We studied theoretically the laser-plasma interaction, and performed experiments to investigate the mechanisms giving rise to optical damage in Borosilicate glass using nanosecond laser pulses at wavelength 1064 nm. Our experimental result shows that the optical damage process generated by nanosecond laser pulses is the result of an optically induced plasma. The plasma is initiated when the laser irradiance frees electrons from the glass. Although it may be debated, the electrons are likely freed by multi-photon absorption and the number density grows via impact ionization. Later when the electron gas density reaches the critical density, the electron gas resonantly absorbs the laser beam through collective excitation since the laser frequency is equal to the plasma frequency. The laser energy absorbed through the collective excitation is much larger than the energy absorbed by multi-photon ionization and impact ionization. Our experimental result also shows the plasma survives until the end of the laser pulse and the optical damage occurs after the laser pulse ceases. The plasma decay releases heat to the lattice. This heat causes the glass to be molten and soft. It is only as the glass cools and solidifies that stresses induced by this process cause the glass to fracture and damage. We also show the experimental evidence of the change of the refractive index of the focusing region as the density of the electron gas changes from sub-critical to overcritical, and the reflection of the over-critical plasma. This reflection limits the electron gas density to be not much larger than the critical density.
We investigate the inversion dynamics in Nd:Cr:GSGG laser rods as a function of pumping frequency in order to optimize Nd:Cr:GSGG Q switched lasers for rapid time to fire applications. By frequency filtering the pump light to the Nd:Cr:GSGG rod and measuring the florescence from the rod, we determine the dynamics for different excitation processes in the laser (i.e. direct excitation of the Nd ions or indirect excitation via Cr ions). We also measure the flashlamp pulse shape using various spectral filters This combination of measurements help us understand the processes contributing and limiting the efficiency of Nd:Cr:GSGG lasers when the lasers must fire on a short time scale.
Using coherence enhanced nonlinear optics we observe absorptive
switching in hot Rubidium atoms. Electromagnetically induced
transparency helps create a larger absorptive Kerr nonlinearity
enabling strong absorptive switching with laser intensities of
10 microwatts per square centimeter. Switching is interpreted in terms of optical pumping into and out of the "dark" state.
Future microwave networks require miniature high-performance tunable elements such as switches, inductors, and capacitors. We report a micro-machined high-performance tunable capacitor suitable for reconfigurable monolithic microwave integrated circuits (MMICs). The capacitor is fabricated on a GaAs substrate using low-temperature processing, making it suitable for post-process integration with MMICs, radio frequency integrated circuits (RFICs) and other miniaturized circuits. Additionally, the insulating substrate and high-conductivity metal provide low-loss operation at frequencies over 20 GHz. The device demonstrates a capacitance of 150 fF at 0 V bias, pull-in at about 15 V to 18 V, and further linear tuning from 290 fF to 350 fF over a voltage range of 7 V to 30 V. Also, the device demonstrates self-resonance frequencies over 50 GHz, and Q’s over 100 at 10 GHz. To enable integration into circuits, a simple equivalent circuit model of the device has been developed, demonstrating a good match to the measured data through 25 GHz. Initial testing to 1 billion cycles indicates that metal fatigue is the primary limitation to reliability and reproducibility, and that dielectric charging does not have a significant impact on the device. This device is promising for high-performance tunable filters, phase shifters, and other reconfigurable networks at frequencies through K-band.