Julien Didierjean - Academia.edu (original) (raw)

Papers by Julien Didierjean

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT form only given. Direct resonant pumping of Er:YAG is a laser configuration studied for ... more ABSTRACT form only given. Direct resonant pumping of Er:YAG is a laser configuration studied for compact eye-safe emitters which applications require kilometer range propagation in the atmosphere, like active imaging, Lidar and wind mapping. The laser emission of these cavities naturally occurs at 1645 nm. But a methane absorption line exists at this wavelength. One way to increase the range of the emitter is to use the 1617 nm emission line which is free of absorption. Recent researches gave nice results in active Q-switched regime at 1645 nm [1] and at 1617 nm [2]. But some applications require a compact, efficient and simple setup with mJ level pulse energy. Our recent work focused on passively Q-switching Er:YAG cavity with direct resonant fiber-coupled diode pumping.A 750 μm diameter 30 mm long Er:YAG single crystal fiber with a doping concentration of 0.5 % is inserted in a Taranis module from Fibercryst for efficient cooling and used as gain medium (Fig. 1 left). It was anti-reflection coated on both ends and actively cooled at 12°C. The pump light is provided by a fiber-coupled laser diode with a 400 μm core diameter and a numerical aperture of 0.22, delivering up to 40 W at 1532 nm. Its spectrum is narrowed by an internal grating, down to 1 nm approximately. The beam is collimated by a 40 mm focal length doublet and then focused a few millimeter inside the Er:YAG crystal thanks to another 40 mm focal length doublet. With this setup, we estimate that the pump beam undergoes between 2 and 3 reflections in the single crystal fiber, allowing a higher population inversion and a better spatial overlap between the pump and the laser signal than in standard rods. This higher population inversion along the gain medium favors the emission of the 1617 nm line. In passively Q-switched mode, a Cr:ZnSe saturable absorber with initial transmission of 85 % led to 330 μJ pulse energy, 61 ns pulse duration at a repetition rate of 1460 Hz. A 80- % initial transmission Cr:ZnSe sample led to 510 μJ energy pulses, 41 ns pulse duration at a repetition rate of 820 Hz. From 34 W to 40 W of pump power, no variation of pulse durations has been observed. The sudden wavelength shift from 1645 nm to 1617 nm has already been observed in [4], and comes from the high losses introduced inside the cavity. In addition, the slightly higher Cr:ZnSe absorption at 1645 nm compared to 1617 nm contributes to the wavelength selection. This wavelength shift happens whatever the incident pump power. A numerical model of this cavity has been developped, including pump propagation inside the crystal with ray tracing, temporal evolution of the population inversion, active and passive Q-switch regime, and thermal effects, based on previous work for actively Q-switched four-levels lasers [4]. Comparison of experimental results with numerical simulations will be presented. This is the first reported passively Q-switched diode-pumped Er:YAG laser operating on the 4I13/2 → 4I15/2 transition.

Journal of the Optical Society of America B, 2014

ABSTRACT We carried out an experimental study of an Er:YAG laser that is passively Q-switched by ... more ABSTRACT We carried out an experimental study of an Er:YAG laser that is passively Q-switched by Cr:ZnSe saturable absorbers and pumped at 1470 nm by a 14 W laser diode. The 1617 nm emission is selected by an appropriate combination of transmissions of the saturable absorber and of the output coupler. With an accurate comparison between actively Q-switched and passively Q-switched operations and with Cr:ZnSe transmission measurements, we demonstrated by experiments and by simulations that the output energy is strongly dependent on the Cr:ZnSe temperature. With a better cooling of the Cr:ZnSe crystal heated by residual pump and signal absorption, the energy per pulse can be doubled, from 110 to 220 μJ, at a repetition rate of 800 Hz.

... Thermo-chemical strengthening of Nd:YAG laser rods. Author(s): Revital Feldman; Yehoshua Shim... more ... Thermo-chemical strengthening of Nd:YAG laser rods. Author(s): Revital Feldman; Yehoshua Shimony; Steven Jackel; Izhak Levy; Yuval Golan. High power Nd:YAG laser rods may easily exceed their fracture strength as a result of thermally induced tensile stress. ...

We present laser operation of 450 μm diameter Er:YAG single crystal fiber pumped at 1470 nm. Pump... more We present laser operation of 450 μm diameter Er:YAG single crystal fiber pumped at 1470 nm. Pump beam confinement leads to low threshold, direct emission at 1617 nm and significant efficiency in passive Q-switching.

