Zsolt Bor

Repigmentation of localized vitiligo with the xenon chloride laser

Sir, Topical 5-aminolaevulinic acid (5-ALA) photodynamic therapy (PDT) has become an effective treatment option in dermatology. We report a 70-year-old man who presented with extensive erythematous patches on his abdomen and infiltrated plaques on his arms and neck. These were preceded by extensive figurate and annular erythema on his trunk and limbs for 10 years. He had a history of congestive cardiac failure, atrial fibrillation and chronic obstructive airway disease. Mycosis fungoides (MF) was confirmed histopathologically and he cleared with a course of oral 8-methoxypsoralen (8-MOP) plus ultraviolet A (PUVA). During the next year his MF progressed in extent and he also developed a solitary tumour (1 ́5 1 ́5 cm) on his left posterior thigh. The extensive patch and plaque MF cleared with a further course of oral 8-MOP PUVA, but the nodule remained and became ulcerated and painful over the next 3 months. Biopsy of this tumour showed an ulcerated epidermis with replacement of the subcutaneous tissue by a dense infiltrate of malignant CD31 T cells (Fig. 1a). There was no lymphadenopathy or organomegaly. Blood investigations were normal. Computed tomographic scans of the thorax and abdomen were negative. The tumour was treated with 5-ALA PDT: 5-ALA 20% in a cream base (Aladerm, Crawford Pharmaceuticals, Milton Keynes, U.K.) was applied, under polythene occlusion, to the tumour. Four hours later, excess 5-ALA was wiped off and fluorescence was graded as satisfactory using Woods light. He received 20 J cm at 20 mW cm using a Waldmann PDT lamp (MSR 1200; 580±740 nm). Irradiance was measured using a calibrated handheld meter (International Light 1400A and Selo33/F/W/QND52 detector with spectral shaping and neutral density filters calibrated by D.Taylor, Gloucester, U.K.). He graded pain during treatment as 8/10 but experienced no other adverse effects. The lesion cleared after five consecutive treatments over 12 weeks. Repeat biopsy showed a lymphohistocytic infiltrate but complete clearing of the original infiltrate of malignant T cells (Fig. 1b). During his course of PDT his generalized patch and plaque MF relapsed. The tumour site has remained clear on clinical examination 1 years later. He has required two courses of PUVA therapy for generalized patch and plaque MF during this period. Topical 5-ALA PDT has been proven to be effective for superficial cutaneous cancers, but there are few reports of its use in treating MF. Shanler et al. treated patch/ plaque-stage cutaneous T-cell lymphoma and showed that protoporphyrin IX accumulated within lymphocytic infiltrates; early therapeutic results were promising. Boehncke et al. using an argon laser at 630 nm showed inhibition of proliferation of malignant transformed T cells in vitro and in vivo. Wolf et al. have demonstrated the efficacy of PDT (20% 5-ALA) using a broad-spectrum source (40 J cm at 44 mW cm) in two patients with MF who cleared after four and five PDT treatments, respectively. However, Amman and Hunziker reported a poor response for an infiltrated plaque of MF to just one PDT treatment using an identical regimen. This suggests that multiple treatments are required to obtain a complete histological response. We have demonstrated the benefits of low light dose, low dose rate topical 5-ALA PDT for nodular MF, but a formal study is needed to confirm our findings.

Phase-sensitive single-pulse autocorrelator for ultrashort laser pulses

A new single-shot phase-sensitive autocorrelator for picosecond and femtosecond measurements is presented. The experimental results show that this device is suitable for the study of chirp in single pulses.

Femtosecond-resolution pulse-front distortion measurement by time-of-flight interferometry

The pulse-front distortion occurring in lenses and lens systems has been measured by a Michelson interferometer. In this technique the plane pulse front from one arm of the interferometer is used as a temporal reference level to map contour lines of equal propagation time on the pulse-front surface. The experimental arrangement is capable of detecting pulse-front distortion with a resolution of 20 fsec, and this can be improved to approximately 1 fsec. The measured value of pulse-front distortion in a telescope (1.1 psec) is in good agreement with the calculated data.

Diode laser based photoacoustic humidity sensors

Abstract Various diode laser based photoacoustic (PA) systems applied in water vapour detection are presented. The dependence of the systems’ performance on the physical and chemical properties of the measured gas is discussed. It was found that the pressure dependence of the measured PA signal is different for amplitude and wavelength modulated lasers. This difference is explained. Linearity in a concentration range of more than four orders of magnitude in combination with typical accuracy of a few percentages was proved.

