Directional random laser source consisting of a HC-ARROW reservoir connected to channels for spectroscopic analysis in microfluidic devices.

Light sources are used in optofluidic devices for real-time system control and quantitative analysis of important process parameters. In this work, we present a random laser source using a hollow-core antiresonant reflecting optical waveguide (HC-ARROW) containing the gain media inside a reservoir to reduce dye bleaching, which is connected to microchannel waveguides to increase beam directionality. The device is pumped externally and emits a highly coherent and collimated laser beam.

Simple and versatile heterodyne whole-field interferometer for phase optics characterization.

A wavefront sensor for thermally induced lens and passive lens characterization based on low-coherence digital speckle interferometry was developed and studied. By illuminating the optical setup with two slightly detuned red diode lasers, whole-field contour interference fringes were generated according to the resulting synthetic wavelength. For fringe pattern visualization the optical setup used the light transmitted through a ground glass plate as object beam. The performance of the sensor was investigated and its versatility was demonstrated by measuring the thermal lens induced in an Er-doped glass sample pumped by a 1.76-W diode laser emitting at 976 nm and by evaluating the wavefront distortion introduced by an ophthalmic progressive lens.

Spectroscopic properties of lead fluoroborate glasses doped with ytterbium.

A new lead fluoroborate glass (PbO-PbF2-B2O3) doped with ytterbium (Yb:PbFB) is presented. Samples with different concentrations of Yb3+ were produced and had their emission cross-sections, fluorescence lifetimes and minimum pump intensities determined. They have high refractive index of 2.2 and a density of 4.4 g/cm3. For a doping level of 1.153x1020 ions/cm3, the fluorescence lifetime, after excitation at 968 nm, is 0.81 ms, which is comparable to Yb:tellurite laser glass. Also, an emission band at 1022 nm is measured with emission cross-section of approximately 1.07x10-20 cm2 and fluorescence effective linewidth of 60 nm, which is comparable to Yb:phosphate laser glass.

Optical properties of Nd doped Bi2O3-PbO-Ga2O3 glasses.

The optical properties of a new family of neodymium doped BPG (Bi2O3-PbO-Ga2O3 ) glasses are presented. We measured a high refractive index, of 2.5, and a transmission cutoff in the far infrared at 8microm. Three intense emission bands are observed centered at 877nm, 1066nm and 1341nm. The emission cross-section is 10 -20 cm 2 and the total spectral linewidth is 30nm at 1066nm. The Judd-Ofelt parameters are calculated and used to evaluate transition probability, radiative lifetime and branching ratios. The optical properties of these Nd:BPG glasses show promise for their use as a new active laser material.

In vitro T cell immune responses to the preS2 antigen of the hepatitis B virus envelope protein in preS2 + S vaccine recipients. Absence of cross-reactivity of subtypes at a major T cell recognition site.

The immune responses to hepatitis B virus envelope antigen were investigated in 16 vaccine recipients after immunization with a recombinant yeast-derived preS2 + S (adw) vaccine for hepatitis B virus. After the completion of the three-slot immunization series, all vaccine recipients developed antibody to the S domain and anti-preS2 antibody. In vitro proliferative responses to preS2 (120-174) peptide were demonstrated in 10 of 16 vaccine recipients. Although reactivity could be demonstrated through the length of the preS2 peptide, the principal site of proliferative activity was contained within the preS2 (146-165) region of the peptide. The principal T cell reactive site coincides with a region of significant amino acid variability of the different hepatitis B virus serotypes. Cross-reactivity with a serotype (ayw) not present in the preS2 + S vaccine could not be demonstrated at this widely recognized T cell epitope. The low level of cross-reactivity demonstrated in a limited subset of the vaccine recipients was mediated through nondominant T cell reactive sites contained in the relatively conserved preS2 (120-146) region of the molecule. The identification of widely recognized but serotype-specific T cell epitopes in the preS2 region of the hepatitis B virus envelope antigen may be an important consideration in future vaccine development.

Enhanced efficiency of a continuous-wave mode-locked Nd:YAG laser by compensation of the thermally induced, polarization-dependent bifocal lens.

Measurements of the bifocal, thermally induced lenses of a cw Nd:YAG laser were obtained. We observed four different focal lengths that are polarization and direction dependent. The focal lengths were used to design stable resonators with large fundamental mode filling in the laser gain medium. The beam is totally polarized in the desired direction even without an intracavity Brewster window. We developed a general approach for the optimization of single-lamp, cw-pumped Nd:YAG lasers. Up to 22 W of cw output power in the vertically polarized TEM(00) mode and 15 W in the horizontal polarization are obtained for moderate lamp currents. Also, we demonstrate mode locking with 56-ps pulse duration at 33 A of lamp current and up to 13 W of average output power.

Mode-locking operation of a pulsed Nd:YAG laser with F(2) BF:LiF color-center crystal in a dual configuration.

Passive stable mode locking of a pulsed Nd:YAG laser was achieved with a long-decay-time saturable absorber in a coupled-cavity longitudinal scheme. In this configuration the saturable absorber (LiF:F(2) ) also behaves as an active medium in intracavity pumping and is the load for the Nd laser. This arrangement provides proper lasing conditions for the F(2) color centers so that the cavity photon lifetime of the color centers is much shorter than the cavity round-trip time of the Nd laser. In this way the Nd pulses are simultaneously Q switched and mode locked. The pulses show a stable temporal profile, with an envelope of 160 ns and a train of mode-locked pulses of less than 200-ps duration.