Coherent coupling of multiple transverse modes in quantum cascade lasers.

Quantum cascade lasers are a unique laboratory for studying nonlinear laser dynamics because of their high intracavity intensity, strong intersubband optical nonlinearity, and an unusual combination of relaxation time scales. Here we investigate the nonlinear coupling between the transverse modes of quantum cascade lasers. We present evidence for stable phase coherence of multiple transverse modes over a large range of injection currents.

Time-domain upconversion measurements of group-velocity dispersion in quantum cascade lasers.

A time-resolved mid-infrared upconversion technique based on sum-frequency generation was applied to measure pulse propagation in lambda approximately 5.0 mum quantum cascade lasers operated in continuous wave at 30 K. The wavelength-dependent propagation delay of femtosecond mid-infrared pulses was measured to determine the total group-velocity dispersion.

Bowtie plasmonic quantum cascade laser antenna.

We report a bowtie plasmonic quantum cascade laser antenna that can confine coherent mid-infrared radiation well below the diffraction limit. The antenna is fabricated on the facet of a mid-infrared quantum cascade laser and consists of a pair of gold fan-like segments, whose narrow ends are separated by a nanometric gap. Compared with a nano-rod antenna composed of a pair of nano-rods, the bowtie antenna efficiently suppresses the field enhancement at the outer ends of the structure, making it more suitable for spatially-resolved high-resolution chemical and biological imaging and spectroscopy.

Near-field imaging of quantum cascade laser transverse modes.

We report near field imaging of the transverse lasing modes of quantum cascade lasers. A mid-infrared apertureless near-field scanning optical microscope was used to characterize the modes on the laser facet. A very stable mode pattern corresponding to a TM(00) mode was observed as function of increasing driving current for a narrow active region quantum cascade laser.

Intra-cavity absorption spectroscopy with narrow-ridge microfluidic quantum cascade lasers.

We demonstrate microfluidic laser intra-cavity absorption spectroscopy with mid-infrared lambda approximately 9mum quantum cascade lasers. A deepetched narrow ridge waveguide laser is placed in a microfluidic chamber. The evanescent tails of the laser mode penetrate into a liquid on both sides of the ridge.

Semiconductor laser insert with uniform illumination for use in photodynamic therapy.

A low-cost semiconductor red laser light delivery system for esophagus cancer treatment is presented. The system is small enough for insertion into the patient's body. Scattering elements with nanoscale particles are used to achieve uniform illumination.