Low-cost detection of lasers

Abstract

Abstract. A low-cost method of detecting lasers based on detecting coherence properties of received light is presented. The method uses an unbalanced Mach-Zehnder interferometer with a modulating piezo-mounted mirror in one arm to discriminate against incoherent background light and identify the presence of laser radiation at the nW level against much brighter backgrounds. The wavelength of the coherent input can be determined by comparing the intensities of the modulation frequency harmonics.

Laser detection utilizing coherence

“…This appears as stronger harmonics of the modulation frequency. It is then possible to determine the wavelength of the incoming light by analysing the ratio of the third harmonic to the fundamental frequency (see Benton [22]). However in some cases this can be unreliable due to large differences in the harmonic powers.…”

“…Cohen [21] employed a polarization based interferometer using an electro-optic modulator to discriminate against incoherent background light and assess the laser wavelength. Mach Zehnder interferometers (MZI) have also been used for laser detection by Benton [22], the substance of which forms the remainder of this paper. In common with many of the above coherence detecting techniques, Benton implemented an asymmetric interferometer to discriminate against incoherent background light.…”

Laser detection using liquid crystal polarization modulators

“…The intensity in detectors 1 and 2 in each polarization mode (labeled x and y) are given from the standard MZI interference equation 19,20 as E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 1 ; 1 1 6 ; 2 8 7…”

“…Unlike the system of Cohen, 20 the LCMs are incorporated into an MZI, building on previous work 19 as a method of obtaining a low-cost laser detection system.…”

Developments in low-cost laser detection: wide field of view implementation and direction determination

“…9 The laser detection system used for this work is composed of a Mach-Zehnder interferometer, combined with a balanced detector composed of two photodiodes at the outputs of the interferometer and a data acquisition unit (USB-6341 Multifunction I/O Device) used to digitize and send the data to a computer. 1 The field of view of this system has been measured and is equal to ±3 • , this value being due to the detector size (3mm long). The aim of this work was to expand the field of view thereby making the device more practical.…”