The major challenge in todays photonic crystal fabrication is the
experimental realization of perfect, disorder-free structures. Macroporous silicon etching is a versatile technique for the manufacturing of large-scale well-ordered porous materials and
three-dimensional photonic crystals. We investigate the degree of
local disorder by scanning electron microscopy and a subsequent
image processing, as well as the homogeneity of our large area
crystals by an optical two-dimensional mapping. The observed
disorder is related to the applied fabrication parameters. The
deduced dependencies help to avoid disorder and to optimize our
The fabrication of three-dimensional photonic bandgap materials and the controlled incorporation of point, linear and planar defects into these crystals is a major challenge in materials research today. We show in this report that these purposes can be achieved by photoelectrochemical etching of lithographically prestructured silicon. Our advanced etching method allows the fabrication of three-dimensional photonic crystals with simple cubic symmetry. The performed calculations suggest complete bandgaps of 5% for the realized bulk structures. By lithographic prestructuring vertical line and planar defects can be induced, whereas horizontal planar defects can be created during the etching step. By combining both structuring techniques point defects can be fabricated.
We present an all-solid-state, transportable photoacoustic spectrometer operated with a continuous-wave optical parametric oscillator. The PPLN-based OPO has a dual cavity configuration (pump-resonant singly-resonant) in order to combine low threshold with good tuning characteristics. A complete spectral coverage between 3.1 and 3.9 μm with a single-frequency output power of 2 x 100 mW is achieved. At 30 seconds lock-in time constant the noise level of the background corresponds to a minimum absorption coefficient of 7.2 x 10-10 cm-1, yielding an ethane detection limit of 25 ppt. The OPO based photoacoustic spectrometer including the wavemeter is installed on a 120 cm x 75 cm breadboard. The ethane concentration of ambient air is determined by a multigas analysis. Additionally an online-measurement of biogenic ethane emissions by a freeze-stressed lima bean leaf is presented. The results indicate a high potential of this transportable spectrometer for biological and medical applications.
An all-solid-state infrared trace gas sensor is presented combining a continuous-wave optical parametric oscillator (OPO) with Cavity Leak-Out spectroscopy (CALOS), a cw version of Cavity Ring Down spectroscopy. The PPLN based pump resonant, singly resonant OPO is pumped at 1064 nm (2 W). Dual cavity design allows to select any desired wavelength within the emission range of the OPO (3.1 - 3.8 μm) and to use different tuning schemes in order to scan absorption features. To detect the CALOS signals the OPO frequency is scanned over the cavity resonance at kHz rates. The high power of the OPO (up to 100 mW at each end of the cavity) allows a strong excitation of the TEM00 mode of the cavity, yielding large detector signals. A noise-equivalent absorption coefficient of 1.6*10-10cm-1/√Hz is reached for integration times up to 180 sec. This corresponds to a detection limit for ethane at sub-ppt level. Measurements at reduced pressure (100 mbar) combined with a scanning of the OPO over cm-1 wide regions allows a multi-gas analysis of ambient air and human breath samples without a cooling-trap.