We present an unique spatial mode switching in Yb:CALGO laser under high-power-pumping. It permit... more We present an unique spatial mode switching in Yb:CALGO laser under high-power-pumping. It permits to automatically stabilize to a TEM00 mode from highly spatial-multimode regime. This atypical behavior is studied and explained in this paper.

CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009

ABSTRACT We present the demonstration of high average power laser emission in CW and Q-switched r... more ABSTRACT We present the demonstration of high average power laser emission in CW and Q-switched regime from a directly grown Yb:YAG crystal fiber. We designed the gain medium by the use of thermal dependant numerical simulations by taking into account the absorption saturation effects due to the quasi-three level behaviour of the Yb3+ transition. The crystal fiber is longitudinally pumped by a fiber-coupled laser diode with a maximum output power of 200 W at 940 nm.

Solid State Lasers XXIII: Technology and Devices, 2014

ABSTRACT We present some anisotropy properties of the Yb:CALGO with a spatial mode switching when... more ABSTRACT We present some anisotropy properties of the Yb:CALGO with a spatial mode switching when pumped in the multihundred watts of power. This allows to automatically stabilize a TEM00 mode from highly spatial-multimode regime. This stabilization is achievable thanks to a polarization mode switching allowed by the particular anisotropic spectroscopy and thermal properties of Yb:CALGO.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT form only given. Er:YAG crystals are good candidates for eye-safe solid-state lasers wit... more ABSTRACT form only given. Er:YAG crystals are good candidates for eye-safe solid-state lasers with output pulses energy in the mJ range, which are required for applications in atmospheric propagation such as active imaging, lidar and wind mapping. Er:YAG crystals can emit at 1645 nm or 1617 nm. The laser emission of Er:YAG naturally occurs at 1645 nm and is unpolarized. In addition, the required high incident pump powers in quasi-three-levels laser such as Er:YAG could lead to a poor beam quality factor (M2) because of well-known thermal effects in rod lasers. Some applications may require emission at 1617 nm with a good M2 factor for long range sensing, as well as linearly polarized output beams for pollutant probing [1]. Therefore, a basic Er:YAG cavity could be provided with an intra-cavity etalon for wavelength selection [2], a reflective polarizer for polarization control, and a pinhole for spatial filtering. In this contribution, we report on a resonant-grating mirror (Fig. 1 left) which can be used to fullfil these three functions, hence simplifying the laser setup [3].

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT Blue lasers have numerous applications in spectroscopy, underwater communication and mat... more ABSTRACT Blue lasers have numerous applications in spectroscopy, underwater communication and material processing. Direct emission in the blue region can be achieved with laser diodes, with powers up to the watt level. Higher powers require efficient laser operating around 950 nm to be frequency doubled to the blue spectrum, which usually suffer from a lower gain than conventional 1μm lasers. Generally, intracavity frequency doubling set-ups and pulsed operation are used to increase the second harmonic generation efficiency, with output powers up to 4 W in cw and 1.3W in pulsed regime. In the past few years, both lasers materials and non linear crystals have progressed enough to allow the very simple extracavity frequency doubling of continuous wave lasers in periodically poled materials to acceptable powers.

Advanced Solid-State Photonics, 2006

ABSTRACT We demonstrate by a systematical study that Nd:GdVO4 has no better thermal management th... more ABSTRACT We demonstrate by a systematical study that Nd:GdVO4 has no better thermal management than Nd:YVO4. Complementary, we present a new method of bonding that effectively reduces temperature elevation in vanadate lasers.

Advanced Solid-State Photonics, 2006

ABSTRACT Yb:CALGO is a very promising crystal because of its broad emission spectrum and good the... more ABSTRACT Yb:CALGO is a very promising crystal because of its broad emission spectrum and good thermal conductivity. Those properties enable us to demonstrate a laser with a quantum defect of 0.8%, the lowest ever measured.

Advanced Solid-State Photonics, 2008

Solid State Lasers XXIII: Technology and Devices, 2014

ABSTRACT We present laser operation of a 750 μm diameter Er:YAG single crystal fibers pumped at 1... more ABSTRACT We present laser operation of a 750 μm diameter Er:YAG single crystal fibers pumped at 1470 nm. Laser output performances are numerically simulated, experimentally measured and compared. In Passive Q-switch regime, we obtained pulse energy of 180 μJ around 500 Hz at 1617 nm without any spectral selecting element. Pulse duration is 33 ns. By controlling the saturable absorber temperature, we succeeded to improve the output energy up to 270 μJ. These results show the interesting potential of Er:YAG single crystal fiber for compact and low power consumption rangefinders.

