C.L. Lee

Microlensed microchip VECSEL

We report a 1.055-mum microchip VECSEL array which uses a microlens-patterned diamond both as a heatspreader and as an array of concave output mirrors. This configuration, which is suitable for laser array operation, is here exploited to perform a systematic study of a set of microchip lasers with the same semiconductor structure but different cavity properties. The transverse mode selection of individual VECSELs is found to depend on the mode-matching conditions and on the microlens aperture size. Mode-matched single-device emission in the fundamental mode (M2~1.1) with pump-limited output power of 70 mW is demonstrated.

Stabilization of a semiconductor disk laser using an intra-cavity high reflectivity grating.

We demonstrate the use of a High Reflectivity Grating (HRG) as an intra-cavity element in a Semiconductor Disk Laser (or Vertical External Cavity Surface Emitting Laser) to stabilise its emission wavelength and polarization characteristics. Operation at 1058nm with up to 645mW of pump-limited output power and an M(2)~1.4 is achieved. We also show that this scheme permits tunable single-frequency operation.

Power-Scaling of Diamond Microlensed Microchip Semiconductor Disk Lasers

Power-scaling of an optically pumped 1040-nm microlensed microchip semiconductor disk laser is reported, where the monolithic cavity and lens structure is embodied in single-crystal diamond. Low threshold and circularly symmetric single-transverse-mode emission (M2<1.2) at output power up to 180 mW is obtained for a mode-matched device having an integrated output coupler of 9.4-mm radius of curvature and a 300-mum aperture. Multitransverse mode operation above 1 W is also presented.

Novel polymer systems for deep UV microlens arrays

We report for the first time a UV curable polymer with effective optical transmission below 300 nm. Through careful control of kinetics, various viscosities can be generated to optimize the film forming properties via spin coating. The transmission of the monomers and films is investigated over a spectral range which spans the 240–370 nm output of ultraviolet AlInGaN light-emitting diodes. The refractive index of the polymer has been measured by ellipsometry to give a value of 1.57 at 280 nm. Using standard lithography techniques with reactive ion etching, arrays of microlenses have been fabricated in this polymer with diameters of 30 µm and below and are characterized by atomic force microscopy and confocal microscopy.

Array-Format Microchip Semiconductor Disk Lasers

We report a detailed study of an array-format 1.055- mum microchip semiconductor disk laser which uses a microlens-patterned diamond both as an array of stabilizing output coupling mirrors and a heatspreader. A thermal study of the devices, using a finite element analysis, is carried out and confirms the thermal management capabilities and power scalability of this microlensed diamond configuration. This design is then exploited to perform a systematic study on a set of microchip lasers having the same semiconductor structure but microlenses with differing characteristics. The transverse mode characteristics of individual semiconductor disk lasers are found to depend on the mode-matching condition and on the microlens aperture size. Mode-matched single-device emission in the fundamental mode (M2 ~ 1.1) with a pump-limited output power of 70 mW is demonstrated. The experimental measurement of the thermal resistance of the device is also shown to agree with the finite element analysis. Finally, array operation, while pumping with a single beam, is reported.

Thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) modified with divinyl benzene and vinyltrimethoxysilane

ABSTRACT The effect of butyl acrylate (BA), divinyl benzene (DVB) and vinyltrimethoxysilane (TMVS) on the thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) was investigated. Glass transition temperature (Tg), melting temperature (Tm) and specific heat capacity of the copolymers were investigated using Differential Scanning Calorimetry. Thermal stability of the copolymers which is associated with the degradation temperature (Td) was studied by Thermogravimetric Analysis. Polyacrylates with Tg ranges between -19°Cand 19°C were obtained. With the incorporation of >7 wt% of DVB, the Tg of the copolymer increases from about −17°C to −10°C even though they have not undergone UV irradiation. Gel content results prove that crosslinking has occurred in the copolymers. With increasing amount of TMVS from 0 wt% to 7 wt%, the Tm of the copolymers prepared at acidic pH is about 40-60°C higher than that at the alkaline pH. However, the addition of TMVS gives no significant effect to the Tg and Td of the copolymer films. The thermal stability of the copolymer has improved with increasing amount of BA and DVB, with DVB being more effective. The highest Td of 425°C with 8% of DVB has been obtained. Consequently, a polyacrylate copolymer with a Tg of about −13°C, a Tm of 170 °C and a Td of about 424°C has been successfully synthesized. Hence, the soft polyacrylate with its relatively high Tm and Td could serve as a superb material especially to be applied in the areas that require high melting temperature and good thermal stability.

Microchip Vertical-External Cavity Surface Emitting Laser using a concave-shaped diamond micromirror

This paper demonstrates a plano-concave microchip vertical-external cavity emitting laser (mu-VECSEL) operating at 1.05 mum. The cavity is composed of a semiconductor structure, comprising an active region grown on top of a distributed Bragg reflector (DBR), and a diamond heatspreader with its outer surface shaped as a spherical microlens. This stable optical cavity has a signal spot diameter of ~19.8 mum on the active region and of ~21 mum at the concave micro-mirror facet.

The impacts of the waterfront development in Iskandar Malaysia

The increasing number of waterfront projects shows that the concept of waterfront development has contributed to the advancement of the Malaysian construction industry. This study seeks to assess the impacts of the implementation of waterfront development in Iskandar Malaysia eliciting the perceived relative importance of these impacts. A comprehensive literature review has been conducted to collate the potential impacts of the waterfront development. A total of 363 sets of questionnaires were distributed to the contractors and developers registered under G7 category of the Construction Industry Development Board in Malaysia. Results show that the most significant influence of the waterfront development is related to economic benefits, while environmental impacts are not considered as a priority for this category of stakeholders. In addition, this study also indicates that the implementation of the waterfront projects has generated numerous job opportunities within the developed region. Moreover, exchanging knowledge in the planning and managing of the waterfront development is imperative to the development of the waterfront projects. Nevertheless, the shortcomings of these developments, such as the negative environmental impact on natural beaches and the coastline (i.e. pollution) as well as human-related issues (i.e. excessive human settlement), should not be taken lightly. This research confirms that the reclamation of land for waterfront development is closely correlated with the destruction of these natural structures.

Temperature tuning of band edge resonant modes in one-dimensional photonic crystals

The transmission characteristics of Si-based 1D photonic crystals was investigated using transfer matrix method. As the temperature and wavelength dependence of Si refractive index induces band edge resonant modes that are temperature tunable, the average wavelength shift per Kelvin of the resonant mode with the largest group index was determined in the vicinity of the band edge. A general linear chirp structure consisting of a constant and chirp component was implemented. Using the simulated annealing algorithm, the structural parameters were optimized and it was found that the average wavelength shift per Kelvin of the band edge resonant mode can be enhanced by 28.9% with high transmission. It was also found that spatial chirping does not affect the wavelength shift. The enhancement was achieved by a uniform increase of PC layer widths. Tunable band edge resonant modes may be exploited in designing optical thermal sensing devices.

Study of carbon density for the development of high efficiency X-ray optics

The properties of amorphous carbon films deposited by magnetron sputtering deposition process was analyzed and characterized with the intention of realizing an excellent design and subsequently to manufacture high performance X-ray mirror utilizing carbon-carbon multilayer stack. The study is focused on the carbon density variation as the deposition process parameters are changed. The experiment has shown a convincing result that various densities can be achieved on the deposited carbon layer by changing the deposition conditions. By installing an aluminum grating in the deposition system in order to enable an external bias voltage supply during the deposition, a 6% different between the highest and lowest densities with very low surface roughness has been achieved.