Kale J. Franz -- Publications

Publications

24. K.J. Franz, M.D. Escarra, A.J. Hoffman, P.Q. Liu, J.J.J. Raftery, S.S. Howard, Y. Dikmelik, J.B. Khurgin, X. Wang, J.-Y. Fan, C. Gmachl "Short Injector Quantum Cascade Lasers," in preparation.

23. Y. Yao, Z.J. Liu, A.J. Hoffman, K.J. Franz, C.F. Gmachl "Voltage Tunability of Quantum Cascade Lasers," IEEE Journal of Quantum Electronics, accepted.

22. A.J. Hoffman, L. Alekseyev, A. Sridhar, P.X. Braun, S.S. Howard, K.J. Franz, D. Wasserman, V.A. Podolskiy, E.E. Narimanov, D.L. Sivco, C. Gmachl "Mid-infrared Semiconductor Optical Metamaterials," Journal of Applied Physics, submitted.

21. J.B. Khurgin, Y. Dikmelik, P.Q. Liu, A.J. Hoffman, M.D. Escarra, K.J. Franz, C.F. Gmachl "Role of interface roughness in the transport and lasing characteristics of quantum-cascade lasers," Applied Physics Letters, 94, 091101 (2009).
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A density-matrix based theory of transport and lasing in quantum-cascade lasers reveals that large disparity between luminescent linewidth and broadening of the tunneling transition changes the design guidelines to favor strong coupling between injector and upper laser level. This conclusion is supported by the experimental evidence.

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20. C.R. Young, R. Cendejas, S.S. Howard, W. Sanchez-Vaynshteyn, A.J. Hoffman, K.J. Franz, Y. Yao, B. Mizaikoff, X. Wang, J.-Y. Fan, C. Gmachl "Wavelength selection for quantum cascade lasers by cavity length," Applied Physics Letters, 94, 091109 (2009).
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A systematic shift in spectral emission wavenumbers in quantum cascade lasers (QCLs) is observed over a variation in cavity lengths from 0.5 to 3 mm resulting in a gain peak shift ranging from 2404 to 2286 cm⁻¹. Thereby, a wavelength selection range of 118 cm⁻¹ is provided, which is sufficiently broad for selecting the laser emission across the entire CO2 absorption band at 2326 cm⁻¹ (4.3 µm). In contrast to current QCL wavelength selection techniques, modifying the cavity length is a straightforward postprocessing procedure. Experimental evidence confirms that this frequency shift is due to a change in threshold voltage and applied electric field as a function of cavity length which is in agreement with the theory.

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19. A.J. Hoffman, P.X. Braun, M.D. Escarra, K.J. Franz, X. Wang, C. Gmachl "Lasing-induced reduction of core heating in high wall plug efficiency quantum cascade lasers," Applied Physics Letters 94, 041101 (2009).
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Quantum cascade (QC) laser core heating is a primary impediment to high device wall plug efficiency (WPE). Here, we demonstrate that efficient photon generation produces a quantifiable reduction in heating of the QC laser core temperature. By superimposing low duty cycle current pulses on a core-heating dc baseline, we observe the instantaneous threshold current and current efficiency evolution as the dc input is varied. From these measurements we recover the laser core temperature T_core. Results agree well with calculations of T_core based on measured thermal resistance and WPE. Using the same thermal model for a laser with negligible WPE, we show that the large WPE of the measured device-—24% for an 80 K heat sink-—results in a core temperature reduction of ~15 K.

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18. Y. Yao, K.J. Franz, Z. Liu, A.J. Hoffman, C.F. Gmachl, "Voltage tuning of gain spectra in quantum cascade lasers," Proc. SPIE 7230, 723012 (2009).
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The voltage tuning of gain spectra in three types of Quantum Cascade laser designs is investigated. The gain spectra of the luminescence device are tunable over the whole voltage operation range for all designs. The lasers are as tunable as the electroluminescence below threshold, while a reduced tunability is observed in all lasers above threshold. This is attributed to the decrease of resistance across the laser active region as the photon density increases. A resumed tunability high above threshold occurs in all lasers based on the anti-crossed designs. Lasers based on the anti-crossed diagonal transition are tunable above threshold, with a tuning range of about 40 cm^-1 (~4% of the laser emission wavenumber) at room temperature, i.e. a tuning rate of 800 cm^-1 per volt per period of active region and injector.

