S. D. Allen

Incoherent mirrorless bistable optical devices

A new class of bistable optical devices is described which do not require resonators or single‐mode lasers. Optical bistability was demonstrated using a LiNbO3 electro‐optic modulator and a multimode laser.

Transient response of hybrid bistable optical devices

The response of a hybrid bistable optical device to step inputs of light was studied experimentally. The results confirm theoretical predictions concerning the dependence of switching time on the applied light increment. For the first time the phenomenon of ’’critical slowing down’’ is observed directly.

The Measurement of Circular Dichroism in the Vacuum Ultraviolet

An instrument is described for the measurement of circular dichroism in the vacuum ultraviolet. A magnesium fluoride Rochon prism serves as polarizer and a stress plate modulator is the ¼‐wave retardation element. CD spectra have been recorded to 165 nm, but substitution of two elements in the optical system by available parts is expected to allow further extension of the wavelength region accessible. A previously used less successful system is also described which used a rotating Rochon prism and a Fresnel rhomb.

Circular dichroism of an optically active benzene chromophore‐1‐methylindan

The gas phase circular dichroism and absorption spectra of a conformationally stable, optically active benzene chromophore, S‐(+)‐1‐methylindan, has been measured from 280 to 170 nm. The structure of the CD spectrum differs from that of the absorption in the B1u region and this observation is interpreted as evidence for the presence of a σ−π* or π−σ* E1g state in addition to the π−π* B1u state. Also, the CD spectrum near 190 nm requires the conclusion that an additional electronic state is located between the analogs of the B1u and E1u states. This state is assigned as E2g, in agreement with consistent theoretical predictions. The observed CD spectra can be accounted for in a consistent manner on the basis of a scheme which uses the results of parametrized calculations of coupled‐oscillator contributions and one‐electron term calculation results due to Caldwell and Kauzmann for the molecule studied.

Multimode integrated optical bistable switch

A multimode integrated optical bistable switch using a LiNbO(3) phase modulator in a noncavity configuration was constructed and tested. Bistability and discriminator operation were observed in this device using a He-Ne laser.

Infrared laser‐induced desorption of H2O and hydrocarbons from optical surfaces

Laser‐induced desorption has been demonstrated for strongly optically absorbing molecules on nominally transparent substrates. Both H2O and hydrocarbon contaminants were desorbed using a pulsed HF/DF laser source at 2.8 and 3.7 μm. Following laser desorption of H2O, the 2.8‐μm damage threshold in CaF2 roughly doubled. Surface mapping of H2O desorption with a 120‐μm‐diam focal spot showed considerable variation with spatial position on polished CaF2, indicating localized concentrations of adsorbate.

Contaminant and defect analysis of optical surfaces by infrared laser induced desorption

Infrared laser induced desorption (LID) has been demonstrated for water and other contaminants on nominally transparent substrates. For the samples measured to date, the LID is defect dominated for both small (120 μm) and large (380 μm) spot sizes. For the larger spot sizes, the data for multiple irradiations of the same site (N/1) can be explained using a simple defect model. The surface damage threshold of these materials correlates with the measured LID fluence, i.e., samples and sites with high contaminant fluences damage at low thresholds. Laser cleaned surfaces of CaF2, BaF2, and NaCl which were dosed with H2O at approximately −100 °C showed no evidence of readsorbed water on subsequent LID testing, indicating a passivation of the surface.

The magnetic circular dichroism spectrum of benzene and toluene and the magnetic moment of the 1E1u state

Abstract The magnetic circular dichroism (MCD) spectra of benzene and toluene in the vapor phase were measured in the 1 E 1u region. The MCD spectrum of benzene is complex and is not interpreted. The MCD spectrum of toluene exhibits a large A -term component, and moment analysis is used to deduce the magnetic moment of the 1 E 1u state of benzene from these data. An LCAO MO calculation results in a magnetic moment in satisfactory agreement with the experimental value. The MCD measurements are the first to be reported in the vacuum UV spectral region.

Laser Chemical Vapor Deposition Using Continuous Wave And Pulsed Lasers

The deposition rate in laser chemical vapor deposition (LCVD) is a function of the surface temperature and therefore also a function of the chang-ing reflectivity of the surface during deposition. The influence of these parame-ters on the LCVD rate of metallic and insulating thin films was investigated using both pulsed and cw laser sources and optical monitoring of the depositing film thickness. Physical properties of the LCVD films are reported.

Calorimetric measurement of LiNbO3 waveguide absorption losses

This paper reports the first measurement of optical‐absorption loss in LiNbO3 waveguides and bulk material. This is also the first demonstration of calorimetry as a feasible technique for measuring waveguide absorption in integrated optics. Results indicate that in LiNbO3 out‐diffused waveguides the absorption is two orders of magnitude lower than the total loss, implying that the predominant loss mechanism is scattering. The ultimate sensitivity limit for calorimetric determination of absorption losses appears to be ∼10−4 dB/cm for optimized geometries.