La spectroscopie dans l'Ultraviolet sous vide et Photoélectronique des Fluoroétylènes. Les 1,1-, cis- et trans-C2H2FCl.

The vacuum ultraviolet absorption spectra of the three fluorochloroethene isomers were measured in the 6-13 eV photon energy range. Additionally, the HeI and NeI photoelectron spectra were recorded. The assignment of the various photoelectron bands is based on MNDO calculations. The vaccum UV absorption spectral features were classified in terms of Rydberg series converging to the first and second ionization energy. Besides the typical pi-pi* transition, other valence transitions were observed and tentatively assigned. In the geminal isomer spectrum the dominant Rydberg series converge to the first ionization limit at 10.02 eV, in the cis and trans isomers the most intense Rydberg transitions converge to the second ionization energy at 11.87 and 12.03 eV respectively. The first ionization energies of these latter compounds, obtained by Rydberg series analysis, are 9.89 and 9.87 eV respectively. An assignment of the vibrational structure observed in both spectra is proposed.ARC - Actions de recherche concertée

High-power high-brightness ridge-waveguide tapered diode lasers at 14xx nm

High-power spatially single-mode diode lasers at 1.4 - 1.5 µm wavelength are of interest as pump lasers for Raman and rare-earth doped fiber amplifiers as well as for material processing and for Light Detection and Ranging (LIDAR) at eye-safe wavelengths. A cost-efficient way to realize high-power high-brightness devices is the tapered resonator concept. We demonstrate InGaAsP/InP based diode lasers with compressively strained quantum wells and wavelengths around 1480 nm which were grown by solid source MBE. From broad area lasers with variations in quantum well number and waveguide layer thickness, parameters for the logarithmic gain model are deduced. With their implementation in 2-dimensional BPM simulations, an optimized resonator geometry is derived. Devices employ a 500 µm ridge section followed by a 2000 µm taper section with 6° angle. Continuous-wave (cw) output powers reach more than 1.5 W. Beam quality is characterized in terms of near field and far field distribution, M2, and astigmatism. An excellent agreement is found between measurement and simulation. For narrow-linewidth operation, devices are provided with anti-reflection coatings on both facets and spectrally stabilized with an external grating. We achieve 0.7 W single mode power and a side mode suppression ratio (SMSR) of 42 dB. Reliability is tested in terms of facet stability and lifetime. Pulsed measurements reveal a power stability up to more than 5 MW/cm2. From cw aging tests at 1 W output power, lifetimes of about 6,000 h are extrapolated

High-peak-power pulsed operation of 2.0 µm (AlGaIn) (AsSb) quantum-well ridge waveguide diode lasers

We have characterized 2.0 µm (aluminium-gallium-indium)(arsenide-antimonide) quantum-well diode lasers in pulsed operation (20-60 ns). A peak power of 1.25 W could be achieved. The near-field distribution on the output facet and the spectral output have been analyzed. Single transverse mode operation can only be maintained at low pulse currents. Above a certain current limit higher order modes occur and fluctuations between these modes have been resolved on a 10 ns time scale. The threshold for thermal and optical damage was investigated for ridge waveguide widths of 6, 8, and 16 µm. No systematic damage threshold could be determined up to current densities as high as 200 kA/cm2

Tunable GaAs-based high power tapered amplifiers in an external cavity setup

In this paper, we report on tapered amplifiers based on the GaInAs/AlGaAs-on-GaAs material system, where the active region consists of a 7 nm thick compressively strained InGaAs single quantum well with an indium content of 31%. The devices comprise an index-guided ridge waveguide section acting as a master oscillator which feeds a gain-guided tapered section. A novel split contact design enables us to separately adjust the currents in the ridge- and the taper section. Therefore, a modulation of the output power can be realized by varying the comparatively small ridge current only

MODFET technology optimization for MMICs using statistical microwave characterization

77 GHz LNAs and TWAs operating from DC to 80 GHz were fabricated successfully (1),(2) using a highly reproducible MODFET technology with mushroom gates of 0.16 mym length. Technology development and optimization were carried out using DC and RF wafer mapping. A high yield high performance transistor process required for 70 to 80 GHz applications was therefore established

(AlGaIn)(AsSb) quantum well diode lasers with improved beam quality

Type-I diode lasers based on the (AIGaIn)(AsSb) material family are ideally suited to cover the 2-3 µm wavelength range. In this paper recent progress in terms of output power, beam quality and wavelength tunability is reported, achieved for broad-area and tapered single emitters as well as for linear broad-area laser arrays. Special attention has been paid to the reduction of the fast axis far-field beam divergence, employing improved vertical waveguide laser designs. Furthermore, tapered diode lasers have been developed in order to increase the slow axis beam quality at high output powers. An improved beam quality is of particular importance as many applications, including coupling the laser output into an optical fiber or into an external resonator, require diode lasers with a low beam divergence and a high brightness rather than sheer output power

Relating mym-wave mapped data to physical parameters for MODFETs.

Modulation doped Alsub0.2Gasub0.8As/Insub0.3Gasub0.7As high electron mobility transistors (HEMT) were statistically characterized at my-wave frequencies. The results provided information to optimize transistor fabrication technology and as well to investigate transistor reliability and reproducibility to allow the design of multi stage low noise amplifiers (LNAs)

GaSb-based micro-mechanical external-cavity laser emitting around 2.3µm

We report on GaSb-based quantum-well diode lasers in a micro-machined external cavity setup using the Littrow-configuration. An electrostatically actuated Si - grating, optimized to achieve a wide tuning range in the 2.3 µm wavelength range, is used as a tuning element

Influence of RIE- induced damage on luminescence and electron transport properties of AlGaAs-GaAs heterostructures.

Reactive ion etching induced damage was systematically studied by photoluminescence (PL), cathodoluminescence (CL) and electronic microwave absorption in GaAs/AlGaAs multiple quantum well (MQW) and two-dimensional electron gas (2DEG) heterostructures. Using QW's of differing widths at various depths, PL and CL characterization of the individual quantum wells allowed a depth sensitive detection of RIE induced damage. Etching was done with CCl sub 2 F sub 2 at constant pressure and exposure time, while the bias voltage was successively increased from 55 to 320 V. A remarkable degradation in PL-intensity was observed for the topmost 1 nm QW located 30 nm beneath the surface, even at the lowest etch bias voltage. In 2 DEG heterostructure samples investigated electrically, both mobility and carrier concentration of the 2 DEG were seen to be strongly reduced. After illumination however, the initial values were almost completely restored, indicating that RIE damage predominantly reduces the e lectron supply efficiency of the AlGaAs barrier, whereas the 2 DEG channel itself is not severely degraded even at the highest etch bias voltage

Indirect optically controlled pseudomorphic HEMT based MMIC oscillator

For the first time an indirect optically controlled monolithic integrated oscillator was fabricated and examined experimentally. The oscillator was designed for a frequency of about 7 GHz. By illuminating a 60x60 square mym photodiode by the light of a pigtailed laser diode (Lambda=840 nm), the free-running frequency of the oscillator was tunable in a range of more than 7 MHz. A locking range of more than 3 MHz was achieved. A phase shift in the output signal of nearly 180 degree has been observed