We present the results on the electromagnetic (em) radiation emitted in the 70 MHz - 1 GHz frequency range from the
laser induced breakdown of atmospheric air. Laser pulses (7 ns) from second harmonic of an Nd:YAG laser (532 nm)
were used to breakdown atmospheric air to form plasma. During the plasma evolution and expansion, dipole moment is
induced in the homonuclear molecules of nitrogen and oxygen (the main components of atmospheric air), which
naturally have no permanent electron dipole moments. The RF spectra originating from the longitudinal oscillation of
these induced dipoles was detected using the RH-799 broadband Diamond antenna. A spectrum analyzer (Agilent PSA
E444A, 3 Hz to 50 GHz) was used to monitor and record the RF spectrum from plasma. By tuning the length of the
antenna, lines corresponding to the different resonant frequency were observed at different laser energies. The total
emitted RF energy was found to be increasing with the input laser energy up to certain input laser energy, beyond which
emission properties were modified drastically. This was observed due to the presence of multiple breakdown sources due
to the self-focusing of the ns laser pulses, modifying the collisions between the plasma electrons and eventually
modifying the induced dipole moment in the detection range. The emitted radiation showed a specific polarization
property associated with the input em radiation.
We present the measurements on the propagation characteristics of the laser generated acoustics shock waves and the
vibrations inside material targets from laser-metal interaction in real time. Laser pulses (7 ns) from second harmonic of a
Nd: YAG laser (532 nm) were used to launch compression waves inside the solid samples. The acoustic measurements
were carried out using a calibrated microphone, while the vibrations induced within the material before getting converted
into ASW in the atmosphere were measured using vibration transducers (piezoelectric accelerometer). The arrival time
of the vibration transducer was used to measure the particle velocity within the material that increased with increasing
laser energy. The measurement of the arrival time of the ASW as a function of the microphone distance from the source
of explosion was carried out. The shock velocity with respect to distance from the source of explosion followed an
exponential decay. The arrival time of the ASWs was found to be increasing with the distance. The shock arrival time
with respect to incident laser energy showed an exponential decay where as the shock velocity was found to be linearly
increasing with the incident laser energy. Overall, acoustic energy has increased with increasing density of the material.
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