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Sekine, Norihiko; Hosako, Iwao |
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Title |
Intensity modulation of terahertz quantum cascade lasers under external light injection |
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2009 |
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Applied Physics Letters |
Abbreviated Journal |
Appl. Phys. Lett. |
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95 |
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201106(1-3) |
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Keywords |
QCL modulation, THz, terahertz |
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Abstract  |
We investigated the light-current characteristics of terahertz (THz) quantum cascade lasers under external light injection, which excites interband transitions in the active materials. It was found that the amount of reduction in the THz power was constant for all injection currents above threshold, and the dependence of the reduction amount on the wavelength of the external light was observed to show a resonancelike feature. The dominant intensity modulation mechanism was found to be the loss change caused by interband transitions in the active region. Further, the effective coupling efficiency plays an important role in the intensity modulation. |
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630 |
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Mannino, Giovanni; Spinella, Corrado; Ruggeri, Rosa; La Magna, Antonino; Fisicaro, Giuseppe; Fazio, Enza; Neri, Fortunato; Privitera, Vittorio |
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Title |
Crystallization of implanted amorphous silicon during millisecond annealing by infrared laser irradiation |
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Journal Article |
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2010 |
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Applied Physics Letters |
Abbreviated Journal |
Appl. Phys. Lett. |
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97 |
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2 |
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3 |
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Keywords |
Annealing |
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We investigated the homogenous nucleation of crystalline grains in amorphous Si during transient temperature pulse of few milliseconds IR laser irradiation. The crystallized volume fraction is ~80%. Significant crystallization occurs in nonsteady regime because of the rapid temperature variation (106 °C/s). Our model combines the time evolution of the crystal grain population with the consumption of the amorphous volume due to the growth of grains. Thanks to the experimental approach based on a laser source to heat α-Si and the theoretical model we extended the description of the spontaneous crystallization up to 1323 K or 250 K above the temperature investigated by conventional annealing. |
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Annealing |
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RPLAB @ gujma @ |
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691 |
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Baeva, E. M.; Sidorova, M. V.; Korneev, A. A.; Smirnov, K. V.; Divochy, A. V.; Morozov, P. V.; Zolotov, P. I.; Vakhtomin, Y. B.; Semenov, A. V.; Klapwijk, T. M.; Khrapai, V. S.; Goltsman, G. N. |
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Thermal properties of NbN single-photon detectors |
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Journal Article |
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2018 |
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Phys. Rev. Applied |
Abbreviated Journal |
Phys. Rev. Applied |
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10 |
Issue |
6 |
Pages |
064063 (1 to 8) |
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Keywords |
NbN SSPD, SNSPD |
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We investigate thermal properties of a NbN single-photon detector capable of unit internal detection efficiency. Using an independent calibration of the coupling losses, we determine the absolute optical power absorbed by the NbN film and, via resistive superconductor thermometry, the temperature dependence of the thermal resistance Z(T) of the NbN film. In principle, this approach permits simultaneous measurement of the electron-phonon and phonon-escape contributions to the energy relaxation, which in our case is ambiguous because of the similar temperature dependencies. We analyze Z(T) with a two-temperature model and impose an upper bound on the ratio of electron and phonon heat capacities in NbN, which is surprisingly close to a recent theoretical lower bound for the same quantity in similar devices. |
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2331-7019 |
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1226 |
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Kerman, A. J.; Dauler, E. A.; Yang, J. K. W.; Rosfjord, K. M.; Anant, V.; Berggren, K. K.; Gol’tsman, G. N.; Voronov, B. M. |
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Constriction-limited detection efficiency of superconducting nanowire single-photon detectors |
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2007 |
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Appl. Phys. Lett. |
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Appl. Phys. Lett. |
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Volume |
90 |
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10 |
Pages |
101110 (1 to 3) |
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Keywords |
SSPD, SNSPD |
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We investigate the source of the large variations in the observed detection efficiencies of superconducting nanowire single-photon detectors between many nominally identical devices. Through both electrical and optical measurements, we infer that these variations arise from “constrictions:” highly localized regions of the nanowires where the effective cross-sectional area for superconducting current is reduced. These constrictions limit the bias-current density to well below its critical value over the remainder of the wire, and thus prevent the detection efficiency from reaching the high values that occur in these devices when they are biased near the critical current density.
This work is sponsored by the United States Air Force under Contract No. FA8721-05-C-0002. |
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0003-6951 |
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1433 |
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Kerman, Andrew J.; Yang, Joel K. W.; Molnar, Richard J.; Dauler, Eric A.; Berggren, Karl K. |
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Title |
Electrothermal feedback in superconducting nanowire single-photon detectors |
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2009 |
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Phys. Rev. B |
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Phys. Rev. B |
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79 |
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10 |
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4 |
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Keywords |
SNSPD |
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We investigate the role of electrothermal feedback in the operation of superconducting nanowire single-photon detectors (SNSPDs). It is found that the desired mode of operation for SNSPDs is only achieved if this feedback is unstable, which happens naturally through the slow electrical response associated with their relatively large kinetic inductance. If this response is sped up in an effort to increase the device count rate, the electrothermal feedback becomes stable and results in an effect known as latching, where the device is locked in a resistive state and can no longer detect photons. We present a set of experiments which elucidate this effect and a simple model which quantitatively explains the results. |
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RPLAB @ gujma @ |
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680 |
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