Imaging of free carriers in semiconductors via optical feedback in terahertz quantum cascade lasers

Mezzapesa, Francesco P.; Columbo, L.; Brambilla, Massimo; Dabbicco, Maurizio; Vitiello, Miriam S.; Scamarcio, Gaetano

doi:10.1063/1.4863671

Cited by 39 publications

(22 citation statements)

References 20 publications

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“…The inherent stability of QCLs against optical feedback [16] has been recently exploited in a number of self-mixing interferometry (SMI) configurations, providing an interesting method to control the emission of THz QCLs by reconfigurable photo-generated anisotropic metamaterials [17], to trace the free carrier distribution in a semiconductor target [18], and to map the real and imaginary refractive index of polymeric materials [12], for example.…”

Section: The General Concept Of Sd-s-snommentioning

confidence: 99%

Phase-resolved terahertz self-detection near-field microscopy

et al. 2018

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At terahertz (THz) frequencies, scattering-type scanning near-field optical microscopy (s-SNOM) based on continuous wave sources mostly relies on cryogenic and bulky detectors, which represents a major constraint for its practical application. Here, we devise a THz s-SNOM system that provides both amplitude and phase contrast and achieves nanoscale (60-70nm) in-plane spatial resolution. It features a quantum cascade laser that simultaneously emits THz frequency light and senses the backscattered optical field through a voltage modulation induced inherently through the self-mixing technique. We demonstrate its performance by probing a phonon-polariton-resonant CsBr crystal and doped black phosphorus flakes.

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Section: The General Concept Of Sd-s-snommentioning

confidence: 99%

Phase-resolved terahertz self-detection near-field microscopy

et al. 2018

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“…Self-mixing interferometry in QCLs has recently shown a strong potential in different configurations, ranging from near field imaging with sub-wavelength spatial resolution (1 -7 m), 38 to the control of the emission of THz QCLs 39 and the detection of free carrier distribution in semiconductors. 40 In our optical setup (Fig 3a) the 2.7 THz radiation emitted by a QCL is collected by a parabolic mirror (p1), directed to a couple of flat mirrors (m1 (moveable with a motorized stage) and m2 (fixed)) and finally focused at the apex of a Pt AFM tip by a second parabolic mirror (p2). The tip is positioned in close proximity to the surface of the sample and is dithered at Ω = 20 KHz (i.e.…”

Section: Detector-less Thz S-snom Microscopymentioning

confidence: 99%

Sub-wavelength near field imaging techniques at terahertz frequencies

Giòrdano

Viti

Mitrofanov

et al. 2018

Quantum Sensing and Nano Electronics and Photonics XV

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Near-field imaging techniques at terahertz (THz) frequencies are severely restricted by diffraction. To date, different detection schemes have been developed, based either on sub-wavelength metallic apertures or on sharp metallic tips. However high-resolution THz imaging, so far, has been relying predominantly on detection techniques that require either an ultrafast laser or a cryogenically-cooled THz detector, at the expenses of a lack of sensitivity when high resolution levels are needed. Here, we demonstrate two novel near-field THz imaging techniques able to combine strongly sub-wavelength spatial resolution with highly sensitive amplitude and phase detection capability. The first technique exploits an interferometric optical setup based on a THz quantum cascade laser (QCL) and on a near-field probe nanodetector, operating at room temperature. By performing phase-sensitive imaging of THz intensity patterns we demonstrate the potential of our novel architecture for coherent imaging with sub-wavelength spatial resolution improved up to 17 μm. The second technique is a detector-less s-SNOM system, exploiting a THz QCL as source and detector simultaneously. This approach enables amplitude-and phase-sensitive imaging by self-mixing interferometry with spatial resolution of 60-70 nm.

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“…The principle of the spatial filter is similar as in the research by Minoni et al 18 Due to the stationary pinhole, the filtering is more effective at longer wavelengths, since its diameter was selected according to the diffraction limited spot size of the 933-nm beam of the IR diode laser, which has initially a distorted, elliptical beam profile caused by the spatial free carrier density distribution and the rectangular-shaped junction. 19,20 In the ultraviolet region, the filtering is not as good as in IR but sufficient since the beam profiles are good naturally. Also the beams are not attenuated much, which provides better signal-to-noise ratios.…”

Section: Design Of the High-resolution Measurement Setupmentioning

confidence: 99%

High-resolution setup for measuring wavelength sensitivity of photoyellowing of translucent materials

Vaskuri

Kärhä

Heikkilä

et al. 2015

Review of Scientific Instruments

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Polystyrene and many other materials turn yellow when exposed to ultraviolet (UV) radiation. All photodegradation mechanisms including photoyellowing are functions of the exposure wavelength, which can be described with an action spectrum. In this work, a new high-resolution transmittance measurement setup based on lasers has been developed for measuring color changes, such as the photoyellowing of translucent materials aged with a spectrograph. The measurement setup includes 14 power-stabilized laser lines between 325 nm and 933 nm wavelengths, of which one at a time is directed on to the aged sample. The power transmitted through the sample is measured with a silicon detector utilizing an integrating sphere. The sample is mounted on a high-resolution XY translation stage. Measurement at various locations aged with different wavelengths of exposure radiation gives the transmittance data required for acquiring the action spectrum. The combination of a UV spectrograph and the new high-resolution transmittance measurement setup enables a novel method for studying the UV-induced ageing of translucent materials with a spectral resolution of 3-8 nm, limited by the adjustable spectral bandwidth range of the spectrograph. These achievements form a significant improvement over earlier methods.

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Imaging of free carriers in semiconductors via optical feedback in terahertz quantum cascade lasers

Cited by 39 publications

References 20 publications

Phase-resolved terahertz self-detection near-field microscopy

Phase-resolved terahertz self-detection near-field microscopy

Sub-wavelength near field imaging techniques at terahertz frequencies

High-resolution setup for measuring wavelength sensitivity of photoyellowing of translucent materials

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