Advanced Solid-State Photonics, 2006

ABSTRACT We present the first demonstration in femtosecond regime of an Yb3+:CaGdAlO4 crystal. Pu... more ABSTRACT We present the first demonstration in femtosecond regime of an Yb3+:CaGdAlO4 crystal. Pulses as short as 47 fs at 1050 nm have been produced.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT With the amplification of 380 fs, 1 mJ ultrashort pulses with a nearly diffraction limit... more ABSTRACT With the amplification of 380 fs, 1 mJ ultrashort pulses with a nearly diffraction limited beam quality, Yb:YAG single crystal fibers (SCF) have recently proven their strong potential as power amplifier. Furthermore, during a first power scaling experiment, up to 250 W continuous wave (cw) power were obtained from an Yb:YAG SCF oscillator at 570 W of pump power. In this paper, we present a power scaling experiment of Yb:YAG SCF amplifiers.

2008 Conference on Lasers and Electro-Optics, 2008

An Ytterbium-doped gain laser medium that would benefit from the spectroscopic and thermal proper... more An Ytterbium-doped gain laser medium that would benefit from the spectroscopic and thermal properties of bulk crystals and the good thermal management of glass fiber will be an ideal candidate to achieve high average power and high peak power laser systems. With the ...

Advanced Solid-State Lasers Congress, 2013

ABSTRACT We report the realization of a frequency doubled, actively Q-switched and linearly polar... more ABSTRACT We report the realization of a frequency doubled, actively Q-switched and linearly polarized oscillator based on Nd:YAG single crystal fiber. A stable laser output of 3W, 300μJ, 25ns at 473nm is reported

Solid State Lasers XXI: Technology and Devices, 2012

Advanced Solid-State Lasers Congress, 2013

ABSTRACT We report on recent progress in single-crystal-fiber amplifiers for the amplification of... more ABSTRACT We report on recent progress in single-crystal-fiber amplifiers for the amplification of cylindrically polarized laser beams. With low thermally induced depolarization, this amplifier concept qualifies for conservation of polarization even at high powers.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT form only given. Direct resonant pumping of Er:YAG is a laser configuration studied for ... more ABSTRACT form only given. Direct resonant pumping of Er:YAG is a laser configuration studied for compact eye-safe emitters which applications require kilometer range propagation in the atmosphere, like active imaging, Lidar and wind mapping. The laser emission of these cavities naturally occurs at 1645 nm. But a methane absorption line exists at this wavelength. One way to increase the range of the emitter is to use the 1617 nm emission line which is free of absorption. Recent researches gave nice results in active Q-switched regime at 1645 nm [1] and at 1617 nm [2]. But some applications require a compact, efficient and simple setup with mJ level pulse energy. Our recent work focused on passively Q-switching Er:YAG cavity with direct resonant fiber-coupled diode pumping.A 750 μm diameter 30 mm long Er:YAG single crystal fiber with a doping concentration of 0.5 % is inserted in a Taranis module from Fibercryst for efficient cooling and used as gain medium (Fig. 1 left). It was anti-reflection coated on both ends and actively cooled at 12°C. The pump light is provided by a fiber-coupled laser diode with a 400 μm core diameter and a numerical aperture of 0.22, delivering up to 40 W at 1532 nm. Its spectrum is narrowed by an internal grating, down to 1 nm approximately. The beam is collimated by a 40 mm focal length doublet and then focused a few millimeter inside the Er:YAG crystal thanks to another 40 mm focal length doublet. With this setup, we estimate that the pump beam undergoes between 2 and 3 reflections in the single crystal fiber, allowing a higher population inversion and a better spatial overlap between the pump and the laser signal than in standard rods. This higher population inversion along the gain medium favors the emission of the 1617 nm line. In passively Q-switched mode, a Cr:ZnSe saturable absorber with initial transmission of 85 % led to 330 μJ pulse energy, 61 ns pulse duration at a repetition rate of 1460 Hz. A 80- % initial transmission Cr:ZnSe sample led to 510 μJ energy pulses, 41 ns pulse duration at a repetition rate of 820 Hz. From 34 W to 40 W of pump power, no variation of pulse durations has been observed. The sudden wavelength shift from 1645 nm to 1617 nm has already been observed in [4], and comes from the high losses introduced inside the cavity. In addition, the slightly higher Cr:ZnSe absorption at 1645 nm compared to 1617 nm contributes to the wavelength selection. This wavelength shift happens whatever the incident pump power. A numerical model of this cavity has been developped, including pump propagation inside the crystal with ray tracing, temporal evolution of the population inversion, active and passive Q-switch regime, and thermal effects, based on previous work for actively Q-switched four-levels lasers [4]. Comparison of experimental results with numerical simulations will be presented. This is the first reported passively Q-switched diode-pumped Er:YAG laser operating on the 4I13/2 → 4I15/2 transition.

