Determination of the spatial snow-depth distribution is important in potential avalanche-starting zones, both for avalanche prediction and for the dimensioning of permanent protection measures. Knowledge of the spatial distribution of snow is needed in order to validate snow depths computed from snowpack and snowdrift models. The inaccessibility of alpine terrain and the acute danger of avalanches complicate snow-depth measurements (e.g. when probes are used), so the possibility of measuring the snowpack using terrestrial laser scanning (TLS) was tested. The results obtained were compared to those of tachymetry and manual snow probing. Laser measurements were taken using the long-range laser profile measuring system Riegl LPM-i800HA. The wavelength used by the laser was 0.9 μm (near-infrared). The accuracy was typically within 30 mm. The highest point resolution was 30 mm when measured from a distance of 100 m. Tachymetry measurements were carried out using Leica TCRP1201 systems. Snowpack depths measured by the tachymeter were also used. The datasets captured by tachymetry were used as reference models to compare the three different methods (TLS, tachymetry and snow probing). This is the first time that the accuracy of TLS systems in snowy and alpine weather conditions has been quantified. The relative accuracy between the three measurement methods is bounded by a maximum offset of ±8 cm. Between TLS and the tachymeter the standard deviation is 1σ = 2 cm, and between manual probing and TLS it is up to 1σ = 10 cm, for maximum distances for the TLS and tachymeter of 300 m.
Recent advances in materials science have made it possible to perform photolithography at the nanoscale using visible light. One approach to visible-light nanolithography (resolution augmentation through photo-induced deactivation) uses a negative-tone photoresist incorporating a radical photoinitiator that can be excited by two-photon absorption. With subsequent absorption of light, the photoinitiator can also be deactivated before polymerization occurs. This deactivation step can therefore be used for spatial limitation of photopatterning. In previous work, continuous-wave light was used for the deactivation step in such photoresists. Here we identify three broad classes of photoinitiators for which deactivation is efficient enough to be accomplished by the ultrafast excitation pulses themselves. The remarkable properties of these initiators result in the inverse scaling of lithographic feature size with exposure time. By combining different photoinitiators it is further possible to create a photoresist for which the resolution is independent of exposure over a broad range of fabrication speeds.
We propose a method to fabricate three-dimensional (3D) metallic movable microparts by the combination of two-photon microfabrication and electroless plating. In this method, polymeric movable microparts with anchors made by two-photon microfabrication are metalized by electroless plating, and then the anchors are removed by laser ablation using a femtosecond pulsed laser. As a result, a metalized freely movable micropart whose motion is restricted to a shaft can be produced. We succeeded in fabricating sophisticated 3D metallic microrotors by adjusting the experimental conditions of both electroless copper plating and laser ablation. #
Distributed feedback (DFB) interband cascade lasers (ICLs) with a 1st order top surface grating were designed and fabricated. Partially corrugated sidewalls were implemented to suppress high order lateral modes. The DFB ICLs have 4 mm long and 4.5 μm wide ridge waveguides and are mounted epi-up on AlN submounts. We demonstrated a continuous-wave (CW) DFB ICL, from a first wafer which has a large detuning of the gain peak from the DFB wavelength, with a side mode suppression ratio of 30 dB. With proper matching of grating feedback and the gain peak wavelength for the second wafer, a DFB ICL was demonstrated with a maximum CW output power and a maximum wall plug efficiency reaching 42 mW and 2%, respectively, at 25 °C. The lasing wavelengths of both lasers are around 3.3 μm at 25 °C.
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