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.
Preliminary results for joining by laser welding of diamonded segments onto the support body of cutting tools are
presented in the paper. Such tools are mainly used for cutting hard materials in construction industry. A new mechatronic
equipment able to perform the complex displacement movements required by the new tehnology is also presented.
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.
We report preliminary measurements on the catastrophic damage threshold and also on the maximum fluence/irradiance
for non-damage of a 355 nm high reflectance mirror, by using a new optical arrangement. Our goal was two-fold: to
determine the ability of a new, variable spot size (zoom) optical system (named VariSpot®) to be used in laser-induced
damage measurements, and also to characterize the damage properties of the mirror under test. The classical
measurement scheme maintains a constant spot size on the target by using a fixed-focus optical system, and the laser
fluence/irradiance on the target is varied by appropriately attenuating the laser beam before the focusing optics. In
contrast, our scheme maintains constant the energy/power of the incoming beam before the focusing optics and uses a
zoom-type optical system to continuously change the spot size and correspondingly the fluence/irradiance on the target,
while keeping constant the working distance (from optics to target). A 355 nm beam representing the third harmonic of
an electro-optically Q-switched, unstable cavity Nd:YAG laser was used as incoming beam. Its spatial diagnostics was
done by using a CMOS-type beam profiler and following the definitions and recommendations of the ISO 11146
standard. The VariSpot optical system represents a prototype with a working distance of approximately 100 mm and
delivering a round and adjustable spot size with diameters from 0.085 mm to 4.3 mm at that distance for the specific 355
nm incoming laser beam. The results show the advantages of using the VariSpot system for such type of measurements
and also reveal reasonable good damage properties of the tested mirror. We briefly discuss the major sources of errors in
the obtained results and also suggest several ways to improve the future measurements using similar arrangements.
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.
The effects of several deposition parameters on the quality of deposited boron nitride (BN) films by pulsed laser deposition (PLD) with short laser pulses are studied. The laser fluence, nitrogen background pressure, Si(100) substrate temperature and laser wavelength were varied in order to find the maximum content of the cubic phase in our BN films. We found that laser fluence and wavelength are affecting strongly the structure of BN films while background pressure and substrate temperature are affecting slightly the film morphology.
A flash-lamp pumped Nd:YAG laser with confocal unstable resonator and super-Gaussian output mirror, multi-pulse passively Q- switched employing Cr4+:YAG and LiF:F2 crystals with small-signal absorption in the 22-82% range, has been developed. At 49 J energy and 1 Hz repetition rate of the pump pulses, using a passive shutter with 37% initial transmission, a train of 12-13 pulses, separated by more than 8 microseconds, with average 52 mJ single pulse energy and 20 ns pulse-width, were measured. Under these conditions, the laser intensity at the optical fiber input face is under the fiber damage level, but output power density is high enough to reach the ablation threshold of various pollution layers deposited on the material surface.
The research is carried on as a project in the frame of the PHARE-TTQM program, a cooperation of INFLPR Bucharest, PRO OPTICA SA Bucharest and FORTH-IESL Heraklion-Greece. A new laser ablation technique, based on the enhanced free running (EFR) mode of operation of a Nd:YAG laser, is presented. In the EFR degree(s) mode it is possible to achieve a regular temporal structure of the laser spiking combined with the control of both amplitude and separation of the individual spikes. The stable fluence and power density of the spikes will increase the precision of the EFR laser ablation in comparison with the short free running technique. The short duration of the EFR spikes, combined with their large time separation, reduces the level of the thermal damage of the substrate. A surface processing laser device operating in EFR mode is under development with PHARE financial support in the Laser Department of INFLPR. Preliminary study of ablation of stone samples from Stavropoleos Monastery, Bucharest, using FORTH-IESL laser facilities, is presented.
The beam quality of solid-state lasers with high average power can be greatly improved using phase conjugators based on stimulated Brillouin scattering (SBS). The common phase conjugators used until now are liquid or gas cells.Using SBS in glass fibers as phase conjugators the field of applications can be expended. The long interaction length and small cross-sections of the fibers result in an appreciable reduction of SBS threshold and avoid optical breakdown which could happen in liquids and gases at high input energies. Other advantages of glass fiber phase conjugators are harmlessness and easy handling. We have experimentally investigate a phase conjugator base don SBS obtained in an undoped quartz fiber with core diameter of 200 micrometers . The SBS threshold reflectivity and phase conjugation capability were measured with 18 ns pulses at 1.06 micrometers wavelength with different input energies.
We describe a pulsed doubly resonant LiB3O5 (LBO) optical parametric oscillator (OPO) pumped with a frequency doubled Q- switched Nd:YAG laser amplifier. The threshold power density near degeneracy was found to be 29 MW/cm2. The OPO was continuously tuned from 970 nm to 1175 nm by rotation of the LBO crystal. The linewidth of the signal radiation at 998 nm, and idler radiation at 1136 nm wavelength, were found to be 10 nm, and 13 nm respectively. The OPO output pulse energy of signal and idler near degeneracy was 1.51 mJ for 18 mJ pump energy.
NiO is a metal-deficient p-type semiconductor with surface defects which are correlated with the non-stoichiometry. The dissociative H2 adsorption on the NiO surface takes place on oxygen-excess sites (over equilibrium). The H2 TPD spectra vary significantly with calcination temperature (stoichiometry) and chemical treatment UV laser radiation enhances H2 adsorption on the defective surfaces (non-stoichiometric) as compared with the stoichiometric ones, even chemically treated. The fourth harmonic of a Q-switched Nd:YAG laser is used for the NiO samples irradiation. The wavelength of the UV laser radiation is 266 nm, under the band-gap of the semiconductor.
We have developed a laser-diode pump system for continuous-wave end-pumping of Nd:YAG lasers. The pump system includes a pair of 1 W diode-arrays mounted in coaxial enclosures, a driver unit and the pump optics. The array wavelength was temperature tuned to achieve the maximum absorption of the pump radiation in the Nd:YAG crystal. The characteristics of the pump system are presented and the pump-beam profile is investigated.
A Q-switched Nd:YAG laser beam and its second and fourth harmonics were focused onto the polished surface of dentine samples in order to compare the ablative effect for the three wavelengths. A photoacoustic technique is applied for the ablation threshold determination. The Scanning Electron Microscope images of the produced craters are investigated and the volume of ablated material is determined. The necessary optical constants for the ablation calculation are experimentally determined.
We describe a source of visible (532 nm) radiation for pumping picosecond optical parametric oscillators. Picosecond pulses generated by a passively Q-switched Nd:YAG oscillator are amplified in two amplifier stages and frequency doubled in a KDP crystal cut for type I or type II phase-matching. Trains of pulses of 7 - 11 mJ over-all energy are generated, single pulse energy is 450 - 600 (mu) J and pulsewidth about 40 ps.
Dynamic stable resonators (DSRs) with Nd:YAG lasers which operate up to 1 KW average pump-power are discussed. Some DSR parameters and an ordering criterion are defined. The theory of DSRs has been extended to the Q-switched mode of operation. Two types of resonators able to operate in Q-switched mode are proposed. An experimental verification of the theoretical calculation was made.
CO2 reduction to CH4, by H2, can be achieved at room temperature over a NiO catalyst under laser irradiation. The H2 adsorption states on NiO surface, pre-irradiated and non-irradiated, were put in evidence by Temperature Programmed Desorption. A 248 nm KrF* excimer laser radiation was used to stimulate the filling of the room temperature H2 adsorption state, considered as the first step of the CO2 methanation mechanism.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.