We have developed a terahertz spectrometer based on difference frequency generation of beams from an ytterbium fiber master oscillator power amplifier (MOPA) system. The spectrometer has a resolution of ∼ 2 GHz. It can be tuned rapidly over several hundred GHz, and a wider frequency range can be covered (0.7–2.5 THz demonstrated) by swapping in alternate seed lasers and adjusting the alignment of the beams into the difference frequency generation (DFG) crystal. The system was constructed entirely from commercially available fiber and fiber components. We present some demonstration data on water vapor absorption lines.

We present line-of-sight measurements with broadband THz radiation through a methane diffusion flame, with the motivation to develop a modality for sensing and imaging within sooty flames. We present the design details of a bespoke high-pressure burner suitable for THz line-of-sight measurements, as well as hard-field tomography imaging from 4 projections. Further we introduce the setup for THz time-domain spectroscopy (TDS) and show the results of TDS measurements of a methane-air diffusion flame at different values of peripheral air co-flow at 3, 5, 10 and 12 l/min. The time-domain waveforms of the THz electric field transmitted through the flame are processed to extract the values of the time delay for each case. The dependence of these values on the air co-flow reveals that after an initial linear increase, the optical density along the sensing path levels out after 12 l/min. This is interpreted in terms of the radial temperature distribution of the gas flow. The effect of these parameters on the correct measurement setup for flame sensing and imaging at various geometries is briefly discussed.

We report on hard-field tomography measurements in the THz spectral range and subsequent image reconstruction of a phantom subject. At THz wavelengths, the traditional hard-field tomography approach to measure attenuation is hindered by a substantial diffusely scattered component. Consequently, we work in optical density image contrast, as opposed to material density typical in high-energy hard-field modalities, such as X-ray CT. The hard-field component of the signal is extracted with a spatial filter, efficiently suppressing the soft-field contributions from the imaged subject. Using time-domain THz spectroscopy, line integrals of the real part of the refractive index are taken, by measuring the delay of the THz pulse across the subject at 12 angles and 0.5 mm steps in the transversal direction for each angle. The delay values are calculated from the location of the first peak in the integrated time-domain waveforms. This is justified by the physics of THz generation with ultrashort pulses in a biased-gap antenna and is shown to be superior to existing alternatives. The resulting tomography projections provide evidence for the hard-field character of the line integrals. The quality of the reconstructed image is interpreted and discussed, together with some limitations and future avenues.

We demonstrate the use of a full-wave electromagnetic field simulator to verify terahertz (THz) transmission-mode spectroscopic measurements of periodic arrays containing subwavelength cylindrical scatterers. Many existing THz scattering studies utilize analytical solutions, which were developed for a single scatterer. For multiple scatterers, a scaling factor equal to the number of scatterers is applied, accounting for interference between far-field radiative contributions from those scatterers but not their near-field mutual coupling. Consequently, analytical solutions do not accurately verify measurements. Conversely, results from the full-wave electromagnetic field simulator elucidate our measurements well, and provide an important insight into how the scattering behavior of cylindrical scatterers is influenced by test conditions.

We have performed 2-dimensional tomographic measurements upon shaped phantoms constructed from material with low optical power, using a time-domain THz arrangement. While the phantom morphology can be successfully reconstructed using the time-delay data, use of the THz pulse amplitude is less reliable, demonstrating distortions that may be a consequence of beam diffraction effect. This effectively masks the true attenuation contrast of the object.

We report the development of a terahertz pulsed spectroscopic imaging system based on the concept of compressive sensing. A single-point terahertz detector, together with a set of 40 optimized two-dimensional binary masks, was used to measure the terahertz waveforms transmitted through a sample. Terahertz time- and frequency-domain images of the sample comprising 20×20 pixels were subsequently reconstructed. We demonstrate that both the spatial distribution and the spectral characteristics of a sample can be obtained by this means. Compared with conventional terahertz pulsed imaging, no raster scanning of the object is required, and ten times fewer terahertz spectra need be taken. It is therefore ideal for real-time imaging applications.

Scattering of terahertz radiation from cylindrical strands is explored as a means of studying the effects of hair on the results of bio-tissue analysis. Strands of fiberglass are aligned either parallel or perpendicular to the polarization vector of the incoming terahertz beam. Spectroscopic results reveal that the materialpsilas intrinsic THz transmission properties are highly dependent on fiber orientation.

We observe that the intensity of water vapour absorption lines in a combustion system containing a diffusion flame is highly dependent on the air flow rate. This implies that the recorded signal originates from (lower temperature) water vapour outside the volume of the flame. Seeding the flame enables water to be used as a fuel region marker.

A 66-year-old man presented with an 18-month history of progressive nail dystrophy involving his left index finger. A diagnostic biopsy specimen confirmed the clinical suggestion of subungual Bowen's disease (carcinoma in situ). Various treatment options were considered, and the decision was made to treat with photodynamic therapy using topical 5-aminolevulunic acid administered as two treatments 4 weeks apart. The patients was reviewed 3 months after treatment and then regularly at 6-months intervals. Thirty months after treatment there remained no clinical evidence of recurrence of the condition with preservation of a normal nail unit. Although the successful treatment of cutaneous Bowen's disease with photodynamic therapy is well documented, this is the first report of the successful treatment of subungual Bowen's disease using topical aminolevulunic acid-photodynamic therapy.

Objective:To assess the efficacy of PDT to: Palliate symptoms, control disease and extend survival in patients with advanced inoperable cancer.Subject and Method:55 Males and 23 females aged between 45-81 years (mean 66 years) with inoperable and advanced lung cancer with > 50% obstructive lesions of the main, lobar or segmental bronchi. Patients had pre-treatment routine clinical radiological, functional and endoscopic assessment with proven histological diagnosis.Protocol of PDT was; Intravenous injection of 2 mg/Kg bodyweight Polyhaematoporphyrin (equivalent to Photofrin) or Photofrin followed 24-72 hours later by illumination of tumour using 630 nm light (Oxford Laser) delivered via an optical fibre with end diffuser. Treatments were carried out under general anaesthesia as a day case procedure. Patients were rebronchoscoped for debridement/retreatment 4-7 days later.Results:There was no treatment related mortality. Two patients developed mild photosensitivity reaction. All patients showed symptomatic improvement with good initial functional and radiological amelioration. Every patient responded to treatment. Seven patients had complete response and negative histology for 3-12 months. After the first treatment average Forced Vital Capacity (FVC) and Forced Expiratory Volume in one second (FEV1) improvement was 0.5 litres and 0.4 litres respectively. Twenty five percent of patients (nr 19) survived more than 2 years, 10% (nr=8) between 1-2 years and the remaining 51 patients less than a year.Conclusion:PDT should be considered as a therapeutic modality for all stages of lung cancer and is an excellent treatment modality for palliation in advanced bronchial malignancies.

A method is presented of monitoring the low level fluorescence emitted by the photosensitizing agent protoporphyrin IX during superficial photodynamic therapy of skin carcinomas, using 630 nm illumination. A fiber optic probe samples the light field which is filtered and recorded by an optical spectrum analyzer. The technique is minimally invasive and can proceed concurrently with light dosimetry measurements. This paper presents in vitro data that define the sensitivity and selectivity of the technique, along with preliminary in vivo measurements. These indicate that it is the rate of phototransformation of the photosensitizer, rather than the total light dose, that determines the optimum treatment duration. Clinically effective treatment therefore depends upon achieving a threshold concentration of drug throughout the volume of the lesion. In this way the effect of phototransformation does not inactivate the drug before complete tumor necrosis occurs.