This paper investigates the impact of the quantum cascade laser’s frequency modulation response on its tuning rate and tunability. We show a significant disparity in laser tuning rates and tunability between single and dual-frequency modulation schemes frequently used in typical direct absorption and wavelength modulation spectroscopy (WMS) techniques. We show that the DC-characterized tuning rate of a laser can be reduced significantly under a specific set of modulation frequencies of the laser injection current. We characterize these effects by simultaneous measurements of higher harmonic WMS of methane and nitrous oxide in the 7.8 µm spectral regions. We further show that WMS signal modulation broadening mechanisms and spectral structure, i.e., its zero-crossings and turning points, can be used to quantify such laser-modulation effects and validate laser frequency response under dual modulation schemes.

We present a novel approach to quantifying and optimizing the amount of information available in radiation patterns. The technique presented and the results obtained are applicable on a broad scale, including those in infrared, nanophotonics and other non-intrusive sensing techniques. We investigate the amount of information lost due to limitations of the detector system. The method, which is based on information principles developed by Shannon, expands on the many conventional approaches to optimizing performance of sensors. The fundamental question of how many bits of information can be extracted by any sensor is addressed. We focus on answering this question for the measurement of the radiation pattern from an antenna array. The effects of a finite detector size, on the structure of the radiation pattern, are presented, and we quantify the relationship between loss of structure and loss of information. The work presented may be extended to a wide range of applications, including remote sensing. While the information content of antenna array radiation patterns is based on the spatial distribution of photons, the method presented is general and may be applied to a variety of distributions, such as lineshape functions, important in spectroscopy, where the information is contained in the frequency distribution of photons.