Single-beam Experiment Research Articles

ChemInform Abstract: Steady‐State Photocapacitance Study of Semiconductor/Electrolyte Junctions. Part 2. Surface State Distribution and Charge Transfer Mechanisms.

AbstractA novel method is presented being based upon photocapacitance measurements without (single beam experiment) or with added interband illumination (dual beam experiment), which allows the determination of the surface state distribution at GaAs/electrolyte interfaces and to follow its evolution during electrochemical processes.

Steady State Photocapacitance Study of Semiconductor/Electrolyte Junctions II. Surface State Distribution and Charge Transfer Mechanisms

AbstractGaAs/electrolyte junctions are characterized by steady state photocapacitance measurements without (single beam experiment) or with added interband illumination (dual beam experiment). This original approach allows to give unambiguously the surface state distribution and to follow its evolution during electrochemical processes: results show the presence of two corrosion related states at EC −0.98 eV and EC −1.14 eV which behave differently under corrosion or photocorrosion conditions. It is shown that surfaces modified by electro‐deposition of discontinuous metal films exhibit metal‐induced surface states responsible for charge transfers.

Squeezing experiments in sodium vapor

We describe our efforts to observe squeezing, and related nonclassical effects, in three forward four-wave mixing experiments using sodium vapor as a nonlinear medium. In a single-beam experiment with homodyne detection, we found optically phase-sensitive noise, which was radio-frequency phase insensitive, in a cw dye-laser beam that had propagated through sodium vapor. The minima of the phase-sensitive noise were always at or above the coherent-state value. In our forward four-wave mixing experiment with probe–conjugate-beam direct detection and correlation, we found that the sodium-vapor interaction produced positive noise correlation between the probe and conjugate beams. The correlation, however, did not exceed the excess noises on these beams, so that a nonclassical behavior was not demonstrated. Finally, our forward four-wave mixing experiment with probe–conjugate-beam combination and homodyne detection did demonstrate the generation of squeezed-state light in our setup. Optically phase-sensitive noise with a minimum falling 4% below the coherent-state level was observed.

Photoselection with intense laser pulses

The method of photoselection uses a polarized photon beam to create a preferentially oriented population of excited state molecules. This population is examined using polarized absorption or emission techniques in order to obtain information about the symmetries of transition moments. Prelaser photoselection was limited in application to exceptionally long-lived states (or stable photoproducts) in perfectly rigid matrices or to strongly fluorescent states in moderately viscous media. With lasers, extension is possible to almost any state with a lifetime of picoseconds or longer, making photoselection a very powerful, general technique. This paper rederives the expected experimental behavior and extends the calculations to include saturation effects, which are prominent in practical laser experiments but were not important in classical studies. Furthermore, it shows that in the nonlinear regime, information on transition moment symmetry is available even from a single beam experiment. One very simple experiment is reported which verifies that one can distinguish ’’planar’’ from ’’linear’’ symmetry in absorbers using absorption methods in very fluid media. These results are most timely for picosecond mode-locked laser experiments but apply also to nanosecond Q switched or even intense continuous wave laser studies.