arXiv subjects

Patrick Georges

Publications and source records attributed to Patrick Georges.

14 recordsLinked to original sources

arXiv2026

Free-space multipass optical parametric amplifier

Scaling the efficiency of optical parametric amplifiers (OPAs) without degrading spatio-temporal pulse quality is fundamentally limited by spatio-temporal walk-off, intensity dependent gain, and back-conversion. Here, we numerically and experimentally demonstrate an OPA architecture based on a free-propagating quasi-periodic geometry that overcomes these bottlenecks. Operating within a single nonlinear crystal, the system utilizes pass-by-pass dichroic idler rejection to suppress back-conversion, a birefringent crystal for temporal resynchronization, and free-space diffraction to improve the spatial overlap along propagation. Starting from 1.9 {\mu}J 330 fs pulses at 515 nm and a continuous-wave seed at 783 nm, the generation of 0.8 {\mu}J 160 fs signal pulses at the same wave-length is obtained at a repetition rate of 500 kHz. This simple architecture achieves a 64% quantum efficiency, a 42% pump-to-signal conversion efficiency, and 80 dB of gain while maintaining excellent spatial and temporal quality, providing a scalable platform for ultrafast sources with arbitrary emission wavelengths

physics.optics↗

arXiv2020

Harnessing subcellular-resolved organ distribution of cationic copolymer-functionalized fluorescent nanodiamonds for optimal delivery of therapeutic siRNA to a xenografted tumor in mice

Diamond nanoparticles (nanodiamonds) can transport active drugs in cultured cells as well as in vivo. However, in the latter case, methods allowing to determine their bioavailability accurately are still lacking. Nanodiamond can be made fluorescent with a perfectly stable emission and a lifetime ten times longer than the one of tissue autofluorescence. Taking advantage of these properties, we present an automated quantification method of fluorescent nanodiamonds (FND) in histological sections of mouse organs and tumor, after systemic injection. We use a home-made time-delayed fluorescence microscope comprising a custom pulsed laser source synchronized on the master clock of a gated intensified array detector. This setup allows to obtain ultra-high-resolution images 120 Mpixels of whole mouse organs sections, with subcellular resolution and single-particle sensitivity. As a proof-of-principle experiment, we quantified the biodistribution and aggregation state of new cationic FNDs able to transport small interfering RNA inhibiting the oncogene responsible for Ewing sarcoma. Image analysis showed a low yield of nanodiamonds in the tumor after intravenous injection. Thus, for the in vivo efficacy assay we injected the nanomedicine into the tumor. We achieved a 28-fold inhibition of the oncogene. This method can readily be applied to other nanoemitters with $\approx$100 ns lifetime.

q-bio.TO↗

arXiv2019

CEP-stable high-energy ytterbium doped fiber amplifier

We report on the CEP stabilization of an Yb-doped fiber amplifier system delivering 30 microjoules, 100 fs pulses at 100 kHz repetition rate. A single shot, every shot, measurement of the CEP stability based on a simple f-2f interferometer is performed, yielding a CEP standard deviation of 320 mrad rms over 1 s. Long-term stability is also assessed, with 380 mrad measured over one hour. This level of performance is allowed by a hybrid architecture including a passively CEP-stabilized front-end based on difference frequency generation, and an active CEP stabilization loop for the fiber amplifier system, acting on a telecom-grade integrated LiNbO3 phase modulator. These results demonstrate the full compatibility of Yb-doped high repetition rate laser for attoscience.

physics.app-ph↗

arXiv2012

High-power diode-pumped Q-switched Er3+:YAG single-crystal fiber laser for active imaging system

We describe an efficient laser emission from a directly grown Er3+:YAG single-crystal fiber that is resonantly pumped using a continuous-wave (CW) laser diode at 1532 nm. In a longitudinal pumping, it emits 12.5 W at 1645 nm with a slope efficiency of 32%, which is the highest ever reported for a directly grown Er:YAG single-crystal fiber laser. Using an off-axis pumping scheme, CW output powers up to 7.3 W can be reached and in Q-switched operation, the laser produces 2 mJ pulses with a duration of 38 ns at the repetition rate of 1 kHz with an M^{2} factor below 1.8. To our knowledge this is the first directly grown Er3+:YAG single-crystal fiber Q-switched laser. In dual-side pumping scheme a laser emission at 1617 nm is achieved with output powers up to 5.7 W representing the highest output power ever achieved by a diode-pumped Er:YAG laser at this wavelength.

physics.optics↗

arXiv2011

High-contrast Ultrabroadband Frontend Source for High Intensity Few-Cycle Lasers

An ultrabroadband seed source for high-power, high-contrast OPCPA systems at 800 nm is presented. The source is based on post compression in a hollow-core fiber followed by crossed polarized waves (XPW) filtering and is capable of delivering 80$μ$J, 5fs, CEP-stable (0.3rad RMS) pulses with excellent spectral and temporal quality

physics.optics↗

arXiv2010

External-cavity designs for phase-coupled laser diode arrays

We describe passive phase-locking architectures based on external-cavity setups to improve the brightness of diode laser bars. Volume Bragg gratings are used to stabilize the lase line. Numerical modelling and experimental results will be presented.

