rangefinders are used to measure the distance from the rangefinder to the
reflecting surface. There are different models with different specifications
for measuring distances from a few meters to tens of kilometers. Recently,
there are those who rotate 360 degrees and build a 3D map of an object. In
general, however, everyone uses a single principle of operation.
A short focused light pulse
with a suitable wavelength and a receiver that is optically focused at the
same point are sent from a laser emitter. The beam fired by the laser
emitter moves at the speed of light reflected into the target and the echo
is received by the receiver. Recently, pulsed infrared laser diodes with a
wavelength of 905nm have been widely used as a transmitter, and avalanche
photodiodes with an optical filter with the same wavelength placed in front
of it have been used as a receiver.
Why it is good to choose a wavelength of 905nm:
- the natural light radiation in this range is low and will not strongly
affect the receiver;
- Several manufacturers in the world produce powerful pulsed laser diodes
with pulsed output power up to 200W in combination with several emitters in
one housing and low cost;
- many natural and artificial materials reflect well without absorbing
- an avalanche photodiode with a sensitivity peak at 905nm and an added
optical filter supplied with a high voltage of the order of 200V have a high
reaction rate up to 0.5nS and a high multiplication / gain factor from M100
We will consider several variants of an active silencer
on a laser rangefinder.
Using a large number of IR LEDs.
IR LED TSHF5210 or TSHF6210 is selected with the following parameters:
Peak wavelength 890 nm
Angle of half intensity ± 10 °
Rise time / Fall time 30ns / 30 ns
In order to achieve the high flashing speed, a large number of drivers are
used, which generate a pulse current of 300 mA with a repetition frequency
of 8 MHz.
The received pulses resemble the reflected signal and prevent the difference
between the reflected signal from lasers and the interfering signal.
The optical filter of the avalanche diode passes a band of 895 to 915nm, at
the same time the Relative Radiant Power of the IR LED at 905nm is 75%,
which is enough to prevent the correct reading of the distance.