A novel, low-cost, camera-based method of detecting a single nanosecond (ns) laser pulse and kHz modulated continuous wave and pulsed lasers has been developed. The detector uses a simple optical modification to a standard rolling shutter color camera combined with image processing techniques to distinguish lasers from other illumination sources and extract a laser’s wavelength and pulse repetition frequency. In addition, the detector is also capable of detecting a single ns laser pulse at any given time. Such a detector has applications in free-space optical communications (FSO comms) as a low-cost broadband method of extracting information from multiple sources and as a detector of laser range finders. A low-cost prototype (≈£600) has been developed using entirely off-the-shelf components and assessed in laboratory and field trial conditions, with the ability to measure laser wavelengths to ±5 nm and pulse repetition frequencies to within ±5 % at a distance of 660 m. In the laboratory, the prototype was also able to detect each of the 1000 pulses generated by a 10 Hz 10 ns 532-nm pulsed laser, as well as 100 pulses sent at random intervals, highlighting its capability to detect a ns pulse at any given time. This novel technology offers a low-cost method of detecting lasers and extracting their pulse repetition frequencies, with a wide field of view and high spatial resolution. Ultimately, this technology has applications in FSO comms for between vehicles or platforms of interest, with a capability of communicating with multiple targets simultaneously.
Plasmonic metamaterials are artificial structures whose optical response can be tailored to achieve several effects by playing with the geometrical parameters of the components. In this talk, we discuss how to apply the metamaterial design rules to develop band-stop linear filters and nonlinear filters, operating as intensity limiters. In both regimes, the filters share some common qualities: their optical response does not change for a broad range of incidence angles, at least up to 30 degrees, and is only weakly dependent on the polarisation of the incident light. These properties make these ultrathin filters useful in open field applications. The metamaterial is based on an array of gold nanotubes (i.e., a cylindrical gold shell with a dielectric core) embedded in a dielectric matrix. In the linear regime, the metamaterial displays an absorption resonance independent of the polarisation and the angle of incidence of the light, which can be tuned throughout the visible spectral range by changing the geometrical parameters of the array. In the nonlinear regime - based on free-electron Au nonlinearity and tested with ns-long pulses at 532 nm - the metamaterial limits the output peak fluence, keeping it constant across several order of magnitudes of the incoming fluence. The proposed metamaterial approach can be useful for designing optical spectral filters and intensity limiters over broad range of wavelengths.
A low-cost camera-based method of detecting continuous-wave (cw) lasers has been developed at Defence Science and Technology Laboratory. The detector uses a simple optical modification to a standard color camera combined with image processing techniques to distinguish lasers from other illumination sources and measure the wavelength, direction, and irradiance of the laser light. Such a detector has applications in collecting information on aircraft laser dazzle incidents, providing the evidence required to inform on aircrew laser exposure events and to assess if engagements are eye safe. A prototype has been developed using entirely commercially available off-the-shelf (COTS) components, costing ≈£600, and assessed in laboratory conditions with the capability of measuring laser wavelengths to ±5 nm and irradiances to ±10 % . A realistic handheld laser engagement scenario, using a range of relevant wavelengths and irradiances, was simulated during the Moonraker trial where the prototype was capable of measuring laser wavelengths to an accuracy of ±10 nm and peak irradiances to ±25 % . All laser engagements were detected over a total data collection period of 9 h with zero false alarms. Comparisons were made with a COTS laser detector, which showed an equivalent performance. This technology offers a low-cost approach to cw laser detection, which is capable of extracting a range of parameters while maintaining a relatively wide field of view and angular resolution.
A novel, low-cost, camera-based method of detecting a single nanosecond laser pulse and kHz modulated continuous wave and pulsed lasers has been developed at DSTL. The detector uses a simple optical modification to a standard rolling shutter colour camera combined with image processing techniques to distinguish lasers from other illumination sources and extract a lasers wavelength and pulse repetition frequency. In addition the detector is also capable of detecting a single nanosecond laser pulse at any given time. Such a detector has applications in free-space optical communications, as a low cost broadband method of extracting information from multiple sources, and as a detector of laser range finders. A low cost prototype (≈£600) has been developed using entirely off-the-shelf components and assessed in laboratory conditions, with the ability to measure laser wavelengths to ±5nm and pulse repetition frequencies to within ±5%. In the laboratory the prototype was also able to detect each of the 1000 pulses generated by a 10Hz 10ns 532nm pulsed laser, as well as 100 pulses sent at random intervals, highlighting its capability to detect a ns pulse at any given time. The prototype was taken to the Moonraker NATO SET-249 field trial, where it was able to measure the pulse repetition frequency of a modulated continuous wave laser source to within ±5% at a distance of 660m. This novel technology offers a low cost method of detecting lasers and extracting their pulse repetition frequencies, with a wide field of view and high spatial resolution.
