Acetylene-filled hollow-fiber mid-IR laser is simple and robust

Types of mid-infrared (mid-IR) lasers are proliferating, with quantum-cascade lasers (QCLs), lasers based on chalcogenide-glass-based gain materials, and the old standby, optical parametric oscillators, among the various sorts. All lasers have their own advantages and disadvantages, so it's never a bad thing to see a new type of laser enter the fray. Scientists at the University of Bath (Bath, England) have unveiled a new mid-IR laser consisting of a silica hollow fiber filled with acetylene gas and pumped with a laser diode. Advantages of the laser—which can lase at a number of transitions between 3.1 and 3.2 μm—include overall simplicity and robustness, and either continuous-wave (CW) or synchronously pumped pulsed emission.

The fiber, which is capped at each end with a small transparent gas cell, has attenuations of 0.11 and 0.10 dB/m at the 1.53 μm pump wavelength and the 3.1–3.2 μm lasing region, respectively. The low loss of the fiber allows the use of a low gas pressure of about 0.3 mBar to produce a high gain per pass. For pulsed operation, the pump laser diode is pulsed at precisely the recirculating frequency of the fiber cavity, which ensures the pump pulses coincide with the recirculating laser pulse. For CW pumping (which produces a CW output), two closely spaced lines were seen. Pump coupling efficiency was 80%—the slope efficiency for CW output was 6.7% (measuring only one of the two bidirectional laser outputs), while for pulsed operation it was 8.8%. Reference: M. R. A. Hassan et al., Optica (2016); http://dx.doi.org/10.1364/optica.3.000218.