This paper discusses a 3D depth-sensing system for mobile application consisting of a structured-light illuminator based on a Vertical-Cavity Surface-Emitting Laser (VCSEL) array and an embedded imaging system equipped with a high-speed CMOS-sensor and a Field Programmable Gate Array (FPGA) device. For structured-light projection, an elliptical array pattern generated with two-photon polymerized micro-optics on top of the VCSEL is employed. To solve the correspondence problem and estimate objects’ distance, we proposed light-weight and robust algorithms in favor of hardware implementation. We demonstrate the validation of the proposed approach with initial experimental results.
A novel diode pumped Tm:YAG laser (Pantec Biosolutions AG) with a more flexible temporal pulse regime is available. This study includes first experiments with model stones on the influence of the pulse regime on the fragmentation rate. For this purpose, ablation experiments were performed on rectangular model stones (BEGO, 40 mm x 10 mm x 5 mm). The laser beam was coupled into a 270 μm light guide and the distal fiber end was positioned in <50 μm to the stone surface. This was located in a basin filled with water, which was moved horizontally with the stone at constant velocity by a computer-controlled translation stage. The ablation rate and the ablation efficiency were determined by subsequent measurement of the depth and width of the resulting crater. The experiments were performed with varying parameters of the novel pulse regime and, for comparison, with standard laser settings. The experiments show significant differences in bubble dynamics and shape, depending on the temporal pulse regime. Lowest values for propulsion were measured for the standard pulse regime. The measured and calculated values for ablation depth, -rate and -efficiency are comparable for all investigated pulse regimes. Especially the ablation efficiency is quite high compared to values which were calculated from published data. In conclusion, these preliminary results show a high potential of the diode pumped Tm:YAG laser with novel laser driver for variable and high efficient lithotripsy. The wide range of available peak power should allow fragmentation as well dusting with the same laser system.
Modern operating microscopes offer high power illumination to ensure optimal visualization, but can also cause thermal damage. The aim of our study is to quantify the thermal effects in vivo and discuss conditions for safe use. In a pilot study on volunteers, we measured the temperature at the skin surface during microscope illumination, including the influence of anaesthesia and the effects of staining, draping, or moistening of the skin. Irradiation within the limit given by safety regulations (200 mW/cm2) results in skin surface temperature of 43 °C. Higher intensities (forearm 335 mW/cm2, back 250 mW/cm2) are tolerated, resulting in reversible hyperaemia. At a very high illumination intensity (750 mW/cm2), pain occurs within 30 s at temperatures of 46 °C±1 °C (hand and forearm), and 43 °C±2 °C (back), respectively. Anaesthesia has no distinct effect on the temperature, whereas staining and drapes result in much higher temperatures (>100 °C). Moistening at practicable flow rates can reduce temperature efficiently when combined with a light absorbing and water absorbent drape. In conclusion, surgeons must be aware that surgical microscope illumination without protective means can cause skin temperatures to rise much above pain threshold, which in our study serves as a (conservative) benchmark for potential damage.
We developed a new surgical procedure to improve the recurrence rate using an Er:YAG laser as dissection tool for the carpal ligament with the objective to ablate a small amount of the carpal ligament and to denaturate its ends. The Er:YAG Laser was transmitted to the applicator via a GeO fiber. With this system we proceeded 10 carpal ligament dissections without any complications in the follow-up period. All patients were free of pain and recurrence.
For hair removal commonly lasers are used with wavelengths being selectively absorbed by melanin .As a consequence, laser radiation leads to an increase of the temperature not only in melanin containing structures of the hair but also in the epidermis. Therefore, we simulated and studied the laser induced temperature development in tissue for various laser wavelengths and various pulse profiles. Modifying the beam parameters can improve the selectivity of the method. Monte- Carlo-Simulations were used to calculate light absorption in dermal structures, considering the tissue specific optical properties. The thermal diffusion in tissue was calculated by a finite difference method. The biological reaction due to the temperature rise was determined by an Arrhenius formalism and depends on temperature and time of laser-tissue interaction. The simulation program allows to calculate the temperature distribution and thermal damage for various temporal pulse profiles, fluence rates and irradiation geometries. Superficial cooling has an important influence and has been considered in the calculations. The results of our simulations for various laser types show differences in the thermal reaction which can be used to optimize the treatment modalities. The potential and limits of laser epilation can be estimated from these results. For example, a series of laser pulses has some advantages compared to a longer single pulse.
Photorefractive keratectomy (PRK) is usually performed by an excimer laser at 193 nm wavelength. Ablatio of corneal tissue is, however, not only possible in the UV region of the optical spectrum but also in the IR where water is an excellent absorber. Therefore, an Er:YAG laser was used at 2.94 micrometer wavelength as an alternative laser light source to perform in vitro studies of corneal ablation and also first clinical experiments to correct myopia of patients with blind eyes.
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