Publications (9)62.53 Total impact
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Article: Ultrafast Rabi flopping and coherent pulse propagation in a quantum cascade laser
Nature Photonics 08/2010; 4(10):706-710. · 29.28 Impact Factor -
Article: Coherent coupling of multiple transverse modes in quantum cascade lasers.
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ABSTRACT: Quantum cascade lasers are a unique laboratory for studying nonlinear laser dynamics because of their high intracavity intensity, strong intersubband optical nonlinearity, and an unusual combination of relaxation time scales. Here we investigate the nonlinear coupling between the transverse modes of quantum cascade lasers. We present evidence for stable phase coherence of multiple transverse modes over a large range of injection currents. We explain the phase coherence by a four-wave mixing interaction originating from the strong optical nonlinearity of the gain transition. The phase-locking conditions predicted by theory are supported by spectral data and both near- and far-field mode measurements.Physical Review Letters 02/2009; 102(1):013901. · 7.37 Impact Factor -
Article: Widely tunable single-mode quantum cascade laser source for mid-infrared spectroscopy
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ABSTRACT: We demonstrate a compact, single-mode quantum cascade laser source continuously tunable between 8.7 and 9.4 μm. The source consists of an array of single-mode distributed feedback quantum cascade lasers with closely spaced emission wavelengths fabricated monolithically on a single chip and driven by a microelectronic controller. Our source is suitable for a variety of chemical sensing applications. Here, we use it to perform absorption spectroscopy of fluids.Applied Physics Letters 12/2007; 91(23):231101-231101-3. · 3.84 Impact Factor -
Article: Time-domain upconversion measurements of group-velocity dispersion in quantum cascade lasers.
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ABSTRACT: A time-resolved mid-infrared upconversion technique based on sum-frequency generation was applied to measure pulse propagation in lambda approximately 5.0 mum quantum cascade lasers operated in continuous wave at 30 K. The wavelength-dependent propagation delay of femtosecond mid-infrared pulses was measured to determine the total group-velocity dispersion. The material and waveguide dispersion were calculated and their contributions to the total group-velocity dispersion were found to be relatively small and constant. The small-signal gain dispersion was estimated from a measurement of the electroluminescence spectrum without a laser cavity, and was found to be the largest component of the total GVD. A negative group-velocity dispersion of beta2 ( =d2beta/d omega2) approximately - 4.6x10-6 ps2/mum was observed at the peak emission wavelength, and good agreement was found for the measured and calculated pulse-broadening.Optics Express 12/2007; 15(24):15898-907. · 3.59 Impact Factor -
Article: Near-field imaging of quantum cascade laser transverse modes.
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ABSTRACT: We report near field imaging of the transverse lasing modes of quantum cascade lasers. A mid-infrared apertureless near-field scanning optical microscope was used to characterize the modes on the laser facet. A very stable mode pattern corresponding to a TM(00) mode was observed as function of increasing driving current for a narrow active region quantum cascade laser. Higher order modes were observed for devices with a larger active region width-to-wavelength ratio operated in pulsed mode close to threshold. A theoretical model is proposed to explain why specific transverse modes are preferred close to threshold. The model is in good agreement with the experimental results.Optics Express 11/2007; 15(20):13227-35. · 3.59 Impact Factor -
Article: Bowtie plasmonic quantum cascade laser antenna.
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ABSTRACT: We report a bowtie plasmonic quantum cascade laser antenna that can confine coherent mid-infrared radiation well below the diffraction limit. The antenna is fabricated on the facet of a mid-infrared quantum cascade laser and consists of a pair of gold fan-like segments, whose narrow ends are separated by a nanometric gap. Compared with a nano-rod antenna composed of a pair of nano-rods, the bowtie antenna efficiently suppresses the field enhancement at the outer ends of the structure, making it more suitable for spatially-resolved high-resolution chemical and biological imaging and spectroscopy. The antenna near field is characterized by an apertureless near-field scanning optical microscope; field confinement as small as 130 nm is demonstrated at a wavelength of 7.0 mum.Optics Express 11/2007; 15(20):13272-81. · 3.59 Impact Factor -
Article: Intra-cavity absorption spectroscopy with narrow-ridge microfluidic quantum cascade lasers.
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ABSTRACT: We demonstrate microfluidic laser intra-cavity absorption spectroscopy with mid-infrared lambda approximately 9mum quantum cascade lasers. A deepetched narrow ridge waveguide laser is placed in a microfluidic chamber. The evanescent tails of the laser mode penetrate into a liquid on both sides of the ridge. The absorption lines of the liquid modify the laser waveguide loss, resulting in significant changes in the laser emission spectrum and the threshold current. A volume of liquid as small as ~10pL may, in principle, be sufficient for sensing using the proposed technique. This method, similar to the related gas-phase technique, shows promise as a sensitive means of detecting chemicals in small volumes of solutions.Optics Express 10/2007; 15(18):11262-71. · 3.59 Impact Factor -
Article: Single-mode laser action in quantum cascade lasers with spiral-shaped chaotic resonators
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ABSTRACT: The authors have fabricated and characterized quantum cascade lasers with spiral-shaped microresonators. The lasers operate in pulsed mode at room temperature with peak optical power greater than 20 mW and in continuous wave at temperatures up to 125 K. They exhibit single-mode emission in both pulsed mode and continuous wave operation, with a 30 dB side-mode suppression ratio at injection currents well above threshold. Subthreshold spectral measurements indicate that the spiral cavities support whispering-gallery-like modes. Single-mode lasing occurs on one of these modes. Far-field profiles reveal enhanced directionality compared to microdisk lasers.Applied Physics Letters 09/2007; 91(13):131106-131106-3. · 3.84 Impact Factor -
Article: Low-threshold continuous-wave operation of quantum-cascade lasers grown by metalorganic vapor phase epitaxy
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ABSTRACT: We report on the realization of InGaAs∕InAlAs quantum-cascade lasers grown by metalorganic vapor phase epitaxy operating in continuous wave with low-threshold current densities at temperatures as high as 188 K. Threshold current densities of 950 A∕cm2 and output powers of 125 mW are measured at 80 K, while 3 mW of continuous output power are measured at 180 K, with a threshold of 2.5 kA∕cm2. In pulsed mode, peak output powers of more than 0.4 W were obtained at 80 K and of 160 mW at 300 K with thresholds of 700 A∕cm2 and 2.75 kA∕cm2, respectively.Applied Physics Letters 12/2004; 85(24):5842-5844. · 3.84 Impact Factor
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Top Journals
- Optics Express (4)
- Applied Physics Letters (3)
- Physical Review Letters (1)
- Nature Photonics (1)
Institutions
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2009
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Harvard University
- School of Engineering and Applied Sciences
Cambridge, MA, USA
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