PDF Reprint Publication Link Copyright 2009 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

17. K.J. Franz, S. Menzel, A.J. Hoffman, D. Wasserman, J. Cockburn, C. Gmachl "High k-space lasing in a dual wavelength quantum cascade laser," Nature Photonics 3, 50-54 (2008).
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We report on a quantum cascade (QC) laser structure with an energy configuration able to establish local population inversion of electrons high in k-space through intrinsic processes. We observe dual wavelength emission from two discrete optical transitions lasing near λ ≈ 9.5 and 8.2 µm. Temperature-dependent performance attributes show that the two transitions are highly coupled: competition for charge carriers is apparent from anti-correlated behaviour in output power. The anti-correlated behaviour is further observed through the temperature dependence of threshold currents, with the secondary transition having a negative characteristic temperature T₀ before it sharply becomes positive. The two optical transitions represent a conventional QC laser transition at k ≈ 0 and another laser transition from non-thermal electrons at k ≈ 3.6×10⁸ m^-1.

16. S.S. Howard, D.P. Howard, K.J. Franz, A.J. Hoffman, D.L. Sivco, C. Gmachl "The effect of injector barrier thickness and doping level on current transport and optical transition width in a λ ~ 8 µm QC structure," Applied Physics Letters 93, 191107 (2008).
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We experimentally study the optical transition width and current transport properties of a set of λ~8.0 µm quantum cascade (QC) structures with varying injector barrier thickness and doping level. For this high-performance QC laser structure, a 50% reduction in doping level and a 33% reduction in injection barrier thickness yield five times stronger luminescence, 20% smaller optical transition linewidth, and improved current-voltage characteristics. These results demonstrate how high-performance QC laser structures can be engineered to produce narrow gain spectra at and above room temperature.

PDF Reprint Publication Link Copyright 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

15. W.O. Charles, K.J. Franz, A. Shen, A. Zhang, B. Li, Y Gong, G.F. Neumark, C. Gmachl, M.C. Tamargo "Molecular Beam Epitaxy Growth of Zn_xCd_1-xSe/Zn_x’Cd_y’Mg_1-x’-y’Se-InP Quantum Cascade Structures," Journal of Crystal Growth 310, 5380 (2008).
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We report growth by molecular beam epitaxy of a Zn_xCd_(1-x)Se/Zn_x'Cd_y'Mg_(1-x'-y')Se quantum cascade (QC) structure that was designed for electroluminescence (EL) at ~4.5 µm. The QC active region is comprised of a two-well asymmetric coupled quantum well (ACQW) structure, which was thoroughly investigated to establish the growth conditions for the QC structure. After growth of several ACQW test samples, the conditions for growth were optimized for the QC structure. In-situ RHEED, photoluminescence (PL), high-resolution X-ray diffraction (HR-XRD) and Fourier transform infrared (FTIR) spectroscopy results were used for characterization. The QC structure grown under these conditions exhibited EL at 4.8 µm, in excellent agreement with the design value.

14. A. Shen, W.O. Charles, B.S. Li, K.J. Franz, C. Gmachl, Q. Zhang, M.C. Tamargo "Wide Band Gap II-VI Selenides for Short Wavelength Intersubband Devices," Journal of Crystal Growth, accepted.
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In this paper, we present our recent progress towards the realization of short wavelength intersubband devices with wide band gap II-VI selenide semiconductors. Intersubband electroluminescence at 4.8 μm was observed in a ZnCdSe/ZnCdMgSe quantum cascade structure at temperatures up to room temperature. We also developed a new ZnCdSe/MgSe quantum structure with metastable MgSe barriers. Intersubband absorption in the 3-5 μm range was observed. Calculations suggest that with this structure intersubband transitions as short as 1.55 μm may be achieved.

13. W.O. Charles, A. Shen, K.J. Franz, C. Gmachl, Q. Zhang, Y. Gong, G.F. Neumark, M.C. Tamargo "Growth and Characterization of Zn_xCd_1-xSe/Zn_x’Cd_y’Mg_1-x’-y’Se Asymmetric Coupled Quantum Well Structures for Quantum Cascade Laser Applications," Journal of Vacuum Science & Technology B 26, 1171 (2008).
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The authors report the growth of a II-VI Zn_xCd_1−xSe / Zn_x'Cd_y'Mg_1−x'−y'Se asymmetric coupled quantum well (asymmetric-CQW) structure that was used to investigate the active region of an intersubband electroluminescence structure designed for emission at λ=4.5 µm. Such a structure could comprise the active region of a quantum cascade laser. The results of photoluminescence and Fourier transform infrared spectroscopy analysis show good agreement with the expected transition energies predicted by simulation results for the asymmetric-CQW structure. High resolution x-ray diffraction analysis indicates high structural quality of the sample and good control of the growth.

