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.
The 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.
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 (M<sup>2</sup> < 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%)
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.
We report on an hybrid fiber/crystal ultra-short pulsed laser delivering high pulse energy and high peak power in the picosecond regime. The laser is composed of a mode-lock fiber oscillator, a pulse picker and subsequent fiber amplifiers. The last stage of the laser is a single pass Nd:YVO<sub>4</sub> solid-state amplifier. We believe that this combination of both technologies is a very promising approach for making efficient, compact and low cost lasers compatible with industrial requirements.
In this study, a polarization maintaining (PM) all-fiber laser oscillator passively mode locked at 1.03 μm is presented. The mode locking is achieved by nonlinear polarization evolution occurring along a long span of standard PM fiber (26 m) spliced between an off-axis polarizer and a Faraday rotator mirror. The influence of the total chromatic dispersion and intra-cavity spectral filtering on pulsed operation is studied. Two experimental configurations have been tested. The first configuration is an all normal dispersion cavity using a looped fibered circulator combined to a 1.5 nm filter used as an end cavity mirror. The second configuration used highly reflective chirped Fiber Bragg Grating (FBG) exhibiting different bandwidths (0.7 nm, 1.1 nm and 1.83 nm). The chromatic dispersion induced is +7.2 ps/nm for each FBG. Stable single-pulse mode locked operation has been demonstrated for each configuration. The study highlights however different mode-locking operations according to the intra-cavity spectral filtering and total chromatic dispersion of the cavity. For the first configuration, pulse duration is about 7 ps. According to the optical spectrum which has a FWHM of 2.2 nm, pulses may be compressed to subpicosecond durations with the help of a suited compressor like bulk gratings. Shortest pulses of 2.2 ps have been obtained at a repetition rate of 3.3 MHz with the second experimental configuration. To our knowledge, this is the smallest pulse duration delivered by a fully fibered mode locked laser operating at a repetition rate lower than 10 MHz without any external pulse compressor.
We present in this study a PM all-fiber laser oscillator passively mode-locked (ML) at 1.03 μm. The laser is based on
Nonlinear Polarization Evolution (NPE) in polarization maintaining (PM) fibers. In order to obtain the mode-locking
regime, a nonlinear reflective mirror including a fibered polarizer, a long fiber span and a fibered Faraday mirror (FM) is
inserted in a Fabry-Perot laser cavity.
In this work we explain the principles of operation of this original laser design that permits to generate ultrashort pulses
at low repetition (lower that 1MHz) rate with a cavity length of 100 m of fiber. In this experiment, the measured pulse
duration is about 6 ps. To our knowledge this is the first all-PM mode-locked laser based on the NPE with a cavity of
100m length fiber and a delivered pulse duration of few picosecondes.
Furthermore, the different mode-locked regimes of the laser, i.e. multi-pulse, noise-like mode-locked and single pulse,
are presented together with the ways of controlling the apparition of these regimes. When the single pulse mode-locking
regime is achieved, the laser delivers linearly polarized pulses in a very stable way.
Finally, this study includes numerical results which are obtained with the resolution of the NonLinear Schrodinger
Equations (NLSE) with the Split-Step Fourier (SSF) algorithm. This modeling has led to the understanding of the
different modes of operation of the laser. In particular, the influence of the peak power on the reflection of the nonlinear
mirror and its operation are studied.
We present a theoretical and experimental study on PM ultra-short fiber laser cavities operating at low repetition rate.
The mode-locking operation in this study always relies on SEmicondutor Saturable Absorber Mirror (SESAM) and intracavity
spectral filtering. Several experimental configurations have been tested and modeled. Repetition rates as low as
7.7 MHz with sub-picosecond pulse duration have been obtained. A longer cavity has also been modeled in order to
determine if stable ultra-short pulsed operation would also possible at lower repetition rates.
We present a thermoreflectance-based metrology concept applied to compound semiconductor thin films off-line
characterization in the solar cells scribing process. The presented thermoreflectance setup has been used to evaluate the
thermal diffusivity of thin CdTe films and to measure eventual changes in the thermal properties of 5 μm CdTe films
ablated by nano and picosecond laser pulses. The temperature response of the CdTe thin film to the nanosecond heating
pulse has been numerically investigated using the finite-difference time-domain (FDTD) method. The computational and
experimental results have been compared.
We report on a high-power ultra-short fiber laser for thin film solar cells micromachining. The laser is based on Chirped
Pulse Amplification (CPA) scheme. The pulses are stretched to hundreds of picoseconds prior to amplification and can
be compressed down to picosecond at high energy. The repetition rate is adjustable from 100 kHz to 1 MHz and the
optical average output power is close to 13 W (before compression). The whole setup is fully fibred, except the
compressor achieved with bulk gratings, resulting on a compact and reliable solution for cold ablation.
We report an actively Q-switched Ytterbium-doped all-in-fibre laser delivering 10ns pulses with high repetition rate (from 100kHz to 1MHz). The laser operation has been validated at three different wavelengths (1040, 1050 and 1064nm). The laser can deliver up to 20Watts average power with an high beam quality (M<sup>2</sup> = 1).
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.