Mode-mismatched dual-beam method to evaluate thermal and electronic laser-induced lensing effects in Cr- and Yb-doped crystals.

We report on a mode-mismatched thermal lens experiment performed to quantitatively evaluate thermal and electronic laser-induced lensing effects in ion-doped crystals Cr:LiSAF, Yb:KYW, and Yb:YAG. The large diameter of the probe beam resulted in a slow thermal effect (∼dozens of milliseconds) two orders of magnitude larger than the electronic one, improving the discrimination of both competitive effects. All thermal and electronic parameters are obtained from transient signals modeled by an analytical equation, valid for small phase shifts in the absence of upconversion effects.

Simple and compact high-power continuous-wave deep ultraviolet source at 261 nm based on diode-pumped intra-cavity frequency doubled Pr:LiYF green laser.

We report the recent progress on diode-pumped high-power continuous-wave Pr:LiYF (YLF) green laser and deep ultraviolet (DUV) laser generation via intracavity frequency doubling. Using two InGaN blue diode lasers as pump source to form a double-end pumping geometry, in this work, we have demonstrated a green laser at 522 nm with a maximum output power of 3.42 W, which is believed to be the highest power ever achieved in all-solid-state Pr lasers in this specific spectral region.

Modeling population and thermal lenses in the presence of Auger Upconversion for Nd(3+) doped materials.

We present a theoretical model to thermal (TL) and population (PL) lenses effects in the presence of Auger upconversion (AU) for analysis of Nd(3+) doped materials. The model distinguishes and quantifies the contributions from TL and PL. From the experimental and theoretical results, the AU cannot be neglected because it plays an important role on the excited state population and therefore on the temperature and polarizability difference between excited and ground states.

Discriminating the role of sample length in thermal lensing of solids.

Thermal lens (TL) is a key effect in laser engineering and photothermal spectroscopy. The amplitude of the TL signal or its dioptric power is proportional to the optical path difference (OPD) between the center and border of the beam, which is proportional to the heat power (Ph). Due to thermally induced mechanical stress and bulging of end faces of the sample, OPD depends critically on the geometry of the sample.

Resonant excited state absorption and relaxation mechanisms in Tb3+-doped calcium aluminosilicate glasses: an investigation by thermal mirror spectroscopy.

Resonant excited state absorption (ESA) and relaxation processes in Tb(3+)-doped aluminosilicate glasses are quantitatively evaluated. A model describing the excitation steps and upconversion emission is developed and applied to interpret the results from laser-induced surface deformation using thermal mirror spectroscopy. The fluorescence quantum efficiency of level (5)D(4) was found to be close to unity and concentration independent while, for the level (5)D(3), it decreases with Tb(3+) concentration.

Very low optical absorptions and analyte concentrations in water measured by Optimized Thermal Lens Spectrometry.

Thermal Lens Spectrometry has traditionally been carried out in the single-beam and the mode-mismatched dual-beam configurations. Recently, a much more sensitive dual-beam TL setup was developed, where the probe beam is expanded and collimated. This feature optimizes Thermal Lens (TL) signal and allows the use of thicker samples, further improving the sensitivity.

Ultrasensitive thermal lens spectroscopy of water.

A recently developed dual-beam configuration that optimizes the thermal lens technique has been used to obtain the absorption spectrum of pure water from 350 to 528 nm. Our results indicate the minimum linear absorption coefficient smaller than 2 x 10(-5) cm(-1) between 360 and 400 nm. This value is lower than previous literature data, and it is blueshifted.

Thermal lens and interferometric method for glass transition and thermo physical properties measurements in Nd2O3 doped sodium zincborate glass.

In this work the time resolved thermal lens method is combined with interferometric technique, the thermal relaxation calorimetry, photoluminescence and lifetime measurements to determine the thermo physical properties of Nd(2)O(3) doped sodium zincborate glass as a function of temperature up to the glass transition region. Thermal diffusivity, thermal conductivity, fluorescence quantum efficiency, linear thermal expansion coefficient and thermal coefficient of electronic polarizability were determined. In conclusion, the results showed the ability of thermal lens and interferometric methods to perform measurements very close to the phase transition region.

Microstructuration induced differences in the thermo-optical and luminescence properties of Nd:YAG fine grain ceramics and crystals.

The temperature and compositional dependences of thermo-optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time-resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80-300 K). The analysis of the time-resolved luminescent properties of Nd(3+) has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd:YAG ceramics.

Angular dependence of the thermal-lens effect on LiSrAlF6 and LiSrGaF6 single crystals.

We apply thermal-lens (TL) spectrometry to measure the angular dependence of the TL effect on colquiriite single crystals. The experiments were performed with LiSrAlF(6) and LiSrGaF(6) using a two-beam mode-mismatched configuration. The results show that it is possible to minimize the TL effect by selecting the appropriate crystal orientation.

Thermal lens and heat generation of Nd:YAG lasers operating at 1.064 and 1.34 microm.

We report on a simple and accurate method for determination of thermo-optical and spectroscopic parameters (thermal diffusivity, temperature coefficient of the optical path length change, pump and fluorescence quantum efficiencies, thermal loading, thermal lens focal length, etc) of relevance in the thermal lensing of end-pumped neodymium lasers operating at 1.06- and 1.3- microm channels.

Discrimination of resonant and nonresonant contributions to the nonlinear refraction spectroscopy of ion-doped solids.

Nonlinear refraction spectroscopy measurements were performed in resonance with absorption lines in Nd3+ and Cr3+ doped crystals. The observed line shapes can be explained by the interference of resonant and nonresonant contributions to the nonlinear refractive index. These effects were fully discriminated using a pump and probe configuration, in which a dispersive line shape was observed on the top of a plateau that was attributed to the polarizability difference between excited and ground states (Deltaalpha).

Nonlinear refraction spectroscopy in resonance with laser lines in solids.

We report a simple extension of the Z-scan technique that permits a spectral line-shape measurement of the real and the imaginary parts of n(2) . In this technique the sample is placed at the peak position of the usual Z-scan curve while the laser frequency is scanned. We employed this method to investigate the nonlinear susceptibility of the R lines of ruby and alexandrite, using a cw dye laser.

Thermal lens study of energy transfer in Yb(3+)/Tm(3+)-co-doped glasses.

Energy transfer (ET) and heat generation processes in Yb(3+)/Tm(3+)-co-doped low-silica calcium-aluminosilicate glasses were investigated using thermal lens and photoluminescence measurements. Stepwise ET processes from Yb(3+) to Tm(3+), with excitation at 0.976 mum, produced efficient emission in the mid-infrared range at around 1.

Nonlinear electronic line shape determination in Yb3+-doped phosphate glass.

Nonlinear refraction spectroscopy has been performed in Yb3+-doped phosphate glass to determinate the line shape of real and imaginary parts of n2 (n2' and n2"). The n2' spectrum presented an asymmetric feature due to the interference of resonant and nonresonant contributions, where the nonresonant term arises from the polarizability difference between excited and ground states (delta alpha). The measurements were performed in the transient regime to determine population dynamics and the pump saturation intensity at 975 nm (peak of the absorption spectrum).

Fluorescence quantum efficiency measurements in the presence of Auger upconversion by the thermal lens method.

Mode-mismatched thermal lens (TL) measurements in Cr3+-doped fluoride crystals (LiSrAIF6 and LiSrGaF6) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upconversion rate that is proportional to the excited-state population, Wup = gammaN(e), the theoretical model developed fits the experimental data well.