Compact optical sources of radiation with high average power are needed for many applications from sensing to imaging and spectroscopy. The control of non-linear effects during the propagation of intense ultra-short laser pulses in various gas allows the generation of novel very intense radiation beams which can be used for sensing and imaging. We discussed non-linear effects during ultrafast laser beam propagation in two very different interaction regimes, long distance propagation in ambient air and short distance propagation at very high intensity and in high density gas, obtained with high peak and high average power laser systems.
We report on a novel method that shows the potential to provide real-time, standoff forensic analysis of samples being irradiated by a high energy laser (HEL). The interaction of the HEL beam with matter produces specific optical signatures that can be detected from the location of the HEL system. A spectroscopic analysis of these signals can then provide useful information to the operator including the impact the laser has on the sample as well as providing data about the its structure and composition.
Laser safety regulating the deployment of kW-class high-energy laser (HEL) technologies in outdoor applications can rapidly cause significant planning and operations issues due to the ranges involved. Safety templates based on a simplistic approach of assuming a continuous wave laser beam incident on a highly reflective totally flat solid surface of infinite size can easily result in ranges of tens of kilometers for kW-class lasers. Due to the complexity of HEL-matter interactions, the assumptions underlying the aforementioned approach are, however, deemed inappropriate. We identify a more suitable approach, which assumes a time-variant reflection pattern as well as a change in the variance of beam divergence as it reflects from the target’s surface. Based on experimental results, we instead propose to assess the nominal ocular hazard distance by applying the American National Standard Institute rules for time-variant multipulse laser exposure and using measured divergence angles from the target’s surface. The resulting safety templates, thus, exhibit a higher fidelity with respect to the behavior of the reflection patterns while reducing the hazard zones.
Laser safety regulating the deployment of kW-class high energy laser (HEL) technologies in outdoor
applications can rapidly cause significant planning and operations issues due to the ranges involved. Safety
templates based on the American National Standard Institute (ANSI) rules can easily result in ranges of tens of
kilometers for kW-class lasers. Due to the complexity of HEL-matter interactions, the assumptions underlying the
aforementioned approach are however deemed inappropriate. In this paper, we identify a more suitable approach
backed by experimental results.
Mid-infrared lasers find interesting applications in laser-based countermeasure technologies, remote sensing,
maritime/terrestrial awareness and so on. However, the development of laser sources in this spectral region is limited.
We present here an alternative solution to the mid-infrared laser which is based on difference-frequency generation
(DFG) in a nonlinear crystal pumped by synchronized and tunable near-infrared fiber lasers that are commercially
available. This idea is not new and has been explored by other groups, but the latest innovations in near-infrared fiber
lasers have enabled the creation of fast-scanning picosecond fiber lasers. One such picosecond system is the
synchronized programmable laser from Genia Photonics that can combine two picosecond fiber laser systems in which
both output pulses are synchronized at the DFG crystal. The first laser was continuously tunable from 1525 nm to 1600
nm and one million different wavelengths can be scanned within one second. For the second fiber laser, its wavelength
was fixed at 1080 nm. In principle, the DFG in a PPLN crystal could produce a tunable mid-infrared source spanning
from 3.32 μm up to 3.7 μm. Other and wider tuning ranges are possible with different choices of pump wavelengths. For
the PPLN crystal used in this work, the DFG phase-matching window for a fixed temperature was 2.6 nm wide and was
broad enough for our 25 ps pulse train having a spectral width of 0.25 nm. The quantum efficiency achieved for the DFG
was 44% at the maximum power available.
We observed multiple filamentation of a Terawatt fs-laser beam (λ = 800 nm, E = 170 mJ/pulse) after 1 km horizontal
propagation in the atmosphere. The interaction of these filaments with the non-transparent targets was studied. The
filaments were strong enough to damage the surface of optical windows like Ge and ZnSe even at long distances and
under turbulent conditions. The damage effects were analysed by studying the modulation transfer function (MTF), the
spectral transmission loss, the ablation depth and the damage threshold. LIBS was applied to estimate the plasma
temperature during the interaction process.
Standoff detection of explosives residues on surfaces at few meters was made using optical technologies based on
Raman scattering, Laser-Induced Breakdown Spectroscopy (LIBS) and passive standoff FTIR radiometry. By
comparison, detection and analysis of nanogram samples of different explosives was made with a microscope
system where Raman scattering from a micron-size single point illuminated crystal of explosive was observed.
Results from standoff detection experiments using a telescope were compared to experiments using a microscope to
find out important parameters leading to the detection. While detection and spectral identification of the micron-size
explosive particles was possible with a microscope, standoff detection of these particles was very challenging due to
undesired light reflected and produced by the background surface or light coming from other contaminants. Results
illustrated the challenging approach of detecting at a standoff distance the presence of low amount of micron or submicron
Proc. SPIE. 6733, International Conference on Lasers, Applications, and Technologies 2007: Environmental Monitoring and Ecological Applications; Optical Sensors in Biological, Chemical, and Engineering Technologies; and Femtosecond Laser Pulse Filamentation
The filament core of a femtosecond laser pulse propagating in an optical medium has extra-ordinary quality for
exploitation that includes high quality tunable pulse generation from the UV to the THz. The peak intensity inside the
filament is also high enough to dissociate/ionize any molecules resulting in remarkably distinct spectra which can be use
for remote sensing of Chem-bio agent.