Mid-infrared (mid-IR) fiber lasers that are based on dysprosium (Dy) as the active laser ion provide emission in the wavelength range between 2.6–3.4 μm and can thus bridge the spectral gap between holmium (Ho) and erbium (Er) based mid-IR lasers. Another distinct feature is the wide choice of pump wavelengths (1.1 μm, 1.3 μm, 1.7 μm, and 2.8 μm) that can be used. To date, pump wavelengths shorter than 1.1 μm have not been reported and all demonstrated pump wavelengths apart from in-band pumping suffer from pump excited state absorption (ESA). In this paper, we report new excitation wavelengths, 0.8 μm and 0.9 μm, for Dy-doped mid-IR fiber lasers. We have measured 18.5% and 23.7% slope efficiency (relative to launched pump power) for 0.8 μm and 0.9 μm pumping wavelengths, respectively. By comparing the residual pump power of experimental and numerical simulation data of a 0.5 m Dy-doped fiber, we have found that these new excitation wavelengths are free from pump ESA. Moreover, the high power laser diodes are commercially available at these new excitation wavelengths; therefore, the realization of a diode-pumped Dy-doped mid-infrared fiber laser might become feasible in the near future.
Muscovite is a naturally occurring crystalline mineral, a mica, with a unique layered structure with planes of low cleavage energy spaced by ~1.3 nm in the crystal structure. It is a dielectric insulator. Freshly cleaved muscovite surfaces are extremely flat, clean and used in many technical applications of the material. Previous laser ablation study of mica using ultraviolet, nanosecond duration pulses, led to a poor finish at the process sites (K. Rubahn et.al., J. Appl. Phys. 86(5), 2847, 1999). Interest in laser processing of the material, other than CO2 laser cutting of mica sheets, was subsequently, and not surprisingly, curtailed. Here-in we report the morphologies of the laser processed site affected by a single, ~150 fs duration, 800nm wavelength, 6 micron spotsize laser pulse focussed on the surface of a mica substrate. A systematic sequence of the morphology as the fluence of the single pulse is increased is obtained. Optical surface profiling and field emission secondary electron microsocopy are used to characterise the site morphology. Time of flight secondary ion mass specroscopy has been used to map the redistribution of key elements at the process site. Muscovite emerges as a fascinating material in its response to a femtosecond laser pulse. Useful marking without creation of debris beyond the footprint of the laser spotsize is achieved at a flunece as low as 2.4 J/cm<sup>2</sup>. There is evidence of plasticity and cavitation within the sequence of morphologies found.
We report on the latest development of our photonics-based brain-machine interface. This work done in collaboration between UNSW and Macquarie University – and supported by the US Office of Naval Research – directly addresses the long-term DARPA challenge of producing implantable chips with 1 million neural connections. To the best of our knowledge, no technology has demonstrated the potential so far to scale up to such a massive number of channels.
The next-generation gravitational wave detectors aim to enhance our understanding of extreme phenomena in the Universe. The high-frequency sensitivity of these detectors will be maximized by injecting squeezed vacuum states into the detector. However, the performance advantages offered by squeezed state injection can be easily degraded by losses in the system. A significant source of loss is the mode mismatch between optical cavities within the interferometer. To overcome this issue, new actuators are required that can produce a highly spherical wavefront change, with minimal higher order aberrations, whist adding low phase noise to the incident beam.
We present a compact design for a 1064 nm Q-Switched waveguide laser based on a liquid crystal transducer. Directly integrating the input-coupling mirror on the chip and utilising a Grin lens to also integrate the modulator optics enables a miniaturised setup. The preliminary experimental results have demonstrated that the Q-switched laser pulses with a pulse width of 45 ns and average output power of 4.5 mW can be achieved with a pump power of 350 mW, when an electrical signal with a repetition rate of 5 kHz, a peak-to-peak voltage of 30 V and a duration of 4 µs is applied. This work was supported by the Office of Naval Research Global (N62909-18-1-2147).
We demonstrate the first stable mode-locking from an Er<sup>3+</sup> doped fluoride fibre laser cavity using various novel two-dimensional saturable absorber materials such as PtSe<sub>2</sub> and MXene operating near 2.8 μm wavelength to the best of our knowledge. The linear cavity includes a high reflective chirped fibre Bragg grating to provide wavelength stability. The observed mode-locked pulse train has a 30 MHz repetition rate and an average power of 223 mW. Our results demonstrate the feasibility of using the novel two-dimensional nanomaterials such as PtSe<sub>2</sub> and MXene into the fibre laser cavity for the application in mid-infrared wavelength regime.
The development of new, compact mid-infrared light sources is critical to enable biomedical sensing applications in resource-limited environments. Here, we review progress in fiber-based mid-IR sources, which are ideally suited for clinical environments due to their compact size and waveguide format. We first discuss recent developments in mid-IR supercontinuum sources, which exploit nonlinear optic phenomena in highly nonlinear materials (pumped by ultrashort pulse lasers) to generate broadband spectra. An emerging alternative approach is then presented, based on broadly tunable mid-IR fiber lasers, using the promising dysprosium ion to achieve orders of magnitude higher spectral power density than typical supercontinua. By employing an acousto-optic tunable filter for wavelength tuning, an electronically controlled swept-wavelength mid-IR fiber laser is developed, which is applied for absorption spectroscopy of ammonia (NH<sub>3</sub>), an important biomarker, with 0.3 nm resolution and 40 ms acquisition time.