Excimer laser induced surface chemical modification of polytetrafluoroethylene

Abstract Polytetrafluoroethylene has a notoriously non adhesive and non reactive character. Its successful surface photochemical modification was performed by irradiating the polytetrafluoroethylene/liquid triethylamine interface with an ArF excimer laser (λ=193 nm). Due to the photochemical treatment the polytetrafluoroethylene surface became more hydrophilic. The water receding contact angle decreased from 94° to 43°. The reaction cross section was determined from the decrease of the contact angles. It was found to be as high as 6.4×10−18 cm2. XPS measurements evidenced the removal of fluorine from the polytetrafluoroethylene, incorporation of alkyl carbon and nitrogen. Photochemical dissociation path of the triethylamine makes probable that it bonded to the fluoropolymer backbone via the α-carbon atom of an ethyl group. A radical, or a photoinduced electron transfer mechanism was suggested to describe this reaction. A selective area electroless plating of silver was performed after pretreating the sample with patterned photomodification. The increased adhesion of the sample was proved by gluing with epoxy resin. As a result of the surface modification the tensile strength of gluing increased by 210× and reached 24% of the value characteristic for the bulk material.

Picosecond dye laser pumped by an excimer laser

A XeCl excimer laser-pumped dye laser generating 40-psec long pulses with 2.5-MW peak power, operating at 382 nm with 10-pps repetition rate is described. Short-pulse generation is achieved by cascade pumping of a quenched dye laser. The laser is simple and versatile. The possibilities of further developments are also discussed.

Pulsed laser ablation mechanisms of thin metal films

The ablation of thin films by single laser pulse is a well known technique with widespread industrial applications. Ablation occurs in a well defined power density region if a supported thin film is illuminated by a single laser pulse. In the literature there are a number of theoretical description of ablation, but a very few based on in-situ experiments. In our study we have directly visualized the ablation processes with fast photography based on application of dye laser probe pulses. The ablation of chromium and tungsten layers supported onto glass substrates with pulses of ArF excimer laser was investigated. The ablated area was illuminated by a delayed short pulse of a fluorescein dye laser or a Rhodamine6G dye laser. Snapshots of initial phase of ablation and the forthcoming material transport were recorded by an optical system and a video camera. Blowing-off mechanisms and thermo-mechanical mechanisms are considered to take place during ablation. Pressures formed during laser ablation were calculated and compared with experimental data. It was found that thermo- desorption of gas adsorbed on to the substrate surface, substrate materials evaporation and film exfoliation by its longitudinal thermal enlargement may be acting during laser ablation of thin films.

Conical structures produced by excimer laser irradiation of polymers

The development of conical structures on the surface of excimer laser ablated polymers, is studied. It is demonstrated that this phenomenon has a lower threshold and an upper limit fluence which values depend on the material. The lower value is equivalent of the ablation threshold of the sample, below which the etch does not occur. In accordance with our assumption the upper limit corresponds to the ablation threshold of the particulate impurities which are responsible for the formation of cones, because these impurities remove from the surface of the polymers with the other ablating fragments when the fluence exceeds the upper limit. The dependence of the apex angles of the cones on the fluence and the number of pulses is investigated. A simple etching model based on the diffraction and interference theories is proposed to explain the formation of the conical structure.

High-tensile strength sticking induced by ArF excimer laser surface treatment of poly(tetrafluoroethylene)

A successful enhancement of sticking of PTFE is demonstrated using ArF excimer laser irradiation in the presence of novel photoreagents. The applied laser fluence was very low at the sample - photoreagent liquid interface compared to the energy density applied in earlier investigations. After the treatment the PTFE films were glued by epoxy resin. It was found that at low doses the tensile strength of the sticking increased rapidly with the UV pulse number and the reached a saturation value, which was 6.66 MPa for triethylamine, 5.56 MPa in the case of 1,2-diaminoethane and 4.64 MPa for triethylene-tetramine. These are around two hundred times higher than the value of the untreated surface. It was found that this procedure makes the metallization and painting of PTFE surface also possible. A photoinduced electron transfer mechanism was suggested to describe the photoreaction, which is responsible for the increase of adhesion features on PTFE surface.

Surface roughness investigations of excimer-laser-ablated cornea

The earlier investigations showed that the corneal haze can be due to the scattering effect of the excimer laser induced surface structure. In this paper a comparative study is presented regarding the development of these. Several human corneas were irradiated by an ArF excimer laser. The applied fluence was 193 mJ/cm2. The developed surface structures after each excimer pulse were investigated by an atomic force microscope under physiological salt solution in natural environment. It was found that the structures of cells and fibers forming the cornea were observable on the ablated surface in the form of surface roughness. Scanning electron microscopic observations were also performed to compare the two surface investigation methods. It was found that this showed the same structures, but differently from the atomic force microscopic observation some distortions appeared produced by preparation processes of the samples, which were necessaries for the electron microscopic investigations.