We developed unconventional laser scanner, which monitors the area with two independent laser beams shaped into lines. These lines are oriented perpendicular to each other. The solution is based on pulsed laser diodes and PIN photodetectors, making the whole platform more compact, lighter and cheaper comparing to the existing alternatives, which most often include an extensive high-resolution video track integrated with a scanning platform of considerable dimensions. The paper discusses the scanning methodology and presents a range analysis in the context of commercially available semiconductor lasers with the desired emission parameters. Another problem discussed in the paper is a method of forming a multimode laser beam into the shape of possibly narrow and homogenous line of light. The first issue can be settled through the application of commercially available aspherical components, while achieving perfect homogeneity requires the design and implementation of a dedicated freeform optical element. The current version of the experimental model is limited to off-the-shelf optical components, while the study also presents the design and simulation of the freeform transmitter.
Sensors detecting angle of incoming light incidence, are basic elements of systems indicating direction to source of emission and Laser Warning Systems (LWS). Onboard satellites, sensors of such type are used to determine sun position. Another sensors are used in military systems. Current method of arrival angle estimations mostly rely on the analysis of slit projection on photosensitive array or quadrant detector. Novel solution in this paper is proposed. It is based on five detectors distributed on side walls of truncated pyramid. Such geometrical configuration of detectors allows to measure in wide field of view with good accuracy offered by a small size of active surface. The proposed algorithm is able to calculate angle of both azimuth and elevation of incoming light. Laboratory tests have also been discussed in the paper.
We discuss the optical configuration and present mathematical modelling of intense electric fields sensor. The device is dedicated for the measurements of high power electromagnetic pulses (HPM) magnitude. For this reason, the sensor head has been designed as all-dielectric component, in order to avoid interferences with the measured fields. The laser source and detector unit are joined with the head through long optical fibres and the whole system utilizes 1.5 μm telecomm fibre technology. The sensor operation is based on Pockels effect induced by electric component of EM wave in bulk LiNbO3 crystal. Collimated laser beam propagating through the crystal is obtained by the application of miniature GRIN lens attached to the end of the fibre. Similarly, the fibre coupling of the beam after it crosses the crystal, is obtained. In the paper the focus is also put on mathematical foundations of full 3-dimentional sensing of E-field, which would enable to measure not only the magnitude, but also to determine the direction to the HPM source.
KEYWORDS: Data transmission, Pulsed laser operation, Signal to noise ratio, Laser applications, Transmitters, Continuous wave operation, Receivers, Free space optics, Modulation, Free space optical communications
Most of the current optical data transmission systems are based on continuous wave (cw) lasers. It results from the tendency to increase data transmission speed, and from the simplicity in implementation (straightforward modulation). Pulsed lasers, which find many applications in a variety of industrial, medical and military systems, in this field are not common. Depending on the type, pulsed lasers can generate instantaneous power which is many times greater when compared with cw lasers. As such, they seem to be very attractive to be used in data transmission technology, especially due to the potentially larger ranges of transmission, or in adverse atmospheric conditions where low power cw-lasersbased transmission is no longer feasible. It is also a very practical idea to implement data transmission capability in the pulsed laser devices that have been around and already used, increasing the functionality of this type of equipment. At the Institute of Optoelectronics at Military University of Technology, a unique method of data transmission based on pulsed laser radiation has been developed. This method is discussed in the paper in terms of both data transmission speed and transmission range. Additionally, in order to verify the theoretical assumptions, modules for voice and data transmission were developed and practically tested which is also reported, including the measurements of Bit Error Rate (BER) and performance vs. range analysis.
KEYWORDS: Signal to noise ratio, Distance measurement, Time metrology, Pulsed laser operation, LIDAR, Signal detection, Prototyping, Laser applications, Algorithm development, Analog electronics
Measurement of vehicles speed by means of displacement measurement with "time of flight" lidar requires gathering of accurate information about distance to the vehicle in a set time interval. As with any pulsed laser lidar, its maximum range is limited by available incoming signal to noise ratio. That ratio determines not only maximum range, but also accuracy of measurement. For fast and precise measurements of speed of the vehicles their displacement should bee measured with centimeter accuracy. However that demand is hard to reach on long distances and poor quality of the echo signal. Improving accuracy beyond given by a single pulse probing requires emission of several probing pulses. Total displacement error will than fall with the square root of the number of executed measurements. Yet this method will not extend available distance beyond the limit set by threshold detection systems. Acquisition of the full waveform of received signals is a method that allows extension of maximum range through synchronic addition of subsequent waveforms. Doing so improves SNR by a well-known factor of square root of the number of carried additions. Disadvantage of this method is that it requires use of fast analog to digital converters for data acquisition, and simple distance calculation algorithms may not give the adequate accuracy due to relatively long sampling period of reasonable priced ADC’s. In this article more advanced algorithms of distance calculations that base on ADC raw data are presented and analyzed. Practical implementation of algorithm in prototype design of laser speed gun is shown along with real life test results.
