High-power 2.3†µm Tm:YLF laser with intracavity upconversion pumping by a Nd:ASL laser at 1051†nm.

A Tm:LiYF4 laser operating on the 3H4 → 3H5 transition is embedded in a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05 µm. This leads to a record-high output power at 2.3 µm for any bulk thulium laser pumped by an upconversion process. The continuous-wave Tm:LiYF4 laser delivers 1.81 W at 2.3 µm for 32 W of laser-diode pump power, making this kind of pumping competitive with direct diode pumping. The intracavity pumping process allows for counteracting the low absorption inherent to upconversion pumping and to dispatch the thermal loads on two separate laser crystals. The proposed laser architecture also features a relatively weak heating of the Tm:LiYF4 crystal and an increased tolerance to Tm3+ absorption. This laser design opens a new paradigm that holds great promise for high-power 2.3-µm solid-state lasers based on thulium ions.

Ce:LYSO, from scintillator to solid-state lighting as a blue luminescent concentrator.

Cerium-doped lutetium-yttrium oxyorthosilicate (Ce:LYSO) is a well-known single crystal scintillator used in medical imaging and security scanners. Recent development of high power UV LED, matching its absorption band, questions the possibility to use Ce:LYSO in a new way: as LED-pumped solid-state light source. Since Ce:LYSO is available in large size crystals, we investigate its potential as a luminescent concentrator. This paper reports an extensive study of the performance in close relation to the spectroscopic properties of this crystal. It gives the reasons why the Ce:LYSO crystal tested in this study is less efficient than Ce:YAG for luminescent concentration: limited quantum efficiency and high losses coming from self-absorption and from excited-state absorption are playing key roles. However, we demonstrate that a Ce:LYSO luminescent concentrator is an innovative source for solid-state lighting. Pumped by a peak power of 3400 W in quasi-continuous wave regime (40 µs, 10 Hz), a rectangular (1 × 22 × 105 mm3) Ce:LYSO crystal delivers a broadband spectrum (60 nm FWHM) centered at 430 nm. At full output aperture (20 × 1 mm2), it emits a peak power of 116 W. On a squared output surface (1 × 1 mm2) it emits 16 W corresponding to a brightness of 509 W cm-2 sr-1. This combination of spectrum power and brightness is higher than blue LEDs and opens perspectives for Ce:LYSO in the field of illumination namely for imaging.

Laser performance of high optical quality 4 at.% Pr3+: Sr0.7La0.3Mg0.3Al11.7O19 (Pr:ASL) single crystals.

In this work, we present the visible laser performance of improved optical quality Czochralski-grown 4 at.% Pr3+-doped Sr0.7La0.3Mg0.3Al11.7O19 (Pr:ASL) single crystals in the deep red (726 nm), the red (645 nm) and the orange (620 nm) range using two different pumping sources. Using a high beam quality frequency doubled Ti:sapphire laser with 1 W output power as pump source, deep red laser emission was reached at a wavelength of 726 nm with 40 mW of output power and a laser threshold of 86 mW. The corresponding slope efficiency was 9%. At 645 nm in the red, up to 41 mW of laser output power were obtained with 15% slope efficiency. Moreover, orange laser emission at 620 nm was demonstrated with 5 mW output power and 4.4% slope efficiency. Using a 10 W multi-diode module as pumping source allowed to obtain the highest output power of a red and deep-red diode-pumped Pr:ASL laser to date. The respective output powers at 726 and 645 nm reached 206 mW and 90 mW.

High peak-power near-MW laser pulses by third harmonic generation at 355†nm in Ca5(BO3)3F nonlinear single crystals.

In this work, the performance of Ca5(BO3)3F (CBF) single crystals was investigated for the third harmonic generation at 355 nm. A high energy conversion efficiency of 16.9% at 355 nm was reached using a two-conversion-stage setup. First, using a high peak power, passively Q-switched Nd3+:YAG/Cr4+:YAG microlaser based gain aperture in micro-MOPA, the second harmonic at 532 nm was achieved with lithium triborate (LBO) crystal, reaching 1.35 MW peak power. On a second step, laser pulses at 355 nm were generated using a 5 mm-long CBF crystal growth by TSSG method with energy, pulse duration and peak power of 479 µJ, 568 ps and 0.843 MW, respectively. These results are currently the highest reported for CBF material.

Temperature stable operation of YCOB crystal for giant-pulse green microlaser.

In this work the performance of two yttrium calcium oxyborate (YCOB) crystals made by Czochralski and Bridgman growth process was measured. By using high peak power, passively Q-switched Nd3+:YAG/Cr4+:YAG microlaser, high conversion second harmonic generation efficiency were obtained. Laser pulses at 532 nm with 1.14 mJ energy and 223 ps duration were obtained with a 15-mm long YCOB crystal that was grown by Bridgman method. The conversion efficiency was 70.2%, comparable with the conversion efficiency of 72.8% that was achieved with 10-mm long lithium triborate (LBO) nonlinear crystal. Also, for the first time, experimental data on temperature tuning in type I YCOB crystal was measured with linear slope in 200°C temperature range equal to -0.057%/°C and -0.064%/°C for the Czochralski and Bridgman grown crystals, respectively. Such YCOB nonlinear crystal can become a serious option for developing laser sources with high-peak power at high repetition rate that can operate in harsh environment.

