Fibercryst (France)

<div>The default approach to building cities vertically is through the construction of towers. Such “common towers” multiply the “value” of a plot of ground by repeatedly stacking the most profitable types of private units vertically. These independent extrusions of land produce spaces that are disconnected from one another and the city below. The widespread proliferation of this default approach is rapidly filling the vertical territory of the world’s cities with privatized stacks of ordinary spaces.</div><div>A critical investigation of “Common Towers” and the conditions that have led to their proliferation exposes opportunities that their presence conceals. There is both architectural and urbanistic potential in the vertical territory above a city that cannot be realized through the “common tower.” This thesis explores the potential of the seamless vertical extension of the unconditionally public realm as a means of driving the three-dimensional organization of spaces within the volume of a city. <br></div>

We have studied and developed two compact nanosecond lasers delivering up to 11 mJ, TEM00 and linearly polarized nanosecond pulses centered at 1064 nm. Their use in ignition of a prototype of aeronautic combustion engine0 is presented.

We present results of numerical and experimental investigation of beam distortions induced in the single-pass Nd:YAG crystal fiber amplifier injected by ns and ps laser pulses counter-propagating to continuous pump beam of up to 110 W power at 808 nm emitted from the fiber coupled laser diode with spectral narrowing by Bragg grating.

There is an increasing need for narrow linewidth, high average power ultraviolet (UV) laser sources for high resolution spectroscopy, remote environmental sensing, laser-induced fluorescence, semiconductor inspection, and LIDAR applications [1,2]. A way to design efficient sources in the UV is to frequency convert diode-pumped solid-state lasers that emit in the near infrared (IR) [3]. In this case, obtaining high nonlinear conversion efficiency requires a large peak power in the fundamental wave. At a fixed repetition rate and average power, this results in a tradeoff between attainable linewidth, related to the pulse duration, and the nonlinear conversion efficiency.

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.

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 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.

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.

Taking advantage of the pump beam confinement and the excellent thermal management offered by Nd:YAG single crystal fibers, we demonstrated a maximum output power of 34 W at 946 nm for an incident pump power of 86 W. A high slope efficiency of 53% was obtained. There was no rollover observed in the efficiency curves and the maximum output power was only limited by the available pump power.