby an image of the illuminated by the lighting device Area is shown. The infrared receiver system can also be off discrete independent Infrared sensors exist.

advantageous Further developments are the subject of the respective subclaims.

The Invention will be described below with reference to an embodiment and associated drawings explained in more detail.

These demonstrate:

1 a quantum cascade laser in a housing which is not the subject of the present invention;

2 the activation of a quantum cascade laser LED;

3 a schematic representation of a lighting device with a quantum cascade laser and a conventional lighting device;

4 a schematic representation of the laser device for measurements over long distances;

5 a schematic representation of the laser device for short measuring sections and large detectors;

6 a schematic structure of a measuring system with pulsed quantum cascade laser, a gas cuvette and a detector;

7 a representation of the pulse packets.

A laser device with a pulsed quantum cascade laser 7 how they z. B. in a gas measuring device 15 or a lighting device 16 can be used by 1 explained in more detail. In the method according to the invention, the effect of a broadband incoherent LED-like light source (hereinafter referred to as quantum cascade laser-LED) is generated by pulsed operation of the quantum cascade laser without mode-selective structuring. The laser device is a quantum cascade laser LED 1 ,

The laser device has a quantum cascade laser 7 which is operable with pulse packets switched at frequencies in the range of 1 Hz to 100 kHz. Because the quantum cascade laser 7 No special cooling required, he can have a heat dissipation device 8th , z. B. one passive heat sink, by means of a fastening device 20 to a housing 4 be coupled, which then z. B. is cooled by an air cooling. The attachment takes place at the back of the housing 23 , The quantum cascade laser 7 , the heat dissipation device 8th and the fastening device 20 are located in the housing 4 , The housing 4 is usually a standard, stan dardmäßiges housing. The quantum cascade lasers used are preferably Fabry-Perot lasers or ridge lasers without mode-selective structuring.

The front of the case 22 has a wall portion permeable to the laser radiation 6 on, in a radiation-side housing opening 18 is appropriate. The wall section 6 can z. B. from a partially IR-transparent polymer such. For example, be formed polyethylene.

Because the quantum cascade laser 7 or the construction technique (solder joints, etc.) can react sensitively to oxidizing gases, the housing 4 for example, with dry nitrogen 5 or another gas 5 , z. As argon, filled and sealed.

For beam shaping is in the radiation-side housing opening 18 on the front of the housing 22 a lens 6 , preferably a Fresnel lens 6 used. By a segmented design of the Fresnel lens 6 a "light fan" as vehicle headlights can be realized. The Fresnel lens 6 For example, by hot pressing of a plastic material such. As polyethylene, be formed.

At the back of the case 23 are several housing feedthroughs 17 appropriate. Through the housing passage 2 becomes a negative contact 21 in the case 4 introduced and with the quantum cascade laser 7 connected. Through the housing passage 3 becomes a positive contact via the heat dissipation device 8th and the holder 2 in the case 4 brought in. Through the other housing bushings 17 If necessary, further contacts, eg. As temperature sensor, introduced into the housing or the gas 5 be replaced. Furthermore, there are bushings 17 for an active heat dissipation device, such. B. a Peltier cooler or for a distance control between quantum cascade laser 7 and the quantum cascade laser 7 facing side 19 the Fresnel lenses, such as. B. a piezoversteller provided.

In 2 is the control of the quantum cascade laser LED 1 shown. From a pulse generator 9 are used to operate the quantum cascade laser LED 1 Pulse trains emitted from individual pulses in the range of 1 ns to 200 ns. The fast pulse sequences are switched on and off with a frequency in the 1 Hz to 100 kHz range, so that the quantum cascade laser LED 1 how a current-modulated LED behaves. The duty ratio between the fast pulse sequences and the time-outs is chosen so that the quantum cascade laser 7 thermally relaxed during the timeout to the initial temperature value.

Between the pulse generator 9 and the quantum cascade LED 1 there is a circuit breaker 10 , with which the forwarding of the pulse trains from the Pulserzeuger 9 to the quantum cascade laser LED 1 can be switched on or off or controlled.

The use of a voltage supply, not shown, with a DC / DC conversion for generating the pulse trains is favorable, since thereby the quantum cascade laser LED 1 is universally applicable.

Thereby, that a 12-volt or a 24-volt electrical system is used for the power supply can, is an insert z. B. in a motor vehicle.

In 3 is a pig launcher 16 with a quantum cascade laser LED 1 and a conventional lighting device 33 shown schematically.

In a spotlight housing 34 There is a quantum cascade laser LED 1 and another of the quantum cascade laser LED 1 different lighting device 33 , This may be, for example, a glow-emitting luminaire, a halogen lamp or a gas discharge lamp.

The two lighting devices 1 and 33 are behind a common headlight cover 35 appropriate.

