Sylvain Girard

Experimental and theoretical investigation of the 4fn↔4fn-15d transitions in YPO4:Pr3+ and YPO4:Pr3+, Ce3+

Excited state absorption spectra from the 4f2 levels of Pr3+ in YPO4 to 4f5d were measured at 293 and 77 K using a pulsed pump-probe technique. The spectra from the 1D2 manifold were recorded by employing a continuous wave probe, whilst those from the 3PJ-1I6 states were recorded by using for the first time a pulsed probe. These experimental results are compared with the numerical predictions of a full calculation of the 4f5d levels and the agreement is found to be good. A detailed study of the UV luminescence properties of the Pr3+ and the Ce3+ ions in the YPO4 host crystal, including the energy transfer between these two ions, is also reported. Fluorescence spectra and decay curves from the lower excited-state levels of the 4f5d and 5d electronic configurations of the Pr3+ and Ce3+ ions, respectively, were measured both at 293 and 77 K. The Pr3+→Ce3+ energy transfer efficiency was evaluated. Further considerations about the possibility to obtain laser emission based on the 5d→4f optical transition seem to indicate that this material is probably not a very good candidate to build a UV tunable laser because of a relatively short lifetime of the emitting level corresponding to a reduced quantum efficiency.

Beneficial effect of Lu3+ and Yb3+ ions in UV laser materials

Abstract Several Lu3+- and Y3+-based oxide and fluoride single crystals with isomorphic structures and doped with Ce3+ (or Pr3+) or codoped with Yb3+ ions have been grown and studied to show the beneficial effects of the Lu3+ and Yb3+ ions on their broad-band UV luminescence properties. Time-resolved color center absorption measurements clearly show the reduction of the usually observed UV laser pump-induced optical losses and thus confirm the previous gain and laser results obtained in these materials. Some preliminary interpretations of the involved mechanisms are advanced.

Accurate efficiency evaluation of energy-transfer processes in phosphosilicate Er3+-Yb3+-codoped fibers

A new approach for the prediction of energy-transfer efficiencies in codoped Er-Yb double-clad fiber (EYDCF) is presented. Ab initio calculations have been performed on the basis of migration-assisted energy-transfer models. The two main Yb energy-transfer parameter that is needed in all modelings based on rate equations can be calculated by use of a simple relation. Our approach also permits the prediction of the laser efficiency of EYDCFs, and a comparison of measured and calculated maximum laser slope efficiency shows a good agreement.

4f2 to 4f5d excited state absorption in Pr3+:YAlO3

Excited-state absorption spectra, from the 3PJ -1I6 or 1D2 manifold to 4f5d levels, recorded in the 23 000-42 000 cm 1 range and calibrated in units of cross sections, are reported and discussed in the case of Pr 3+ -doped YAlO3. The 4f5d! 4f 2 Pr 3+ emission between 30 000 and 44 000 cm 1 is then observed, showing the possibility of UV laser operation following two-step excitation pumping using near-UV-visible pump photons.

Absolute excited state absorption cross section measurements in Er3+:LiYF4 for laser applications around 2.8 µm and 551 nm

Using a pump-probe technique, absolute excited state absorption cross sections are measured in various Er3+ doped laser crystals in a wavelength domain extending from 0.53 to 2.9 µm. The gain cross section around 2.8 µm and the population ratio between the involved levels 4I11/2 and 4I13/2 are measured for different Er3+ concentrations and pumping wavelengths. The cross sections for the transitions involved in the upconversion pumping processes of the characteristic green emission of Er:LiYF4 are also estimated and discussed. A comparison is made between these results and those obtained semi-theoretically by using the Judd-Ofelt formalism.

20 W continuous-wave cladding-pumped Nd-doped fiber laser at 910 nm

We demonstrate a double-clad fiber laser operating at 910 nm with a record power of 20 W. Laser emission on the three-level scheme is enabled by the combination of a small inner cladding-to-core diameter ratio and a high brightness pump source at 808 nm. A laser conversion efficiency as high as 44% was achieved in CW operating regime by using resonant fiber Bragg reflectors at 910 nm that prevent the lasing at the 1060 nm competing wavelength. Furthermore, in a master oscillator power-amplifier scheme, an amplified power of 14.8 W was achieved at 914 nm in the same fiber.

Generation of 520 mW pulsed blue light by frequency doubling of an all-fiberized 978 nm Yb-doped fiber laser source

Pulsed blue light at 489 nm has been generated by second-harmonic-generation of a nanosecond pulsed master-oscillator power amplifier system based on a short Yb(3+) doped single-mode fiber amplifier at 978 nm and an external-cavity diode laser as seed source. The Yb(3+)-doped fiber was core-pumped by a W type Nd(3+) doped double-clad fiber laser operating on the transition near 930 nm ((4)F(3/2)→(4)I(9/2)). 520 mW of average power was generated at 489 nm using a periodically poled MgO:LiNbO(3), corresponding to a conversion efficiency of 34%.

Serrodyne optical frequency shifting for heterodyne self-mixing in a distributed-feedback fiber laser

We describe an all-fiberized coherent detection system at 1.55 microm using heterodyne self-mixing modulation in a distributed-feedback fiber laser. Frequency shifting of the optical feedback is based on serrodyne phase modulation with an integrated electro-optic modulator, which is a significant advance in the simplification of the self-mixing detection scheme for class B lasers. Accurate measurement of the optical phase difference between the laser electric field and the backscattered electric field demonstrates nanometric displacement detection on noncooperative targets.

High-peak-power nanosecond pulse generation by stimulated Brillouin scattering pulse compression in a seeded Yb-doped fiber amplifier

We demonstrate the generation of nanosecond and multikilowatt peak-power pulses in a double-clad Yb-doped fiber amplifier seeded by a spectrally narrowed gain-switched laser diode. Injected pulses with 100 ns duration were simultaneously compressed and amplified by the combination of high amplifier gain and stimulated Brillouin scattering. A maximum peak power of 20 kW has been obtained, corresponding to a single-pass gain of +57 dB in terms of peak power. Part of this output signal was also converted into IR continuum light by splicing a length of single-mode fiber at the end of the fiber amplifier.

Generation of picosecond blue light pulses at 464 nm by frequency doubling an Nd-doped fiber based Master Oscillator Power Amplifier

We demonstrate 308 mW of single-mode laser emission at 464 nm from a frequency doubled picosecond fiber based Master Oscillator Power Amplifier (MOPA). The laser system consisted of a gain-switched and spectrally narrowed Fabry-Perot laser diode emitting at 928 nm, which was amplified in a two-stage amplifier based on W-type double-clad Nd-doped fibers. Output pulses with a duration of 90 ps at a repetition rate of 41 MHz were frequency-doubled in a periodically poled MgO-doped Congruent Lithium Niobate. A conversion efficiency of 14.8% was achieved in single-pass configuration.