Data collected in real S-on-1 LIDT experiments performed with a nanosecond, 1064 nm automated station are used to calculate the damage probability with the ISO-recommended (conventional) method and the recently-suggested cumulative method. The damage probability points versus fluence for each type of calculation are fitted using both, linear and nonlinear curves. The resultant four data sets corresponding to each real experiment are used to compare important parameters as: statistical uncertainty of damage probability points, fitting errors, damage threshold fluences for actual number of pulses, and the extrapolated threshold fluences for very large number of pulses. We suggest and analyze also a limit case of the cumulative method, when the damage probability points are calculated for each interrogated site. Both, the recently-suggested cumulative method, and our limit case, look very promising.
The effective area of a laser spot is an important quantity used to characterize the laser-induced damage threshold of optical materials according to ISO 21254-1:2011 standard. A method for measuring the effective area/diameter of spots from pulsed laser beams using charge-coupled device camera-based beam profilers is presented. Factors affecting the measurement’s accuracy, as the background noise and the size of the summation area, were evaluated using MATLAB®. To minimize the noise contribution, we use an iterative method similar to the one used to measure the second-moment-based spot sizes. We find that the two analyzed components of the background noise, its zero-mean noise and its offset, have an opposite effect on the measurements of the effective area/diameter as compared with the second-moment-based measurements. We prove that there is an upper limit of the relative error of such iterative measurements of effective area, the iteration limit parameter, and that it is a measurable quantity. We measure the effective area/diameter of laser spots with different sizes from a Nd:YAG laser at 1064 nm, 6 ns pulse duration, 10 Hz repetition frequency, and estimate the standard uncertainty of the measurements. Further, we generalize the effective area/diameter concept to include elongated (elliptical/rectangular) spots.
We report on our approach to measure the quantity named effective pulse duration as defined in the ISO 21254-1:2011 standard, which deals with laser-induced damage (LID) threshold measurements. The approach is applied to measure pulses from two laser sources: an injection-seeded electro-optically Q-switched Nd:YAG nanosecond system with 10-Hz pulse repetition frequency, and a fully integrated Ti:sapphire laser with 150–400 fs and 2-kHz pulse repetition frequency. For comparison, the full-width-half-maximum (FWHM) of the same pulses is also measured. The analysis and description of the measurement process, the experimental results, and the corresponding uncertainties are presented. A smaller combined uncertainty is obtained for the effective pulse duration than for the FWHM-defined pulse duration for each time scale involved in experiments. This suggests that the effective pulse duration is the appropriate parameter to characterize the pulse duration in LID experiments.
An automated test station to measure the laser-induced damage threshold (LIDT) according to ISO 21254-1,2,3,4:2011
standards is presented. The laser is a single longitudinal mode, 500 mJ, 6 ns, Q-switched, 10 Hz, linearly polarized, 1064
nm laser, with 2-nd and 3-rd harmonic capabilities. The machine is able to operate the S-on-1 test (S = 500), or the Type
2 endurance (durability) test. The main blocks of the station are described, emphasizing some original solutions.
Preliminary results of LIDT measurements using the S-on-1 test on several coatings and on uncoated fused silica
substrates with various degrees of roughness are also presented.
A compact near-diffraction-limited picosecond microchip oscillator-amplifier system was developed. When pumped by 0.9-W average power pulsed radiation, the microchip generated 9-μJ energy pulses of 400-ps duration at 1-kHz rate, in a nearly TEM00 transversal mode (beam quality factor, M2 < 1.1). The microchip output was amplified up to 12-mJ pulse-energy at 1-10 Hz repetition rate in a two-pass flash-pumped Nd:YAG amplifier. We used the 1064-nm output beam for nonlinear conversion to 532-nm second harmonic (SH) and
266-nm fourth harmonic (FH). The pulse-energy of SH and FH output was 6-mJ and 1.6-mJ, respectively, which corresponds to 50 % and 13 % conversion efficiency.
A compact single-frequency nanosecond green laser oscillator-amplifier system was developed. The single longitudinal
mode oscillator consists in a cavity-coupled acousto-optically Q-switched Nd:YAG microlaser emitting pulses of 50 μJ
energy, 10 nanosecond duration at 1064 nm wavelength. The oscillator pulses were amplified at 1-10 Hz repetition rate
in a two-pass Nd:YAG amplifier up to 28 mJ energy. Infrared amplified radiation was frequency doubled (532 nm) in a
KTP crystal with as much as 50% conversion efficiency. The pulsed green laser, with more than 1.5 m coherence length,
was used as light source for the holography unit in the sensor of a multi-task device for nondestructive diagnosis in art
conservation procedures.
An old type HOLOBEAM type Nd:YAG laser system was upgraded to reach technical requirements for diamond and
diamond like materials drilling. A particular alignment protocol was tested to assure the best quality of the hole
geometry. Various processing procedures were tested and important differences in bore quality are noticed for different
materials and laser operating regimes. Dedicated user friendly software was made to drive the laser beam and holder
actuators, for different hole drilling geometries.
Fundamental 1064 nm wavelength radiation of a diode pumped passively Q-switched Nd:YAG microchip laser was frequency doubled by periodically poled (PP) and conventional type II KTP crystals. Second harmonic (SH) conversion efficiency of 60% and 47% has been achieved with PPKTP and KTP crystals, respectively. SH pulse energy of as much as 6 μJ, at 900 Hz repetition rate, has been obtained for 10 μJ pulse energy of the input 1064 nm radiation focused with a waist radius of 25 μm inside the 8 mm long PPKTP crystal. We estimated an effective nonlinear coefficient of 6.9 pm/V and a thermal acceptance FHWM bandwidth of 5.78°C for the PPKTP sample.
Due to the continuous technological development in microelectronics and generally in precise materials micromachining there is a continuous need to develop more effective techniques to clean impurities from the surface. Current cleaning techniques used in microelectric devices fabrication lines have an integrated action on the whole surface or on a great part of it, are polluting the ambient and are not efficient for submicron particles. Due to this needs we have studied laser cleaning of silicon wafers with regards to direct applications in semiconductor manufacturing. We have analyzed the ablation effect of laser radiation of 1.06 micrometers on different materials currently used in microelectronic industry and the cleaning effect on a silicon support.
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