Adrien Aubourg

Passively Q-switched diode-pumped Er:YAG solid-state laser.

We demonstrated laser operation of a passively Q-switched diode-pumped Er:YAG solid-state laser emitting at 1645 or 1617 nm depending on the initial transmission of the Cr:ZnSe saturable absorber. The crystal emitted up to 10 W at 1645 nm and up to 8 W at 1617 nm in CW mode while pumped with 65 W of incident pump power at 1533 nm. In passive Q-switched mode with 40 W of incident power, 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 at 1645 nm. An 80% initial transmission Cr:ZnSe sample led to 510 μJ energy pulses, 41 ns pulse duration at a repetition rate of 820 Hz with a central wavelength change from 1645 to 1617 nm. This is the first reported passively Q-switched diode-pumped Er:YAG laser operating on the (4)I(13/2)→(4)I(15/2) transition.

Resonant diode-pumping of Er:YAG single crystal fiber operating at 1617 nm

We demonstrated laser operation of a Er:YAG single crystal fiber at 1617 nm. Pumped on both sides by a laser diode at 1532 nm, a 600 μm diameter- 60 mm long- single crystal fiber produced an output power of 5.5 W once the wavelength 1617 nm was selected by an intracavity etalon. In Q-switched operation with an acousto-optic modulator, the laser produced an energy of 0.5 mJ at 100 Hz repetition rate with a pulse duration of 28 ns. The Watt level in average power was achieved for a repetition rate of 3 kHz with a pulse duration maintained around 30 ns.

Oxide crystal-fibers grown by micro-pulling-down technique and applications for lasers and scintillators

We demonstrated growth of YAG, LuAG and CALGO single crystal fibers with doping Nd, Yb, Er, and Ce by the micro-pulling-down technique. Those fibers have applications in high power lasers and scintillating detectors. For laser operation, average power of 65 W energy of 4 mJ and peak power above 7 MW have been demonstrated in various configurations. Those results push the limits of end-pumped bulk crystals in terms of average power and exceed the limits of pulsed fibers lasers in terms of energy. For scintillating applications, high density/high light yield detectors are developed for nuclear science and medical applications.

Single crystal fiber for laser sources

Single crystal fiber (SCF) is a hybrid laser architecture between conventional bulk laser crystals and active optical fibers allowing higher average powers than with conventional crystals and higher energy than with fibers in pulsed regime. The pump beam delivered by a fiber-coupled laser diode is confined by the guiding capacity of the SCF whereas the signal beam is in free propagation. In this paper, we study the pump guiding in the SCF and give an overview of the results obtained using SCF gain modules in laser oscillators and amplifiers. We report about up to 500 μJ nanosecond pulses at the output of a passively Q-switched Er:YAG SCF oscillator at 1617 nm. High power experiments with Yb:YAG allowed to demonstrate up to 250 W out of a multimode oscillator. High power 946 nm Nd:YAG SCF Q-switched oscillators followed by second and fourth harmonic generation in the blue and the UV is also presented with an average power up to 3.4 W at 473 nm and 600 mW at 236.5 nm. At 1064 nm, we obtain up to 3 mJ with a nearly fundamental mode beam in sub-nanosecond regime with a micro-chip laser amplified in a Nd:YAG SCF. Yb:YAG SCF amplifiers are used to amplify fiber based sources limited by non-linearities such as Stimulated Brillouin Scattering with a narrow linewidth laser and Self Phase Modulation with a femtosecond source. Using chirped pulse amplification, 380 fs pulses are obtained with an energy of 1 mJ and an excellent beam quality (M2<1.1).

Wavelength selection, spatial filtering and polarization control of an Er:YAG laser cavity by resonant-grating mirror

Summary 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].

Picosecond Yb-doped fiber laser source with a repetition rate continuously tunable between 11 and 18 GHz

Electro-optical combs generated from continuous-wave sources through amplitude and phase modulations have the potential to generate picosecond pulses with multi-GHz tunable repetition rates. They find applications in polarized Gamma ray production [1], imaging and picosecond acoustics. However, the development of such combs is mainly carried out with 1.5 μm laser sources [1, 2]. Only few developments exist so far in the Ytterbium gain window around 1 μm, where power scaling towards high average power and high energy is obvious. In this talk, we will report on the development of a picosecond (one) laser system operating at 1030 nm with a continuously tunable repetition rate between 11 and 18 GHz at the W-level average power.

Diode-pumped and passively Q-switched Er:YAG laser emitting at 1617 nm

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.

Diode pumped Er:YAG single crystal fiber laser passively Q-switched with Cr:ZnSe saturable absorber emitting at 1645 nm or 1617 nm

Summary 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.

Diode-pumped 1617 nm Er:YAG laser with micro-pulling down single-crystal fibers

We demonstrated diode-pumped laser operation at 1617 nm with Er:YAG 60 mm long and 600 µm diameter single-crystal fibers. We obtained 5.5 W in cw and 0.5 mJ 30 ns pulses at 100 Hz in Q-switched operation.