Application Analysis of Near-Infrared-Illuminators Using Diode Laser Light Sources
We describe a new class of eye safe near infrared (~810 nm) illuminators based on diode laser sources. These illuminators are the most efficient available by a large margin. We show examples of how the high output allowed by lasers can be used to illuminate very large areas and improve images in difficult lighting situations. We also show examples of how the narrow spectral band of laser light can be used with filtered cameras to achieve unique results in applications such as facial recognition in open daylight. Application data on effective ranges and other factors are presented. Comparisons are made with other lighting systems such as arc lamps, tungsten lamps and light emitting diodes. We also compare results of systems that operate without supplemental light such as intensifi ed cameras and thermal infrared cameras.
Recently a revolutionary new technology has become available for applications in security and surveillance systems. The technology is derived from diode laser-based near infrared (NIR) illuminators developed for automotive night vision systems—primarily at Ford Motor Company. These systems make use of proprietary optical concepts that allow high power (20 watts or more) diode lasers to be used with complete safety in illumination devices. The characteristics of diode lasers allow performance features achievable in no other way, as will be shown in this paper. We describe the basic concepts of these illuminators, their unique features and illustrations of their applications.
Diode lasers are attractive light sources for security applications because of several unique features. Diode lasers are the most effi cient light sources known. Efficiencies of 60% or more have been demonstrated and more gains are coming. The compact size of the source allows very effi cient optics. High effi ciency translates into lower heat loads and thus allows more power to be delivered in compact units. Of course high effi ciency results in less power consumption, which is important self powered systems. Typical laser power used in our units is in the range of fi ve to forty watts. Diode lasers emit light in a very narrow wavelength band—typically about one or two nanometers wide. This is very useful when one wants to reject light from high ambient lighting or bright sources in the fi eld of view. Our systems can use light over a wide range of wavelengths. Typically we use light in the 800–900 nanometer range. These wavelengths are compatible with commonly available CCD and CMOS cameras.
Diode lasers can be modulated extremely rapidly to facilitate strobe effects. This can be useful if rapidly moving objects are being observed.
A typical illuminator system consists of one or more diode lasers, a power supply, an optical system that provides an eye safe beam and a tamper proof enclosure. The optical system in the types we are discussing makes use of a class of optics termed sheet optics.
To read the complete white paper visit, www.electrophysics.com (PDF).