K. T. Tsen

Arizona State University, Mesa, AZ, United States

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Publications (126)270 Total impact

  • J.west, K.t.tsen, S.h.lin
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    ABSTRACT: We have used a wavefunction-based model to interpret the absorption spectrum of F-center/OH− defect pairs in CsCl, CsI and CsBr. It is demonstrated that the analysis of the absorption spectrum of these defect systems can provide information such as the position vector of the center of charge of the defect molecule, the orientation of the intrinsic dipole moment, the electronic wavefunctions and energy levels of the defect system and the lattice reconfiguration due to the presence of the defect molecule.
    Modern Physics Letters B 04/2012; 09(26n27). · 0.69 Impact Factor
  • K. T.tsen
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    ABSTRACT: Recent experimental results obtained from time-resolved Raman studies in GaAs-AlAs and GaAs-AlxGa1−xAs multiple quantum well structures are reviewed. Particular emphasis is made on (1) electron-phonon and phonon-phonon interactions and their association with the hot-phonon effects in the hot-carrier dynamics of multiple quantum well structures; and (2) the transport properties of photoexcited electron-hole plasma and excitons in semiconductor multiple quantum well structures.
    Modern Physics Letters B 11/2011; 06(12). · 0.69 Impact Factor
  • C.chia, Otto F.sankey, K. T.tsen
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    ABSTRACT: We present a comprehensive theory for time-resolved Raman scattering from non-equilibrium electrons in direct bandgap semiconductors. Specifically, we include (1) the effects of probing with ultrashort laser pulse: (2) the effects of finite carrier collision time; (3) the effects of band structure; and (4) the effects of damping in the optical transition, in the calculations of Raman scattering cross section. Both elastic and inelastic scattering processes are taken into account in formulating the effects of carrier collision time. The effects of damping in the optical transitions have to be considered for the experimental condition of probing with above-bandgap laser excitations even if under some circumstances they do not drastically change the lineshape of the single-particle-scattering spectrum due to spin-density fluctuations.
    Modern Physics Letters B 11/2011; 07(06). · 0.69 Impact Factor
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    ABSTRACT: We report experimental results on the inactivation of encephalomyocarditis virus, M13 bacteriophage, and Salmonella typhimurium by a visible femtosecond laser. Our results suggest that inactivation of virus and bacterium by a visible femtosecond laser involves completely different mechanisms. Inactivation of viruses by a visible femtosecond laser involves the breaking of hydrogen∕hydrophobic bonds or the separation of the weak protein links in the protein shell of a viral particle. In contrast, inactivation of bacteria is related to the damage of their DNAs due to irradiation of a visible femtosecond laser. Possible mechanisms for the inactivation of viruses and bacteria are discussed.
    Journal of Biomedical Optics 07/2011; 16(7):078003. · 2.75 Impact Factor
  • Shaw-Wei D. Tsen, K. T. Tsen
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    ABSTRACT: We report inactivation of encephalomyocarditis virus and salmonella typhimurium by a visible femtosecond laser. Our results show that inactivation of virus and bacterium by an ultrashort pulsed laser light might involve completely different mechanisms. Inactivation of viruses by an ultrashort pulsed laser might involve disruption of their protein coat through laser-induced excitation of large-amplitude acoustic vibrations. On the other hand, inactivation of bacteria is most likely related to the disruption of their metabolism by the DNA relaxation process caused by irradiation of ultrashort pulsed lasers.
    02/2011
  • Journal of Healthcare Engineering. 06/2010; 1(2):185-196.
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    ABSTRACT: We report a photonic approach for selective inactivation of viruses with a near-infrared ultrashort pulsed (USP) laser. We demonstrate that this method can selectively inactivate viral particles ranging from nonpathogenic viruses such as M13 bacteriophage, tobacco mosaic virus (TMV) to pathogenic viruses like human papillomavirus (HPV) and human immunodeficiency virus (HIV). At the same time sensitive materials like human Jurkat T cells, human red blood cells, and mouse dendritic cells remain unharmed. Our photonic approach could be used for the disinfection of viral pathogens in blood products and for the treatment of blood-borne viral diseases in the clinic. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
    Proc SPIE 02/2010;
  • K T Tsen, D K Ferry
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    ABSTRACT: Subpicosecond time-resolved Raman spectroscopy has been employed to investigate electron-phonon interactions and phonon dynamics in InN. The electron-longitudinal optical phonon scattering rate and the decay dynamics of longitudinal optical phonons in InN have been directly measured. Our results indicate that hot-phonon effects can play an important role in the electron relaxation and transport in InN. The carrier dependence of the lifetime of the longitudinal optical phonons has also been measured. The results suggest that more theoretical work is needed to account for the dependence of the lifetime of longitudinal optical phonons on the photoexcited carrier density.
    Journal of Physics Condensed Matter 04/2009; 21(17):174202. · 2.22 Impact Factor
