Rainer Martini

Stevens Institute of Technology, Physics and Engineering Physics, Faculty Member

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Dephasing of Bloch oscillations due to carrier-carrier scattering: coherent versus incoherent scatterers

The practical application of Bloch oscillations in semiconductor superlattices as THz emitters is... more The practical application of Bloch oscillations in semiconductor superlattices as THz emitters is hampered by the low emission power and the rapid dephasing of the coherent signal. At higher excitation densities the quadratic scaling of the THz emission power saturates due to the stronger dephasing of the signal. We adopt an approach previously employed for the investigation of the dephasing of interband dynamics in four wave mixing to study the dephasing of the intraband dynamics responsible for the THz emission. We demonstrate that for higher carrier densities the dominant dephasing process at low temperatures is carrier-carrier scattering. The experiments are performed on a superlattice consisting of 9.7-nm GaAs wells separated by 1.7-nm AlGaAs barriers

Intraband Coherence after Energy Relaxation

Springer series in chemical physics, 1998

ABSTRACT

Superradiant emission from Bloch oscillations in semiconductor superlattices

Physical review, Nov 15, 1996

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Spatial coherence of a coherently excited carrier ensemble detected by the far-field THz-radiation pattern

White paper on the future of plasma science for optics and glass

Plasma Processes and Polymers, Aug 2, 2018

This paper reflects on the future of low-temperature plasma science in relation to the manufactur... more This paper reflects on the future of low-temperature plasma science in relation to the manufacturing and novel uses of glass. The text summarizes the current state of the art on the major topics discussed, such as glass processing, optics and photonics, healthcare issues, building and fenestration applications. It also identifies several challenges that are driven by applications, and which are compatible with roadmaps for their respective industries. The frontiers of plasma science are discussed, for example, in relation to the use of plasmas as an active optical element in fast-response adaptive optics systems, optical metamaterials, and the development of next-generation nanolithography. Future demand for the successful implementation of plasma-based technologies in the glass, optics, and photonic industries will depend on further progress in plasma science. Hence, some needs and recommendations concerning both fundamental and applied plasma research are summarized.

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Weather-proof Quantum Communications

We identify a weather-proof channel for quantum communications using 3950 nm photons, and report ... more

All-optical amplitude modulation of a middle-infrared quantum cascade laser

We demonstrated the all-optical modulation in the optical emission power of a standard middle inf... more We demonstrated the all-optical modulation in the optical emission power of a standard middle infrared quantum cascade laser by optically illuminating its front facet with femtosecond near infrared pulse train. The modulation frequency is found up to 10.35 GHz, much faster than the observed laser current response, only 3 GHz.

Experiments on linewidth reduction by fast electrical feedback

Infrared Physics & Technology, Feb 1, 1996

We report our first results on broadband electrical feedback applied to tunable lead-salt diode l... more We report our first results on broadband electrical feedback applied to tunable lead-salt diode lasers. We use a heterodyne technique in combination with electronic frequency discrimination to reduce the diode-laser linewidth. The loop band width is about 10 MHz. We present results on high-frequency modulation to study the frequency response of the diode laser. From this experiment we are able to estimate the carrier tuning rate of the used lead-salt diode laser. Preliminary results in linewidth reduction by fast electrical feedback promise the possibility to apply the fast electrical feedback technique to lead-salt diode lasers.

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Recent results in quantum cascade lasers and intersubband transitions in GaN/AlGaN multiple quantum wells

Physica E-low-dimensional Systems & Nanostructures, Mar 1, 2002

ABSTRACT Quantum cascade (QC) lasers have been fabricated with Ge0.25Se0.75 chalcogenide lateral ... more ABSTRACT Quantum cascade (QC) lasers have been fabricated with Ge0.25Se0.75 chalcogenide lateral waveguide claddings. Aside from a strongly (up to ∼50%) reduced waveguide loss this device lay-out also displays a significantly reduced stray capacitance and improved high-speed modulation properties. This has been exploited for the first use of QC lasers in optical wireless communications as well as for gain-switched and actively mode-locked QC-lasers. Optical devices based on intersubband (IS) transitions face a rising interest also in other wavelength ranges due to their anticipated ultrafast electron dynamics. We present initial measurements of IS-transitions in the fiber-optics wavelength range in GaN/AlGaN samples grown by molecular beam epitaxy. IS-absorption at wavelengths of 1.44, 1.41, and are measured for 11, 12, and wide GaN quantum wells, respectively. We also measured the IS electron scattering time by conventional pump–probe technique. Using as pump- and as probe-wavelength, we obtain an electron scattering time of .