A novel, low-cost, camera-based method of detecting Continuous Wave (CW) lasers has been developed at DSTL. The detector uses a simple optical modification to a standard colour camera combined with image processing techniques to distinguish lasers from other illumination sources, as well as measuring the wavelength, direction and irradiance of the laser light. Such a detector has applications in collecting information on aircraft laser dazzle incidents: providing the evidence required to inform on aircrew laser exposure events and to assess if engagements are eye safe. A prototype has been developed using entirely Commercially available Off-The-Shelf (COTS) components, costing ≈£600, and assessed in the laboratory conditions, with the capability of measuring laser wavelengths to ±5nm and irradiances to ±10%. A realistic hand-held laser engagement scenario, using a range of relevant wavelengths and irradiances, was simulated during the Moonraker trial where the prototype was capable of measuring laser wavelengths to an accuracy of ±10nm, and peak irradiances to ±25%. Comparisons were made with a COTS laser detector, and showed an equivalent performance. This technology offers a low cost approach to CW laser detection, which is capable of extracting a range of parameters, whilst maintaining a relatively wide Field of View (FOV) and angular resolution.
The laser-induced damage thresholds of commercial off-the-shelf visible and shortwave infrared cameras are measured under laboratory and outdoor conditions for infrared laser exposure times varying from microseconds to continuous wave. The damage threshold results are compared with a simple thermal model, which shows strong correlation with the experimental data, allowing the model to be used to predict camera damage thresholds across a range of exposure durations and wavelengths.
We report a feasibility study of Time-of-Flight technique in Short- and Mid-Wavelength Infrared spectral region using a Mercury Cadmium Telluride detector. For the demonstration we employed an all-optical modulator operated by optical pumping with 800 nm, 100 femtosecond pulses and measured the broadening of the signal pulses traversing through a few centimetres of silica rod. The measured signal was analysed to reconstruct the pulse broadening and to retrieve the group velocity dispersion of silica. We show that in Time-of-Flight measurements based on all-optical modulation in combination with Mercury Cadmium Telluride detector, the limiting resolution factor is the speed of the modulator rise time governed by the optical pump.
Applications involving the outdoor use of pulsed lasers systems can be affected by atmospheric turbulence and scintillation. In particular, deterministic prediction of the risk of injury or damage due to pulsed laser radiation can be difficult due to uncertainty over the focal plane fluence of radiation that has traversed through a turbulent medium. In this study, focussed beam profiles of nanosecond laser pulses are recorded for visible laser pulses that have traversed 1400m paths through turbulent atmospheres. Beam profiles are also taken under laboratory conditions. These pulses are characterised in terms of their peak focal plane fluence, total collected energy and Strehl ratio. Measured pulses are then compared statistically to pulse profiles generated by a two-dimensional phase screen propagation model based on the Von Karman power spectrum distribution. The model takes into account the refractive index structure constant (𝐶𝑛2), the wavelength, the path geometry and macroscopic beam steering. Analysis shows good correlation between the measured and simulated data, inferring that the Von Karman phase screen model can be used to predict focal plane fluence distributions for outdoor applications.
We have used near IR pump – Mid IR probe techniques to compare the feasibility and potential of using free standing nano-porous and micro-porous silicon (ordered hole arrays) as optically controlled modulators operating in the Mid-Wave Infrared (MWIR) covering the range from 3.3-5 μm. We employed 800 nm pumping pulses with the duration of 60 fs to reduce 4 μm light transmission modulation to about 25% and 45% for both silicon structures, respectively, at excitation powers of 50mW (4 mJ=cm2). However, at 5 μm both structures shown similar contrast of about 60%. The time resolved measurements revealed a fast sub-picosecond rise time for both structures suggesting that the optically generated carriers are a dominant mechanism for the modulation. However, the measurements demonstrated a significant difference in the relaxation dynamics. The nanoporous silicon demonstrated recovery as fast as a few tens of picoseconds and a possibility to effectively work in the GHz regime, while hole arrays shown almost three orders of magnitude slower response making it suitable for the MHz regime.
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