physics.optics↗

arXiv2007

On thermal effects in solid state lasers: the case of ytterbium-doped materials

A review of theoretical and experimental studies of thermal effects in solid-state lasers is presented, with a special focus on diode-pumped ytterbium-doped materials. A large part of this review provides however general information applicable to any kind of solid-state laser. Our aim here is not to make a list of the techniques that have been used to minimize thermal effects, but instead to give an overview of the theoretical aspects underneath, and give a state-of-the-art of the tools at the disposal of the laser scientist to measure thermal effects. After a presentation of some general properties of Yb-doped materials, we address the issue of evaluating the temperature map in Yb-doped laser crystals, both theoretically and experimentally. This is the first step before studying the complex problem of thermal lensing (part III). We will focus on some newly discussed aspects, like the definition of the thermo-optic coefficient: we will highlight some misleading interpretations of thermal lensing experiments due to the use of the dn/dT parameter in a context where it is not relevant. Part IV will be devoted to a state-of-the-art of experimental techniques used to measure thermal lensing. Eventually, in part V, we will give some concrete examples in Yb-doped materials, where their peculiarities will be pointed out.

physics.optics↗

arXiv2007

Femtosecond laser Fourier transform absorption spectroscopy

A femtosecond mode-locked laser is used for the first time as a broadband infrared source for high resolution Fourier transform absorption spectroscopy. Demontration is made with a Cr^4+:YAG laser. The entire nu_1+nu_3 vibration-rotation band region of acetylene, observed after passing through a single pass 80-cm long cell, is simultaneously recorded between 1480 and 1600 nm, in 7.9 s with a signal to noise ratio equal to 1000. Two hot bands of the most abundant acetylene isotopologue and the n1+n3 band of the ^13C^12CH_2 are also present. The noise equivalent absorption coefficient at one second averaging is equal to 7 10^{-7} cm^{-1}.Hz^{-1/2} per spectral element.

physics.optics↗

arXiv2006

Direct and absolute temperature mapping and heat transfer measurements in diode-end-pumped Yb:YAG

We report direct and absolute temperature measurements in a diode-end-pumped Yb:YAG crystal, using a calibrated infrared camera, with a 60-$μ$m spatial resolution. The heat transfer coefficient has been measured, for the first time to our knowledge, with four different types of thermal contact (H = 0.25, 0.28, 0.9 and 2.0 for bare contact, graphite layer, indium foil and heat sink grease respectively). The dynamics of thermal effects is also presented.

physics.optics↗

arXiv2006

New 3D multipass amplifier based on Nd:YAG or Nd:YVO4 crystals

We report on new simple and efficient multipass amplifiers using prisms or corner cubes to perform several passes in different planes of incidence. This scheme provides an optimized overlap between the signal passes and the pumped volume. We investigated our amplification geometry with Nd:YAG and Nd: YVO4 crystals : the use of a low doped (0.3%) Nd:YVO4 crystal allowed better thermal behaviour and higher performances. We amplified a pulsed microlaser (110 mW of average power at 1064 nm) and obtained a diffraction-limited output beam with an average power of 5.7 W for 15 W of pump power and a small-signal gain of 56 dB in a 6-pass configuration.

physics.optics↗

arXiv2006

Picosecond laser source at 1 MHz with continuous tunability in the visible red band

We report the first demonstration to our knowledge of a continuously tunable picosecond laser operating around 1 MHz. The emission can be tuned from 640 to 685 nm and the repetition rate from 200 kHz to 1 MHz with a pulse duration of less than 200 ps. The system is based on a Nd:YVO4 passively Q-switched microchip laser providing a few tens of nJ per pulse. Two cascaded stages of amplification are then used to increase the pulse energy to several microJ . The frequency doubled radiation is then used to pump a periodically-poled-niobate-lithium (PPLN)-based optical parametric generator in an all-solid-state architecture. 20 nJ of tunable signal radiation are obtained. We also demonstrated 300-ps pulses generation in the UV (355 nm) at 1 MHz.

physics.optics↗

arXiv2006

Passively mode-locked diode-pumped Nd:YVO4 oscillator operating at ultra-low repetition rate

We demonstrate the operation of an ultra low repetition rate, high peak power, picosecond diode pumped Nd:YVO4 passively mode locked laser oscillator. Repetition rates even below 1 MHz were achieved with the use of a new design multiple-pass cavity and a semiconductor saturable absorber. Long term stable operation at 1.2 MHz, pulse duration of 16.3 ps and average output power of 470 mW corresponding to 24 KW peak power pulses is reported. This is, to our knowledge, the lowest repetition rate high peak power pulses ever generated directly from a picosecond laser resonator without cavity dumping.

physics.optics↗

arXiv2006

Passively Q-switched diode-pumped Cr4+:YAG/Nd3+:GdVO4 monolithic microchip laser

the realization of high repetition rate passively Q-switched monolithic microlaser is a challenge since a decade. To achieve this goal, we report here on the first passively Q-switched diode-pumped microchip laser based on the association of a Nd:GdVO4 crystal and a Cr4+:YAG saturable absorber. The monolithic design consists of 1 mm long 1% doped Nd:GdVO4 optically contacted on a 0.4 mm long Cr4+:YAG leading to a plano-plano cavity. A repetition rate as high as 85 kHz is achieved. The average output power is approximately 400 mW for 2.2 W of absorbed pump power and the pulse length is 1.1 ns.

physics.optics↗

arXiv2006

Single-Frequency High-Power Continuous-Wave Oscillation at 1003 nm of an Optically Pumped Semiconductor Laser

This work reports single-frequency laser oscillation at 1003.4 nm of an optically pumped external cavity semiconductor laser. By using a gain structure bonded onto a high conductivity substrate, we demonstrate both theoretically and experimentally the strong reduction of the thermal resistance of the active semiconductor medium, resulting in a high power laser emission. The spectro-temporal dynamics of the laser is also explained. Furthermore, an intracavity frequency-doubling crystal was used to obtain a stable single-mode generation of blue (501.5 nm) with an output power around 60 mW.

physics.optics↗