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12. K.J. Franz, W.O. Charles, A. Shen, A.J. Hoffman, M.C. Tamargo, C. Gmachl "ZnCdSe/ZnCdMgSe Quantum Cascade Electroluminescence," Applied Physics Letters 92, 121105 (2008).
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This letter reports electroluminescence emission from a ZnCdSe/ZnCdMgSe quantum cascade (QC) structure. With a two-well QC active region design, the II-VI heterostructure was grown lattice matched on an InP substrate by molecular beam epitaxy. Deep etched mesas were electrically pumped at current densities up to 10 kA/cm, producing optical emission centered near 4.8 µm, in good agreement with the structure design. The light is predominantly TM polarized, confirming its intersubband origin. Electroluminescence was observed from 78 to 300 K.

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11. A.J. Hoffman, S. Schartner, S.S. Howard, K.J. Franz, F. Towner, C. Gmachl "Low voltage-defect quantum cascade laser with heterogeneous injector regions," Optics Express 15, 15818 (2007).
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We demonstrate an In_0.635Al_0.356As/In_0.678Ga_0.322As strain compensated quantum cascade laser that employs heterogeneous injector regions for low voltage defect operation. The active core consists of interdigitated undoped and doped injectors followed by nominally identical wavelength optical transitions. The undoped injector regions are designed with reduced voltage defect while the doped injectors are of a more conventional design. The measured average voltage defect is less than 79 meV. At 80 K, a 2.3 mm long, back facet high reflectance coated laser has an emission wavelength of 4.7 μm and outputs 2.3 W pulsed power with a peak wall-plug efficiency of 19%.

PDF Reprint Publication Link This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.

10. A.J. Hoffman, L. Alekseyev, S.S. Howard, K.J. Franz, D. Wasserman, V.A. Podolskiy, E.E. Narimanov, D.L. Sivco, C. Gmachl "Negative refraction in semiconductor metamaterials," Nature Materials 6, 946 (2007).
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An optical metamaterial is a composite in which subwavelength features, rather than the constituent materials, control the macroscopic electromagnetic properties of the material. Recently, properly designed metamaterials have garnered much interest because of their unusual interaction with electromagnetic waves. Whereas nature seems to have limits on the type of materials that exist, newly invented metamaterials are not bound by such constraints. These newly accessible electromagnetic properties make these materials an excellent platform for demonstrating unusual optical phenomena and unique applications such as subwavelength imaging and planar lens design. 'Negative-index materials', as first proposed, required the permittivity and permeability to be simultaneously less than zero, but such materials face limitations. Here, we demonstrate a comparatively low-loss, three-dimensional, all-semiconductor metamaterial that exhibits negative refraction for all incidence angles in the long-wave infrared region and requires only an anisotropic dielectric function with a single resonance. Using reflection and transmission measurements and a comprehensive model of the material, we demonstrate that our material exhibits negative refraction. This is furthermore confirmed through a straightforward beam optics experiment.

9. H. Lu, A. Shen, M.C. Tamargo, W. Charles, I. Yokomizo, M. Munoz, Y. Gong, G.F. Neumark, K.J. Franz, C. Gmachl, C.Y. Song, H.C. Liu "Study of intersubband transitions of Zn_xCd_1−xSe/Zn_xCd_yMg_1−x−ySe multiple quantum wells grown by molecular beam epitaxy for midinfrared device applications," Journal of Vacuum Science & Technology B 25, 1103 (2007).
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Two Zn_xCd_1−xSe/Zn_x'Cd_y'Mg_1−x'−y'Se multiple quantum well structures were grown by molecular beam epitaxy. The quantum well layer thickness of the multiple quantum well region was varied in order to tune the intersubband transition energy. The high crystalline quality of the material was demonstrated by high resolution x-ray diffraction. Contactless electroreflectance (CER) spectroscopy and Fourier transform infrared (FTIR) spectroscopy were used to characterize the intersubband transitions. Excellent agreement between the estimated value obtained by CER and the value measured by FTIR was achieved. Intersubband absorption at 6.89 and 5.37 µm was observed demonstrating the ability to tune the properties of these wide band gap II-VI materials for mid-IR intersubband device applications.