Wavelet filtered modelling applied to measurements of a waveguide's THz time domain response

Proceedings, IEEE Tenth International Conference on Terahertz Electronics

A quasi-optical de-embedding technique for characterizing waveguides is demonstrated using wideba... more A quasi-optical de-embedding technique for characterizing waveguides is demonstrated using wideband time-resolved terahertz spectroscopy. A transfer function representation is adopted for the description of the signal in the input and output port of the waveguides. The time domain responses were discretised and the waveguide transfer function was obtained through a parametric approach in the z-domain after describing the system with

A New All-Optical Imaging Scheme based on QWIP technology

Bulletin of the American Physical Society, Mar 15, 2006

imaging applications have gained increasing interest over the recent decades due to favorable lig... more imaging applications have gained increasing interest over the recent decades due to favorable light propagation, night imaging as well as chemical sensing applications. However, the scalability of the existing techniques towards high resolution in the multi-megapixel range is one of the major challenges in today's IR imaging technologies. Here we present an alternative solution using an all-optical wavelength conversion scheme. QWIP has been successfully proven their potential in IR imaging applications. Yet the fundamental conversion process from IR light to electric current has been one of the major restrictions in such system. To overcome this problem we propose the use of an all-optical conversion scheme, which utilizes an interband resonant optical NIR beam to probe the electrical population of the QW structure. In this methodology the incident MIR radiation changes the occupation of the QWs, which in turn influences the NIR transmission. Hence the irradiated MIR images can be probed by spatially resolved measurement of the NIR transmission, as has been demonstrated by Nada et al. for all-optical switching purposes. In this talk we present an implementation scheme of the all-optical QWIP readout technique together with theoretical calculations of the sensitivity of the proposed device and its temperature dependence. First experimental results will be presented also. The Authors thankfully acknowledge financial support by US Army, Picatinny Arsenal.

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Frequency-Stabilized CO (Δv=2) Laser System for Sub-Doppler Molecular Spectroscopy

Laser in Forschung und Technik / Laser in Research and Engineering, 1996

We report a frequency-stabilized CO-overtone laser system for precision spectroscopy applications... more We report a frequency-stabilized CO-overtone laser system for precision spectroscopy applications. The laser frequency is stabilized in a frequency-offset locking scheme (FOL) on combination frequencies of two CO2 laser standards. This FOL technique allows us to sweep the laser frequency in a well-defined and linear manner with very high frequency accuracy. The uncertainty is smaller than 40 kHz (corresponding to Δv/v=4·10-10 at v=100 THz). This stabilized laser system enables us to record line shapes of molecular saturation signals in a computer-controlled experiment.

OPTICAL COMMUNICATION SYSTEMS | Free Space Optical Communications

Free space communication under scattering and scintillation effects

A combination of scattering and scintillation effects is considered to compare the resilience of ... more A combination of scattering and scintillation effects is considered to compare the resilience of mid-IR and near-IR free space communication links. Beam-wander rw(t) under different scintillation conditions for mid-IR and near- IR beams are recorded simultaneously in real-time by a unique broad-band camera. The correlation coefficients show that both beams undergo the same pathway and experience the same scattering and scintillation effect which allows to identify and distill wavelength dependent effects. Using the frequency dependence in the observed beam wander allows for classification of our simulated atmospheric turbulence. Under these lab conditions, perceived refractive index structure parameter C_n^2 is extracted for each wavelength and a long-term radius is estimated for a long-distance link. In addition, the transmissivity and broadening of beams are calculated using discrete ordinate method to account for the scattering by fog. Considering both scattering and scintillatio...

A New Optical Flow Estimation Method In Joint EO/IR Video Surveillance

Electro-Optical (EO) and Infra-Red (IR) sensors have been jointly deployed in many surveillance s... more Electro-Optical (EO) and Infra-Red (IR) sensors have been jointly deployed in many surveillance systems. In this work we study the special characteristics of optical flow in IR imagery, and introduce an optical flow estimation method using co-registered EO and IR image frames. The basic optical flow calculation is based on the combined local and global (CLG) method

Spatial mapping of the near-field radiation pattern of a 7-GHz planar resonator

Summary form only given. In summary, we demonstrate the application of the external electro optic... more

White paper on the future of plasma science for optics and glass

Plasma Processes and Polymers

A New All-Optical Imaging Scheme based on QWIP technology

Bulletin of the American Physical Society, 2006

Submitted for the MAR06 Meeting of The American Physical Society A New All-Optical Imaging Scheme... more Submitted for the MAR06 Meeting of The American Physical Society A New All-Optical Imaging Scheme based on QWIP technology DEBING ZENG, GANG CHEN, RAINER MARTINI, Dept. of Physics and Engr. Physics, Stevens Institute of Technology — Infrared imaging applications have gained increasing interest over the recent decades due to favorable light propagation, night imaging as well as chemical sensing applications. However, the scalability of the existing techniques towards high resolution in the multi-megapixel range is one of the major challenges in today’s IR imaging technologies. Here we present an alternative solution using an all-optical wavelength conversion scheme. QWIP has been successfully proven their potential in IR imaging applications. Yet the fundamental conversion process from IR light to electric current has been one of the major restrictions in such system. To overcome this problem we propose the use of an all-optical conversion scheme, which utilizes an interband resonant...

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Weather-proof Quantum Communications

We identify a weather-proof channel for quantum communications using 3950 nm photons, and report ... more

Comparison of mid- and near-infrared link losses in simulated scattering and turbulent environment

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