applications Defence
readily available. It works in a very similar way to a CO2
laser; the problem of heat build-up in the gain medium is simply removed by taking some big pumps and bringing new [cooler] medium into the resonator. The only remaining problem to solve is that of the small line-width pumping source,’ he adds, explaining that optical pumping of DPALs requires a high-specification excitation. ‘We’re developing some new diodes to supply that small line-width pumping.’
The wavelengths used for pumping DPAL gas lasers, Neukum explains, are 766, 852, or 780nm. ‘The first thing we have to do is to make special wafers for these wavelengths – they’re not in a range that industrial customers ask for very often. The next step is to apply a line-narrowing technique; we add a virtual Bragg grating onto the outside of the diodes. This VBG is a grating that selects one particular line, which is subsequently amplified.’
Getting a stable wavelength from a laser diode usually needs careful control of both temperature and drive current, but when using these virtual Bragg grating-equipped diodes, Neukum explains, a degree of wavelength control happens outside of the diode itself, and so the requirements on other parameters are less rigidly prescribed. ‘The nice thing about this VBG diode is that the wavelength is locked, and the line-width is very small. For applications in which you need a very stable line-width, you don’t necessarily need to have a very stable temperature.’ Currently, this technology is still being developed in the company’s labs, although customers are beginning to build their first demonstrator systems at the few- hundred Watt level.
Blowing a missile out of the sky is one way of using lasers to protect a target, but advanced guided missiles can be dissuaded without being
destroyed. According to Neukum, the use of laser diodes in infrared countermeasures (or IRCMs) is significant. In these applications a 1.8-2µm wavelength is used to disrupt and dazzle the sensors on a surface-to-air missile, preventing it from homing in on its target aircraft. In these applications, he says, the diodes are used directly, without an additional gain medium.
technology convergence in the home and barracks Petteri Uusimaa is president and CEO of Modulight (Tampere, Finland), which produces high power IR diode lasers for many applications, including use in laser range-finders. ‘This technology used to be limited to use by defence and military customers, but it has now found its way into many consumer applications,’ he says. ‘Sports rangefinders are used in hunting, sailing, golf, and other areas. This demand has significantly influenced our production, because the quantities needed for kinds of consumer activities are significantly higher than those required by defence customers.’ As with most manufactured goods, higher quantities lead
these days, handheld
thermal imaging is available to any armed force
to lower unit costs. ‘We’ve been working for the last two years to ramp up the quantities of these devices we produce, while also lowering costs,’ he says. Military customers, however, demand more than a simple sporting rangefinder. UK photonics distributor Armstrong Optical now markets its IR513 multi-function thermal imager, which combines both visible and thermal-
as the cost of technology falls, handheld thermal imaging such as this is a possibility for every soldier on the battlefield
band infrared imaging with a laser rangefinder, a digital compass, GPS, altitude sensor and RS 232 read-out. As well as telling the user the range of a target, the device will give its location and bearing – even in conditions of total darkness. The device is produced in China, and is already in use by the PRC’s armed forces. ‘It’s typical of the kind of devices that are appearing on the marketplace at the moment,’ says Ian Johnstone, sales and marketing director at Armstrong Optical. ‘Rather than having a separate laser rangefinder, target locator, thermal imager and viewing system, it’s all built into one box. The user could be sat on a hilltop, looking at the target 5km away, and he or she would be able to call in the coordinates of the target to an attacking force, day or night.’ Devices such as these are becoming more
readily available, as the costs of the components fall. ‘These days,’ says Johnstone, ‘handheld thermal imaging is available to any armed force. Around 25 years ago, however, every thermal imaging device would have been based on a cooled detector – maybe only a few pixels that were opto-mechanically scanned across a field of view. Uncooled detectors came onto the market about 15 years ago, and they’re now approaching a price level low enough to make them available to the
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