Frequency and amplitude modulation of ultra-compact terahertz quantum cascade lasers using an integrated avalanche diode oscillator

Mode-locked comb sources operating at optical frequencies underpin applications ranging from spectroscopy and ultrafast physics, through to absolute frequency measurements and atomic clocks. Extending their operation into the terahertz frequency range would greatly benefit from the availability of compact semiconductor-based sources. However, the development of any compact mode-locked THz laser, which itself is inherently a frequency comb, has yet to be achieved without the use of an external stimulus. High-power, electrically pumped quantum cascade lasers (QCLs) have recently emerged as a promising solution, owing to their octave spanning bandwidths, the ability to achieve group-velocity dispersion compensation and the possibility of obtaining active mode-locking. Here, we propose an unprecedented compact architecture to induce both frequency and amplitude self-modulation in a THz QCL. By engineering a microwave avalanche oscillator into the laser cavity, which provides a 10 GHz self-modulation of the bias current and output power, we demonstrate multimode laser emission centered around 3 THz, with distinct multiple sidebands. The resulting microwave amplitude and frequency self-modulation of THz QCLs opens up intriguing perspectives, for engineering integrated self-mode-locked THz lasers, with impact in fields such as nano- and ultrafast photonics and optical metrology

A review identifying the effectiveness of minimum quantity lubrication (MQL) during conventional machining

Government legislation and public opinion are the main drivers behind the movement of manufacturing companies towards sustainable production. Fundamentally, companies want to avoid future financial penalties and the industry is therefore under pressure to adapt new techniques and practices in order to become environmentally friendly. The cost efficiency of metal cutting operations is highly dependent on accuracy, excellent surface finish and minimized tool wear and, to this end, has traditionally made abundant use of cutting fluid in machining operations. However, these cutting fluids have been a major contributor to environmental and health issues. In recent years, an enormous effort to eradicate these adverse effects has been made with one important focus being the implementation of minimum quantity lubrication (MQL). In the present work, the authors have reviewed the current state of the art in MQL with a particular focus on drilling, turning, milling and grinding machining operations. Overall, it is concluded that MQL has huge potential as a substitute for conventional flood cooling