Continuous wave terahertz transmission imaging of nonmelanoma skin cancers.

Background And Objective: Continuous wave terahertz imaging has the potential to offer a safe, noninvasive medical imaging modality for delineating human skin cancers. Terahertz pulse imaging (TPI) has already shown that there is contrast between basal cell carcinoma and normal skin. Continuous-wave imaging offers a simpler, lower cost alternative to TPI.

Terahertz inverse synthetic aperture radar (ISAR) imaging with a quantum cascade laser transmitter.

A coherent transceiver using a THz quantum cascade (TQCL) laser as the transmitter and an optically pumped molecular laser as the local oscillator has been used, with a pair of Schottky diode mixers in the receiver and reference channels, to acquire high-resolution images of fully illuminated targets, including scale models and concealed objects. Phase stability of the received signal, sufficient to allow coherent image processing of the rotating target (in azimuth and elevation), was obtained by frequency-locking the TQCL to the free-running, highly stable optically pumped molecular laser. While the range to the target was limited by the available TQCL power (several hundred microwatts) and reasonably strong indoor atmospheric attenuation at 2.

Frequency stabilization of a single mode terahertz quantum cascade laser to the kilohertz level.

A simple analog locking circuit was shown to stabilize the beat signal between a 2.408 THz quantum cascade laser and a CH(2)DOH THz CO(2) optically pumped molecular laser to 3-4 kHz (FWHM). This is approximately a tenth of the observed long-term (t approximately sec) linewidth of the optically pumped laser showing that the feedback loop corrects for much of the mechanical and acoustic-induced frequency jitter of the gas laser.

Terahertz sideband-tuned quantum cascade laser radiation.

A compact, tunable, narrowband terahertz source was demonstrated by mixing a single longitudinal mode 2.408 THz, free running quantum cascade laser with a 2-20 GHz microwave sweeper in a conventional corner-cube-mounted Schottky diode. The sideband spectra were characterized with a Fourier transform spectrometer, and the radiation was tuned through several D(2)O rotational transitions to estimate the longer term (t > or = several sec) bandwidth of the source.

Transformation of the multimode terahertz quantum cascade laser beam into a Gaussian, using a hollow dielectric waveguide.

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.

The Energy Levels of the nu(5)/2nu(9) Dyad of HNO(3) from Millimeter and Submillimeter Rotational Spectroscopy.

In this paper we show that the rotational structure of the nu(5)/2nu(9) infrared band near 11 &mgr;m can be synthesized to high accuracy from pure rotational measurements in the millimeter- and submillimeter-wave region. The analysis uses an internal axis system Hamiltonian that accounts for the rotational dependence of the torsional splitting in 2nu(9), the induced torsional splitting in nu(5), and all of the infrared line positions, including those in the regions of strongest mixing and of highest excitation. This model also predicts the strength of the 2nu(9) infrared band due to the strong Fermi mixing with nu(5).