Simple and useful approximations, valid at infrared wavelengths, to the equations for synchrotron radiation are presented and used to quantify the brightness and power advantage of current synchrotron radiation light sources over conventional infrared broadband laboratory sources. The Daresbury Synchrotron Radiation Source (SRS) and the Brookhaven National Synchrotron Light Source (vacuum ultraviolet) [NSLS(VUV)] storage rings are used as examples in the calculation of the properties of infrared synchrotron radiation. The pulsed nature of the emission is also discussed, and potential areas of application for the brightness, power, and time structure advantages are presented. The use of infrared free electron lasers and undulators on the next generation of storage ring light sources is briefly considered.

Infrared synchrotron radiation from electron storage rings.

We observed an interaction of single-walled carbon nanotube films with obliquely incident nanosecond laser radiation in visible and infrared regions generating unipolar voltage pulses replicating the shape of the laser pulses. The photoelectric signal significantly depends on the laser polarization and has maximum value at the laser beam incidence angle of ±65° and at the film thickness of 350 nm. The results are explained in the framework of the photon-drag effect.

Photon-drag effect in single-walled carbon nanotube films.

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements, respectively, utilize the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods we propose is an easy to handle all-electric approach, which is demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.

http://www.physik.uni-regensburg.de/forschung/ganichev/reprints/JApplPhys_105_013106.pdf

Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures

A complete theory for waveguide laser modes for oversized metallic and dielectric waveguides with circular cross section has been developed for the submm wavelength region. The experimental investigations have been done by a submm heterodyne technique for the first stage using a Schottky barrier diode in an open structure mixer.

Investigations of optically pumped submillimeter wave laser modes

We report on the observation of photon helicity driven currents in graphene. The directed net electric current is generated in single layer graphene by circularly polarized terahertz laser radiation at normal as well as at oblique incidence and changes its sign upon reversing the radiation helicity. The phenomenological and microscopic theories of the observed photocurrents are developed. We demonstrate that under oblique incidence the current is caused by the circular photon drag effect in the interior of graphene sheet. By contrast, the effect at normal incidence stems from the sample edges, which reduce the symmetry and result in an asymmetric scattering of carriers driven by the radiation field. Besides a photon helicity dependent current we also observe photocurrents in response to linearly polarized radiation. The microscopic mechanisms governing this effect are discussed.

Photon helicity driven electric currents in graphene

Although photon drag was first observed ten years ago [1] [2] detectors utilizing this effect have been largely confined to CO 2 laser wavelengths. Commercially available detectors are calibrated for 10.6 μm and although they can be used at other wavelengths various pitfalls can arise. Figure 1 shows the voltage responsivity of a typical p-type germanium detector between 2.5 and 13 μm. It is disconcerting to find that not only does the responsivity vary rapidly with wavelength, but the sign of the signal changes five times.

M. F. Kimmitt

Papers

Photon Drag Detection