We present results from laser annealing experiments in Si using a passively Q-switched Nd:YAG microlaser.
Exposure with laser at fluence values above the damage threshold of commercially available photodiodes results in
electrical damage (as measured by an increase in photodiode dark current). We show that increasing the laser
fluence to values in excess of the damage threshold can result in annealing of a damage site and a reduction in
detector dark current by as much as 100x in some cases. A still further increase in fluence results in irreparable
damage. Thus we demonstrate the presence of a laser annealing window over which performance of damaged
detectors can be at least partially reconstituted. Moreover dark current reduction is observed over the entire
operating range of the diode indicating that device performance has been improved for all values of reverse bias
voltage. Additionally, we will present results of laser annealing in Si waveguides. By exposing a small (<10 um)
length of a Si waveguide to an annealing laser pulse, the longitudinal phase of light acquired in propagating through
the waveguide can be modified with high precision, <15 milliradian per laser pulse. Phase tuning by 180 degrees is
exhibited with multiple exposures to one arm of a Mach-Zehnder interferometer at fluence values below the
morphological damage threshold of an etched Si waveguide. No reduction in optical transmission at 1550 nm was
found after 220 annealing laser shots.
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.
Sensitive, real-time chirp and spectral phase diagnostics along with full field reconstruction of femtosecond laser pulses
are performed using a single rapid-scan interferometric autocorrelator. Single shot diagnostics are possible when the
second-harmonic spectrum is available. A novel graphical representation distinguishes between temporal and spectral
phase distortions. Examples are presented that illustrate the sensitivity and fidelity of the scheme even with low signal-to-
Simultaneous near-field fluorescence lifetime imaging and atomic force microscopy identify radiative, interface and subsurface defect recombination sites in GaAs/GaInP heterostructures. This instrumentation helps characterize samples for laser cooling.
KEYWORDS: Semiconductors, Signal to noise ratio, Microscopes, Luminescence, Gallium arsenide, Single photon, Atomic force microscopy, Semiconductor lasers, Near field scanning optical microscopy, Fluorescence lifetime imaging
We investigate the role of surface defects on semiconductor fluorescence lifetime using near-field scanning optical
microscopy (NSOM) and time correlated single photon counting (TCSPC). A conventional far-field microscope is used
to excite a GaAs sample and subsequent fluorescence is collected with a fiber coupled near-field probe. With the
application of custom fitting algorithms, we find fluorescence lifetimes in the vicinity of surface defects to be
significantly reduced with respect to fluorescence lifetimes measured in defect free regions.
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.
We extract the chirp of an ultrashort laser pulse accurately in real-time using a simple modified auto-interferometric correlation (MOSAIC) technique. Through the use of our newly developed time-domain algorithm, chirp information is accessible with signal-to-noise levels approaching unity. Correction algorithms have been developed to accommodate signal distortions due to bandwidth limitations, autocorrelator misalignment, and non-quadratic detector response.
The chirp of an ultrashort laser pulse can be extracted accurately in real-time using a simple modified autointerferometric correlation (MOSAIC) technique. Our newly developed time-domain algorithm is well suited for low signal-to-noise conditions. We display results revealing high sensitivity to chirp with signal-to-noise levels approaching the noise floor. Correction algorithms have been developed to accommodate signal distortions arising from bandwidth limitations, interferometer misalignment, and non-quadratic detector response.
We present an overview of laser cooling of solids. In this
all-solid-state approach to refrigeration, heat is removed radiatively when an engineered material is exposed to high power laser light. We report a record amount of net cooling (88 K below ambient) that has been achieved with a sample made from doped fluoride glass. Issues involved in the design of a practical laser cooler are presented. The possibility of laser cooling of semiconductor sensors is discussed.