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8. A. Shen, H. Lu, M.C. Tamargo, W. Charles, I. Yokomizo, C.Y. Song, H.C. Liu, S.K. Zhang, X. Zhou, R.R. Alfano, K.J. Franz, C. Gmachl "Intersubband transitions in molecular-beam-epitaxy-grown wide band gap II-VI semiconductors," Journal of Vacuum Science & Technology B 25, 995 (2007).
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The authors report the study of intersubband transitions in ZnCdMgSe-based wide band gap II-VI semiconductors. The samples were prepared by molecular beam epitaxy on InP substrates. Both ZnCdSe/ZnCdMgSe multiple quantum wells and CdSe/ZnCdMgSe quantum dot multilayer stacks were grown. Strong intersubband absorption was observed in the samples. The results show that these materials are very promising for fabricating intersubband devices in the mid- and near-infrared spectral ranges.

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7. K.J. Franz, D. Wasserman, A.J. Hoffman, D.C. Jangraw, K.-T. Shiu, S.R. Forest, C. Gmachl "Evidence of cascaded emission in a dual-wavelength Quantum Cascade laser," Applied Physics Letters 90, 091104 (2007).
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This letter reports on a quantum cascade laser that exhibits simultaneous dual-wavelength emission from two consecutive optical transitions in each active region. These "cascaded" transitions—a second-excited state to first-excited state and a first-excited state to ground state—yield light at ~9.5 and ~8.2 µm, respectively, in good agreement with simulations. The two lasing wavelengths have similar thresholds at the leading edge of a current pulse.

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Copyright 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

6. A. Shen, H. Lu, M.C. Tamargo, W. Charles, I. Yokomizo, K.J. Franz, C. Gmachl, S.K. Zhang, X. Zhou, R.R. Alfano, H.C. Liu "Intersubband absorption in CdSe/ZnCdMgSe self-assembled quantum dot multi-layers," Applied Physics Letters 90, 071910 (2007)
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The authors report the observation of intersubband absorption in multilayers of CdSe/Zn_xCd_yMg_1−x−ySe self-assembled quantum dots. The samples were grown by molecular beam epitaxy on InP substrates. For samples with the CdSe dot layers doped with Cl and with the deposited CdSe equivalent layer thickness between 5.2 and 6.9 ML, peak absorption between 2.5 and 3.5 µm was observed. These materials are promising for intersubband devices operating in the mid- and near-infrared ranges.

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5. S. Zhang, X. Zhou, A. Shen, W. Wang, R. Alfano, H. Lu, W.O. Charles, I. Yokomizo, M.C. Tamargo, K.J. Franz, C. Gmachl "Optical Properties of Heavily Doped n-type CdSe Quantum Dots for Intersubband Device Applications," Proceedings of the Materials Research Society 959E, 0959-M06-05 (2006).
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In this research, interband and intersubband optical properties of heavily doped n-type CdSe quantum dots were investigated by temperature dependent photoluminescence (PL) spectroscopy, picosecond time-resolved PL spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Two doped and one undoped CdSe quantum dot samples with multiple QD layers were grown over ZnCdMgSe barrier layers on InP (001) substrate by molecular beam epitaxy. Heavy doping leads to decreasing of activation energy of nonradiative recombination centers, however, does not affect the luminescence efficiency of doped quantum dots. Time resolved PL experiments show that the PL decay times of the doped samples have weak dependence on dot size and are much longer than that of the undoped sample. The two doped CdSe QD samples show strong Intersubband IR absorption that peaked at 2.54 μm, 2.69 μm and 3.51 μm.

4. H. Lu, A. Shen, W. Charles, I. Yokomizo, M.C. Tarmargo, K.J. Franz, C. Gmachl, M. Munoz "Optical characterization of intersubband transitions in Zn_xCd_1−xSe/Zn_x'Cd_y'Mg_1−x'−y'Se multiple quantum well structures by contact-less electroreflectance," Applied Physics Letters 89, 241921 (2006).
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Contactless electroreflectance was measured at room temperature to characterize a wide range of the possible optical transitions in Zn_xCd_1−xSe/Zn_x'Cd_y'Mg_1−x'−y'Se multi-quantum-well structures grown by molecular beam epitaxy. Based on these measurements, the authors predict and then verify the anticipated intersubband transition energies. They investigate a representative Zn_0.5Cd_0.5Se/Zn_0.20Cd_0.19Mg_0.61Se structure, for which the E1-E2 transition energy is predicted to be 178 meV (6.97 µm). Intersubband absorption using Fourier transform infrared spectroscopy exhibits a peak at 180 meV (6.89 µm), in excellent agreement with the contactless electroreflectance measurements.

