- S13 #02-15, Optical Materials and Devices Lab,
Department of Physics, 1 Science Drive 3, National University of Singapore,
Singapore- 117552 - +6581199091
- I am a researcher working in the field of diamond photonics. Previously, I had worked on Terahertz spectroscopy and m... moreI am a researcher working in the field of diamond photonics. Previously, I had worked on Terahertz spectroscopy and metamaterials as part of my PhD at Department of Physics and NUS. My research interests lie mainly in spectroscopy and photonics.edit
- Andrew Bettioledit
Lloyd's mirror is the simplest interferometer based on wavefront division using a simple plane mirror. Invariably, in this setup, interference fringes are preceded by the Fresnel's straight-edge diffraction. Computerisation of... more
Lloyd's mirror is the simplest interferometer based on wavefront division using a simple plane mirror. Invariably, in this setup, interference fringes are preceded by the Fresnel's straight-edge diffraction. Computerisation of this experiment using scanning photo-detector mounted on stepper motor controlled mechanical translation stage, leads to extraction of wavelength information from the noisy diffraction fringes. Experimental results are presented using interference as well as diffraction fringes.
ABSTRACT We have investigated the nonlinear optical properties, optical limiting thresholds, and figures of merits for five different phthalocyanine thin films, achieved through doping in PMMA polymer, using the Z-scan technique at 800 nm... more
ABSTRACT We have investigated the nonlinear optical properties, optical limiting thresholds, and figures of merits for five different phthalocyanine thin films, achieved through doping in PMMA polymer, using the Z-scan technique at 800 nm with 2 ps laser pulse excitation. From the open-aperture Z-scan data we derived that these molecules exhibit strong two photon absorption (2PA) with the nonlinear absorption coefficients in the range of 15-200 cm/GW.
Research Interests:
The ability to control the porosity and hence the refractive index of porous silicon makes it an interesting material for photonic applications. Layers with refractive indices as low as 1.5 up to that of bulk crystalline silicon can be... more
The ability to control the porosity and hence the refractive index of porous silicon makes it an interesting material for photonic applications. Layers with refractive indices as low as 1.5 up to that of bulk crystalline silicon can be easily fabricated by varying the electrochemical ...
Research Interests:
ABSTRACT Fourier transform interferometry is commonly performed by means of mechanically scanning interferometers such as a Michelson and characterized by one scanning mirror. This results in severe limitations of the capability of... more
ABSTRACT Fourier transform interferometry is commonly performed by means of mechanically scanning interferometers such as a Michelson and characterized by one scanning mirror. This results in severe limitations of the capability of measuring fast signals. To overcome this drawback, we present a multi-channel FTIR spectrometer (MC-FTIR) that is capable of single-shot operation no matter how short the single pulse is, provided it delivers sufficient photons for the signal to exceed the noise. It can capture fast transient signals, limited by the signal-to-noise ratio and data transfer rate of the detector. Our device is based on a micro/nanomanufactured 3D multimirror array (MMA) which allows collecting a whole interferogram simultaneously. MMAs are manufactured by means of a patented multiple moving mask grey-level deep X-ray lithography process. Up to 640 mirror cells, generating optical path differences from 0 to about 1 mm, were achieved so far at optical quality. We have demonstrated sub-millisecond pulses and a theoretical spectral resolution of 10 cm-1 in the mid-IR. The optical system is similar to a Czerny-Turner mount with the MMA replacing the grating and an MCT focal plane array (FPA) capturing the interferogram. Our MC-FTIR enables extension of FTIR-based IR spectroscopy to arbitrarily short pulses and to fast transient signals. As the optical system is small and rugged, the instrument lends itself readily to field applications. Ongoing work is aimed at emerging applications including biomedical, laser-induced breakdown spectroscopy, and spectroscopy of synchrotron radiation.