Journal of the Optical Society of America B, 2014

ABSTRACT We carried out an experimental study of an Er:YAG laser that is passively Q-switched by ... more ABSTRACT We carried out an experimental study of an Er:YAG laser that is passively Q-switched by Cr:ZnSe saturable absorbers and pumped at 1470 nm by a 14 W laser diode. The 1617 nm emission is selected by an appropriate combination of transmissions of the saturable absorber and of the output coupler. With an accurate comparison between actively Q-switched and passively Q-switched operations and with Cr:ZnSe transmission measurements, we demonstrated by experiments and by simulations that the output energy is strongly dependent on the Cr:ZnSe temperature. With a better cooling of the Cr:ZnSe crystal heated by residual pump and signal absorption, the energy per pulse can be doubled, from 110 to 220 μJ, at a repetition rate of 800 Hz.

... Thermo-chemical strengthening of Nd:YAG laser rods. Author(s): Revital Feldman; Yehoshua Shim... more ... Thermo-chemical strengthening of Nd:YAG laser rods. Author(s): Revital Feldman; Yehoshua Shimony; Steven Jackel; Izhak Levy; Yuval Golan. High power Nd:YAG laser rods may easily exceed their fracture strength as a result of thermally induced tensile stress. ...

We present laser operation of 450 μm diameter Er:YAG single crystal fiber pumped at 1470 nm. Pump... more We present laser operation of 450 μm diameter Er:YAG single crystal fiber pumped at 1470 nm. Pump beam confinement leads to low threshold, direct emission at 1617 nm and significant efficiency in passive Q-switching.

We present an unique spatial mode switching in Yb:CALGO laser under high-power-pumping. It permit... more We present an unique spatial mode switching in Yb:CALGO laser under high-power-pumping. It permits to automatically stabilize to a TEM00 mode from highly spatial-multimode regime. This atypical behavior is studied and explained in this paper.

CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009

ABSTRACT We present the demonstration of high average power laser emission in CW and Q-switched r... more ABSTRACT We present the demonstration of high average power laser emission in CW and Q-switched regime from a directly grown Yb:YAG crystal fiber. We designed the gain medium by the use of thermal dependant numerical simulations by taking into account the absorption saturation effects due to the quasi-three level behaviour of the Yb3+ transition. The crystal fiber is longitudinally pumped by a fiber-coupled laser diode with a maximum output power of 200 W at 940 nm.

Solid State Lasers XXIII: Technology and Devices, 2014

ABSTRACT We present some anisotropy properties of the Yb:CALGO with a spatial mode switching when... more ABSTRACT We present some anisotropy properties of the Yb:CALGO with a spatial mode switching when pumped in the multihundred watts of power. This allows to automatically stabilize a TEM00 mode from highly spatial-multimode regime. This stabilization is achievable thanks to a polarization mode switching allowed by the particular anisotropic spectroscopy and thermal properties of Yb:CALGO.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT form only given. Er:YAG crystals are good candidates for eye-safe solid-state lasers wit... more ABSTRACT form only given. Er:YAG crystals are good candidates for eye-safe solid-state lasers with output pulses energy in the mJ range, which are required for applications in atmospheric propagation such as active imaging, lidar and wind mapping. Er:YAG crystals can emit at 1645 nm or 1617 nm. The laser emission of Er:YAG naturally occurs at 1645 nm and is unpolarized. In addition, the required high incident pump powers in quasi-three-levels laser such as Er:YAG could lead to a poor beam quality factor (M2) because of well-known thermal effects in rod lasers. Some applications may require emission at 1617 nm with a good M2 factor for long range sensing, as well as linearly polarized output beams for pollutant probing [1]. Therefore, a basic Er:YAG cavity could be provided with an intra-cavity etalon for wavelength selection [2], a reflective polarizer for polarization control, and a pinhole for spatial filtering. In this contribution, we report on a resonant-grating mirror (Fig. 1 left) which can be used to fullfil these three functions, hence simplifying the laser setup [3].

