D. D. Arnone

Terahertz Pulsed Imaging of Skin Cancer in the Time and Frequency Domain

Terahertz Pulsed Imaging(TPI) is a new medical imaging modality forthe detection of epithelial cancers. Overthe last two years this technique has beenapplied to the study of in vitrobasal cell carcinoma (BCC). Usingtime-domain analysis the contrast betweendiseased and normal tissue has been shownto be statistically significant, andregions of increased terahertz (THz)absorption correlated well with thelocation of the tumour sites in histology.Understanding the source of this contrastthrough frequency-domain analysis mayfacilitate the diagnosis of skin cancer andrelated skin conditions using TPI. Wepresent the first frequency-domain analysisof basal cell carcinoma in vitro,with the raw power spectrum giving aninsight into the surface features of theskin. Further data manipulation is requiredto determine whether spectral informationcan be extrapolated at depth. These resultshighlight the complexity of working inreflection geometry.

Terahertz pulsed imaging of basal cell carcinoma ex vivo and in vivo

Background  Terahertz radiation lies between the infrared and microwave regions of the electromagnetic spectrum and can be used to excite large amplitude vibrational modes of molecules and probe the weak interactions between them. Terahertz pulsed imaging (TPI) is a noninvasive imaging technique that utilises this radiaton.

Intersubband electroluminescence from Si/SiGe cascade emitters at terahertz frequencies

The quantum cascade laser provides one possible method of realizing high efficiency light emitters in indirect band gap materials such as silicon. Electroluminescence results from Si/SiGe quantum cascade emitters are presented demonstrating edge emission from heavy-hole to heavy-hole transitions and light-hole to heavy-hole transitions. In surface-normal emission, only light-hole to heavy-hole electroluminescence is observed as predicted by theory. Intersubband emission is demonstrated at 2.9 THz (103 μm wavelength), 8.9 THz (33.7 μm), and 16.2 THz (18.5 μm) from the Si/SiGe quantum cascade heterostructures.

The use of Fourier-transform infrared spectroscopy for the quantitative determination of glucose concentration in whole blood

Fourier-transform infrared transmission spectroscopy has been used for the determination of glucose concentration in whole blood samples from 28 patients. A 4-vector partial least-squares calibration model, using the spectral range 950-1200 cm(-1), yielded a standard-error-of-prediction of 0.59 mM for an independent test set. For blood samples from a single patient, we found that the glucose concentration was proportional to the difference between the values of the second derivative spectrum at 1082 cm(-1) and 1093 cm(-1). This indicates that spectroscopy at these two specific wavenumbers alone could be used to determine the glucose concentration in blood plasma samples from a single patient, with a prediction error of 0.95 mM.

Enhanced coherent terahertz emission from indium arsenide in the presence of a magnetic field

We demonstrate enhancement of terahertz (THz) emission from indium arsenide at 170 K in magnetic fields (B) up to 8 T. An order of magnitude increase in visible to terahertz conversion efficiency was observed, with no suggestion of saturation of the TE polarization at higher magnetic fields. Free-space electro-optic sampling measurements confirmed the coherent nature of this radiation over the field range investigated, and gave an insight into the carrier motion subsequent to photoexcitation, which may be responsible for the observed THz power enhancement.

Interwell intersubband electroluminescence from Si/SiGe quantum cascade emitters

The quantum cascade laser provides one potential method for the efficient generation of light from indirect materials such as silicon. While to date electroluminescence results from THz Si/SiGe quantum cascade emitters have shown higher output powers than equivalent III–V emitters, the absence of population inversion within these structures has undermined their potential use for the creation of a laser. Electroluminescence results from Si/SiGe quantum cascade emitters are presented demonstrating intersubband emission from heavy to light holes interwell (diagonal) transitions between 1.2 THz (250 μm) and 1.9 THz (156 μm). Theoretical modeling of the transitions suggests the existence of population inversion within the system.

Terahertz pulse imaging of in-vitro basal cell carcinoma samples

Summary form only given. The use of Terahertz Pulse Imaging (TPI) for the analysis of skin cancer has been investigated. Our initial experiments have focused on the analysis of basal cell carcinoma (BCC), the most common form of skin cancer. BCC seldom metastasize but can be locally very invasive. The current diagnosis of carcinomas is by visual examination, where suspicious lesions require biopsy and subsequent histological diagnosis, which is painful, time consuming and may require additional tissue removal. The use of TPI as a diagnostic tool for skin cancer is of particular interest as its long wavelengths lead to a reduction in Rayleigh scattering and a resultant axial resolution of approximately 80 /spl mu/m. The spectroscopic information of TPI may prove to be advantageous in the discrimination between tumor types, which is unattainable using other methods such as ultrasound. Through the use of TPI, unnecessary biopsies could be avoided, by providing in-vivo measurements before surgery to identify the type and depth of tumor present.

Terahertz Pulse Spectroscopy of Biological Materials: L-Glutamic Acid

We report the terahertzpulse spectra of L-glutamic acid. Thereare a number of well-resolved transitionsin the 1.75–2.5 THz (58–83 cm-1)region. These are compared with publishedtheoretical data on intra andintermolecular transitions. We could notfind any correlation with the theoreticalvalues. However, it was noted that thetheoretical model did not include anycrystalline or hydrogen-bonding effects.

Picosecond intersubband dynamics in p-Si/SiGe quantum-well emitter structures

We report time-resolved (ps) studies of the dynamics of intersubband transitions in p-Si/SiGe multiquantum-well structures in the far-infrared (FIR) regime, ℏω<ℏωLO, utilizing the Dutch free electron laser, (entitled FELIX—free electron laser for infrared radiation). The calculated scattering rates for optic and acoustic phonon, and alloy scattering have been included in a rate equation model of the transient FIR intersubband absorption, and show excellent agreement with our degenerate pump-probe spectroscopy measurements where, after an initial rise time determined by the resolution of our measurement, we determine a decay time of ∼10 ps. This is found to be approximately constant in the temperature range from 4 to 100 K, in good agreement with the predictions of alloy scattering in the Si0.7Ge0.3 wells.

Si-based electroluminescence at THz frequencies

Experimental results of electroluminescence in the terahertz gap, at 6 THz (or 40 μm) from Si/SiGe multi quantum well structures, grown by a commercial chemical vapour deposition system are presented. Theoretical simulations were used to design the heterolayer structure and to explain the emission and absorption features. Electrical and materials characterisation is also presented to demonstrate the quality of the heterolayers.