N-Type Bismuth Telluride Nanocomposite Materials Optimization for Thermoelectric Generators in Wearable Applications.

Thermoelectric materials could play a crucial role in the future of wearable electronic devices. They can continuously generate electricity from body heat. For efficient operation in wearable systems, in addition to a high thermoelectric figure of merit, , the thermoelectric material must have low thermal conductivity and a high Seebeck coefficient.

Type VIII Si based clathrates: prospects for a giant thermoelectric power factor.

Although clathrate materials are known for their small thermal conductivity, they have not shown a large thermoelectric power factor so far. We present the band structures of type VIII Si, Ge, and Sn clathrates as well as the alkali and alkaline-earth intercalated type VIII Si clathrates. Our calculations revealed that this group of materials has potentially large power factors due to the existence of a large number of carrier pockets near their band edges.

The convergence of longitudinal excitons onto the Γ5 transverse exciton in GaN and the thermal activation energy of longitudinal excitons.

The crystal orientation dependence of GaN excitons was investigated via the photoluminescence (PL) technique. The PL emissions at a temperature of 10 K were obtained from two experimental configurations where the emission K vector (the propagation vector) was either parallel (K ∥ c) or perpendicular (K ∥ c) to the crystal c-axis. Longitudinal, transverse and donor-bound excitons were observed in the two configurations.

Trans-rectal ultrasound-coupled spectral optical tomography of total hemoglobin concentration enhances assessment of the laterality and progression of a transmissible venereal tumor in canine prostate.

Objectives: To evaluate whether trans-rectal spectral optical tomography of total hemoglobin concentration (HbT) can image longitudinal and lateral developments of a canine transmissible venereal tumor (TVT) in a canine prostate.

Methods: A near-infrared (NIR) applicator was integrated with a trans-rectal ultrasound (TRUS) transducer to perform ultrasound (US)-coupled optical tomography of the canine prostate. Spectral detection at 785 and 830 nm enabled quantitation of HbT.

Trans-rectal ultrasound-coupled near-infrared optical tomography of the prostate, part II: experimental demonstration.

We demonstrate trans-rectal optical tomography of the prostate using an endo-rectal near-infrared (NIR) applicator integrated with a transrectal ultrasound (TRUS) probe. The endo-rectal NIR applicator incorporated a design presented in our previously reported work. A continuous-wave NIR optical tomography system is combined with a commercial US scanner to form the dual-modality imager.

Endoscopic, rapid near-infrared optical tomography.

This is believed to be the first demonstration of near-infrared (NIR) optical tomography employed at the endoscope scale and at a rapid sampling speed that allows translation to in vivo use. A spread-spectral-encoding technique based on a broadband light source and linear-to-circular fiber bundling was used to provide endoscopic probing of many source-detector fibers for tomography as well as parallel sampling of all source-detector pairs for rapid imaging. Endoscopic NIR tomography at an 8 Hz frame rate was achieved in phantoms and tissue specimens with a 12 mm probe housing eight sources and eight detectors.

Bimorph piezo deformable mirror for femtosecond pulse shaping.

We have developed a bimorph piezoceramic deformable mirror with 28 independently controlled vertical sectors. When used in a reflective 2 f setup the mirror enables phase compensation in the range of a few hundred radians. We have demonstrated that such a compressor is able to compress femtosecond laser pulses that had been initially stretched by a factor of 60 close to their initial shape.

Piezo-driven deformable mirror for femtosecond pulse shaping.

We have developed a deformable, gold-coated mirror based on piezoelectric actuators with 15-micros response time. With 20 independent channels we were able to compress 72-fs pulses from a Ti:sapphire oscillator down to 45 fs in a 4f zero-dispersion compressor arrangement. Spectral interference was used to measure the mirror performance, while the spectral phase interferometry for direct electric field reconstruction (SPIDER) technique was used for the laser pulse characterization.

Photography of shock waves during excimer laser ablation of the cornea. Effect of helium gas on propagation velocity.

Shadow photography of shock waves excited by means of a xenon chloride excimer laser was performed to determine the shock wave propagation velocity in air, nitrogen and helium. Energy densities between 500 and 2,000 mJ/cm2 were used to ablate a rotating rubber cylindrical target and porcine corneas. In ablating the rubber cylinder, a shock wave velocity of 3.

Increased efficiency for sum-frequency generation for broadband input fields.

A new method of efficient sum-frequency generation for broadband input fields is theoretically analyzed and experimentally demonstrated. The method involves using an arrangement with two or more nonlinear mixing crystals, with a time-delay line situated between the crystals, for one of the fundamental fields relative to the other. The delay line temporally shifts the fundamental fields, one relative to another, by a time longer than their coherence time.

Theory of mode-locked intracavity second-harmonic generation in a ring laser.

We model the dynamics of a Q-switched mode-locked intracavity second-harmonic-generation (SHG) ring laser. Numerical studies show that a long train of constant-pulse-duration short pulses at the second-harmonic and fundamental frequencies result. The efficiency of the mode-locked intracavity SHG laser is comparable with that of the mode-locked fundamental-frequency laser not containing SHG.

Birefringence of solid-state laser media: broadband tuning discontinuities and application to laser line narrowing.

Spectral consequences that result from using birefringent media with broadband gain inside of laser cavities containing polarizing elements are described. We show that the laser intensity is modulated as a function of the output frequency unless the cavity elements are carefully aligned so that their polarization axis coincides with a principal optical axis of the gain medium. Analysis of the tuning characteristics of a birefringent polarizationdependent gain medium is exploited to provide a simple method for line narrowing the laser output.

The two-photon laser-induced fluorescence of the tumor-localizing photosensitizer hematoporphyrin derivative. Resonance-enhanced 750 nm two-photon excitation into the near-UV Soret band.

The tumor-localizing photosensitizer hematoporphyrin derivative (HPD) is shown to undergo a simultaneous two-photon excitation into the near-ultraviolet Soret band system upon intense laser irradiation at 750 nm, a spectral region where there is no significant HPD one-photon absorbance in aqueous solution. Subsequent to this excitation, internal conversion and vibrational relaxation occur, resulting in the population of the vibrationless level of the first electronically excited singlet state. This state relaxes by two channels, the emission of fluorescence in the spectral region 600-700 nm and intersystem crossing into the triplet manifold, followed by near-resonant electronic energy transfer with surrounding oxygen to result in the generation of highly reactive singlet molecular oxygen (1 delta g).

Observation of resonantly enhanced sum-frequency generation involving sodium Rydberg states.

A large, dc-electric-field-induced nonlinear optical susceptibility is exploited to produce ultraviolet radiation in the range 2453-2476 A by the process of sum-frequency generation in sodium. The interaction is resonantly enhanced at the first intermediate level by the 3 (2)P(3/2) state and at the second intermediate level by a Rydberg state. Conversion efficiencies of 10(-5) have been obtained; improvement of this value by a factor of 10(3) should be possible.