For the scene illumination, the distance d of the quantum cascade laser 7 from the side facing the quantum cascade laser 19 the Fresnel lens 6 smaller than the lens focal length, creating a divergent beam 11 is produced. By segmented design of the Fresnel lens 6 a "light fan" as vehicle headlights can be realized. In that parts of the headlight 16 such as As an unillustrated reflector or the Schweinwerferabdeckung 35 can be used for both visible and infrared light, such a headlight 16 be made easily and inexpensively.

For the detection of infrared light, the z. B. from a lighting device, as in 3 described, an infrared receiver system can be used, the z. B. a heat has mebildgerät. Furthermore, also infrared detectors 14 on the basis of thermopiles, solometers or pyrodetectors as well as a phase-synchronous detection method conceivable. The infrared receiver system can also consist of discrete, independent infrared sensors. With such a system z. B. in fog the view of a motor vehicle driver can be significantly improved. Such a system thus contributes significantly to the increase in safety.

By changing the distance d between the quantum cascade lasers 7 and the side facing the quantum cascade laser 19 the lens 6 can the shape of the beam 11 to be changed. The change of the distance d can z. B. by a change in the size of the heat dissipation device 8th be made. The change in the distance d can also be achieved, for example, by a piezo-converter or an electromagnetic device (pot coil) integrated in the housing.

In 4 is a quantum cascade laser LED 1 schematically shown for measurements over long distances. To measure over long distances, the beam must 11 be collimated. This is the distance d of the quantum cascade laser 7 from the Fresnel lens 6 equal to the lens focal length selected.

In 5 is a quantum cascade laser LED 1 for a direct image of the beam 11 shown on a large, not shown detector. For short measuring distances and large detectors (eg Pyrodetektoren) the beam 11 directly through the Fresnel lens 6 again on a focus 12 be focused by the distance d of the quantum cascade laser 7 from the side facing the quantum cascade laser 19 the Fresnel lens 6 greater than the lens focal length is selected.

In 6 is the schematic structure of a gas measuring device 15 with a quantum cascade laser LED 1 , a gas cuvette 13 and a detector 14 shown. The gas cuvette 13 has a gas cuvette housing 24 , a side wall for light entry 25 through which the quantum cascade laser 7 emitted beam 11 in the gas cuvette interior 27 can enter and a side wall for light emission 26 on, through which the beam 11 again from the gas cell interior 27 can escape. The gas cuvette interior 27 is filled with gas. Alternatively, the gas cell interior 27 also be filled with a liquid. Then the gas measuring device 15 also be used as a liquid measuring device.

The detector 14 has a detector housing 28 and a sensor 29 by means of a sensor holder 30 at the back of the detector 36 is attached, on. The sensor 29 and the sensor holder 30 are located in the detector housing 28 , The detector housing 28 has a radiation entrance opening 31 on the front of the detector 37 on, through which the beam 11 into the detector 14 can occur. At the back of the detector 36 are housing bushings 32 arranged by the z. B. lines not shown in the detector housing 28 can be introduced.

It is conceivable that the gas measuring device 15 to detect the radiation 11 a thermal detector 14 having. Such detectors 14 are cheap and well suited for the detection of infrared light.

It is also conceivable that the quantum cascade laser 7 and the detector unit 14 are mounted on a common substrate. This allows a compact design of the gas measuring device 15 achieved and optical components can be saved.

Especially with a gas measuring device 15 It may be beneficial if the quantum cascade laser 7 outgoing radiation 11 is coupled in an unillustrated infrared optical fiber. This can cause the radiation 11 of the quantum cascade laser 7 be redirected and the arrangement of the gas cell 13 be made according to the respective requirements of the measurement.

In 7 are the pulse packets 38 shown as a function of time. The switching frequency 1 / time does not necessarily have to be constant. For lighting purposes, eg. As in vehicles, it may be advantageous to a "sleep" mode with relatively low switching frequency, z. B. 10 Hz, to have. When observing an interesting object with an IR camera, the switching frequency can be increased to ensure better capture of moving objects or to achieve brighter illumination.

Also in the gas sensor, it may be advantageous if the switching frequency is not constant. At a low gas concentration, a relatively small switching frequency suffice. In a sudden Increase in gas concentration over a certain threshold, the switching frequency can be increased, to quickly detect the increased gas concentration to ensure.

Likewise, the in 7 shown pulse height of a single pulse 39 can not remain constant, but can during the Pulspaketes 38 or by Pulspaket 38 to pulse package 38 be varied. This also applies to the pulse duration and the distances of individual pulses. This allows a good adaptation to different applications. In 7 is the laser drive signal, z. As operating voltage at the laser (volts) or operating current (ampere), plotted on the ordinate.

