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Diamond Laser Group

Current PhD Projects

The following projects are areas for which we are seeking PhD candidates. If you are interested, please email your CV to rich.mildren@mq.edu.au.

Diamond Brillouin lasers (Supervisors: Rich Mildren, David Spence)

There is increasing demand for millimeter wave oscillators of high fidelity and power to support progress in fields such as wireless communications and radar. Photonics-based oscillators currently represent the state-of-the-art in high frequency generation, however, most development has been restricted to the microwave region while higher frequencies (> 30 GHz) remain a major challenge. Diamond is a promising material in this context due to its extremely high Brillouin frequency, which provides a route to low-noise millimeter wave oscillators as well as outstanding power handling ability. This project builds on our recent breakthrough in demonstrating a diamond Brillouin laser to investigate designs tailored towards millimeter wave generation. The properties of the diamond-based oscillators will be characterized for devices designed for low-noise and high power operation. Advantages to be gain by operation at reduced temperature will also be investigated. In the latter stages of the project, it is aimed to tailor device properties to address the needs of applications. The key outcome of this project is the development of a novel approach millimeter wave generation with large potential upsides in frequency range, power and noise-figure. There is also anticipated collateral benefits in the field of narrow-linewidth lasers.

Nano- and atom-scale structuring of patterning diamond surfaces using 2-photon induced carbon ejection (Supervisors: Rich Mildren, James Downes)

Optical techniques for processing materials with a resolution less than the wavelength of light have advanced significantly in recent years. However, despite the highly selective nature of light-matter interactions, efforts to increase resolution to the atomic scale are hampered by rapid and efficient dissipation of the absorbed energy to the surrounding matrix. We have recently shown that diamond surfaces exhibit the remarkable capability for patterning on ultra-deep sub-wavelength (<20 nm) length scales when exposed to intense ultraviolet light. Furthermore, the detailed shape of structures depends sensitively on the polarization with respect to lattice bond directions. These findings reveal that photons couple strongly to localized electronic states associated with the surface carbon - carbon bonds, potentially providing an enabling mechanism for targeted single atom ejection. In this project, we propose to use this optical technique to demonstrate atomic-scale structuring by exploiting the optical field enhancement at the apex of a conducting tip in scanning probe microscopy. This project will develop new techniques for solving current challenges in fabrication of diamond devices for future applications in nano-machines, ultra-dense information storage and low-loss nano-optical components.

High power CW wavelength conversion to the UV-C and yellow by intracavity harmonic generation in diamond Raman lasers (Supervisors: Rich Mildren, David Spence)

Efficient conversion of continuous wave laser beams to important spectral regions such as the yellow and UV-C is a major challenge that becomes severely heightened when high powers are needed. We have recently shown that diamond Raman lasers enable efficient and high power conversion of cw beams by virtue of its outstanding combination of high Raman gain and thermal conductivity. Our demonstrations to date for diamond placed in external cavity have enabled cw beam conversion with output powers of up to 105 W at the first Stokes at 1.24 microns (and on-going work to demonstrate high power output at the 1.5 micron second Stokes wavelength). The cavity design is well suited to accommodate a chi-2 nonlinear element which can take advantage of the high intracavity Stokes field for efficient generation at the second harmonic. In this PhD project, this approach will be used to demonstrate converters to the yellow (eg., 570-580 nm) and to the UV-C (eg., 285-290 nm). This study will demonstrate practical and efficient converters to these wavelengths using mature pump drive lasers and capable generating output powers at the tens-of-watt level.

Direct diode pumping of diamond lasers (Supervisors: David Spence and Rich Mildren)

Combining the output beams from multiple laser sources is the only practical way to scale solid-state laser outputs to the next order of power levels. Amongst the several approaches currently the subject of intense research, beam combination in a Raman medium offers an approach for scaling beam power and brightness with some highly attractive advantages. The automatic phase-matching and beam clean-up properties inherent in the Raman interaction provides a simple method of combination compared to those requiring active phase control. Diamond is the ideal candidate for high average power Raman beam combination owing to its high Raman gain coefficient and its ultrahigh thermal conductivity. The recent availability of large (approx. 1 cm long) synthetic single crystals with high optical quality has enabled us to recently demonstrate its suitability as an outstanding material in almost all categories of Raman laser performance (efficient, wide wavelength range, cw-to-ultrafast) with demonstrated steady-state powers above 100 W and with much higher powers predicted. In this PhD project, is aimed to demonstrate beam combination of diode lasers in diamond for the first time, to elucidate designs enabling power scaling to kW levels.

Low-threshold waveguide diamond lasers (Supervisors: Rich Mildren, Robert Williams)

Amongst all Raman crystals, diamond has been found to be an outstanding material in almost all aspects of Raman laser performance including efficiency, wavelength range, and power, and across cw-to-ultrafast temporal formats. Many aspects of performance, such as efficiency and power handling capability, may be further enhanced by tightly confining the light in optical waveguides. Methods for manufacturing waveguides in single crystal diamond are advancing rapidly, and opportunities now exist to investigate some types of low-loss diamond waveguides. This project will develop planar and rib-waveguide diamond structures with the aim to demonstrate efficient, low-threshold wavelength converters in the visible and infrared. By exploiting the waveguide property for mitigating thermal effects, we aim to investigate devices operating at ultra-high power density. By exploiting the enhanced nonlinearity, the project aims to enable efficient wavelength conversion at mid-infrared wavelengths and extend wavelength reach beyond the multiphonon band at wavelengths longer than 6 microns.