Glass drilling and welding applications realized with the help of femtosecond lasers attract industrial attention , however, desired tasks may require systems employing high numerical aperture (NA) focusing conditions, low repetition rate lasers and complex fast motion translation stages. Due to the sensitivity of such systems, slight instabilities in parameter values can lead to crack formations, severe fabrication rate decrement and poor quality overall results. A microfabrication system lacking the stated disadvantages was constructed and demonstrated in this report. An f-theta lens was used in combination with a galvanometric scanner, in addition, a water pumping system that enables formation of water films of variable thickness in real time on the samples. Water acts as a medium for filament formation, which in turn decreases the focal spot diameter and increases fluence and axial focal length . This article demonstrates the application of a femtosecond (280fs) laser towards two different micromachining techniques: rapid cutting and welding of transparent materials. Filament formation in water gives rise to strong ablation at the surface of the sample, moreover, the water, surrounding the ablated area, adds increased cooling and protection from cracking. The constructed microfabrication system is capable of drilling holes in thick soda-lime and hardened glasses. The fabrication time varies depending on the diameter of the hole and spans from a few to several hundred seconds. Moreover, complex-shape fabrication was demonstrated. Filament formation at the interface of two glass samples was also used for welding applications. By varying repetition rate, scanning speed and focal position optimal conditions for strong glass welding via filamentation were determined.
We report on laser-induced damage threshold (LIDT) and UV-laser excited defect formation measurements in large
aperture KDP crystals developed as doublers and triplers for mega-Joule laser. Measurements of LIDT were performed
according to the ISO 11254-2 standard for repetitive pulses with duration ~ 4 ns and repetition rate of 10 Hz. The results
for different laser wavelengths (1064, 532 and 355 nm) and polarizations are presented. The largest LIDT was observed
for 532 nm pulses and the 1064 nm wavelength had a strong dependence on laser polarization. The LIDT values at 532
nm and 355 nm also depended on the crystal cutting angle, which is different for doublers and triplers. A comparison of
LIDT with earlier reported crystal absorptance at different wavelengths is also performed.
The UV-laser induced defect formation was investigated by the means of pump-probe technique. The excitation was
performed with a single pulse of ns Nd:YAG laser (355 or 266 nm wavelength) and probing with another Nd:YVO4 laser
system (532 nm) operating at 1kHz. This gave us a temporal resolution of 1ms. The transient absorption of defect states
relaxed non-exponentially and fully disappeared in ~10 s. A comparison is made between crystal grown by distinct
growth methods and between different laser polarizations. An influence of laser conditioning on UV induced defect state
formation is also revealed.
We report the measurements of the linear and non linear absorption at 1064, 532 and 355 nm in samples of KDP crystals fabricated with the rapid growth process developed for NIF and LMJ high power lasers. Measurements were performed according to the ISO11551 standard by the "pulse" or "gradient" calorimetric method using a pulsed, diodepumped, Q-switched Nd:YAG laser. Time resolved spectroscopy method was used for the investigation of defects formation, responsible for the non linear absorption at 355 nm.
We report polarization dependent measurements of absorptance of some crystal performed according to the ISO11551 standard by the 'pulse' or 'gradient' calorimetric method at 1064 and 532 nm using a pulsed, diode-pumped, Q-switched YAG:Nd laser.