GaAs tunnel p-n junctions with peak current densities up to 45 A cm−2 were grown by metallorganic vapor-phase epitaxy. These tunnel diodes are suitable for intercell ohmic contacts between the case of integrated tandem photovoltaic subcells in solar cells based on GaAs. The peak current is high enough for concentration up to C=1000.

The paper reports the efficient UV and terahertz generation from a 1.29 mm thick and Type I, θ = 28.9 ∘ cut B i B 3 O 6 (bismuth triborate, BIBO) crystal using femtosecond and nanoseconds laser pulses. We have employed 800 nm wavelength pulses of 50 and 140 fs obtained from a Ti:sapphire laser amplifier and oscillators at 1 kHz and 80 MHz repetition rates, respectively. The conversion efficiency of second-harmonic generation (SHG) was ∼ 50 % while that obtained for terahertz (THz) generations was of the order of 1.85 × 10 − 5 % . In addition, LDS-698 dye laser radiation tunable between 650–700 nm was also used as a source for SHG between the 325–350 nm range. The dye laser was pumped by SHG (532 nm) radiation from an electro-optically Q -switched Nd:YAG laser having a pulse repetition rate of 10 Hz and a pulse width of 10 ns. A conversion efficiency of 4.01% was obtained for generation of UV at 343.5 nm. Finally, we have measured the transmission, refractive index, absorbance, and conductivity properties of BIBO crystal in the THz domain. We also ascertained the coherence length, relative permittivity and reflectivity of the crystal.

No abstract

No abstract

We report a technique for the efficient generation of tunable coherent deep UV radiation and its application in studies of RDX and TNT at the ppm level on the basis of their absorption characteristics. The obtained experimental absorption data are compared with conventional spectrophotometric data. The UV radiation in the range 200-260 nm has been generated by the type-I noncollinear third harmonic of the dye laser radiation (600-700 nm) and also by sum frequency mixing (SFM) of Nd:YAG output (1064 nm) with the second harmonic of the dye laser in β-barium borate (BBO) crystal. The maximum conversion efficiency of the generated signal is estimated to be 57.5% at λ = 218.9 nm wavelength. Apart from measurements of the absorbance of RDX and TNT at different concentrations in their respective solutions, the minimum detection concentrations have also been ascertained. The estimated minimum detectable concentration of RDX is 8.47⋅10 -9 M, whereas that for TNT is 35.7⋅10 -9 M. The data were obtained using only ~100 µJ/pulse of laser energy.Introduction. Explosives are chemical compounds or their mixtures capable of storing large amounts of energy in a compact form and subsequently releasing large volumes of hot gases when exploded [1]. Their illegal use by criminals and extremist groups has reached an alarming level. In addition, some slightly water-soluble explosives such as TNT (0.01 % at 298 K), are responsible for contamination of groundwater, thus threatening public health. These problems have attracted global attention towards developing sensitive detection and identification techniques capable of assisting law enforcement agencies in detecting the explosives at various crowded public places such as airports, theatres, railway stations, etc. For forensic purposes, investigation of bomb blast sites requires not only sensitive detection of submicrogram levels but also specific identification techniques for different explosive components in an exhibited sample. Lasers have made studies of explosives possible under controlled conditions. Several laser-based effects which occur in different regions of optical spectrum such as opto-acoustic effect and multi-photon dissociation [2,3] in the IR region, desorption in the visible region, and photochemical, photothermal, photoablation and laser-induced fluorescence effects in the UV region [4,5] have been exploited to detect and identify explosives. FTIR absorption/transmission curves of explosives provide useful information about different functional groups. The absorption peak located near 6 µm is due to the presence of the -NO 2 group; it has been recognized as a characteristic peak of all secondary explosives.Here we report the study of transmission/absorption characteristics of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT) for the first time by using deep UV radiation tunable in the range 200-260 nm, which was generated by sum frequency mixing (SFM) of a tunable dye-laser output with that of Nd:YAG laser in a β-barium borate (BBO) crystal.