Thomas A. Rabson

Ferroelectric switching of a field-effect transistor with a lithium niobate gate insulator

A field‐effect transistor in which the ferroelectric lithium niobate (LiNbO3) replaces the oxide in a conventional metal‐oxide‐semiconductor transistor has been fabricated. The channel conductance of this device has been shown to be strongly affected by the application of voltage pulses between the gate of the device and the substrate. A reduction of channel current of nearly 140 μA was observed after the application of a voltage pulse of −30 V and partially restored with a+10‐V pulse. This behavior was found to be consistent with the influence of the polarization charge of the LiNbO3 layer on the carriers in the channel. This is the first observation of such behavior in a metal‐ferroelectric‐semiconductor field‐effect transistor without the growth of a buffer layer between the semiconductor and ferroelectric to prevent charge injection.

Deposition and analysis of lithium niobate and other lithium niobium oxides by rf magnetron sputtering

The deposition of thin films of lithium niobate (LiNbO3) on silicon with rf magnetron sputtering has been investigated. A matrix of experiments was designed to determine the effect of several parameters on the resulting film quality. Under optimized conditions, oriented polycrystalline films of LiNbO3 are produced that exhibit a columnar grain structure with the polar axis normal to the substrate surface. Deviations from sputtering parameters optimized for producing LiNbO3, have been shown to produce films of varying proportions of either LiNb3O8 or Li3NbO4 with LiNbO3. The stoichiometry, microstructure, and electrical properties of selected films have been investigated with Rutherford backscattering, diffractometry, transmission electron microscopy, and a variety of electrical measurement techniques.

Low-loss thin-film LiNbO(3) optical waveguide sputtered onto a SiO(2)/Si substrate.

We report what is to our knowledge the first successful attempt in prism coupling a laser beam into a lithium niobate optical waveguide grown on a thermally oxidized (100) Si substrate by magnetron rf sputtering. Bragg x-ray diffraction, Rutherford backscattering, and birefringence measurements confirm that the sputtered films were nearly stoichiometric as well as highly textured lithium niobate. The refractive indices were n(TE) = 2.199 +/- 0.002 and n(TM) = 2.263 +/- 0.002. The lowest propagation loss in the waveguide was determined to be 1.9 +/- 0.1 dB/cm at a wavelength of 633 nm.

Nonlinear dynamic theory for photorefractive phase hologram formation

A nonlinear dynamic theory is developed for the formation of photorefractive volume phase holograms. A feedback mechanism existing between the photogenerated field and free‐electron density, treated explicitly yields the growth and saturation of the space‐charge field in a time scale characterized by the coupling strength between them. The expression for the field reduces in the short time limit to previous theories and approaches in the long time limit the internal or photovoltaic field. Additionally, the phase of the space‐charge field is shown to be time dependent.

Deposition and physical characterization of thin films of lithium niobate on silicon substrates

Thin films (0.1–0.6 μm) of LiNbO3 have been deposited on silicon substrates by reactive rf sputtering. Under optimized deposition conditions the resulting thin films of LiNbO3 were optically transparent and adhered well to the silicon substrates. X‐ray diffraction showed the films were oriented polycrystalline with the c axis normal to the silicon surface. Rutherford backscattering and Auger electron spectroscopy were used to evaluate the physical properties of these films. Potential applications of this technology include nonvolatile electronic and optical memories, and optical detectors.

Characterization of iron‐doped lithium niobate for holographic storage applications

A detailed study of eight systematically chosen Fe : LiNbO3 crystals is presented. Correlation between the photorefractive sensitivity and various chemical properties of Fe : LiNbO3 is investigated in order to ascertain optimum performance of the crystals in holographic storage and display applications. Concentrations of Fe2+ and Fe3+ ions have been determined from optical and EPR spectra, while impurities have been detected from x‐ray‐emission and infrared spectra. Particular emphasis is placed on investigating the dependence on Fe2+ and Fe3+ ion concentrations of the photorefractive sensitivity. The photorefractive sensitivity is shown to depend primarily on the concentration of Fe2+ ions in Fe : LiNbO3. This fact seems to suggest that Fe2+ ions are the impurity centers responsible for the photorefractive effect in Fe : LiNbO3. Spectral dependence of the photorefractive sensitivity and its modification due to oxygen annealing are also reported. Our results indicate that an unannealed Fe : LiNbO3 crystal...

Efficient Second Harmonic Generation of Picosecond Laser Pulses

Efficient conversion to the second harmonic (SH) using KD2PO4 and CsH2AsO4 crystals inside a folded cavity of a high‐power‐dye mode‐locked Nd3+: glass laser is reported. For the first time, frequency‐doubled picosecond light pulses have been obtained in CsH2AsO4 with peak powers of the order of 109 W/cm2 at 0.531 μ for an effective pump power density of 4×109 W/cm2.

Continuous wave uv radiation tunable from 285 nm to 400 nm by harmonic and sum frequency generation

Broadly tunable cw uv radiation has been generated by frequency doubling and sum frequency mixing in ADP, ADA, and RDP, using the output of a Kr laser, a Rh6G dye laser, and an oxazine 1 dye laser. Continuous tunable uv radiation has been obtained from 285 nm to 400 nm with a maximum power of 750 microW at 313 nm and with powers in excess of 5 microW from 290 nm to 390 nm.

Volume holographic recording and storage in Fe-doped LiNbO3 using optical pulses

Volume holographic recording and storage in Fe‐doped LiNbO3 using single 30–75‐nsec duration optical pulses at 694.3 and 531 nm from Q‐switched ruby and frequency‐doubled Nd:glass lasers, respectively, is reported. The recording sensitivity for a pulsed writing source is found to be better than that estimated for a cw source. A sensitivity of 2 mJ/cm2 at 476 nm and 2.5 mJ/cm2 at 488 nm to record a hologram of 1% diffraction efficiency is the best sensitivity figure yet reported. The orders of magnitude of improvement in sensitivity is attributed to higher fractional concentration of Fe2+.

Stimulated parametric fluorescence induced by picosecond pump pulses

Stimulated parametric fluorescence emission tunable over the range from 0.96 to 1.16 μ has been obtained using a barium sodium niobate crystal pumped by a frequency‐doubled and mode‐locked Nd3+:glass laser. The pump radiation in the form of a train of picosecond pulses produced infrared parametric fluorescence pulses, less than 10 psec in duration and with average peak powers on the order of 300 W when pumped with a power density of 300 MW/cm2.