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    ABSTRACT: Recently, femtosecond laser technology has been shown to be effective in the inactivation of non-pathogenic viruses. In this paper, we demonstrate for the first time that infectious numbers of pathogenic viruses such as Human Immunodeficiency Virus (HIV) can be reduced by irradiation with subpicosecond near infrared laser pulses at a moderate laser power density. By comparing the threshold laser power density for the inactivation of HIV with those of human red blood cells and mouse dendritic cells, we conclude that it is plausible to use the ultrashort pulsed laser to selectively inactivate blood-borne pathogens such as HIV while leaving the sensitive materials like human red blood cells unharmed. This finding has important implications in the development of a new laser technology for disinfection of viral pathogens in blood products and in the clinic.
    Proc SPIE 01/2009;
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    ABSTRACT: We demonstrate for the first time that human immunodeficiency virus (HIV) can be inactivated by irradiation with subpicosecond near-infrared laser pulses at a moderate laser power density. By comparing the threshold laser power density for the inactivation of HIV with those of human red blood cells and mouse dendritic cells, we conclude that it is plausible to use the ultrashort pulsed laser to selectively inactivate blood-borne pathogens such as HIV while leaving sensitive materials like human red blood cells unharmed. This finding has important implications in the development of a new laser technology for disinfection of viral pathogens in blood products and in the clinic.
    Journal of Physics Condensed Matter 05/2008; 20(25):252205. · 2.22 Impact Factor
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    ABSTRACT: The inactivation of viruses such as M13 bateriophages subject to excitations by a very low power visible femtosecond laser has been studied. Our experimental results show that for a visible femtosecond laser having lambda = 425nm and a pulse width of 100 fs, the M13 bacteriophages are inactivated when the laser power density is greater than or equal to 50 MW / cm2. The functionality of M13 bacteriophages has been shown to be critically dependent on the pulse width as well as power density of the excitation laser. Our work demonstrates that by using a very low power visible femtosecond laser, it is plausible to inactivate viruses such as the M13 bacteriophages through Impulsive Stimulated Raman Scattering (ISRS) process. These experimental findings lay down the foundation for a novel new avenue of selectively inactivating microorganisms while leaving the sensitive materials unharmed by manipulating and controlling with femtosecond laser systems.
    Proc SPIE 03/2008;
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    ABSTRACT: Time-resolved Raman spectroscopy on a subpicosecond time scale has been used to study the phonon dynamics of both the A1(LO) and the E1(LO) phonons in InN. From the temperature-dependence of their lifetimes, we demonstrate that both phonons decay primarily into a large wavevector TO phonon and a large wavevector TA/LA phonon consistent with the accepted phonon dispersion relationship for wurtzite InN. Their lifetimes have been found to decrease from 2.2 ps, at the low electron-hole pair density of 5×1017cm-3 to 0.25 ps, at the highest density of 2×1019cm-3. Our experimental findings demonstrate that carrier-density dependence of LO phonon lifetime is a universal phenomenon in polar semiconductors.
    Proc SPIE 02/2008;
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    ABSTRACT: Gallium nitride (GaN), aluminum nitride, indium nitride (InN), and their alloys have long been considered as promising materials for device applications. Recently, growth of high quality InN as well as InxGa1−xN have been demonstrated. In particular, progress in the manufacturing of very high quality, single-crystal InN thin films has opened up a new challenging research avenue in the Ill-nitride semiconductors. In contrast to earlier beliefs, it has recently been found that InN has a relatively narrow bandgap, only ∼0.8 eV. Consequently, it is expected that InN has the smallest effective mass of the III-N semiconductors. As a result, very high electron mobility and a very large saturation velocity are expected. Recent single-particle Raman scattering, supported by ensemble Monte Carlo simulations suggest that steady velocities of the order of 5 × 107 cm/s can be found in high quality, single crystal wurtzite films of InN [1]. Here, we report on these calculations for the transport and properties of the non-equilibrium longitudinal optical phonons. We use a high quality, single-crystal wurtzite InN film grown on GaN and study the transport with picosecond/subpicosecond Raman spectroscopy. The built-in polarization and piezoelectric stress lead to an electric field of ∼80 kV/cm in the sample, which is oriented in the growth direction. From the Raman data [1], we can determine not only the average velocities (the drift velocity), but also the distribution function of the carriers along the field direction.
    12/2007: pages 143-146;
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    ABSTRACT: We demonstrate an unconventional and revolutionary method for selective inactivation of micro-organisms by using near-infrared femtosecond laser pulses. We show that if the wavelength and pulse width of the excitation femtosecond laser are appropriately selected, there exists a window in power density that enables us to achieve selective inactivation of target viruses and bacteria without causing cytotoxicity in mammalian cells. This strategy targets the mechanical (vibrational) properties of micro-organisms, and thus its antimicrobial efficacy is likely unaffected by genetic mutation in the micro-organisms. Such a method may be effective against a wide variety of drug resistant micro-organisms and has broad implications in disinfection as well as in the development of novel treatments for viral and bacterial pathogens.
