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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.

1. Single-frequency diamond lasers tailored for space and quantum applications (Supervisors: Rich Mildren, David Spence)

There is an emerging needs for high power narrow-linewidth lasers for space and quantum applications. Recently, we discovered that diamond is proficient at generating of narrow-linewidth output due to intrinsic benefits in operating stably on a single narrow frequency (ie., single longitudinal mode SLM). The Raman gain mechanism of diamond lasers completely avoids the main mode destabilization effect of spatial hole burning that plagues population-inversion lasers. Hence SLM operation is achieved using very simple cavity designs (without wavelength-selecting elements). First demonstrations of this principle were made at 1.2 microns for powers up to a few watts. SLM operation is also obtained when including a second-harmonic element in the laser cavity to generate output at visible wavelengths. Indeed, we showed that the second-harmonic element greatly increases stability through enhanced mode competition, leading to SLM powers in the orange (607 nm) at powers up to 60 W. Two experimental projects are envisaged that aim to 1) develops frequency stabilization schemes that provide compatibility with simple high-power pumps and 2) develop enhanced techniques to control Brillouin scattering in diamond lasers which may be an issue when scaling to higher powers. This research has excellent potential to lead to industry placements in space adaptive optics applications (with out industry partner) and careers in quantum engineering.

2. 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.

3. 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.

4. 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.

5. Low-threshold waveguide diamond lasers (Supervisors: Rich Mildren)

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.