RESUMO
Optical feedback tolerance is experimentally investigated on a 600-mum-long quantum-dash based Fabry-Pérot laser emitting at 1.57mum. While quantum-dashes are structurally intermediate to quantum-wells and quantum-dots, the observed behaviour is distinctly like that of a quantum-well based laser but with greater stability. Coherence collapse and low-frequency fluctuation regimes are observed and are reported here. The onset of the coherence collapse regime is experimentally determined and is found to vary from -29 dB to -21 dB external feedback level when increasing the current from twice to nine times the threshold current.
RESUMO
This article presents a device for the study of physisorbed elements on polished surfaces (diameter ⩽56 mm) of the kind used in mass metrology. The technique is based on mass spectrometry of molecules desorbed after heating under vacuum of the analyzed surface. We describe a first application of the device to study current and future mass standards in order to understand how their surface reactivity depends on storage conditions, cleaning processes, and polishing methods. Surface contamination analysis by thermal desorption mass spectrometry to examine the effect of cleaning on pure iridium is given as an example.
RESUMO
We describe a transportable distance measurement system based on synthetic wavelength interferometry. Two frequency-doubled Nd:yttrium aluminum garnet lasers at 532 nm are used to generate a synthetic wavelength of approximately 2.5 cm. A nonpolarizing interferometric system has been set up to eliminate polarization cross-talk issue. A superheterodyne detection was performed to measure the synthetic phase and to determine absolute distances. The capability to achieve fringe interpolation of 2pi/5600 has been demonstrated and an agreement in distance measurement at the 4 microm level has been achieved, compared to an optical interferometric 3 m long displacement bench.