We have realized photonic crystal lasers that permit the introduction of analyte within the peak of the optical field of the lasing mode. We have explored the design compromises for developing such sensitive low-threshold spectroscopy sources, and demonstrate the operation of photonic crystal lasers in different ambient organic solutions. We show that nanocavity lasers can be used to perform spectroscopic tests on femtoliter volumes of analyte, and propose to use these lasers for high-resolution spectroscopy with single-molecule sensitivity.
We have fabricated photonic crystal nanocavity lasers, based on a high-quality factor design that incorporates fractional edge dislocations. Lasers with InGaAsP quantum well active material emitting at 1550 nm were optically pumped with 10 ns pulses, and lased at threshold pumping powers below 220 W, the lowest reported for quantum-well based photonic crystal lasers, to our knowledge. Polarization characteristics and lithographic tuning properties were found to be in excellent agreement with theoretical predictions. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1511538͔The quest for a compact nanocavity laser, with highquality factor (Q) and small mode volume (V mode ), has been a central part of research in the field of integrated optics. Photonic crystals, 1 and planar photonic crystals in particular ͑PPC͒, 2 are promising manufacturable geometries for the realization of compact optical nanocavities and their integration with waveguides, modulators, and detectors. So far, there have been several reports on room-temperature lasing in PPC nanocavities, 3-7 and more recently, new high-Q cavity designs based on modification of two-dimensional ͑2D͒ photonic crystals have been proposed. 4,8 In this letter, we report the experimental application of one of these designs. The cavities are based on fractional edge dislocations, 8 and are used for the construction of a low-threshold laser in which the high field from the laser surrounds a void for chemical sensing or strong coupling to atomic light sources.Our laser design uses the simplest triangular lattice single-defect cavity containing a fractional edge dislocation. The cavity consists of a defect hole that is smaller than surrounding holes which define the photonic crystal mirror. The row that contains the defect hole is elongated by moving the two photonic crystal half planes a fraction of a lattice constant apart in the ⌫X direction, introducing a dislocation with width p ͑Fig. 1͒. We have shown earlier 8 that by tuning this p parameter, Q factors of single-defect cavities are significantly improved, and can reach values of over 10 000 when p/aϭ10% (a is the lattice constant͒. These high-Q values are obtained while maintaining a very small mode volume of V mode Ϸ0.1( /2). 3 The cavity used in our laser was originally designed for cavity quantum electrodynamic experiments and nanospectroscopy. Light sources or absorbing molecules can be placed into the small hole within the center of the 2D photonic crystal cavity, where the optical field intensity is the strongest. On the other hand, it is clear that the presence of a hole at the point of maximum field intensity is not desirable in low-threshold laser designs, since the overlap with the gain region ͑e.g., quantum wells͒ is decreased. Therefore, we expect even better cavity designs to yield further improvements over the performance of the lasers described here.Our structures are fabricated in InGaAsP quantum well material. Metalorganic chemical vapor deposition was used to grow the active laser structure o...
Time-resolved photoluminescence measurements reveal a minority carrier lifetime of >412 ns at 77 K under low excitation for a long-wavelength infrared InAs/InAs0.72Sb0.28 type-II superlattice (T2SL). This lifetime represents an order-of-magnitude increase in the minority carrier lifetime over previously reported lifetimes in long-wavelength infrared InAs/Ga1−xInxSb T2SLs. The considerably longer lifetime is attributed to a reduction of non-radiative recombination centers with the removal of Ga from the superlattice structure. This lifetime improvement may enable background limited T2SL long-wavelength infrared photodetectors at higher operating temperatures.
Glutaminase, which converts glutamine to glutamate, is involved in Warburg effect in cancer cells. Two human glutaminase genes have been identified, GLS (GLS1) and GLS2. Two alternative transcripts arise from each glutaminase gene: first, the kidney isoform (KGA) and glutaminase C (GAC) for GLS; and, second, the liver isoform (LGA) and glutaminase B (GAB) for GLS2. While GLS1 is considered as a cancer therapeutic target, the potential role of GLS2 in cancer remains unclear. Here, we discovered a series of alkyl benzoquinones that preferentially inhibit glutaminase B isoform (GAB, GLS2) rather than the kidney isoform of glutaminase (KGA, GLS1). We identified amino acid residues in an allosteric binding pocket responsible for the selectivity. Treatment with the alkyl benzoquinones decreased intracellular glutaminase activity and glutamate levels. GLS2 inhibition by either alkyl benzoquinones or GLS2 siRNA reduced carcinoma cell proliferation and anchorage-independent colony formation, and induced autophagy via AMPK mediated mTORC1 inhibition. Our findings demonstrate amino acid sequences for selective inhibition of glutaminase isozymes and validate GLS2 as a potential anti-cancer target.
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