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Mecozzi A, Shtaif M. Coherent detection with an incoherent local oscillator. OPTICS EXPRESS 2018; 26:33970-33981. [PMID: 30650827 DOI: 10.1364/oe.26.033970] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Accepted: 12/02/2018] [Indexed: 06/09/2023]
Abstract
We demonstrate the feasibility of fully coherent reconstruction of the complex envelope of arbitrary optical fields while using an incoherent source as a local oscillator (LO). The reconstruction relies on a signal processing procedure that we describe, and the only requirement from the system is that the receiver's electrical bandwidth and sampling rate are at least twice as high as the bandwidth of the received signal and of the LO. The proposed scheme is particularly attractive in spectral regions where no high-quality lasers are available.
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2
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Consolino L, Jung S, Campa A, De Regis M, Pal S, Kim JH, Fujita K, Ito A, Hitaka M, Bartalini S, De Natale P, Belkin MA, Vitiello MS. Spectral purity and tunability of terahertz quantum cascade laser sources based on intracavity difference-frequency generation. SCIENCE ADVANCES 2017; 3:e1603317. [PMID: 28879235 PMCID: PMC5580883 DOI: 10.1126/sciadv.1603317] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Accepted: 08/05/2017] [Indexed: 05/20/2023]
Abstract
Terahertz sources based on intracavity difference-frequency generation in mid-infrared quantum cascade lasers (THz DFG-QCLs) have recently emerged as the first monolithic electrically pumped semiconductor sources capable of operating at room temperature across the 1- to 6-THz range. Despite tremendous progress in power output, which now exceeds 1 mW in pulsed and 10 μW in continuous-wave regimes at room temperature, knowledge of the major figure of merits of these devices for high-precision spectroscopy, such as spectral purity and absolute frequency tunability, is still lacking. By exploiting a metrological grade system comprising a terahertz frequency comb synthesizer, we measure, for the first time, the free-running emission linewidth (LW), the tuning characteristics, and the absolute center frequency of individual emission lines of these sources with an uncertainty of 4 × 10-10. The unveiled emission LW (400 kHz at 1-ms integration time) indicates that DFG-QCLs are well suited to operate as local oscillators and to be used for a variety of metrological, spectroscopic, communication, and imaging applications that require narrow-LW THz sources.
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Affiliation(s)
- Luigi Consolino
- Consiglio Nazionale delle Ricerche (CNR)–Istituto Nazionale di Ottica and European Laboratory for Non-Linear Spectroscopy, Via Carrara 1, 50019 Sesto Fiorentino (Firenze), Italy
| | - Seungyong Jung
- Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA
| | - Annamaria Campa
- Consiglio Nazionale delle Ricerche (CNR)–Istituto Nazionale di Ottica and European Laboratory for Non-Linear Spectroscopy, Via Carrara 1, 50019 Sesto Fiorentino (Firenze), Italy
| | - Michele De Regis
- Consiglio Nazionale delle Ricerche (CNR)–Istituto Nazionale di Ottica and European Laboratory for Non-Linear Spectroscopy, Via Carrara 1, 50019 Sesto Fiorentino (Firenze), Italy
| | - Shovon Pal
- National Enterprise for nanoScience and nanoTechnology (NEST), CNR–Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - Jae Hyun Kim
- Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA
| | - Kazuue Fujita
- Central Research Laboratory, Hamamatsu Photonics K.K., Hamakita-ku, Hamamatsu 434-8601, Japan
| | - Akio Ito
- Central Research Laboratory, Hamamatsu Photonics K.K., Hamakita-ku, Hamamatsu 434-8601, Japan
| | - Masahiro Hitaka
- Central Research Laboratory, Hamamatsu Photonics K.K., Hamakita-ku, Hamamatsu 434-8601, Japan
| | - Saverio Bartalini
- Consiglio Nazionale delle Ricerche (CNR)–Istituto Nazionale di Ottica and European Laboratory for Non-Linear Spectroscopy, Via Carrara 1, 50019 Sesto Fiorentino (Firenze), Italy
| | - Paolo De Natale
- Consiglio Nazionale delle Ricerche (CNR)–Istituto Nazionale di Ottica and European Laboratory for Non-Linear Spectroscopy, Via Carrara 1, 50019 Sesto Fiorentino (Firenze), Italy
| | - Mikhail A. Belkin
- Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA
- Corresponding author. (M.A.B.); (M.S.V.)
| | - Miriam Serena Vitiello
- National Enterprise for nanoScience and nanoTechnology (NEST), CNR–Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
- Corresponding author. (M.A.B.); (M.S.V.)
