R. Moncorgé

Growth, spectroscopic characterization, and laser performance of Nd:LuVO_4, a new infrared laser material that is suitable for diode pumping

The spectroscopic properties and laser operation of a new neodymium-doped vanadate crystal, Nd:LuVO4, grown by the flux technique are reported. Polarized absorption and emission spectra were recorded at low and room temperatures, excited-state absorption was measured near 1060 and 1340 nm, and laser emission at 1066 nm was obtained after pumping near 809 and 880 nm.

High power diode-pumped Yb3+:CaF2 femtosecond laser

We report what is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb3+:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at. % Yb3+ -doped sample and prisms for dispersion compensation we obtained pulses as short as 150 fs, with 880 mW of average power and up to 1.4-W average output power, with a pulse duration of 220 fs, centered at 1049 nm. The laser wavelength could be tuned from 1040 to 1053 nm in the femtosecond regime. Using chirped mirrors for dispersion compensation, the oscillator provided up to 1.74 W of average power, with a pulse duration of 230 fs, corresponding to a pulse energy of 20 nJ and a peak power of 85 kW.

Nd doped crystals for medical laser applications

Abstract Some secondary laser lines of the Nd3+ ion in crystals like YAG and YAP are now being used or re-examined very seriously for several purposes. So, after a brief description of the main parameters characterizing the general optical and thermomechanical properties of these ‘well-known’ materials, a discussion is developed here concerning the interest of these particular lines for specific medical applications and a comparison is made with other existing solutions. Then, the operational characteristics (laser performance, thermal behaviour) and the effects (laser-tissue effects) of some of the laser systems we have studied for these applications, already commercially available systems as well as prototypes, are presented. In the end, the potential of Nd:KGW, another emerging Nd doped laser material, is analysed.

Compact diode-pumped passively Q-switched tunable Er-Yb double-clad fiber laser

Efficient repetitive passive Q switching of a cladding-pumped Er-Yb fiber laser has been demonstrated by use of an external-cavity configuration containing a Co(2+): ZnS crystal as a saturable absorber. Energies of as much as 60muJ in pulses of durations as short as 3.5 ns (FWHM), corresponding to a peak power of >10kW, have been generated, and the maximum slope efficiency with respect to the absorbed pump power was 13%. Using a bulk diffraction grating in the Littrow configuration to provide wavelength-selective feedback, we tuned the passively Q -switched fiber laser over 31 nm from 1532 to 1563 nm. The prospects for further improvement in performance are discussed.

Luminescence properties of Y2O3 single crystals doped with Pr3+ or Tm3+ and codoped with Yb3+, Tb3+ or Ho3+ ions

Abstract We have recorded fluorescence spectra and measured fluorescence lifetimes in yttria (Y2O3) single crystals doped with only Tm3+ or Pr3+ ions or codoped with Yb3+, Tb3+ or Ho3+ ions. The crystals were grown in the form of crystal fibers by using the laser heated pedestal growth (LHPG) technique. The codoped (Yb, Tm) and (Yb, Pr) crystals were studied for their potential as upconversion laser systems. Evidence is shown of cooperative and multi-step energy transfers giving rise to very efficient visible emissions after pulsed infrared excitation. As to the codoped (Tm, Ho) and (Tm, Tb) crystals, they are studied to examine the effect of the codopants on the infrared emission properties of the Tm3+ ions. Indeed, we found a very attractive fluorescence around the eye-safe wavelength of 1.55 μm which corresponds to a 3H4→3F4 transition of Tm3+. This transition occurs with a large enough stimulated emission cross section to be practical for laser application, and the Tb3+ or the Ho3+ ions are introduced to reduce the problem of bottlenecking due to a lower laser state lifetime longer than that of the upper state.

High power tunable diode-pumped Yb3+:CaF2 laser

Results of diode-pumped cw laser operation of an Yb3+:CaF2 single crystal are reported for what is to our knowledge the first time. With a 5-at.% Yb3+ -doped sample we obtained 5.8-W output power at 1053 nm for 15 W of incident power at 980 nm. The laser wavelength could be tuned from 1018 to 1072 nm, and a small-signal gain as high as 1.8 was achieved, showing the great potential of Yb3+:CaF2 as an amplifier medium for femtosecond pulses.

On Yb:CaF2 and Yb:SrF2 : Review of spectroscopic and thermal properties and their impact on femtosecond and high power laser performance

We present an overview of laser results we obtained with Yb-doped calcium fluoride and its isotype strontium fluoride. In order to study the laser performance in femtosecond and high power regimes, spectral and thermal properties are first discussed including the potential of these crystals at room and cryogenic temperatures. Experimental demonstrations of high-power and ultrashort pulse oscillators and amplifiers are presented and analyzed.

Excited state absorption and passive Q-switch performance of Co2+ doped oxide crystals

Abstract Excited state absorption spectra (ESA) of the LiGa 5 O 8 (LGO), MgAl 2 O 4 (MALO) and LaMgAl 11 O 19 (LMA) crystals doped with the tetrahedral Co 2+ ion were studied under excitation at the 4 A 2 → 4 T 1 ( 4 F) transition. The ESA band was observed near 710–740 nm and assigned to the 4 T 2 → 4 T 1 ( 4 P) transition of the Co 2+ ion. The lifetime of the 4 T 2 level of Co 2+ ion at room temperature was estimated to be 130–350 ns depending on the crystal host. Absorption saturation measurements were performed and ground state and excited state absorption cross sections were estimated at the wavelengths of 1.34 and 1.54 μm. The crystals studied were used to Q-switch flashlamp-pumped 1.34 μm Nd 3+ :YAlO 3 and 1.54 μm Er 3+ :glass lasers. Passive Q-switching of a diode pumped 1.35 μm Nd:KGd(WO 4 ) 2 laser was demonstrated using Co 2+ :MALO saturable absorber.

Diode-pumped Pr(3+):KY(3)F(10) red laser.

We report the first observation to our knowledge of room-temperature continuous-wave laser operation of a Pr(3+):KY(3)F(10) single crystal at 644.5 nm, pumped by a blue GaN laser diode emitting at 446 nm. With a 2.5% transmission output coupler and a nonoptimized optical cavity, an output power of 39 mW was obtained at 644.5 nm with a laser threshold of 125 mW and a differential slope efficiency of 23%.

Visible laser operation of Pr3+-doped fluoride crystals pumped by a 469 nm blue laser

We report continuous-wave (CW) laser operation of Pr3+-doped LiLuY4, LiYF4 and KY3F10 single crystals in the Red, Orange and Green spectral regions by using a new pumping scheme. The pump source is an especially developed compact, slightly tunable and intracavity frequency-doubled diode-pumped Nd:YAG laser delivering a CW output power of 0.9W at 469.12 nm. At this pump wavelength, efficient room temperature laser emissions corresponding to the 3P0→3F2, 3P0→3H6 and 3P1→3H5 Pr3+ transitions are observed. While a maximum slope efficiency of 45% is obtained in the red with Pr:LiYF4, the demonstration is made for the first time of the orange laser operation of Pr:KY3F10 at about 610 nm.