Yves Hernandez

High-average-power second-harmonic generation from periodically poled silica fibers

The generation of 236 mW of second-harmonic power in a 32-cm-long periodically poled silica fiber, corresponding to an average conversion efficiency of 15.2+/-0.5%, is reported. This represents the highest normalized second-harmonic conversion and the highest average second-harmonic power ever reported for a periodically poled silica fiber, to our knowledge. The enhancement is attributed to an improved design of the specialty twin-hole fiber and the extension of the nonlinear interaction length.

All-fiber frequency-doubled visible laser

All-fiber ns-pulsed visible laser at λ=521u2009u2009nm is realized by frequency doubling an Yb-doped fiber laser with a periodically poled silica fiber. A 50-mW second-harmonic (SH) output power is produced that is over 6-orders of magnitude greater than previous results obtained with poled fibers in the visible spectral range. The normalized conversion efficiency of 0.3%/W is to date the largest demonstrated with poled fiber technology. Furthermore, 21% conversion efficiency is achieved for the doubling of 8-ps pulses from a neodymium-doped yttrium vanadate solid-state laser. The advances are made possible by the precision and flexibility offered by using the continuous periodic UV erasure, as opposite to photolithographic methods, for the fabrication of over 20-cm-long χ(2)-gratings for quasi-phase matched SH generation.

All Fibre High repetition rate, High Power Picosecond Laser and UV generation

We report on a 93W, 1.1µJ, 83MHz, 35ps MOPA fibre laser based on an Yb mode-locked fibre oscillator and a rod-type LMA amplifier. This configuration can generate up to 20W at 343nm and we demonstrated over 2W at 257nm.

236mW average second-harmonic power generated from periodically poled silica fibres

Thermally poled silica fibres are an attractive all-fibre solution to frequency conversion of high power fibre lasers. In comparison to nonlinear crystals, they offer inherently lower insertion losses, higher optical damage threshold, greater stability and ruggedness intrinsic to all-fibre solutions. Moreover, the relatively low second-order-nonlinearity (0.1–0.2pm/V) can be compensated by extending the length of the periodically poled fibre.

Single-Mode Ring Fiber Laser with Longitudinal Mach-Zehnder Mode Filter

A novel single-longitudinal-mode erbium doped ring fiber laser with Mach-Zehnder mode filter is proposed. The output power is 15 dBm at 1547 nm with a 50-dB side-mode suppression ratio and a 13-kHz linewidth.

High energy, femtosecond fiber laser source at 1750 nm for 3-photon microscopy (Conference Presentation)

We present an ultrafast fiber laser system at a central wavelength of 1750 nm for imaging applications, in particular 3-photon microscopy. It generates an output pulse train with an adjustable repetition rate ranging from 1 MHz to 21 MHz. After temporal compression the pulse duration is 220 fs and the maximum achieved pulse energy is 20 nJ.nThe laser system consists of a polarization maintaining (PM) Erbium-doped fiber oscillator which emits a stable output pulse train at a fixed repetition rate of 42 MHz. The oscillator generates soliton pulses centered at a wavelength of 1560 nm and a spectral width of 7 nm. Mode-locking is initiated and stabilized by a semiconductor saturable absorber mirror. The output pulses are picked in a PM fiber coupled acousto-optic modulator to an adjustable repetition rate of 1 – 21 MHz. A consecutive Erbium-doped PM fiber amplifier (EDFA) boosts the energy of the soliton pulses from pJ to nJ level. The directly emitted pulses have a duration of 2 ps which can be compressed to a pulse duration of 115 fs by using a passive standard fiber. The uncompressed pulses are soliton-self-frequency shifted by Raman scattering to wavelengths longer than 1700 nm in 7 m of passive PM1550 fiber at a pulse energy of 1.1 nJ. The central wavelength can be adjusted by the pump power of the EDFA. To boost the pulse energy of the wavelength shifted pulses, the Raman stage is followed by a single-clad Thulium-doped fiber (TDF) amplifier. It consists of a 1560/1750 nm wavelength division multiplexer (WDM) and 0.9 m of TDF. To diminish nonlinear effects during amplification, the pulses are stretched with 25 m of normal dispersion fiber (NDF) inserted between the WDM and the TDF. Although on the very short wavelength amplification band, the pulses are amplified up to more than 40 nJ of pulse energy at an injected pump power of 4.1 W. After the fiber amplifier, the pulses are coupled out and propagate through a spectral filter, a triplet of l/4, l/2, and l/4 waveplates, an isolator, and a grating compressor. As the WDM, NDF, and TDF are not PM, the polarization state has to be readjusted to linear with the waveplates before entering the isolator. The added group delay dispersion of 2.17 ps2 by the NDF is compensated in a free space standard grating compressor built of two 600 lines/mm gratings. The transmission of the grating compressor is 60 %. To achieve optimum compression to a pulse duration of 220 fs at a pulse energy of 20 nJ, the compressor in combination with spectral filtering around 1750 nm has to be carefully adjusted. The maximum output pulse energy of 20 nJ is constant ranging from 1 MHz to 7 MHz, but is reduced at higher repetition rates down to 8.7 nJ. The output pulse duration is nearly constant at 220 fs for all repetition rates. Further amplification of the pulses is currently under investigation. This system will be used in future for the application of 3-photon microscopy.

High-power picosecond fiber-based laser operating at 515 nm

We have developed a fiber-based laser source operating at 515 nm. The experimental setup is composed of a 1030 nm picosecond fiber laser, a Volume Bragg Grating (VBG) based compressor, and a Second Harmonic Generation (SHG) module. The 1030 nm picosecond fiber laser is made with an ANDi mode-lock all-fiber oscillator using a tilted Fiber Bragg Grating (FBG) for spectral filtering. A bandpass filter centered at 1030 nm permits to reduce the bandwidth of the laser to 1.5 nm. A Chirped Fiber Bragg Grating (C-FBG) based stretcher increases the pulse duration to about 90 ps for avoiding nonlinear effects during amplification. A fiber pre-amplifier followed by a double-clad 15 µm core LMA fiber amplifier pumped with a 27 W multimode diode are subsequently used. The total available power at 1030 nm is 14 Watts. SHG is achieved with a type I non-critical phase-matching (NCPM), 15 mm long, Lithium Triborate (LBO) crystal. The 515 nm signal is near diffraction limit (M2 < 1.2). The emitted average output power is 5.8 W, the pulse duration is 2.1 ps and the repetition rate is 89 MHz (SHG efficiency is 45%)

Two photon microscopy with a 1064 nm femtosecond fiber laser

We developed a compact femtosecond fiber laser operating at 1064 nm. The laser delivers 80 fs pulses at a repetition of 43 MHz and average power of 1 Watt. It has been used in a two photon microscope for imaging a rabbit bone sample.

Impact of pumping configuration on all-fibered femtosecond chirped pulse amplification

We experimentally compared the co- and counter-propagative pumping scheme for the amplification of ultra-short optical pulses. According to pumping direction we show that optical pulses with a duration of 75 fs and 100mW of average output power can be obtained for co-propagative pumping, while pulse duration is never shorter than 400 fs for the counter-propagative case. We show that the impact of non-linear effects on pulse propagation is different for the two pumping configurations. We assume that Self Phase Modulation (SPM) is the main effect in the copropagative case, whereas the impact of Stimulated Raman Scattering is bigger for the counter-propagative case.