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3
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Keeley J, Freeman J, Bertling K, Lim YL, Mohandas RA, Taimre T, Li LH, Indjin D, Rakić AD, Linfield EH, Davies AG, Dean P. Measurement of the emission spectrum of a semiconductor laser using laser-feedback interferometry. Sci Rep 2017; 7:7236. [PMID: 28775327 PMCID: PMC5543105 DOI: 10.1038/s41598-017-07432-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 06/28/2017] [Indexed: 11/09/2022] Open
Abstract
The effects of optical feedback (OF) in lasers have been observed since the early days of laser development. While OF can result in undesirable and unpredictable operation in laser systems, it can also cause measurable perturbations to the operating parameters, which can be harnessed for metrological purposes. In this work we exploit this 'self-mixing' effect to infer the emission spectrum of a semiconductor laser using a laser-feedback interferometer, in which the terminal voltage of the laser is used to coherently sample the reinjected field. We demonstrate this approach using a terahertz frequency quantum cascade laser operating in both single- and multiple-longitudinal mode regimes, and are able to resolve spectral features not reliably resolved using traditional Fourier transform spectroscopy. We also investigate quantitatively the frequency perturbation of individual laser modes under OF, and find excellent agreement with predictions of the excess phase equation central to the theory of lasers under OF.
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Affiliation(s)
- James Keeley
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Joshua Freeman
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Karl Bertling
- School of Information Technology and Electrical Engineering, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Yah Leng Lim
- School of Information Technology and Electrical Engineering, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Reshma A Mohandas
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Thomas Taimre
- School of Mathematics and Physics, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Lianhe H Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Dragan Indjin
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Aleksandar D Rakić
- School of Information Technology and Electrical Engineering, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Edmund H Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - A Giles Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Paul Dean
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK.
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4
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Röben B, Lü X, Hempel M, Biermann K, Schrottke L, Grahn HT. Terahertz quantum-cascade lasers as high-power and wideband, gapless sources for spectroscopy. OPTICS EXPRESS 2017; 25:16282-16290. [PMID: 28789135 DOI: 10.1364/oe.25.016282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 05/18/2017] [Indexed: 06/07/2023]
Abstract
Terahertz (THz) quantum-cascade lasers (QCLs) are powerful radiation sources for high-resolution and high-sensitivity spectroscopy with a discrete spectrum between 2 and 5 THz as well as a continuous coverage of several GHz. However, for many applications, a radiation source with a continuous coverage of a substantially larger frequency range is required. We employed a multi-mode THz QCL operated with a fast ramped injection current, which leads to a collective tuning of equally-spaced Fabry-Pérot laser modes exceeding their separation. A continuous coverage over 72 GHz at about 4.7 THz was achieved. We demonstrate that the QCL is superior to conventional sources used in Fourier transform infrared spectroscopy in terms of the signal-to-noise ratio as well as the dynamic range by one to two orders of magnitude. Our results pave the way for versatile THz spectroscopic systems with unprecedented resolution and sensitivity across a wide frequency range.
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5
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Cole WT, Hlavacek NC, Lee AW, Kao TY, Hu Q, Reno JL, Saykally RJ. A Terahertz VRT spectrometer employing quantum cascade lasers. Chem Phys Lett 2015. [DOI: 10.1016/j.cplett.2015.08.027] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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6
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Bianco F, Miseikis V, Convertino D, Xu JH, Castellano F, Beere HE, Ritchie DA, Vitiello MS, Tredicucci A, Coletti C. THz saturable absorption in turbostratic multilayer graphene on silicon carbide. OPTICS EXPRESS 2015; 23:11632-11640. [PMID: 25969255 DOI: 10.1364/oe.23.011632] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We investigated the room-temperature Terahertz (THz) response as saturable absorber of turbostratic multilayer graphene grown on the carbon-face of silicon carbide. By employing an open-aperture z-scan method and a 2.9 THz quantum cascade laser as source, a 10% enhancement of transparency is observed. The saturation intensity is several W/cm2, mostly attributed to the Pauli blocking effect in the intrinsic graphene layers. A visible increase of the modulation depth as a function of the number of graphene sheets was recorded as consequence of the low nonsaturable losses. The latter in turn revealed that crystalline disorder is the main limitation to larger modulations, demonstrating that the THz nonlinear absorption properties of turbostratic graphene can be engineered via a proper control of the crystalline disorder and the layers number.
