Edward A. Whittaker
Stevens Institute of Technology
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Featured researches published by Edward A. Whittaker.
Optics Letters | 1998
Khosrow Namjou; Simin Cai; Edward A. Whittaker; Jérôme Faist; Claire F. Gmachl; Federico Capasso; Deborah L. Sivco; Alfred Y. Cho
We report what we believe are the first spectroscopic measurements to be made with a room-temperature quantum-cascade distributed-feedback laser. Using wavelength modulation spectroscopy, we detected N(2)O and CH(4) in the chemical fingerprint wavelength range near 8microm . The noise equivalent absorbance for our measurement was 5 parts in 10(5), limited by excess amplitude modulation on the laser output, which corresponds to a 1-Hz bandwidth detection limit of 250 parts N(2)O in 10(9) parts N(2) in a 1-m path length.
IEEE Journal of Quantum Electronics | 2002
Federico Capasso; Roberto Paiella; Rainer Martini; Raffaele Colombelli; Claire F. Gmachl; Tanya L. Myers; Matthew S. Taubman; Richard M. Williams; C. G. Bethea; Karl Unterrainer; Harold Y. Hwang; Deborah L. Sivco; A. Y. Cho; A. M. Sergent; H. C. Liu; Edward A. Whittaker
Following an introduction to the history of the invention of the quantum cascade (QC) laser and of the band-structure engineering advances that have led to laser action over most of the mid-infrared (IR) and part of the far-IR spectrum, the paper provides a comprehensive review of recent developments that will likely enable important advances in areas such as optical communications, ultrahigh resolution spectroscopy and applications to ultrahigh sensitivity gas-sensing systems. We discuss the experimental observation of the remarkably different frequency response of QC lasers compared to diode lasers, i.e., the absence of relaxation oscillations, their high-speed digital modulation, and results on mid-IR optical wireless communication links, which demonstrate the possibility of reliably transmitting complex multimedia data streams. Ultrashort pulse generation by gain switching and active and passive modelocking is subsequently discussed. Recent data on the linewidth of free-running QC lasers (/spl sim/150 kHz) and their frequency stabilization down to 10 kHz are presented. Experiments on the relative frequency stability (/spl sim/5 Hz) of two QC lasers locked to optical cavities are discussed. Finally, developments in metallic waveguides with surface plasmon modes, which have enabled extension of the operating wavelength to the far IR are reported.
Applied Optics | 1994
James M. Supplee; Edward A. Whittaker; W. Lenth
We present a comprehensive theory for heterodyne absorption spectroscopy with phase-modulated light. The general equations presented allow for an arbitrary modulation index and an arbitrary modulation frequency. We use this description for three purposes: First, we review the special cases of so-called frequency modulation and wavelength modulation spectroscopy. Second, we present the additional case of large-index, high-frequency modulation. Third, we present an overview of how the absorption signal depends on the experimental parameters of modulation frequency and modulation index. This overview may be helpful to experimentalists in choosing these parameters, for it provides a systematic understanding of how moving around in parameter space changes certain features of the signal, while leaving other features invariant.
Applied Physics Letters | 2001
Roberto Paiella; Rainer Martini; Federico Capasso; Claire F. Gmachl; Harold Y. Hwang; Deborah L. Sivco; James N. Baillargeon; Alfred Y. Cho; Edward A. Whittaker; H. C. Liu
Quantum cascade (QC) lasers, based on intersubband transitions in semiconductor quantum wells, are characterized by ultrafast (picosecond) carrier lifetimes. An important consequence of this unique property is the expected absence of relaxation oscillations in the transient response of these devices. Here, we discuss and experimentally verify this prediction by measuring the modulation response of several 8-μm-QC lasers, properly processed and packaged for high-speed operation, up to 10 GHz.
Optics Express | 2009
Paul Corrigan; Rainer Martini; Edward A. Whittaker; Clyde G. Bethea
Mid-infrared (MIR) free space optical communication has seen renewed interest in recent years due to advances in quantum cascade lasers. We present data from a multi-wavelength test-bed operated in the New York metropolitan area under realistic weather conditions. We show that a mid-infrared source (8.1 microm) provides enhanced link stability with 2x to 3x greater transmission over near infrared wavelengths (1.3 microm & 1.5 microm) during fog formation and up to 10x after a short scavenging rain event where fog developed and visibility reduced to approximately 1 km. We attribute the improvement to less Mie scattering at longer wavelengths. We confirm that this result is generally consistent with the empirical benchmark Kruse model at visibilities above 2.5 km, but towards the 1 km eye-seeing limit we measured the equivalent MIR visibility to be > 10 km.
Applied Optics | 1992
H. C. Sun; Edward A. Whittaker
When used for trace-gas detection, laser absorption spectroscopy is usually limited by false absorption signals that are traceable to interferometric effects induced by windows and other pairs of optical surfaces. Here we introduce a new technique that can selectively reject these étalon fringes while preserving the true absorption signal over a wide range of étalon free spectral range to absorption linewidth ratios. We present a theoretical analysis and experimental verification by using a tunable lead salt diode laser.
Applied Optics | 1993
H. C. Sun; Edward A. Whittaker; Y. W. Bae; C. K. Ng; V. Patel; W. H. Tam; S. McGuire; B. Singh; B. Gallois
By applying both low-frequency wavelength modulation and high-frequency phase modulation to a laser diode, we develop a sensitive, high-bandwidth chemical diagnostic tool that is applicable to a variety of gas-phase processing environments. Specific chemical species are identified and monitored through their infrared absorption spectra, and the modulation methods allow for sensitive detection that is free of window and other reflection-driven interference fringes. Absorbance limits of 5.3 x 10(-8) and 1.9 x 10(-7) are obtained for an AlGaAs diode laser and a lead-salt diode laser, respectively. We discuss applications to plasma etching and chemical vapor deposition.
Applied Physics Letters | 1994
H. C. Sun; V. Patel; B. Singh; C. K. Ng; Edward A. Whittaker
We report the use of a tunable diode laser locked to a molecular vibrational absorption line as a sensitive plasma etching endpoint detector. Measurements were made on multilayer silicon wafers etched in a SF6 plasma discharge. We show that polycrystalline silicon to silicon dioxide endpoint transitions on wafers with exposed area as small as 33 mm2 should be observable by detecting the etch end product SiF4. The method shows considerable potential as an endpoint detection technique for applications such as contact hole etching wherein very small areas are being etched.
Journal of Applied Physics | 2001
Rainer Martini; Claire Gmachi; Alessandro Tredicucci; Federico Capasso; Albert L. Hutchinson; Deborah L. Sivco; Alfred Y. Cho; Edward A. Whittaker
High duty cycle operation of quantum cascade superlattice lasers with graded superlattice active regions is investigated with the goal of achieving high average optical power. The optical output power increases with pulse width and decreases with heat sink temperature. This behavior is explained on the basis of the laser core temperature oscillations during the pulsed, high duty cycle operation. Between 175 and 325 K heat sink temperature, optimum duty cycles vary from 10% to 1% and average power levels vary from 50 to 1 mW for various lasers used in this study.
Applied Physics Letters | 1993
H. C. Sun; Edward A. Whittaker
We report on the real‐time in situ detection of SF6 in a plasma etching reactor with μTorr sensitivity using a tunable diode laser absorption spectrometer. The spectrometer employs combined wavelength and frequency modulation of the laser diode, an approach which allows for sensitive, interference fringe‐free detection of the SF6. The dual modulation scheme also provides a feedback signal which enables the laser to be frequency locked to the absorption line.