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We a present a new two-pulse photoluminescence correlation technique and use it to study ultrafast dynamics of photoexcited carriers in few monolayer thick deep-UV GaN/AlN quantum wells with picosecond time resolution. Our results show that our technique can be used to study carrier dynamics in nanostructures using photoluminescence in a very simple way.
We present experimental and theoretical results of confined plasmons in graphene micro- and nano-structures. We present a FDTD technique to accurately model the measured data and demonstrate the importance of interactions between plasmonic structures.
Our study reveals temperature dependent optical properties of excitons and trions in monolayer MoS2 using absorption and photoluminescence (PL) spectroscopy. The extremely large trion binding energy is directly extracted from our data.
We present results on the relaxation dynamics of photoexcited carriers in MoS2 using optical-pump terahertz-probe spectroscopy. Our measurements indicate that carrier recombination is accelerated at low temperatures where defect-assisted recombination becomes more efficient.
Our ultrafast optical pump-probe measurements of 2D atomic material MoS2 show that the interband and intraband relaxation dynamics of photoexcited carriers vary significantly as a function of the number of atomic layers. Coherent phonon oscillations are also observed in our measurements.
Graphene has emerged as the semiconductor with the highest reported mobility of carriers at room temperature making it suitable for terahertz applications. The plasmon frequencies of graphene are also in the terahertz range. Plasmons in graphene interact strongly with electrons and holes and plasmon emission and absorption are the fastest mechanisms for electon-hole recombination and generation. Plasmon...
We present results on the relaxation dynamics of photoexcited carriers in graphene using optical-pump terahertz-probe spectroscopy. Our measurements indicate that carrier cooling is extremely slow at low temperatures where electron-optical phonon cooling becomes inefficient.
We present results from measurements of ultrafast thermal transport in Graphene. We find that on picosecond time scales and 5-20 micron length scales hot carriers, instead of the phonons, are the dominant carriers of thermal energy. The thermal transport is found to be diffusive with a diffusivity of ~500 cm2/s.
We report on the physics, epitaxial growth, fabrication, and characterization of optoelectronic devices based on intersubband transitions in the AlN/GaN material system. While in 1999, only results of optical absorption experiments could be shown, photodetectors and modulators with operation frequencies beyond 10 GHz as well as optically pumped light emitters have been demonstrated recently. This...
We demonstrate amplification of picosecond pulses centered at 1550 nm using Slab-Coupled Waveguide Amplifiers. For bias currents less than 1 A, we obtained a maximum unsaturated gain of 12.3 dB and a pulse saturation energy of ∼50 pJ.
We have obtained optical pulses via hybrid modelocking in monolithic slab coupled optical waveguide lasers with average powers exceeding 220 mW at a wavelength of 1550 nm.
Using pump-probe techniques, we study the ultrafast relaxation dynamics of photoexcited carriers in graphene. We find an initial fast relaxation transient (70–120 fs), followed by a slower relaxation process (0.4–1.7 ps). We relate the measured time scales to carrier-carrier and carrier-phonon intraband and interband scattering processes and also to crystal disorder in the material.
We present experimental results on the optical absorption spectrum of graphene from near-IR to THz frequencies for the first time. At near-IR and mid-IR wavelengths the interband optical absorption is found to have a flat spectrum consistent with the relativistic massless Dirac-Fermion energy dispersion relation of electrons and holes in graphene. At THz frequencies intraband absorption dominates...
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