Application of antimonide diode lasers in photoacoustic spectroscopy

First investigations of photoacoustic (PA) spectroscopy (PAS) of methane using an antimonide semiconductor laser are reported. The laser fabrication is made in two steps. The structure is firstly grown by molecular beam epitaxy, then a metallic distributed-feedback (DFB) grating is processed. The laser operates at 2371.6 nm in continuous wave and at room temperature. It demonstrates single-mode emission with typical tuning coefficients of 0.04 nm mA(-1) and 0.2 nm K(-1). PA detection of methane was performed by coupling this laser into a radial PA cell. A detection limit of 20 ppm has been achieved in a preliminary configuration that was not optimised for the laser characteristics.     

Variation en fonction de la temperature de l'energie liberee lors de la recristallisation d'argent de haute purete deforme par laminage

The results of isothermal calorimetric determination of the stored energy for 99.999% pure polycrystalline rolled silver are reported. The stored energy values were found to be linearly related to the recrystallization temperature. An explanation of this effect is given in terms of the specific heat difference between the rolled and annealed states.

---

Zusammenfassung Die isotherme kalorimetrische Bestimmung der gespeicherten Energie von 99,999% reinem, polykristallinem Walzsilber wurde beschrieben. Die Werte für die gespeicherte Energie sind der Rekristallisationstemperatur proportional. Eine Erklärung für diesen Effekt wurde in Form eines Ausdruckes des Unterschiedes zwischen spezifischer Wärme von gewalztem und getempertem Silber gegeben.

---

99,999%. , . .

     

Picosecond timescale carrier dynamics of InAs quantum dots: The role of a continuum background

We have investigated the ultrafast carrier dynamics in Molecular Beam Epitaxy (MBE)-grown InAs/InGaAs/GaAs quantum dots emitting at 1.3 μm by means of time resolved photoluminescence upconversion measurements with a time resolution of about 200 fs. The detection energies scan the spectral region from the energy of the quantum dot excitonic transition up to the barrier layer absorption edge. We found, under high excitation intensity, that the intrinsic electronic states are populated mainly by carriers directly captured from the barrier.     

Structure of foliations of codimension greater than one

We study the structure of a foliation of high codimension which admits a transverse foliation. We introduce four families of open saturated sets. These open sets have a simple characterization and allow us to establish a structure theorem as in codimension 1.     

Improvements to Vehicle Routeing Heuristics

An interactive method for the vehicle routeing problem has been developed, which attempts to refine routes produced by existing methods. Improvements have been found for some of the standard problems, and the new shortest-distance solutions are reported here.     

Nonlinear mixing between the emission of a cw laser and a femtosecond laser

We mix the emission of a femtosecond Ti:sapphire laser with the emission of a continuous wave infrared laser in a beta-barium borate crystal. Green light with a center wavelength of 527 nm and a spectral width of 2.5 nm resulting from sum frequency generation is detected. An intensity study verifies that a nonlinear χ⁽²⁾ process is at the origin of the green light generation. The experimentally obtained conversion efficiency of 7 × 10⁻¹⁰ is in good agreement to simple theoretical considerations.