Actoprobe team had developed custom Tip Enhancement Raman Spectroscopy System (TERS) with specially developed Ultra High Aspect Ratio probes for AFM and TERS measurements for small pixel infrared FPA sidewall characterization. Using this system, we report on stimulated Raman scattering observed in a standard tip-enhanced Raman spectroscopy (TERS) experiment on GaSb materials excited by 637-nm pump laser light. We explain our results by TERS-inherent mechanisms of enormous local field enhancement and by the special design and geometry of the ultrahigh-aspect-ratio tips that enabled conditions for stimulated Raman scattering in the sample with greatly enhanced resonance Raman gain when aided by a microcavity to provide feedback mechanism for the Raman emission. The approach has great potential for further, orders-of-magnitude, progress in TERS enhancement by significantly increasing its nonlinear component. We report development of novel class of probes for atomic force microscopy (AFM active optical probe - AAOP) by integrating a laser source and a photodetector monolithically into the AFM probe. The AAOPs are designed to be used in a conventional AFM and would enhance its functionality to include that of the instruments (NSOM, TERS, hybrid AFM).
External quantum efficiency (EQE) is a parameter widely used in various photonic devices. In laser refrigeration of solids, materials with high EQE are essential for achieving net cooling. Pulsed power-dependent photoluminescence measurement is developed and demonstrated to be a rapid and efficient tool to determine the EQE and screen the sample quality before the fabrication process for the application of laser cooling in semiconductors. EQE values obtained from this technique are shown to be consistent with results from other more precise, but time-consuming measurements for various samples at different temperatures.
Laser cooling in InGaP|GaAs double heterostructures (DHS) has been a sought after goal. Even though very high external quantum efficiency (EQE) has been achieved, background absorption has remained a bottleneck in achieving net cooling. The purpose of this study is to gain more insight into the source of the background absorption for InGaP|GaAs DHS as well as GaAs|AlGaAs DBRs by employing an excite-probe thermal Z-scan measurement.
The state of current research in laser cooling of semiconductors is reviewed. Record external quantum
efficiency (99.5%) is obtained for a GaAs/InGaP heterostructure bonded to a dome lens at 100 K by
All-optical Scanning Laser Calorimetry (ASLC). Pulsed-Power-dependent photoluminescence
measurement (Pulsed-PDPL) is proved to be an efficient way to determine the quantum efficiency and
screen the sample quality before processing and fabrication. Second harmonic generation (767nm)
from a 5ns Er:YAG laser is used as the pump source for the pulsed-PDPL experiment.
External quantum efficiency of semiconductor photonic devices is directly measured by
wavelength-dependent laser-induced temperature change (scanning laser calorimetry) with very high
accuracy. Maximum efficiency is attained at an optimum photo-excitation level that can be determined with
an independent measurement of power-dependent photoluminescence. Differential power-dependent
photoluminescence measurement is used to quickly screen the sample quality before processing.
The state of current research in laser cooling of semiconductors is reviewed. Emphasis is placed on the characterization
of external quantum efficiency and absorption efficiency in GaAs/InGaP double heterostuctures. New experimental
results will be presented that characterize device operation as a function of laser excitation power and temperature.
Optimum carrier density is obtained independently and used as a screening tool for sample quality. The crucial
importance of parasitic background absorption is discussed.
We characterize high quantum efficiency double GaAs/InGaP heterostructures used in semiconductor laser cooling. To
identify potential samples for laser cooling, measuring the nonradiative recombination rate coefficient is necessary. We
describe a technique called power dependent photoluminescence measurement, which when combined with timeresolved
photoluminescence lifetime determines the nonradiative recombination coefficient.
Doping of the clad layers in thin GaAs/GaInP heterostructures, displaces the band energy discontinuity, modifies
the carrier concentration in the active GaAs region and changes the quality of the hetero-interfaces. As a result,
internal and consequently external quantum efficiencies in the double heterostructure are affected. In this paper,
the interfacial quality of GaAs/GaInP heterostructure is systematically investigated by adjusting the doping
level and type (n or p) of the cladding layer. An optimum structure for laser cooling applications is proposed.
A novel third-order optical parametric oscillator (OPO) based on four-wave mixing process in bulk TiO2 crystal is
theoretically characterized. The OPO is assumed to be synchronously pumped by pulses of either 100 fs duration at
800 nm or 100 ps at 1.06 &mgr;m. For the former case, its signal is tunable from 0.45 to 0.8 &mgr;m by changing the crystal
orientation; for the latter case, the OPO is tunable from approximately 0.6 to 1.06 &mgr;m. The threshold conditions are
also calculated considering the effect of group velocity mismatch (GVM) between the pump pulse and the signal (or
idler) pulse. The threshold is dependent on signal wavelength since GVM increases as signal wavelength decreases.
Using a 2 mm-length crystal and assuming optimum focusing, the threshold for the singly resonant condition is 710
mW at 700 nm for the former case and 93.6 W for all the signal wavelengths for the latter case. The threshold
condition is also calculated assuming different pumping pulse widths. The result shows the ideal pulse width is
around 2 ps, for which the threshold power is 1.42 W for all the signal wavelengths.
We demonstrate a non-contact, spectroscopic technique to measure
the temperature change of semiconductors with very high precision.
A temperature resolution of less than 100 μK has been obtained with
bulk GaAs. This scheme finds application in experiments to study
laser cooling of solids. We measure a record external quantum
efficiency of 99% for a GaAs device.
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