The article presents the main aspects related to the development of nonconventional asymmetric laser data transmission system. It describes the principle of data transmission in both the direction away from the laser transmitter, wherein a pulse position modulation is used, and in the opposite direction, where the modulation of the reflected radiation is performed. The results presented in the article confirm the possibility of using the described technology in the civilian area for monitoring and telemetry, where devices without radiation sources are taken into account. In military applications, the system can be used to identify own objects and forces on the battlefield by the application of pulsed laser rangefinders which are currently a standard battle equipment.
LIDAR system for real-time standoff detection of bio-agents is presented and preliminary experimental results are
discussed. The detection approach is based on two independent physical phenomena:
(1) laser induced fluorescence (LIF),
(2) depolarization resulting from elastic scattering on non-spherical particles.
The device includes three laser sources, two receiving telescopes, depolarization component and spectral signature
analyzing spectrograph. It was designed to provide the stand-off detection capability at ranges from 200 m up to several
kilometers. The system as a whole forms a mobile platform for vehicle or building installation. Additionally, it's
combined with a scanning mechanics and advanced software, which enable to conduct the semi-automatic monitoring of
a specified space sector.
For fluorescence excitation, 3-rd (355 nm) and 4-th (266 nm) harmonics of Nd:YAG pulsed lasers are used. They emit
short (~6 ns) pulses with the repetition rate of 20 Hz. Collecting optics for fluorescence echo detection and spectral
content analysis includes 25 mm diameter f/4 Newton telescope, Czerny Turner spectrograph and 32-channel PMT.
Depending on the grating applied, the spectral resolution from 20 nm up to 3 nm per channel can be achieved.
The system is also equipped with an eye-safe (1.5 μm) Nd:YAG OPO laser for elastic backscattering/depolarization
detection. The optical echo signal is collected by Cassegrain telescope with aperture diameter of 12.5 mm.
Depolarization detection component based on polarizing beam-splitter serves as the stand-off particle-shape analyzer,
which is very valuable in case of non-spherical bio-aerosols sensing.
Following article presents LIDAR for stand off detection of aerosols which was constructed in Institute of
Optoelectronics in Military University of Technology. LIDAR is a DISC type system (DIfferential SCattering) and is
based on analysis of backscattering signal for two wavelengths (λ1 = 1064 nm and λ2 = 532
nm) - the first and the
second harmonic of Nd:YAG laser. Optical receiving system is consisted of aspherical mirror lens, two additional
mirrors and a system of interference filters. In detection system of LIDAR a silicon avalanche photodiode and two
different amplifiers were used. Whole system is mounted on a specialized platform designed for possibility of LIDAR
scanning movements. LIDAR is computer controlled. The compiled software enables regulation of the scanning platform
work, gain control, and control of data processing and acquisition system. In the article main functional elements of
LIDAR are shown and typical parameters of system work and construction are presented. One presented also first results
of research with use of LIDAR. The aim of research was to detect and characterize scattering aerosol, both natural and
anthropogenic one. For analyses of natural aerosols, cumulus cloud was used. For analyses of anthropogenic aerosols one
used three various pyrotechnic mixtures (DM11, M2, M16) which generate smoke of different parameters. All scattering
centers were firstly well described and theoretical analyses were conducted. Results of LIDAR research were compared
with theoretical analyses and general conclusions concerning correctness of LIDAR work and its application were
drawn.
Theoretical and practical aspects of laser application in the field of underwater remote sensing have been presented. A
multi-level analysis and computational results dealing with 0.532 μm laser wavelength were performed to determine the
expected capabilities of underwater laser penetration with regard to the Lidar system developed in Optoelectronics
Institute of Military University of Technology in Warsaw. Since the device is to perform underwater measurements from
above the water level, the influence of the water-atmosphere interface had to be included in the analysis. Sea water
characteristics concerning electromagnetic radiation propagation have been widely considered covering the mechanisms
of absorption, scattering and the effective attenuation typical for representative types of sea waters. Software application
developed in Mathcad environment enabled to model the impact of both absorption and scattering coefficients of
different types of sea water on geometrical and energetic parameters of laser beam propagating in the underwater
environment. The impact of reflectance properties of the remotely sensed underwater object on the reflected signal level
has been investigated as well. Analytical approach covered both "echo" signal reflected from an underwater object and
background noise signal level generated mainly by the sunlight and diffuse atmospheric illumination.
Single crystals of double tungstates find applications as laser materials having very good parameters. One of the intensively investigated material sis KGD(WO4)2 doped with rare earth elements. Single crystal of KGd(WO4)2 were grown with the use of Top Seeded Solution Growth technique from K2W2O7 solvent. The crystals have low absorption loses and show high lasing efficiency. Optical investigations of as grown KGW:Nd single crystal confirmed their good optical quality and high absorption coefficient near 810 nm, what in connection with strong luminescence near 1067 nm allows fabrication of diode pumped microchip lasers working both in CW and giant pulse regime. Absorption and luminescence spectra of Nd3+ doped KGW single crystals are presented. Laser action was obtained in form of 128.5 kHz train of 100 ns giant pluses due to YAG:Cr4+ passive Q-switch.
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