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3. K.J Franz, K.-T. Shiu, S.R. Forrest, C. Gmachl "A dual-wavelength quantum cascade laser with two optical transitions in each active region," Proceedings of the Conference on Indium Phosphide and Related Materials (IPRM) pp. 26-29 (2006).
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We report on a novel quantum cascade laser design that utilizes wide active region quantum wells to create a lasing transition between the second- and first-excited states of the constituent wells. Electroluminescence and lasing spectra confirm the presence of the optical transition at the expected energy, but also show the conventional transition between energy levels resulting from excited and ground states of the original quantum wells. As a result, the laser produces simultaneous dual-wavelength emission at 8.2 μm and 9.3 μm.

PDF Reprint Publication Link This article may be found at IEEE Xplore. © 2006 IEEE. A reprint of this article may be downloaded for personal use only. Any other use requires prior permission of the author and the IEEE.

2. K.J. Franz, J.L. Alleman, K.M. Jones, A.C. Dillon, M.J. Heben "Carbon single-wall nanotube growth in a volumetrically confined arc discharge system," DOE Journal of Undergraduate Research 4, 66 (2004).
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Carbon nanotubes hold significant promise for a vast number of materials applications due to their unique mechanical, electrical, and gas storage properties. Although carbon single-wall nanotubes (SWNTs) have been synthesized since 1993 by the arc discharge method, and numerous other synthesis methods have since been developed, no method has yet produced 100% pure carbon nanotubes. Instead, a significant amount of impurities—various carbon structures and metal catalysts—are present in the raw soot. While arc discharge was the first method for SWNT synthesis, it also produces more impure raw soot in comparison to the more recently developed laser vaporization, which has produced the purest raw soot to date but is much slower. Geometry and thermal gradient are appreciably different between traditional arc discharge systems and laser vaporization systems. We report that, by incorporating some characteristics inherent to a laser vaporization system into an arc discharge system, improvement in the yield of SWNT raw soot may be achieved. This is accomplished by confining the arc within a 50 mm diameter quartz tube, similar to laser vaporization. We find through transmission electron microscopy and Raman spectroscopy that SWNTs are made in significant numbers in this confined arc discharge system, comparable to laser vaporization synthesized material. Further study is, however, required to prove reproducibility and attain an exact value for the purity of the produced raw soot.

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1. K.J. Franz and P.P. Faletra "DNA Dilemma: A perspective on U.S. Patent and trademark Office philosophy concerning life patents," DOE Journal of Undergraduate Research 2, 25 (2002).
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The lack of a solid set of criteria for determining patentability of subject matter—particularly subject matter dealing with life—has recently been of increasing public concern in the United States. Alarm for patent practices related to life systems ranges from patents being granted on biochemical processes and the knowledge of these processes to the patenting of entire organisms. One of the most volatile concerns is the patenting of human genes or parts of genes since this genetic material is the basic informational molecule for all life. Current patent law, legislated in 1952, has been interpreted by the U.S. Supreme Court to allow broad patents of DNA, biochemical processes, and what are generally considered "inventions" of life systems. Several issues are addressed in this paper regarding the unsound reasoning underlying both the interpretation and execution of patent law. Lapses in logic provide a gateway for businesses and individuals to take patenting to an illogical and unworkable extreme. Patent Office disorder of this magnitude is unnecessary and has great potential for harming the mission that the patent office was designed to serve. Recently disclosed patent-granting guidelines suggest the United States Patent and Trademark Office is not upholding its Constitutional responsibility of promoting the progress of science.

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Presentations

45. K.J. Franz, J.J.J. Raftery, P.Q. Liu, A.J. Hoffman, M.D. Escarra, S.S. Howard, Y. Dikmelik, J.B. Khurgin, X. Wang, J.-Y. Fan, C. Gmachl "Negative Differential Resistance and Pulse Instabilities in Minimalized Quantum Cascade Laser Structures," Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, June 2009. accepted

44. C. Young, R. Cendejas, S.S. Howard, W. Sanchez-Vaynshteyn, A.J. Hoffman, K.J. Franz, Y. Yao, B. Mizaikoff, X. Wang, J. Fan, C.F.Gmachl, "Enhancing Wavelength Selection for Quantum Cascade Laser Based Chemical Sensors by Cavity Length Variation," poster presentation, Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, June 2009. accepted

43. A.J. Hoffman, P.X. Braun, M.D. Escarra, S.S. Howard, K.J. Franz, X. Wang, J.-Y. Fan, C. Gmachl "Characterizing Quantum Cascade Lasers Using Instantaneous Power and Threshold Measurements," Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, June 2009. accepted

42. Y. Yao, K.J. Franz, X. Wang, C.F. Gmachl "Widely Voltage Tunable Quantum Cascade Lasers," Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, June 2009. submitted

