Measurement of bound states in the continuum by a detector embedded in a photonic crystal.

We directly measure optical bound states in the continuum (BICs) by embedding a photodetector into a photonic crystal slab. The BICs observed in our experiment are the result of accidental phase matching between incident, reflected and in-plane waves at seemingly random wave vectors in the photonic band structure. Our measurements were confirmed through a rigorously coupled-wave analysis simulation in conjunction with temporal coupled mode theory. Polarization mixing between photonic crystal slab modes was observed and described using a plane wave expansion simulation. The ability to probe the field intensity inside the photonic crystal and thereby to directly measure BICs represents a milestone in the development of integrated opto-electronic devices based on BICs.

High tuning stability of sampled grating quantum cascade lasers.

Predictable tuning behavior and stable laser operation are both crucial for laser spectroscopy measurements. We report a sampled grating quantum cascade laser (QCL) with high spectral tuning stability over the entire tuning range. We have determined the minimum loss margin required to suppress undesired lasing modes in order to ensure predictable tuning behavior. We have quantified power fluctuations and drift of our devices by measuring the Allan deviation. To demonstrate the feasibility of sampled grating QCLs for high-precision molecular spectroscopy, we have built a simple transmission spectroscopy setup. Our results prove that sampled grating QCLs are suitable light sources for highly sensitive spectroscopy measurements.

Higher order modes in photonic crystal slabs.

We present a detailed investigation of higher order modes in photonic crystal slabs. In such structures the resonances exhibit a blue-shift compared to an ideal two-dimensional photonic crystal, which depends on the order of the slab mode and the polarization. By fabricating a series of photonic crystal slab photo detecting devices, with varying ratios of slab thickness to photonic crystal lattice constant, we are able to distinguish between 0th and 1st order slab modes as well as the polarization from the shift of resonances in the photocurrent spectra. This method complements the photonic band structure mapping technique for characterization of photonic crystal slabs.

Image contrast enhancement in confocal ultramicroscopy.

Ultramicroscopy allows for the 3D reconstruction of centimeter sized samples with a spatial resolution of several micrometers. Nevertheless, in poorly cleared or very large specimens the images may suffer from blurring and low contrast levels. To address these problems, ultramicroscopy was combined with the principle of confocal microscopy using a slowly rotating Nipkow disk. This configuration was tested by comparing images from mouse hippocampal neurons and mouse liver blood vessels recorded in confocal and conventional mode. It was found that confocality minimizes the background noise and considerably improves the signal-to-noise ratio when applied to ultramicroscopy.