With the quantum cascade laser LED 1 average power spectral densities of> 1 mW / (mm ² · sr · μm) can be achieved. This is many times higher than with available IR LEDs, which are only available in a wavelength range of 3 to 5 μm. This is also many times higher than can be achieved with thermal emitters.

Another advantage of the invention is that gas measuring devices 15 can be realized with significantly better properties than before. This also applies to liquid measuring devices. Next, the cost of the control and detection electronics compared to the laser spectroscopic measuring systems is reduced, so that there are significant cost advantages. This allows laser-based systems to compete for the first time with non-dispersive infrared measuring devices without giving up important advantages of laser measuring technology.

With these high spectral power densities are thus faster and more sensitive infrared measuring devices with compact but specific and highly sensitive sensors, in the production and process measuring technology, in the automotive sector, used in safety technology and in climate and environmental sensors can be possible. in this connection can also exploit the better collimability to thermal emitters become.

The inventive method can also be used for scene lighting in the infrared. Infrared light in the spectral range between 8 and 12 microns penetrates much better fog, so that equipped with infrared and infrared infrared device motor vehicle, ship or aircraft can be controlled much safer in the fog, as with the usual equipment. The lighting device according to the invention 16 provides additional security over previous passive infrared sensors. Additional infrared lighting enhances the detection safety of people and animals on the road and results in a reduction of malfunctions. For stationary use, the function of infrared detectors, such. B. of motion detectors, the object protection can be improved by an additional infrared lighting.

The inventive method is an ideal light source for the aforementioned applications. It can be used in existing lighting equipment, such. B. headlights 16 , can be integrated and can be operated via the usual 12 V / 24 V vehicle electrical system. The spectral range is also adapted to the range of natural emission of objects near room temperature (10 μm), so that the same detection systems as for passive detection can be used.

In automotive applications, the blendedness of using such additional light sources is an important issue. The highly polarized beam 11 a quantum cascade laser LED 1 can be blocked in direct reflex by suitable polarization filters in front of the corresponding IR sensors. The radiation is narrow band, so that suitable filters can be used in front of broadband receivers. Above all, however, the good modulability of the quantum cascade laser LED 1 Phase-synchronous lockin detection is possible up to the 100 kHz range. Thus, stray and glare of another vehicle can be effectively suppressed.

A sensitive measurement method, such as the Lockin method, for scene analysis is only possible because the modulability in performance is possible without problems over the operating current and better than with thermal emitters. The modulability is only due to the heat balance of the quantum cascade laser 7 limited.

For scene analysis, a low duty cycle <1% (ie pulse train on / off duty cycle) can be used. Thus, the thermal load of the component is low, so that this in existing arrangements, such. B. a headlight 16 , can be installed.

Claims (13)

Method for generating the effect of a broadband incoherent LED-like light source by pulsed operation of a quantum cascade laser ( 7 ) without mode-selective structuring, in which the quantum cascade laser ( 7 ) with pulse packets ( 38 ) is operated from individual very short pulses in the range from 1 ns to 200 ns, the pulse packets ( 38 ) with frequencies in the range of 1 Hz to 100 kHz on and off. Method according to claim 1, characterized in that that to generate the pulse trains a power supply with a DC / DC conversion is used. Method according to claim 2, characterized in that that the power supply from the electrical system of a motor vehicle, in particular a 12 V or 24 V electrical system is used. Method according to at least one of the preceding claims 1 to 3, characterized in that the frequency with which the pulse packets ( 38 ) be switched on and off, is variable. Method according to at least one of the preceding claims 1 to 4, characterized in that the pulse height and / or pulse duration of the individual pulse ( 39 ) and / or the pulse intervals of individual pulses ( 39 ) in the course of the pulse packet ( 38 ) and / or in different pulse packets ( 38 ) can be varied. Use of a method according to one of claims 1 to 5 in a gas measuring device. Use of a method according to claim 6, characterized in that the gas measuring device ( 15 ) a gas cuvette ( 13 ) having. Use of a method according to claim 6 or 7, characterized in that the gas measuring device ( 15 ) for detecting the radiation, a thermal detector ( 14 ) having. Use of a method according to at least one of the preceding claims 6 to 8, characterized in that the quantum cascade laser ( 7 ) and the detection unit ( 14 ) are mounted on a common substrate. Use of a method according to one of the preceding claims 1 to 5 in a lighting device. Use of a method according to one of claims 1 to 5 in a lighting device, in particular a headlight ( 16 ), characterized in that another illumination device (other than the quantum cascade laser) ( 33 ) is provided. Use of a method according to claim 11, characterized in that the different from the quantum cascade laser illumination device ( 33 ) has a Glühemissionsleuchtkörper, a halogen lamp or a gas discharge lamp. Use of a method according to claim 11 or 12, characterized in that parts of the headlight ( 16 ) are usable for visible and infrared light.