41. M.D. Escarra, A.J. Hoffman, S.S. Howard, K.J. Franz, X. Wang, J.-Y. Fan, C.F. Gmachl "Ultra Low Voltage Defect in Quantum Cascade Lasers," Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, June 2009. submitted

40. P.Q. Liu, A.J. Hoffman, M.D. Escarra, K.J. Franz, J.B. Khurgin, Y. Dikmelik, X. Wang, J.-Y. Fan, C.F. Gmachl "Quantum Cascade Lasers with Ultra-Strong Coupling Injection," Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, June 2009. submitted

39. Y. Dikmelik, J.B. Khurgin, P.Q. Liu, M.D. Escarra, A.J. Hoffman, K.J. Franz, C.F. Gmachl, X. Wang "Intersubband Absorption Loss in High-Performance Mid-Infrared Quantum Cascade Lasers," Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, June 2009. submitted

38. Y. Yao, K.J. Franz, Z. Liu, A.J. Hoffman, C.F. Gmachl, "Voltage tuning of gain spectra in quantum cascade lasers," Photonics West, San Jose, CA, Feb 2009.

37. K.J. Franz, P.Q. Liu, A. J. Hoffman, S.S. Howard, M.D. Escarra, Y. Dikmelik, J.B. Khurgin, X. Wang, J.-Y. Fan, C. Gmachl "Short Injector Regions for Improved Quantum Cascade Laser Performance," International Quantum Cascade Laser School and Workshop (IQCLSW), Monte Verita, Switzerland, Sept 2008. Invited Abstract Presentation

36. W.O. Charles, K.J. Franz, A. Shen, Q. Zhang, C. Gmachl, M.C. Tamargo "Growth and Characterization of ZnxCd1-xSe/Znx’Cdy’Mg1-x’y’Se Quantum Cascade Emitters," International Quantum Cascade Laser School and Workshop (IQCLSW), Monte Verita, Switzerland, Sept 2008.

35. M.D. Escarra, A.J. Hoffman, S.S. Howard, K.J. Franz, X. Wang, M Fong, C.F. Gmachl "Improved Voltage Efficiency in Quantum Cascade Lasers," poster presentation, International Quantum Cascade Laser School and Workshop (IQCLSW), Monte Verita, Switzerland, Sept 2008. Abstract

34. Y. Dikmelik, J.B. Khurgin, A.J. Hoffman, S.S. Howard, K.J. Franz, C.F. Gmachl "Excited-State Absorption in High-Power Mid-Infrared Quantum Cascade Lasers," poster presentation, International Quantum Cascade Laser School and Workshop (IQCLSW), Monte Verita, Switzerland, Sept 2008.

33. Y. Yao, Z. Liu, A.J. Hoffman, K.J. Franz, and C.F. Gmachl "Voltage tunability of quantum cascade lasers," International Quantum Cascade Laser School and Workshop (IQCLSW), Monte Verita, Switzerland, Sept 2008. Abstract

32. K.J. Franz, W.O. Charles, A. Shen, A.J. Hoffman, M.C. Tamargo, C. Gmachl "Quantum Cascade Electroluminescence from a ZnCdSe/ZnCdMgSe on InP Structure," Mid-Infrared Optoelectronics Materials and Devices (MIOMD) IX, Freiburg, Germany, Sept 2008. Abstract

31. A.J. Hoffman, M.D. Escarra, S.S. Howard, K.J. Franz, X. Wang, J.-Y. Fan, C. Gmachl "Strategies for Improved Wall-plug Efficiency in Quantum Cascade Lasers," Mid-Infrared Optoelectronics Materials and Devices (MIOMD) IX, Freiburg, Germany, Sept 2008.

30. A. Shen, W.O. Charles, B.S. Li, K.J. Franz, C. Gmachl, Q. Zhang, M.C. Tamargo "Wide Band Gap II-Selenides for Short Wavelength Intersubband Devices," International Conference on Molecular Beam Epitaxy, Vancouver, Canada, August 2008. Abstract

29. K.J. Franz, S. Menzel, D. Wasserman, A.J. Hoffman, J.W. Cockburn, C. Gmachl "High k-Space Lasing in Excited State Quantum Cascade Lasers," International Conference on the Physics of Semiconductors (ICPS), Rio de Janeiro, Brazil, July 2008. Abstract Presentation

28. K.J. Franz, W.O. Charles, A. Shen, A.J. Hoffman, M.C. Tamargo, C. Gmachl "Electroluminescence from a ZnCdSe/ZnCdMgSe Quantum Cascade Structure," International Conference on the Physics of Semiconductors, poster presentation, Rio de Janeiro, Brazil, July 2008. Abstract