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7
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Miao W, Lou Z, Xu GY, Hu J, Li SL, Zhang W, Zhou KM, Yao QJ, Zhang K, Duan WY, Shi SC, Colombelli R, Beere HE, Ritchie DA. Demonstration of a fully integrated superconducting receiver with a 2.7 THz quantum cascade laser. OPTICS EXPRESS 2015; 23:4453-8. [PMID: 25836482 DOI: 10.1364/oe.23.004453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
We demonstrate for the first time the integration of a superconducting hot electron bolometer (HEB) mixer and a quantum cascade laser (QCL) on the same 4-K stage of a single cryostat, which is of particular interest for terahertz (THz) HEB/QCL integrated heterodyne receivers for practical applications. Two key issues are addressed. Firstly, a low power consumption QCL is adopted for preventing its heat dissipation from destroying the HEB's superconductivity. Secondly, a simple spherical lens located on the same 4-K stage is introduced to optimize the coupling between the HEB and the QCL, which has relatively limited output power owing to low input direct current (DC) power. Note that simulation techniques are used to design the HEB/QCL integrated heterodyne receiver to avoid the need for mechanical tuning. The integrated HEB/QCL receiver shows an uncorrected noise temperature of 1500 K at 2.7 THz, which is better than the performance of the same receiver with all the components not integrated.
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8
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Wienold M, Röben B, Schrottke L, Grahn HT. Evidence for frequency comb emission from a Fabry-Pérot terahertz quantum-cascade laser. OPTICS EXPRESS 2014; 22:30410-30424. [PMID: 25606987 DOI: 10.1364/oe.22.030410] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report on a broad-band terahertz quantum-cascade laser (QCL) with a long Fabry-Pérot ridge cavity, for which the tuning range of the individual laser modes exceeds the mode spacing. While a spectral range of approximately 60 GHz (2 cm(-1)) is continuously covered by current and temperature tuning, the total emission range spans more than 270 GHz (9 cm(-1)). Within certain operating ranges, we found evidence for stable frequency comb operation of the QCL. An experimental technique is presented to characterize frequency comb operation, which is based on the self-mixing effect.
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9
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Preußler S, Wenzel N, Braun RP, Owschimikow N, Vogel C, Deninger A, Zadok A, Woggon U, Schneider T. Generation of ultra-narrow, stable and tunable millimeter- and terahertz- waves with very low phase noise. OPTICS EXPRESS 2013; 21:23950-23962. [PMID: 24104306 DOI: 10.1364/oe.21.023950] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The interference between two spectral lines of the frequency comb of a fiber femtosecond laser is used to generate millimeter-wave and terahertz tones. The two lines are selected by stimulated Brillouin scattering (SBS) amplification. All other modes are strongly rejected based on polarization discrimination, using the polarization-pulling effect that is associated with SBS. The inherent high spectral quality of a femtosecond fiber laser comb allows generation of millimeter- and terahertz waves with linewidths below 1 Hz, and a phase noise of -105 dBc/Hz at 10 kHz offset. The generation, free-space transmission and detection of continuous waves at 1 THz are demonstrated as well. Lastly, the generated millimeter-wave carriers are modulated by 40 Gbit/s data. The entire system consists of a fiber laser and standard equipment of optical telecommunications. Besides metrology, spectroscopy and astronomy, the method can be utilized for the emergent field of wireless millimeter-wave and THz-communications at ultra-high data rates.
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10
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Steiger A, Kehrt M, Monte C, Müller R. Traceable terahertz power measurement from 1 THz to 5 THz. OPTICS EXPRESS 2013; 21:14466-14473. [PMID: 23787634 DOI: 10.1364/oe.21.014466] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The metrology institute in Germany, the Physikalisch-Technische Bundesanstalt (PTB), calibrates the spectral responsivity of THz detectors at 2.52 THz traceable to International System of Units. The Terahertz detector calibration facility is equipped with a standard detector calibrated against a cryogenic radiometer at this frequency. In order to extend this service to a broader spectral range in the THz region a new standard detector was developed. This detector is based on a commercial thermopile detector. Its absorber was modified and characterized by spectroscopic methods with respect to its absorptance and reflectance from 1 THz to 5 THz and at the wavelength of a helium-neon laser in the visible spectral range. This offers the possibility of tracing back the THz power responsivity scale to the more accurate responsivity scale in the visible spectral range and thereby to reduce the uncertainty of detector calibrations in the THz range significantly.