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT Blue lasers have numerous applications in spectroscopy, underwater communication and mat... more ABSTRACT Blue lasers have numerous applications in spectroscopy, underwater communication and material processing. Direct emission in the blue region can be achieved with laser diodes, with powers up to the watt level. Higher powers require efficient laser operating around 950 nm to be frequency doubled to the blue spectrum, which usually suffer from a lower gain than conventional 1μm lasers. Generally, intracavity frequency doubling set-ups and pulsed operation are used to increase the second harmonic generation efficiency, with output powers up to 4 W in cw and 1.3W in pulsed regime. In the past few years, both lasers materials and non linear crystals have progressed enough to allow the very simple extracavity frequency doubling of continuous wave lasers in periodically poled materials to acceptable powers.

Advanced Solid-State Photonics, 2006

ABSTRACT We demonstrate by a systematical study that Nd:GdVO4 has no better thermal management th... more ABSTRACT We demonstrate by a systematical study that Nd:GdVO4 has no better thermal management than Nd:YVO4. Complementary, we present a new method of bonding that effectively reduces temperature elevation in vanadate lasers.

Advanced Solid-State Photonics, 2006

ABSTRACT Yb:CALGO is a very promising crystal because of its broad emission spectrum and good the... more ABSTRACT Yb:CALGO is a very promising crystal because of its broad emission spectrum and good thermal conductivity. Those properties enable us to demonstrate a laser with a quantum defect of 0.8%, the lowest ever measured.

Advanced Solid-State Photonics, 2008

Solid State Lasers XXIII: Technology and Devices, 2014

ABSTRACT We present laser operation of a 750 μm diameter Er:YAG single crystal fibers pumped at 1... more ABSTRACT We present laser operation of a 750 μm diameter Er:YAG single crystal fibers pumped at 1470 nm. Laser output performances are numerically simulated, experimentally measured and compared. In Passive Q-switch regime, we obtained pulse energy of 180 μJ around 500 Hz at 1617 nm without any spectral selecting element. Pulse duration is 33 ns. By controlling the saturable absorber temperature, we succeeded to improve the output energy up to 270 μJ. These results show the interesting potential of Er:YAG single crystal fiber for compact and low power consumption rangefinders.

Advanced Solid-State Photonics, 2006

ABSTRACT We present the first demonstration in femtosecond regime of an Yb3+:CaGdAlO4 crystal. Pu... more ABSTRACT We present the first demonstration in femtosecond regime of an Yb3+:CaGdAlO4 crystal. Pulses as short as 47 fs at 1050 nm have been produced.

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

ABSTRACT With the amplification of 380 fs, 1 mJ ultrashort pulses with a nearly diffraction limit... more ABSTRACT With the amplification of 380 fs, 1 mJ ultrashort pulses with a nearly diffraction limited beam quality, Yb:YAG single crystal fibers (SCF) have recently proven their strong potential as power amplifier. Furthermore, during a first power scaling experiment, up to 250 W continuous wave (cw) power were obtained from an Yb:YAG SCF oscillator at 570 W of pump power. In this paper, we present a power scaling experiment of Yb:YAG SCF amplifiers.

2008 Conference on Lasers and Electro-Optics, 2008

An Ytterbium-doped gain laser medium that would benefit from the spectroscopic and thermal proper... more An Ytterbium-doped gain laser medium that would benefit from the spectroscopic and thermal properties of bulk crystals and the good thermal management of glass fiber will be an ideal candidate to achieve high average power and high peak power laser systems. With the ...

Advanced Solid-State Lasers Congress, 2013

ABSTRACT We report the realization of a frequency doubled, actively Q-switched and linearly polar... more ABSTRACT We report the realization of a frequency doubled, actively Q-switched and linearly polarized oscillator based on Nd:YAG single crystal fiber. A stable laser output of 3W, 300μJ, 25ns at 473nm is reported

Solid State Lasers XXI: Technology and Devices, 2012

Advanced Solid-State Lasers Congress, 2013

ABSTRACT We report on recent progress in single-crystal-fiber amplifiers for the amplification of... more ABSTRACT We report on recent progress in single-crystal-fiber amplifiers for the amplification of cylindrically polarized laser beams. With low thermally induced depolarization, this amplifier concept qualifies for conservation of polarization even at high powers.