The above-identified co-pending application is directed to a portable solid state light emitting device employing light emitting diodes (LEDs) and laser diodes (LDs). The device disclosed in that application is an infrared zoom illuminator capable of providing either a narrowly focused beam of infrared light energy from the light source or for illuminating a relatively large area, depending upon the manner of operation of the focusing element in the device. Since the light emitted from the infrared light source is not visible to the naked eye, a person who is not wearing infrared night vision equipment cannot determine whether the device is operating. Provisions may be made to provide an on/off indicator light on the device which emits light in the visible wavelength range. This still, however, does not satisfactorily tell an operator if the infrared laser light source is burned out or otherwise inoperative.
Even though the infrared light is invisible, there is a strong temptation on the part of some users of such devices to turn them around and look into them to see if the device is on or off. The intensity of laser light in the infrared region produced by devices of the type disclosed in the above-identified co-pending application, or by other laser light sources, is such that even a momentary exposure of the eye to such light may cause irreparable damage to the retain resulting in partial or total, permanent blindness. Consequently, such laser light sources typically are provided with warning labels on them to warn users never to look into the light source or to point the device at someone who is in near proximity to it. Even so, a substantial danger of accidental blinding still exists.
The above-noted dangers are described in safety manuals given to operators of such devices. A great danger for permanent eye damage from devices of the type disclosed in the above-identified co-pending application occurs in what is known as Class III laser beam intrusion. Class IV devices are also a source of danger. Typically, this is for intrusion in the zero to ten inch range (or slightly beyond). By intrusion, it is meant that an object (such as the eye of the operator of the device) is placed within the emitted beam of laser light at a distance which is equal to or less than the intrusion distance. For Class III beam intrusion, this "danger zone" range is a maximum of ten inches, obviously extending down to zero inches.
Consequently, it is desirable to provide a safety shutoff system to turn off the laser light source automatically if any one or anything intrudes into the laser beam within the danger zone distance.