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Affiliation(s)
- Andreas Steiger
- Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, D-10587 Berlin, Germany.
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11
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Dyer GC, Norquist CD, Cich MJ, Grine AD, Fuller CT, Reno JL, Wanke MC. Rectified diode response of a multimode quantum cascade laser integrated terahertz transceiver. OPTICS EXPRESS 2013; 21:3996-4004. [PMID: 23481934 DOI: 10.1364/oe.21.003996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We characterized the DC transport response of a diode embedded in a THz quantum cascade laser as the laser current was changed. The overall response is described by parallel contributions from the rectification of the laser field due to the non-linearity of the diode I-V and from thermally activated transport. Sudden jumps in the diode response when the laser changes from single mode to multi-mode operation, with no corresponding jumps in output power, suggest that the coupling between the diode and laser field depends on the spatial distribution of internal fields. The results demonstrate conclusively that the internal laser field couples directly to the integrated diode.
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Affiliation(s)
- Gregory C Dyer
- Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185, USA
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12
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Wienold M, Tahraoui A, Schrottke L, Sharma R, Lü X, Biermann K, Hey R, Grahn HT. Lateral distributed-feedback gratings for single-mode, high-power terahertz quantum-cascade lasers. OPTICS EXPRESS 2012; 20:11207-11217. [PMID: 22565743 DOI: 10.1364/oe.20.011207] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report on terahertz quantum-cascade lasers (THz QCLs) based on first-order lateral distributed-feedback (lDFB) gratings, which exhibit continuous-wave operation, high output powers (>8 mW), and single-mode emission at 3.3-3.4 THz. A general method is presented to determine the coupling coefficients of lateral gratings in terms of the coupled-mode theory, which demonstrates that large coupling strengths are obtained in the presence of corrugated metal layers. The experimental spectra are in agreement with simulations of the lDFB cavities, which take into account the reflective end facets.
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Affiliation(s)
- M Wienold
- Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany.
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13
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Terahertz active photonic crystals for condensed gas sensing. SENSORS 2011; 11:6003-14. [PMID: 22163939 PMCID: PMC3231430 DOI: 10.3390/s110606003] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Revised: 05/18/2011] [Accepted: 05/31/2011] [Indexed: 11/18/2022]
Abstract
The terahertz (THz) spectral region, covering frequencies from 1 to 10 THz, is highly interesting for chemical sensing. The energy of rotational and vibrational transitions of molecules lies within this frequency range. Therefore, chemical fingerprints can be derived, allowing for a simple detection scheme. Here, we present an optical sensor based on active photonic crystals (PhCs), i.e., the pillars are fabricated directly from an active THz quantum-cascade laser medium. The individual pillars are pumped electrically leading to laser emission at cryogenic temperatures. There is no need to couple light into the resonant structure because the PhC itself is used as the light source. An injected gas changes the resonance condition of the PhC and thereby the laser emission frequency. We achieve an experimental frequency shift of 10−3 times the center lasing frequency. The minimum detectable refractive index change is 1.6 × 10−5 RIU.
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14
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Vitiello MS, Xu JH, Kumar M, Beltram F, Tredicucci A, Mitrofanov O, Beere HE, Ritchie DA. High efficiency coupling of Terahertz micro-ring quantum cascade lasers to the low-loss optical modes of hollow metallic waveguides. OPTICS EXPRESS 2011; 19:1122-1130. [PMID: 21263652 DOI: 10.1364/oe.19.001122] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We demonstrate that azimuthally polarized surface emitting Terahertz quantum cascade lasers fabricated in a micro-ring resonator geometry can be coupled to cylindrical hollow aluminum waveguides reaching efficiencies as high ≈98%, when a collimating lens is used. By placing the waveguide in close contact with the QCL in a simple back-to-back geometry, the laser mode can be perfectly matched with the low loss TE(01) waveguide mode showing attenuation losses as low as ≈2.3-2.7 dB/m at 3.2 THz.
