Lateral mode constrictions for broad-ridge quantum cascade lasers.

We develop a method for analyzing the lateral modes of broad-ridge quantum cascade lasers (QCLs) that incorporate an intracavity lateral constriction. The calculations provide results that are in good agreement with the recent data taken on broad-ridge QCLs that incorporate such lateral constrictions. We conclude by providing design principles for broad-ridge QCLs that implement an intracavity lateral constriction.

Class of resonator for slab waveguide lasers.

We describe a class of laser resonator, incorporating a feedback collimator (FBC), that provides feedback that is mode-matched onto a higher-order lateral mode of a slab waveguide laser. In addition, this same resonator, in outcoupling, converts the stabilized higher-order lateral mode into an essentially laterally collimated output beam with a width that exceeds twice the width of the laser-active region. This output beam should have excellent beam quality. Here, we develop the FBC resonator design principles and describe both refractive and reflective versions. Finally, we compare the efficiencies and thresholds of an FBC resonator and an angled-ridge resonator applied to a broad-ridge quantum cascade laser.

Spectrally narrow mid-infrared optically pumped lasers with partial surface DBR.

An optically pumped mid-infrared edge-emitting laser is described, in which a Distributed Bragg Reflector grating partially occupies the surface, and provides spectral narrowing in a high power device. A quasi-continuous-wave power of 3 Watts is obtained at 3.6 µm that is contained within a spectral width of 7 nm.

Segmented mirror phasing using the focal-plane intensity.

We develop a method for subaperture piston phase retrieval in a telescope using a segmented primary mirror. We assume that the mirror subapertures are arranged on a two-dimensional lattice, and in addition, the separate subaperture point-spread functions are focused and overlapped on the focal plane. Therefore, the residual errors are the subaperture piston phase errors, represented as a phasor, a unit modulus complex number, for each subaperture. Under these conditions, we find considerable simplicity in the calculated optical transfer function (OTF) at special subaperture lattice spatial frequencies. We then construct a phasor-based error function based on the modulus squared of the difference between the measured OTF and the calculated OTF. The remaining steps in our piston phase retrieval algorithms are developed by calculating the error-function variation, with respect to each phasor element. The resulting equations for the error gradient are then used iteratively, in a phasor-based algorithm, to find the minimum of the error function. In the applications, we simulate photon-noise-limited piston retrieval for a segmented primary with 18 hexagonal subapertures. When we invoke phase diversity, the piston retrievals prove unique and accurate.