ABSTRACT Proton beam writing (PBW) is a high-resolution direct write lithographic technique suitable for the fabrication of micro/nano optical components with smooth vertical sidewalls. In the present work PBW was used to fabricate smooth... more
ABSTRACT Proton beam writing (PBW) is a high-resolution direct write lithographic technique suitable for the fabrication of micro/nano optical components with smooth vertical sidewalls. In the present work PBW was used to fabricate smooth micro cavities in negative tone photoresist SU-8 and Rhodamine B doped SU-8. Two different laser cavities based on whispering gallery mode resonators were fabricated using PBW. The laser cavities in Rhodamine B doped SU-8 resist were optically pumped with a pulsed frequency doubled Nd: YAG laser, and emits light in the chip plane at 643 nm. The presented laser cavities showed pump threshold as low as 3 μJ/mm2, which is the lowest threshold reported in planar cavities fabricated in Rhodamine B dye based polymer laser cavities.
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Research Interests:
ABSTRACT Proton beam writing is a high-resolution direct write lithographic technique capable of producing three dimensional, high aspect ratio structures with smooth and vertical sidewalls. In this work, the fabrication of high quality... more
ABSTRACT Proton beam writing is a high-resolution direct write lithographic technique capable of producing three dimensional, high aspect ratio structures with smooth and vertical sidewalls. In this work, the fabrication of high quality SU-8 optical microdisk resonator with a Q factor of 104 is demonstrated. Simulations carried out using finite difference time domain (FDTD) are in good agreement with experimental results. By introducing rhodamine B laser dye into a SU-8 resist spiral microdisk cavity lasing was achieved with threshold pump fluence of 127 μJ/mm2 when pumped with a 532 nm pulsed Nd:YAG laser.
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Research Interests:
We present our results from the detailed investigations of both metal free-base and metal substituted dinaphthoporphycenes using the Z-scan technique with picosecond pulses. The compounds exhibited singular nonlinear absorption properties... more
We present our results from the detailed investigations of both metal free-base and metal substituted dinaphthoporphycenes using the Z-scan technique with picosecond pulses. The compounds exhibited singular nonlinear absorption properties because of their molecular structure allowing us to access the two-photon and three-photon absorption states with different peak intensities when excited at the wavelength of 800nm. This type of behaviour is explained using the unique energy level configuration of porphycene molecules.
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Ultrafast nonlinear optical (NLO) properties of four novel Corroles in the visible spectral range (660 nm-800 nm) were evaluated using picosecond Z-scan technique. Ultrafast excited state dynamics have also been appraised with picosecond... more
Ultrafast nonlinear optical (NLO) properties of four novel Corroles in the visible spectral range (660 nm-800 nm) were evaluated using picosecond Z-scan technique. Ultrafast excited state dynamics have also been appraised with picosecond (ps) and femtosecond (fs) degenerate pump-probe techniques using excitation wavelengths of 800 nm and 600 nm, respectively.
Abstract Ultrafast excited state dynamics of dinaphthoporphycenes were investigated using femtosecond and picosecond degenerate pump-probe techniques at 600 nm and 800 nm, respectively. Femtosecond pump-probe data indicated photo-induced... more
Abstract Ultrafast excited state dynamics of dinaphthoporphycenes were investigated using femtosecond and picosecond degenerate pump-probe techniques at 600 nm and 800 nm, respectively. Femtosecond pump-probe data indicated photo-induced absorption at 600 nm resulting from two-photon/single photon excitation, whereas picosecond pump-probe data demonstrated photo-bleaching which was a consequence of three-photon absorption.
Research Interests:
Research Interests:
Research Interests:
Ultrafast nonlinear optical (NLO) properties of four novel Corroles in the visible spectral range (660-800 rim) were evaluated using picosecond Z-scan technique. Ultrafast excited state dynamics have also been appraised with picosecond... more
Ultrafast nonlinear optical (NLO) properties of four novel Corroles in the visible spectral range (660-800 rim) were evaluated using picosecond Z-scan technique. Ultrafast excited state dynamics have also been appraised with picosecond (ps) and femtosecond (fs) degenerate pump-probe techniques using excitation wavelengths of 800 and 600 nm, respectively. The excitation by 800 nm photons resulted in two-photon absorption at adequately high peak intensities, thereby facilitating the access to higher excited states (S-n). The nonradiative relaxation mechanisms from these states, reflected in the pump-probe data, consisted of double-exponential decay with a slow component in the range of 54-277 ps and faster component in the range of 2.0 to 2.5 ps. When excited with 600 run photons (unfocused), photoinduced absorption was observed with the first excited state S-1 being populated, and as a consequence single decay was observed in the data of all molecules studied. These retrieved lifetim...