We report a fast pump modulation scheme in a terahertz time domain spectroscopy (THz-TDS) system by utilizing the intensity modulation from the megahertz repetition rate of the pump pulse for lock-in detection. In conventional THz-TDS, the modulation required for the high signal-to-noise ratio lock-in detection is achieved through the use of an optical chopper or an AC bias. Here, we propose the use of an electro-optic modulator (EOM), operated as a pulse picker, to vary the repetition rate of the pump pulse, relative to the probe pulse, allowing us to directly use the megahertz laser repetition rate as the reference modulation frequency for lock-in detection.
View Article and Find Full Text PDFWe developed a surface plasmon resonance (SPR)-enhanced angular Goos-Hänchen (GH) shift measurement system capable of tracking small refractive index changes with high sensitivity in a liquid environment. Our method can be performed in angular interrogation schemes, where we demonstrate a simple zero-finding algorithm to locate the SPR angle instead of the complicated data processing algorithms used in conventional sensors. We also propose a displacement interrogation scheme for dynamic measurement of small refractive index changes in the sample.
View Article and Find Full Text PDFTaiwan J Ophthalmol
January 2018
Presbyopia results from loss or insufficiency of the eye's accommodative ability, and clinically manifests as the inability to focus near objects on the retina. It is one of the most common causes of visual impairment worldwide especially in adults of productive or working age. Various means of compensating for the loss of accommodative ability have been devised from optical tools such as spectacles and contact lenses, to topical medications and to surgical procedures.
View Article and Find Full Text PDFWe present the use of a "double optical pump" technique in terahertz time-domain emission spectroscopy as an alternative method to investigate the lifetime of photo-excited carriers in semiconductors. Compared to the commonly employed optical pump-probe transient photo-reflectance, this non-contact and room temperature characterization technique allows relative ease in achieving optical alignment. The technique was implemented to evaluate the carrier lifetime in low temperature-grown gallium arsenide (LT-GaAs).
View Article and Find Full Text PDFGaAs/Al0.1Ga0.9As core-shell nanowires (CSNWs), with average lateral size of 125 nm, were grown on gold nanoparticle-activated Si (100) and Si (111) substrates via molecular beam epitaxy.
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