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Affiliation(s)
- Miriam S Vitiello
- CNR-Istituto Nazionale di Fisica Applicata Nello Carrara, Sesto Fiorentino, Italy.
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15
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Jirauschek C. Monte Carlo study of intrinsic linewidths in terahertz quantum cascade lasers. OPTICS EXPRESS 2010; 18:25922-25927. [PMID: 21164938 DOI: 10.1364/oe.18.025922] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Based on a coupled simulation of carrier transport and optical cavity field, the intrinsic linewidth in resonant phonon terahertz quantum cascade lasers is self-consistently analyzed. For high power structures, values on the order of Hz are obtained. Thermal photons are found to play a considerable role at elevated temperatures. A linewidth enhancement factor of 0.5 is calculated for the investigated designs.
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Affiliation(s)
- Christian Jirauschek
- Institute for Nanoelectronics, Technische Universität München, D-80333 Munich, Germany.
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16
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Steiger A, Gutschwager B, Kehrt M, Monte C, Müller R, Hollandt J. Optical methods for power measurement
of terahertz radiation. OPTICS EXPRESS 2010; 18:21804-21814. [PMID: 20941081 DOI: 10.1364/oe.18.021804] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Precision power measurements of terahertz (THz) radiation are required to establish metrological applications in the THz spectral range. However, traceability to the International System of Units (SI) has been missing in the THz region in the past. The Physikalisch-Technische Bundesanstalt (PTB), as the national metrology institute of Germany, determines the spectral responsivity of detectors for THz radiation by using two complementary optical methods: source- and detector-based radiometry. Both approaches have been successfully prototyped, and a pyroelectric THz detector with a well-defined aperture is used to verify the consistency of the two independent calibration methods. These primary investigations led to the design of a new measurement facility for the determination of THz radiant power and the responsivity calibration of THz detectors traceable to the SI.
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Affiliation(s)
- Andreas Steiger
- Physikalisch-Technische Bundesanstalt, Abbestr 2-12, D-10587 Berlin, Germany.
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17
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Richter H, Greiner-Bär M, Pavlov SG, Semenov AD, Wienold M, Schrottke L, Giehler M, Hey R, Grahn HT, Hübers HW. A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler. OPTICS EXPRESS 2010; 18:10177-10187. [PMID: 20588872 DOI: 10.1364/oe.18.010177] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We report on the development of a compact, easy-to-use terahertz radiation source, which combines a quantum-cascade laser (QCL) operating at 3.1 THz with a compact, low-input-power Stirling cooler. The QCL, which is based on a two-miniband design, has been developed for high output and low electrical pump power. The amount of generated heat complies with the nominal cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power. Special care has been taken to achieve a good thermal coupling between the QCL and the cold finger of the cooler. The whole system weighs less than 15 kg including the cooler and power supplies. The maximum output power is 8 mW at 3.1 THz. With an appropriate optical beam shaping, the emission profile of the laser is fundamental Gaussian. The applicability of the system is demonstrated by imaging and molecular-spectroscopy experiments.
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Affiliation(s)
- H Richter
- German Aerospace Center (DLR), Institute of Planetary Research, Berlin, Germany.
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18
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Hensley JM, Montoya J, Allen MG, Xu J, Mahler L, Tredicucci A, Beere HE, Ritchie DA. Spectral behavior of a terahertz quantum-cascade laser. OPTICS EXPRESS 2009; 17:20476-20483. [PMID: 19997276 DOI: 10.1364/oe.17.020476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In this paper, the spectral behavior of two terahertz (THz) quantum cascade lasers (QCLs) operating both pulsed and cw is characterized using a heterodyne technique. Both lasers emitting around 2.5 THz are combined onto a whisker contact Schottky diode mixer mounted in a corner cube reflector. The resulting difference frequency beatnote is recorded in both the time and frequency domain. From the frequency domain data, we measure the effective laser linewidth and the tuning rates as a function of both temperature and injection current and show that the current tuning behavior cannot be explained by temperature tuning mechanisms alone. From the time domain data, we characterize the intrapulse frequency tuning behavior, which limits the effective linewidth to approximately 5 MHz.
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Affiliation(s)
- J M Hensley
- Physical Sciences Inc, 20 New England Business Center, Andover, Massachusetts 01810-1077, USA.
