Multiphoton vibrational pumping on optically prepared NO2 molecules

Reported is the collisionless infrared multiphoton excitation of NO₂ molecules initially prepared in an electronically excited state. From the shape of the infrared induced blue-shifted fluorescence spectrum the probability distribution P(n) for the net absorption of n photons has been deduced.     

Studies in laser safety of new high-output systems: 2. TEA CO2 laser impacts

The new TEA (transversely excited atmospheric pressure) CO₂ laser can produce ionization of air. No information is as yet available of the effect of this new high-power output laser on man. Repeated impacts of 30 mJ pulses with 100 kW, which produced ionization of air, caused non-specific superficial coagulation necrosis which healed promptly.     

Maximizing band gaps in two-dimensional photonic crystals by using level set methods

The optimal design of photonic band gaps for two-dimensional square lattices is considered. We use the level set method to represent the interface between two materials with two different dielectric constants. The interface is moved by a generalized gradient ascent method. The biggest gap of GaAs in air that we found is 0.4418 for TM (transverse magnetic field) and 0.2104 for TE (transverse electric field).     

Junction field-effect-transistor-based germanium photodetector on silicon-on-insulator

We propose and demonstrate a novel Ge photodetector on silicon-on-insulator based on a junction field effect transistor structure, where the field-effect transistor gate is replaced by a Ge island with no contact on it. Light incident on the Ge switches on the device by altering the conductance of the Si channel through secondary photoconductivity. The device's sensitivity is also enhanced by a vast reduction in parasitic capacitance. In cw measurements, proof-of-concept detectors exhibit up to a 33% change in Si channel conductance by absorbing only 200 nW of power at 1.55 microm. In addition, pulsed response tests have shown that rise times as low as 40 ps can be achieved.     

A simple self-triggered plasma shutter

A simple self-triggered plasma shutter for switching a high power laser beam was demonstrated. The triggering action comes from the surface plasma of a metal target. Several materials were tested and it was found that for copper, the amplitude fluctuation in the triggering was only 5%.