Detection of laser radiation by the warning system may indicate an attempt to track by a certain type of weaponry. Obtaining information about this intention increases the chances of the protected vehicle surviving on the battlefield. Depending on the type of threat and the equipment of the protected vehicle, various defense scenarios can be implemented, e.g. placing a smokescreen, maneuver to avoid hitting. Information about location the source of laser radiation can be automatically transferred to the weapon system and to convey this information through the battlefield management system to other platforms nearby. This information can be used by these platforms to locate and neutralize the source of danger. The warning system to fulfill its functions, it must detect the sources of laser radiation and should be resistant to optical interference. Considering the characteristics of the laser beam and the propagation of laser radiation in the atmosphere, the sensors of the warning system should work in the optical spectrum defined by laser sources, compensate for the signal dynamics resulting from the variable power of the sources and the distance between the radiation source and the warning system. The warning system as an element of the optoelectronic surveillance system should be equipped with a database of signatures of optical signals occurring on the battlefield (laser sources and interferences). Systems on the protected platform should be integrated to ensure aggregation obtained information and, in this way, improve the probability of threat detection and reduce false alarm probability.
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.
Airborne laser scanning (ALS) is a popular tool for acquiring data for geographical and urban analysis, but also is increasingly used in measurements related to widely understood vegetation monitoring. Based on the application of the Multispectral Laser Reflectance Scanner (MLRS) developed and constructed at the Institute of Optoelectronics of the Military University of Technology, it is possible to analyze the vegetative status of plants. One of the most important parameters of such analysis is the distinction of plant health based on the density of foliage, as well as in terms of the occurrence of drying and wilting phenomena. The article presents and discusses changes in the reflectance spectra of healthy and wilting or drying plants. Also presented are examples of digital surface models, enriched with information on the condition of vegetation, obtained during one of the field tests of the MLRS scanner.
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.
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 LiNbO<sub>3</sub> 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.
Proc. SPIE. 10159, Laser Technology 2016: Progress and Applications of Lasers
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.
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.
The paper presents reflectance characteristics of plants. The objects of the research were the selected plants, taking
the various levels of organization and structure into consideration, as well as the state of plant health and growth.
Reflectance spectrum was analyzed in the range of wavelengths from 0,2 to 2,5 μm. The values of reflectance for three
wavelengths (λ<sub>1</sub>=850 nm, λ<sub>2</sub>=905 nm, λ<sub>3</sub>=1550 nm) were analyzed with the particular emphasis. The sample tests were
performed immediately after biological material taking and in the several 24-hour time intervals. The time intervals
enabled the process of plants wilting and drying. The reflectance measurements were repeated until the moment of plant
complete dried out. All measurements were performed with the use of the spectrometer Lambda 900 (Perkin Elmer)
equipped with the 150 mm integrating sphere PELA1001 dedicated for the measurements of the hemispherical
reflectance both of diffuse and specular type. On the basis of the obtained results one calculated the values of signal
ratios for the three selected wavelengths: 850/1550nm, 905/1550nm, and 850/905nm. The collected spectra and
reflectance characteristics enabled the analyses of both results similarities and differences, which enabled the
determination of the reflectance changes tendency associated with the typical processes occurring in plants.
The analyses of plants reflectance characteristics were made for the use of the laser system for identification of
terrain elements and their physico-chemical properties.
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 (λ<sub>1</sub> = 1064 nm and λ<sub>2</sub> = 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
In the work, analyses of chosen materials were presented in order to analyze the possibility of development of a laser
scanning system. One showed results of research and analyses of data related to reflection characteristics of various
materials with consideration of different ranks of composition and structure complication. Analyses were carried out for
three wavelengths of electromagnetic radiation: λ<sub>1</sub> = 850 nm, λ<sub>2</sub> = 900 nm, λ<sub>3</sub> = 1500 nm in reference to both natural and anthropogenic materials. The influence of atmospheric extinction on values of received proportions of signals for the
chosen wavelengths was investigated and the method of signal correction was compiled. Correction was made taking
into account character of reflection obtained from materials, various atmospheric conditions stated by the atmospheric
visibility, and spectral characteristics of the atmospheric extinction. The proposed method of atmospheric extinction
correction provides minimization of real values falsification and decrease in obtained measurement errors, which does
not exceed the value of 5% for the analyses from a distance of 0.5 km with atmospheric visibility of 10 km, and for the
analyses from a distance of 1 km with atmospheric visibility of 20 km.
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.