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19
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Khosropanah P, Baryshev A, Zhang W, Jellema W, Hovenier JN, Gao JR, Klapwijk TM, Paveliev DG, Williams BS, Kumar S, Hu Q, Reno JL, Klein B, Hesler JL. Phase locking of a 2.7 THz quantum cascade laser to a microwave reference. OPTICS LETTERS 2009; 34:2958-2960. [PMID: 19794781 DOI: 10.1364/ol.34.002958] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We demonstrate the phase locking of a 2.7 THz metal-metal waveguide quantum cascade laser (QCL) to an external microwave signal. The reference is the 15th harmonic, generated by a semiconductor superlattice nonlinear device, of a signal at 182 GHz, which itself is generated by a multiplier chain (x12) from a microwave synthesizer at approximately 15 GHz. Both laser and reference radiations are coupled into a bolometer mixer, resulting in a beat signal, which is fed into a phase-lock loop. The spectral analysis of the beat signal confirms that the QCL is phase locked. This result opens the possibility to extend heterodyne interferometers into the far-infrared range.
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Affiliation(s)
- P Khosropanah
- SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
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20
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Mahler L, Amanti MI, Walther C, Tredicucci A, Beltram F, Faist J, Beere HE, Ritchie DA. Distributed feedback ring resonators for vertically emitting terahertz quantum cascade lasers. OPTICS EXPRESS 2009; 17:13031-13039. [PMID: 19654707 DOI: 10.1364/oe.17.013031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We present distributed-feedback Terahertz quantum cascade lasers operating in a double-metal ring waveguide. High power collimated emission in a single spectral mode is observed in the vertical direction. A double-slit configuration is employed to achieve both good electrical contacts and efficient power out-coupling. The optical properties of the devices are interpreted with the aid of finite element simulations.
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Affiliation(s)
- Lukas Mahler
- NEST, CNR-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126, Pisa, Italy.
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Mahler L, Tredicucci A, Beltram F, Walther C, Beere HE, Ritchie DA. Finite size effects in surface emitting Terahertz quantum cascade lasers. OPTICS EXPRESS 2009; 17:6703-6709. [PMID: 19365498 DOI: 10.1364/oe.17.006703] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We analyze surface-emitting distributed feedback resonators for Terahertz quantum cascade lasers fabricated from double-metal waveguides. We explain the influence on resonances and surface-emission properties of the finite length and width of the gratings in connection with absorbing boundary conditions, and show that, contrary to the infinite case, the modes on either side of the photonic band-gap have finite surface losses. The lateral design of the resonator is shown to be important to avoid transverse modes of higher order and anti-guiding effects. Experimental findings are indeed in excellent agreement with the simulations. Both modeling and fabrication can easily be applied to arbitrary gratings, of which we discuss here a first interesting example.
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Affiliation(s)
- Lukas Mahler
- NEST CNR-INFM, Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126, Pisa, Italy.
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Rabanus D, Graf UU, Philipp M, Ricken O, Stutzki J, Vowinkel B, Wiedner MC, Walther C, Fischer M, Faist J. Phase locking of a 1.5 Terahertz quantum cascade laser and use as a local oscillator in a heterodyne HEB receiver. OPTICS EXPRESS 2009; 17:1159-1168. [PMID: 19188942 DOI: 10.1364/oe.17.001159] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We demonstrate for the first time the closure of an electronic phase lock loop for a continuous-wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark-shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K.
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Affiliation(s)
- D Rabanus
- European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile.
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Danylov AA, Waldman J, Goyette TM, Gatesman AJ, Giles RH, Linden KJ, Neal WR, Nixon WE, Wanke MC, Reno JL. Transformation of the multimode terahertz quantum cascade laser beam into a Gaussian, using a hollow dielectric waveguide. APPLIED OPTICS 2007; 46:5051-5. [PMID: 17676114 DOI: 10.1364/ao.46.005051] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
We demonstrate that a short hollow dielectric tube can act as a dielectric waveguide and transform the multimode, highly diverging terahertz quantum cascade laser beam into the lowest order dielectric waveguide hybrid mode, EH(11), which then couples efficiently to the free-space Gaussian mode, TEM(00). This simple approach should enable terahertz quantum cascade lasers to be employed in applications where a spatially coherent beam is required.
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Affiliation(s)
- Andriy A Danylov
- Submillimeter-Wave Technology Laboratory, University of Massachusetts Lowell, Lowell, Massachusetts 01854, USA.
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