27. Y. Dikmelik, J.B. Khurgin, A.J. Hoffman, S.S. Howard, K.J. Franz, C.F. Gmachl "Excited-State Absorption in High-Power Mid-Infrared Quantum Cascade Lasers," poster presentation, Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, May 2008. Abstract

26. K.J. Franz, W.O. Charles, A. Shen, A.J. Hoffman, M.C. Tamargo, C. Gmachl "Intersubband Electroluminescence from a ZnCdSe/ZnCdMgSe Quantum Cascade Structure," Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, May 2008. Abstract Presentation

25. S. Menzel, K.J. Franz, D. Wasserman, A.J. Hoffman, J.W. Cockburn, C.F. Gmachl "Laser Action at High k-Space Values in Anti-Correlated Multi-Wavelength Quantum Cascade Lasers," Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, May 2008. Abstract

24. A.J. Hoffman, S. Schartner, S.S. Howard, K.J. Franz, F. Towner, C. Gmachl "Low Voltage Defect Heterogeneous Quantum Cascade Laser," Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, May 2008. Abstract

23. M.A. Talukder, F.-S. Choa, C.R. Menyuk, K.J. Franz, S.S. Howard, C.F. Gmachl "Novel Heat Removal Waveguide Structure for High Performance Quantum Cascade Lasers," poster presentation, Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, May 2008. Abstract

22. W.O. Charles, K.J. Franz, A. Shen, M.C. Tamargo, C. Gmachl "Growth and properties of wide band gap II-VI multi-quantum well structures for mid-infrared quantum cascade lasers," American Physical Society March Meeting, New Orleans, LA, Mar 2008. Abstract

21. M.D. Escarra, A.J. Hoffman, S.S. Howard, K.J. Franz, A. Sridhar, C. Gmachl "High Efficiency Quantum Cascade Lasers," American Physical Society March Meeting, New Orleans, LA, Mar 2008. Abstract

20. K.J. Franz, S. Menzel, A.J. Hoffman, D. Wasserman, J. Cockburn, C. Gmachl "Excited State Quantum Cascade Lasers and Lasing in k-Space," PRISM/PCCM/MIRTHE Industry Day, Princeton, NJ, Mar 2008. Presentation

19. K.J. Franz, S. Menzel, A.J. Hoffman, D. Wasserman, J.W. Cockburn, C. Gmachl "High k-Space Lasing in a Dual Optical Transition Quantum Cascade Laser," poster presentation, 15th International Winterschool on New Developments in Solid State Physics, Bad Hofgastein, Salzburg, Austria, Feb 2008. Abstract

18. K.J. Franz, A.J. Hoffman, S.S. Howard, Z.J. Liu, S. Menzel, S. Schartner, D. Wasserman, C. Gmachl "Mid-Infrared Quantum Cascade Lasers," 15th International Winterschool on New Developments in Solid State Physics, Bad Hofgastein, Salzburg, Austria, Feb 2008.

17. S.S. Howard, A.J. Hoffman, K.J. Franz, D.P. Howard, T. Ko, D.L. Sivco, C.F. Gmachl "Effect of Injection Barrier Thickness and Doping on Transport and Gain in a λ = 8.2 μm Quantum Cascade Laser," IEEE LEOS Annual Meeting, Lake Buena Vista, FL, Oct 2007. Abstract

16. A.J. Hoffman, S. Schartner, S.S. Howard, K.J. Franz, F. Towner, C. Gmachl "Low-Voltage Defect Quantum Cascade Laser with Heterogeneous Injector Regions," IEEE LEOS Annual Meeting, Lake Buena Vista, FL, Oct 2007. Abstract

15. W.O. Charles, A. Shen, K.J. Franz, C. Gmachl, Q. Zhang, Y. Gong, G.F. Neumark, M.C. Tamargo "Asymmetric Coupled Quantum Well Structure for Quantum Cascade Laser Applications," North American Conference on Molecular Beam Epitaxy (NAMBE), Albuquerque, NM, Sept 2007.

