Daniel Tod Smithey

Hydroxypropyl Methylcellulose Acetate Succinate-Based Spray-Dried Dispersions: An Overview

Spray-dried dispersions (SDDs) of low-solubility drugs have been prepared using the polymer hydroxypropyl methylcellulose acetate succinate (HPMCAS). For a variety of drug structures, these SDDs provide supersaturation in in vitro dissolution determinations and large bioavailability increases in vivo. In bile-salt/lecithin in vitro solutions, these SDDs provide amorphous drug/polymer colloids and an increased concentration of free drug and drug in micelles relative to crystalline or amorphous drug. As dry powders, the SDDs are a single amorphous phase in which the drug remains amorphous and dispersed and does not crystallize over storage times relevant for practical drug products. A melting temperature (Tm)/glass-transition temperature (Tg) (K/K) versus log P map for 139 compounds formulated as SDDs provides a perspective on an appropriate formulation strategy for low-solubility drugs with various physical properties.

Complete experimental characterization of the quantum state of a light mode via the Wigner function and the density matrix: application to quantum phase distributions of vacuum and squeezed-vacuum states

We have used the recently demonstrated method of optical homodyne tomography (OHT) to measure the Wigner quasiprobability distribution (Wigner function) and the density matrix for both a squeezed-vacuum and a vacuum state of a single spatial-temporal mode of the electromagnetic field. This method consists of measuring a set of probability distributions for many different Hilbert-space representations of the field-quadrature amplitude, using balanced homodyne detection, and then using tomography to obtain the Wigner function. Once the Wigner function is obtained, one can acquire the density matrix, including its complex phase. In the case of a pure state, this technique yields an experimentally determined complex wavefunction, as demonstrated here for the vacuum. The density matrix represents a complete quantum mechanical characterization of the state. From the measured density matrix we have obtained the Pegg–Barnett optical phase distribution, and from the Wigner function, the Wigner optical phase distribution.

Long holographic lifetimes in bacteriorhodopsin films

The D85N genetic variant of bacteriorhodopsin (BR) displays a nearly permanent lifetime of the photochromic P(490) state. We present pump-probe measurements that demonstrate this behavior. However, diffraction efficiency measurements made from holograms recorded in a hydrated D85N film show markedly different decay behavior, suggesting that a molecular diffusion process is occurring in the film. Holograms recorded with different grating frequencies display correspondingly different decay times, thus supporting this hypothesis. A thin D85N film was fabricated that was chemically cross linked, resulting in the elimination of diffusion of BR molecules within the polymer matrix. This film exhibits a grating lifetime of the order of weeks or more, thus permitting the long-term holographic storage of information.

Ultrafast measurement of optical-field statistics by dc-balanced homodyne detection

The technique of dc-balanced, pulsed homodyne detection for the purpose of determining optical-field statistics on short time scales is analyzed theoretically. Such measurements provide photon-number and phase distributions associated with a repetitive signal light field in a short time window. Time- and space-varying signal and local-oscillator pulses are treated, thus generalizing earlier treatments of photoelectron difference statistics in homodyne detection. Experimental issues, such as the effects of imperfect detector balancing on (time-integrated) dc detection and the consequences of background noise caused by non-mode-matched parts of the multimode signal field, are analyzed. The Wigner, or joint, distribution for the two field-quadrature amplitudes during the sampling time window can be directly determined by tomographic inversion of the measured photoelectron distributions. It is pointed out that homodyne detection provides a new method for the simultaneous measurement of temporal and spectral information. Although the theory is generally formulated, with both signal and local-oscillator fields being quantized, emphasis is placed on the limit of a strong, coherent local-oscillator field, making semiclassical interpretation possible.

Experimental determination of number–phase uncertainty relations

An experimental determination of the uncertainty product for the phase and photon number of a mode of the electromagnetic field is performed. The expectation value of the commutator that sets the lower bound for the uncertainty product is also determined experimentally. This is accomplished by using optical homodyne tomography to measure the density matrix of a small-photon-number coherent state. The experimental results agree with the quantum-mechanical predictions.

Red-shifted photochromic behavior of a bacteriorhodopsin film made from the L93T genetic variant

We present experimental results demonstrating the red-shifted photochromic behavior of a gelatin film made from L93T, a genetic variant of bacteriorhodopsin. The red shift of the absorbance spectrum on illumination with visible light is due to a short M-state lifetime and a longer-lived O state whose absorption peaks at 610 nm. Pump-probe measurements show the O state to have a lifetime of approximately 2.2 s in the gelatin film, with a single exponential decay behavior. We also present holographic kinetic results for both red (633-nm) and blue (442-nm) readout wavelengths.

Bit-error-rate issues for holographic data storage in bacteriorhodopsin films

Photochromic films made from bacteriorhodopsin (BR) possess many desirable characteristics for a candidate holographic optical data storage medium. These properties include optical erasability, high spatial resolution, adequate diffraction efficiency, flexible film formats, durability, an optimal recording/readout wavelength of about 680 - 690 nm, and potentially inexpensive cost. In this paper, we experimentally study the raw bit-error-rate (BER) achievable with BR films made from the genetic variant known as D85N. Experimental data is collected for digital bit patterns fabricated as chrome-on- glass masks, at two different spatial resolutions. The results show that films fabricated from D85N have good potential for use in holographic data storage systems, but that further effort must be devoted to the film fabrication process in order to minimize optical nonuniformity and scattering losses.