Background of the invention Field of the invention The invention relates to an IR laser pointer comprising an IR laser diode, a power source for providing electric current, and an energizing circuit for applying electric current from said battery to said IR laser diode for causing the laser diode to emit light.

An IR laser pointer is used in order to mark an object that is observed through a night vision viewer, the light spot generated by the IR laser pointer being superimposed on the object.

Description of the Prior Art If the light spot generated by an IR laser pointer is too intense in relation to the ambient IR light existing in the field of view of a night vision viewer, the object on which the light spot is superimposed will be heavily lightened up so that the person looking through the night vision viewer will be blinded by the bright light emitted by the lightened up object. As far as IR laser pointers are concerned there is accordingly a need of the possibility to vary the intensity of the IR light spot generated by the pointer but existing laser pointers in general, including IR laser pointers, have a fixed light intensity. The need of being able to control the light intensity of the light spot generated by the pointer seems to be specific for IR laser pointers but so far no proposals in that direction have been presented. This may be due to the fact that the simplest way of varying the intensity of the light spot

generated by a laser diode, viz. by altering the drive current of the laser diode introduces a complication due to the laser light-current characteristic. There is a threshold current below which the laser diode does not lase. Therefore, control of the output power of the laser diode by control of the drive current in the manner applied e. g. with an LED is difficult particularly for low output power. This is because the threshold current varies from one laser diode to the other and is also temperature dependent.

Brief Summary of the Invention A primary object of the present invention is to provide an IR laser pointer of the kind referred to above wherein the light intensity of the light spot generated by the IR laser diode can be safely controlled, and for this purpose the IR laser pointer of the invention according to claim 1 is characterized in that the energizing circuit is operable to apply a pulsating electric current from said battery to said IR laser diode for causing the laser diode to emit pulses of light, and that control means are provided for adjusting the intensity of the light spot generated by the IR laser diode by pulse width modulation of the pulsating electric current.

Further advantageous features of the invention are defined in the dependent claim.

Brief Description of the Drawing In order to explain the invention in more detail an illustrative embodiment thereof will be described below with reference to the accompanying drawing in which FIG 1 is a side view of an IR laser pointer, and

FIG 2 is a block diagram of a complete electronics configuration for driving the laser diode of the IR laser pointer and varying the intensity of the light spot via pulse width modulation.

Detailed Description of the Invention According to FIG 1 the IR laser pointer of the invention can be of a conventional mechanical design comprising a cylindrical housing 10 enclosing an exchangeable battery and an electronic drive circuitry and having at one end of the housing an optical system 11 for emitting the IR light generated by the IR laser diode as a beam.

With reference to FIG 2 the IR (or near-IR) laser diode 12 is energised via an electronic laser diode driver circuitry 13 by a battery 14.

A representative IR laser diode for use in the laser pointer of the invention is Sony SLD234VL generating an optical output power of 50 mW at a forward current of 70 mA and a forward voltage of 2.0 V. The wave length of the light from the IR diode is 785 nm. Another suitable IR diode is Lasermate Corporation LD808-5I generating an optical output power of 5 mW at a forward current of 25 mA and a forward voltage of 2.4 V. The wave length of the light from the latter IR diode is 808 nm. A suitable battery for use in the laser pointer of the invention is a lithium cell DL1/3N having a capacity of 160 mAh.

The IR laser diode 12 is driven with pulses from a programmable pulse generator 15 powered from the battery 14 via the laser diode driver power control 13. The brightness of the IR laser diode and thus the intensity of the light spot generated by the diode and emitted through the optical system 11 is controlled by controlling the output power of the IR laser diode by means of pulse width modulation. The

user sets the desired spot brightness using a multi- position switch 16 which controls an oscillator 17 connected to the pulse generator 15 the operating member 18 of the switch being available on the outside of the housing 10.

Preferably, in the circuit described means are provided to compensate for the change in laser diode characteristics with temperature. One possible way of achieving this is to incorporate a thermistor into the circuit in series with the laser diode to provide a compensation in the current as the temperature changes.

Another method of controlling the power output of the IR diode is to use a photo diode which could be built into the capsule of the IR diode.