14. K.J. Franz, S. Menzel, A.J. Hoffman, D. Wasserman, K.-T. Shiu, S.R. Forrest, C. Gmachl "Excited State Optical Transitions in Quantum Cascade Lasers for Low Thresholds and Multi-Wavelength Emission," International Conference on Intersubband Transitions in Quantum Wells (ITQW), Ambleside, Cumbria, U.K., Sept 2007. Abstract Presentation

13. S.S. Howard, A.J. Hoffman, K.J. Franz, T. Ko, C. Gmachl. "Current Injection Transition Broadening in Quantum Cascade Lasers." International Conference on Intersubband Transitions in Quantum Wells (ITQW), Ambleside, Cumbria, U.K, September, 2007. Abstract

12. K.J. Franz, D. Wasserman, A.J. Hoffman, K.-T. Shiu, S.R. Forrest, C. Gmachl "Cascaded Emission in a Dual-Wavelength Quantum Cascade Laser," Conference on Lasers and Electro-Optics (CLEO), Baltimore, MD, May 2007. Abstract Presentation

11. K.J. Franz, D. Wasserman, A.J. Hoffman, K.-T. Shiu, S.R. Forrest, C. Gmachl "Cascaded Emission in a Dual-Wavelength Quantum Cascade Laser," PRISM/PCCM/MIRTHE Industry Day, Princeton, NJ, Mar 2007.

10. K.J. Franz, K.-T. Shiu, S.R. Forrest, C. Gmachl "Monolithic Mid-Infrared Integration of a Quantum Cascade Laser and a Passive Semiconductor Waveguide," American Physical Society March Meeting, Denver, CO, Mar 2007. Abstract Presentation

9. S. Zhang, X. Zhou, A. Shen, W. Wang, R. Alfano, H. Lu, W.O. Charles, I. Yokomizo, M.C. Tamargo, K.J. Franz, C. Gmachl "Optical Properties of Heavily Doped n-type CdSe Quantum Dots for Intersubband Device Applications," MRS Fall Meeting, Boston, MA, Nov 2006.

8. A. Shen, H. Lu, M. C. Tamargo, W. Charles, I. Yokomizo, C.Y. Song, H.C. Liu, S. K. Zhang, X. Zhou, R. R. Alfano, K.J. Franz, C. Gmachl "Intersubband Transitions in MBE-grown Wide Bandgap II-VI Semiconductors," North American Conference on Molecular Beam Epitaxy (NAMBE), Durham, NC, Oct 2006.

7. K.J. Franz, K.-T. Shiu, S.R. Forrest, C. Gmachl "Excited state and dual-wavelength quantum cascade lasers," CLEO Semiconductor Laser Workshop, Long Beach, CA, June 2006.

6. K.J. Franz, K.-T. Shiu, S.R. Forrest, C. Gmachl "A dual-wavelength quantum cascade laser with two optical transitions in each active region," Indium Phosphide and Related Materials Conference (IPRM), Princeton, NJ, May 2006. Abstract

5. T. Gennett, C. Engtrakul, K.J. Franz, J.L. Alleman, P.A. Parilla, K.M. Jones, J. Blackburn, K.E.H. Gilbert, A.C. Dillon, M.J. Heben "Novel chamber design for arc synthesis of carbon nanotubes," Materials Research Society Fall Meeting, Boston, MA, Nov 2005.

4. C. Engtrakul, J.M. Nedeljkovic, Y.-H. Kim, M. Jones, R.J. Ellingson, M.C. Hanna, S.P. Ahrenkiel, K.M. Jones, M.F. Davis, T.J. McDonald, K.J. Franz, T. Gennett, A.C. Dillon, K.H. Gilbert, P.A. Parilla, J.L. Alleman, S.B. Zhang, O.I. Micic, G. Rumbles, A.J. Nozik, M.J. Heben "Self-organization of semiconductor quantum nanocrystals on carbon single-wall nanotubes into close-packed linear arrays," Materials Research Society Fall Meeting, Boston, MA, Nov 2004.

3. K.J. Franz, J.L. Alleman, K.M. Jones, A.C. Dillon, M.J. Heben "Single-wall carbon nanotube growth through volumetric confinement in arc discharge," poster presentation, American Vacuum Society Rocky Mountain Chapter Regional Meeting, Golden, CO, Aug 2004.

2. K.J. Franz, J.L. Alleman, K.M. Jones, A.C. Dillon, M.J. Heben "Carbon single-wall nanotube growth in a volumetrically confined arc discharge system," poster presentation, AAAS Annual Meeting, Seattle, WA, Feb 2004.

1. K.J. Franz and P.P. Faletra "DNA Dilemma: A perspective on U.S. Patent and trademark Office philosophy concerning life patents," poster presentation, AAAS Annual Meeting, Boston, MA, Feb 2002.

Patents

1. Kale J. Franz and Claire Gmachl, "Excited State Quantum Cascade Photon Source," United States, filed 4 May 2007. [ Application ]

last updated 3 March 2009