Thomas Hasenberg

We report the development of secondary ion mass spectrometry (SIMS) with continuous sample rotation to achieve high resolution that is independent of depth during compositional and dopant sputter depth profiling. Sample rotation reduces the ion beam-induced surface roughness that often limits the depth resolution in SIMS. To illustrate the effects of sample rotation on SIMS analysis, measurements both with and without rotation were performed on a molecular beam epitaxy grown AlGaAs/GaAs superlattice with 100 periods and 5-nm-thick layers, and a boron delta-doped (atomically planar) Si sample, with dopant concentrations from 1016–1021 atoms/cm3 at depths of 0.5–2.0 μm.

Objectives: Although laser lithotripsy is now the preferred treatment option for urolithiasis due to shorter operation time and a better stone-free rate, the optimal laser settings for URS (ureteroscopic lithotripsy) for less operation time remain unclear. The aim of this study was to look for quantitative responses of calculus ablation and retropulsion by performing operator-independent experiments to determine the best fit versus the pulse energy, pulse width, and the number of pulses. Methods: s. The retropulsion was monitored using a high-speed camera, and the laser-induced craters were evaluated with a 3-D digital microscope. The best fit to the experimental data is done by a design of experiment software. Results: The numerical formulas for the response surfaces of ablation speed and retropulsion amplitude are generated. Conclusions: The longer the pulse, the less the ablation or retropulsion, while the longer pulse makes the ablation decrease faster than the retropulsion. The best quadratic fit of the response surface for the volume of ablation varied nonlinearly with pulse duration and pulse number.

The combination of carrier transport-type optical nonlinearity and absorption saturation is examined for a hetero n-i-p-i sample at wavelengths between 966 and 985 nm and for intensities up to 1000W∕cm2. Transmission changes are found to depend on the interplay between the shift, narrowing, and increasing peak height of an excitonic absorption resonance. Transmission changes previously attributed to absorption saturation are found to be due to carrier transport nonlinearity. Absorption saturation contributed to transmission change for intensities greater than 100W∕cm2, a larger value than previously reported; however saturation intensity still appears to have been reduced by charge separation and a correspondingly slower electron-hole relaxation rate.

Laser treatment on a large size of prostate gland often encounters significant bleeding that can prolong the entire procedure and cause urinary complications. The current study investigates the feasibility of dual-wavelength (532 and 980 nm) application to achieve rapid hemostasis for 532-nm laser prostatectomy. Porcine kidney and bleeding phantom models were tested to quantify the degree of the irreversible tissue coagulation and to estimate the time for the complete hemostasis, respectively. The ex vivo kidney testing verifies that the dual-wavelength created up to 40% deeper and 25% wider coagulation regions than a single wavelength does. The bleeding phantom testing demonstrates that due to the enhanced thermal effects, the simultaneous irradiation yields the complete photocoagulation (~11 seconds) whereas 532 or 980 nm hardly stops bleeders. Numerical simulations validate that the combined optical-thermal characteristics of both the wavelengths account for the augmented thermal coagulation. The dual-wavelength-assisted coagulation can be a feasible treatment to entail the rapid hemostasis and to facilitate the laser prostatectomy in an effective manner.