This application is the national phase under 35 U.S.C.§371 of PCT/IB2007/000994 filed Apr. 17, 2007, which claims priority to Great Britain Application No. 0607655.8 filed Apr. 18, 2006, the subject matter of both is incorporated herein by reference in its entirety.
This invention relates to apparatus for use in operator training with, and the testing and evaluation of, infrared sensors for missile detection. More especially, this invention relates to apparatus for use in the testing and evaluation of infrared sensors which are for missile detection and which integrate incident energy over a finite time period.
Apparatus is known for use in operator training with, and the testing and evaluation of, infrared sensors for missile detection. The known apparatus comprises an infrared illumination source for illuminating the sensors. The infrared illumination source may be a lamp such for example as a xenon arc lamp or a quartz halogen lamp. Alternatively, the infrared illumination source may be thin filaments of carbon or a metal. The apparatus tests and evaluates the infrared missile detection sensors by illuminating them. The infrared missile detection sensors may be positioned on, for example, an aircraft.
In the above mentioned known apparatus, the use of infrared illumination sources such for example as the lamps or the thin filaments has proved to be a limiting factor in the generation of high powers in the mid-infrared wavelength range of 3-5 μm. More specifically, problems associated with the known apparatus using the lamps or the thin filaments are as follows.
It is an aim of the present invention to reduce the above mentioned problems.
Accordingly, in one non-limiting embodiment of the present invention there is provided apparatus for use in operator training with, and the testing and evaluation of, missile detection systems which use infrared sensors which integrate incident energy over a finite time period, which apparatus comprises at least one infrared illumination source for illuminating the sensors, characterised in that the infrared illumination source is a pseudo continuous wave laser infrared illumination source with signal duty and peak power controlled by means of an amplitude, pulse width and pulse repetition interval modulation circuit, whereby the laser infrared illumination source operates at shorter repetition intervals than the finite time period so that the laser infrared illumination source appears to the infrared sensors to be a real missile signature.
The apparatus of present invention is advantageous over known apparatus in that it uses a pseudo continuous wave laser infrared illumination source. The advantages of the pseudo continuous wave laser infrared illumination source as compared with known infrared illumination sources such as those mentioned above are as follows.
In a first embodiment of the present invention, the apparatus is one in which the pseudo continuous wave laser infrared illumination source is an optical parametric oscillator which is pumped by a laser.
The pump laser may be an yttrium aluminium garnet (YAG) laser. Other types of laser may be employed. A single optical parametric oscillator is able to give sufficient power in the apparatus of the present invention.
The modulation circuit may comprise an acousto-optic modulator. The acousto-optic modulator is preferably positioned before the optical parametric oscillator. Such positioning allows the use of common, high-efficiency, low-cost modulators as opposed to the customised, low-efficiency modulators that would be required for the longer wavelengths at the optical parametric oscillator output. Preferably the optical parametric oscillator is a periodically poled lithium niobate crystal but other optical parametric oscillators may be employed.
In the first embodiment of the apparatus of the invention, the pseudo continuous wave laser infrared illumination source may include at least one mirror for separating unwanted wavelength signals, at least one mirror for creating a cavity for the optical parametric oscillator, at least one lens for focusing the laser beam into the optical parametric oscillator, and at least one beam sink for unwanted wavelengths.
Preferably, there are two of the mirrors for separating unwanted wavelengths. Preferably there are two of the mirrors for creating a cavity for the optical parametric oscillator. Preferably there are two of the beam sinks for unwanted wavelengths.
The laser may include an optical unit for shaping the beam in order to set the required beam divergence and output aperture size. The optical unit may be a faceted optical unit. Preferably, the faceted optical unit is a faceted mirror unit.
The faceted mirror unit preferably comprises a diverging lens, a reflector, and a faceted compound mirror for receiving reflected infrared energy from the reflector. The faceted mirror unit preferably also includes a window to seal the apparatus against environmental effects.
In a second embodiment of the present invention, the apparatus is one in which the pseudo continuous wave laser infrared illumination source is a quantum cascade laser.