    Journal of Physics Condensed Matter 10/2007; 19(47):472201. · 2.22 Impact Factor
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    ABSTRACT: Hemorrhage has been shown to increase inducible nitric oxide synthase (iNOS) and deplete ATP levels in tissues and geldanamycin limits both processes. Moreover, it is evident that inhibition of iNOS reduces caspase-3 and increases survival. Thus we sought to identify the molecular events responsible for the beneficial effect of geldanamycin. Hemorrhage in mice significantly increased caspase-3 activity and protein while treatment with geldanamycin significantly limited these increases. Similarly, geldanamycin inhibited increases in proteins forming the apoptosome (a complex of caspase-9, cytochrome c, and Apaf-1). Modulation of the expression of iNOS by iNOS gene transfection or siRNA treatment demonstrated that the level of iNOS correlates with caspase-3 activity. Our data indicate that geldanamycin limits caspase-3 expression and protects from organ injury by suppressing iNOS expression and apoptosome formation. Geldanamycin, therefore, may prove useful as an adjuvant in fluids used to treat patients suffering blood loss.
    Journal of Applied Physiology 10/2007; 103(3):1045-55. · 3.43 Impact Factor
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    ABSTRACT: We demonstrate for the first time that, by using a visible femtosecond laser, it is effective to inactivate viruses such as bacteriophage M13 through impulsive stimulated Raman scattering. By using a very low power visible femtosecond laser having a wavelength of 425 nm and a pulse width of 100 fs, we show that M13 phages were inactivated when the laser power density was greater than or equal to 50 MW cm−2. The inactivation of M13 phages was determined by plaque counts and depended on the pulse width as well as power density of the excitation laser.
    Journal of Physics Condensed Matter 07/2007; 19(32):322102. · 2.22 Impact Factor
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    ABSTRACT: Subpicosecond time-resolved Raman spectroscopy has been used to measure the lifetime of the A1(LO) and E1(LO) phonon modes in InN at T = 10 K for photoexcited electron–hole pair density ranging from 5 × 1017 to 2 × 1019 cm−3. The lifetime has been found to decrease from 2.2 ps at the lowest density to 0.25 ps at the highest density. Our experimental findings demonstrate that the carrier-density dependence of LO phonon lifetime is a universal phenomenon in polar semiconductors.
    Journal of Physics Condensed Matter 05/2007; 19(23):236219. · 2.22 Impact Factor
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    ABSTRACT: Longitudinal optical phonons in InN have been studied by time-resolved Raman spectroscopy on a subpicosecond time scale. The lifetimes of both the A<sub>1</sub>( LO ) and E<sub>1</sub>( LO ) phonons have been directly measured. From the temperature dependence of their lifetimes, the authors demonstrate that both phonons decay primarily into a large wave vector TO phonon and a large wave vector TA/LA phonon, consistent with the accepted phonon dispersion relationship for wurtzite InN.
    Applied Physics Letters 05/2007; · 3.52 Impact Factor
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    ABSTRACT: Electron–longitudinal optical phonon scattering rate in InN has been directly measured by subpicosecond time-resolved Raman spectroscopy. The experimental results show that for a thick layer of InN grown on GaN, the average total electron–longitudinal optical phonon scattering rate is (5.1±1.0)×1013 s−1. This enormous electron–longitudinal optical phonon scattering rate, which is comparable to that observed in GaN, has been attributed to the extremely polar nature of InN.
    Applied Physics Letters 04/2007; 90(17):172108-172108-3. · 3.52 Impact Factor
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    ABSTRACT: ZnO nanorods were grown by catalyst-assisted vapor phase transport on Si(001), GaN(0001)/c-Al2O3, and bulk ZnO(0001) substrates. Morphology studies as well as X-ray diffraction and transmission electron microscopy showed that ZnO nanorods grew mostly perpendicular to the GaN(0001) and ZnO(0001) substrate surface, whereas a more random directional distribution was found for nanorods on Si(001). Integral optical properties of fabricated nanorods were studied by steady-state photoluminescence and time-resolved photoluminescence. Stimulated emission was observed from ZnO nanorods on GaN(0001)/c-Al2O3 substrates, most likely due to their vertical orientation. Near-field scanning optical microscopy was applied to investigate luminescent properties of individual rods. Raman spectroscopy revealed biaxial compressive strain in the nanorod samples grown on Si(001). Conductive atomic force microscopy showed that nanorods are electrically isolated from each other. I-V spectra of individual nanorods were measured.
    Proc SPIE 03/2007;

Publication Stats

1k Citations
270.00 Total Impact Points

Institutions

  • 1986–2011
    • Arizona State University
      • • Department of Physics
      • • School of Electrical, Computer and Energy Engineering
      • • Center for Solid State Electronics Research
      Mesa, AZ, United States
    • University of Illinois, Urbana-Champaign
      • Department of Electrical and Computer Engineering
      Urbana, IL, United States
  • 2006
    • Walter Reed Army Institute of Research
      Silver Spring, Maryland, United States