Dielectric frame, Sellmeier equations, and phase-matching properties of the monoclinic acentric crystal GdCa4O(BO3)3.

We directly measured the phase-matching properties of the biaxial GdCa4O(BO3)3 (GdCOB) crystal using the sphere method. We studied second-harmonic generation and difference frequency generation in two principal planes of the crystal. All these data allowed us to refine the Sellmeier equations of the three principal refractive indices. These equations are valid over the entire transparency range of GdCOB and then could be used to calculate the tuning curves of infrared optical parametric generation.

Rise in power of Yb:YCOB for green light generation by self-frequency doubling.

Spectroscopic properties and self-frequency-doubling laser performance are presented for Yb:YCa4O(BO3)3 (Yb:YCOB) crystals oriented for type I second-harmonic generation in the ZX plane. In a plane-concave cavity 10 cm long, up to 330 mW of green light (544.5 nm) is obtained for 14.7 W of laser diode incident pump power. Broad emission bands and weak anisotropy in the 1060-1100 nm range between the two eigenstates of polarization may explain the instability of the self-frequency-doubled output power.

240 kW peak power at 266 nm in nonlinear YAl3(BO3)4 single crystal.

We report the fourth harmonic generation at 266 nm using a type I YAl3(BO3)4 (YAB) single crystal from a Q-switch microchip laser Nd:YAG/Cr4⁺:YAG frequency doubled with a LiB3O5 (LBO) crystal. 240 kW peak power at 266 nm corresponding to a mean conversion efficiency of 12.2% from 532 to 266 nm has been obtained with a 2.94 mm thick YAB crystal. The influences of optical homogeneity and absorption on the conversion efficiency are discussed.

Magic mode switching in Yb:CaGdAlO4 laser under high pump power.

We present unique spatial-mode switching in a cw Yb:CALGO laser when pumped at a multihundred-watts power level. It permits us to automatically stabilize to a TEM(00) mode from a highly spatial multimode regime. This stabilization is achievable thanks to polarization-mode switching allowed by the particular spectroscopic and thermal properties of Yb:CALGO crystal. This atypical and unexpected behavior is studied in detail in this Letter and explained by analysis of the thermo-optical coefficients for CALGO.

Sub-100-fs Yb:CALGO nonlinear regenerative amplifier.

We report on the first diode-pumped Yb:CaGdAlO4 regenerative amplifier in the sub-100-fs regime. It generates pulses at a central wavelength of 1047 nm with up to 24 µJ energy (after compression) at a repetition rate of 50 kHz. The measured pulse duration is 97 fs, with a spectral bandwidth of 19 nm. We describe in detail how nonlinear effects are optimally used to compensate gain narrowing in order to overcome the 100 fs barrier.

Nonlinear optical properties of Ca5(BO3)3F crystal.

A high quality Ca(5)(BO(3))(3)F (CBF) crystal, grown by flux method, was investigated for its non linear optical properties. This material is non hygroscopic and possesses a moderate birefringence suitable for UV light generation. On the basis of its refractive index dispersion curves, it is inferred that CBF has great potential applications as non linear optical material, notably for UV light generation at 355 and 266 nm. In order to characterize its non linear optical properties, CBF samples were first cut and oriented in phase matching conditions for second harmonic generation of 1064 nm. Experimental results demonstrate that CBF has the moderate NLO coefficients. The optical conversion efficiency from 1064 nm to 532 nm was investigated for the first time: up to 54% were achieved. Non linear d(eff) coefficients were also estimated as well as the external angular acceptance bandwidth of SHG at 1064 nm.

Diode-pumped Nd:YAG laser emitting at 899 nm and below.

We present what is, to the best of our knowledge, the first diode-pumped Nd:YAG laser emitting at 899 nm and below, based on the (4)F(3/2) - (4)I(9/2) transition, generally used for a 946 nm emission. A power of 630 mW at 899 nm has been achieved in cw operation and 16 mW at 884 nm with a fiber-coupled laser diode emitting 9 W at 808 nm. Intracavity second-harmonic generation in cw mode has also been demonstrated with a power of 100 mW at 450 nm by using a LiB(3)O(5) nonlinear crystal.

First measurement of the nonlinear coefficient for Gd(1-X)Lu(X)Ca(4)O(BO(3))(3) and Gd(1-X)Sc(X)Ca(4)O(BO(3))(3) crystals.

The effective nonlinear coefficient and temperature acceptance bandwidth of three Lu and Sc co-doped GdCa(4)O(BO(3))(3) type nonlinear crystals were measured. NCPM for SHG in to the blue-UV spectral region can be obtained by controlling the co-dopant concentration. Measurements were based on intra-cavity SHG of a CW Ti:Sapphire laser, and the effective nonlinear coefficients were found to be in the range of 0.5 to 0.6 pm/V for the three crystals used. The FWHM temperature acceptance bandwidth was measured to be more than 35 degrees C using a 6 mm long Gd(0.871)Lu(0.129)Ca(4)O(BO(3))(3) crystal. A maximum of 115 mW at 407.3 nm in a single direction was measured using a 6.5 mm long Gd0.96Sc0.04Ca(4)O(BO(3))(3) crystal.