Usually, there will be an array of the quantum cascade lasers, for ensuring that there is sufficient power for their use in the apparatus of the invention. In addition, because of the slight variation in the spectral response between individual quantum cascade lasers, an array of lasers will ensure a greater spectral diversity should that be required for a particular application.
In the second embodiment of the invention, the apparatus may include collimating means for collimating the laser beam.
The apparatus may be one in which the array of quantum cascade lasers is an array of quantum cascade laser chips, and in which the collimating means comprises at least one collimating lens for each one of the quantum cascade laser chips. The collimating means may also comprise at least one faceted optical unit for increasing size of the output aperture.
Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:
Referring to
The modulation circuit comprises an acousto-optic modulator 8 for modulating and controlling a laser beam 10 in order to create a precise temporal output profile for the laser beam 10. As shown in
The laser head contains a laser source, a power supply and other necessary laser component parts.
The apparatus 2 includes two mirrors 12, 14 for separating unwanted wavelength signals, and two mirrors 16, 18 forming a meniscus to create a cavity for the optical parametric oscillator 4. A lens 20 focuses the laser beam 10 into the optical parametric oscillator 4. Beam sinks 22, 24 are provided for unwanted wavelengths. A faceted optical unit 26 is provided for shaping the beam 25 into beam 28 in order to set the required divergence and aperture size.
As shown in
In operation of the faceted optical unit 26 shown in
Referring now to
The number of the quantum cascade lasers 42 employed in the array 40 is dictated by the power required from the apparatus 38. Low power applications may require as few as one laser. In low power applications the laser beam 52 aperture may be increased and the beam shaped using one or more faceted optical units such as described in
In the apparatus 38, modulation is achieved by means of modulation drive circuits 53. Each quantum cascade laser 42 has a modulation drive circuit 53 that controls pulse width, pulse repetition interval and pulse amplitude. The quantum cascade lasers 42 are capable of very high pulse repetition frequencies. Such operating frequencies are much faster than the time constant of infrared sensors for missile detection, creating a pseudo-continuous wave beam that the sensors determine to be a realistic threat. The use of the three modulation parameters in combination maximizes the dynamic range of the system. Further, the use of duty modulation to control output power provides a near-linear and repeatable control function so that the apparatus 38 produces a more accurate and reproducible source than is achievable with known apparatus comprising an infrared illumination source for illuminating the sensors. The relatively low individual power from the quantum cascade lasers 42 means that the array 40 is required for demanding applications, and the array 40 may be in the order of tens of the quantum cascade lasers 42. The use of the array 40 means that pulses from individual channels can be interleaved, thereby reducing the pulse repetition frequency requirements of each channel by a factor proportional to the number of quantum cascade lasers 42 in the array 40. Consequently, an increase in array size may provide further improvements to the overall system dynamic range.
Atmospheric effects can influence the quality and performance of a laser based system through the process of scintillation. The risk of these effects is addressed by the apparatus 38 shown in
It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected.
Number | Date | Country | Kind |
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0607655.8 | Apr 2006 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2007/000994 | 4/17/2007 | WO | 00 | 3/3/2009 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2007/119163 | 10/25/2007 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4173777 | Richmond et al. | Nov 1979 | A |
4607849 | Smith et al. | Aug 1986 | A |
5693951 | Strong, III | Dec 1997 | A |
5756992 | Spindler | May 1998 | A |
6587486 | Sepp et al. | Jul 2003 | B1 |
20030174315 | Byren et al. | Sep 2003 | A1 |
20060027823 | Hill et al. | Feb 2006 | A1 |
Number | Date | Country |
---|---|---|
3238897 | Apr 1984 | DE |
3238987 | Apr 1984 | DE |
2 330 449 | Apr 1999 | GB |
2 400 644 | Oct 2004 | GB |
WO 9500813 | Jan 1995 | WO |
WO-9722230 | Jun 1997 | WO |
WO-03062773 | Jul 2003 | WO |
Number | Date | Country | |
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20090194697 A1 | Aug 2009 | US |