B. Bourliaguet

Observation of quadratic spatial solitons in periodically poled lithium niobate

We report what are to our knowledge the first observation and characterization of quadratic spatial solitons in periodically poled lithium niobate (PPLN). Using a Nd:YAG (1064-nm) source, we observed self-trapped solitary-wave propagation over more than six diffraction lengths as a result of the cascaded quadratic nonlinear process. Low-threshold operation (5-kW peak power) was measured for the quasi-phase-matched PPLN structure designed for frequency doubling.

Collisions between type II two-dimensional quadratic solitons.

We report experimental and numerical results that describe collisions between two-dimensional type II quadratic solitons excited in a KTP crystal by fundamental waves of orthogonal polarization. Our results provide experimental evidence of the possibility of both inelastic collision (when two quadratic solitons merge at input into a single soliton at output) and quasi-elastic collision.

Pulsed OPO brightness improvement by means of intracavity spatial filtering

The design and operation of a pulsed optical parametric oscillator (OPO) with an intracavity spatial filter is described. This filter, designed to select a single high-order transverse mode, improves the brightness of the generated parametric waves by decreasing their divergence. This process is confirmed by experiments carried out on a KTP OPO pumped at 532 nm, operating close to degeneracy in a singly resonant regime. Comparison of the output energy and beam quality for the OPO with and without intracavity filtering demonstrated a five-fold increase in brightness.

Threshold energy for vector soliton formation in KTP

We present theoretical and experimental results to outline the conditions for the existence of vectorial solitary waves in KTP with imbalanced fundamental frequency waves (FFs). We demonstrate that the minimum energy for soliton formation can be at nonzero fundamental frequency imbalance or at zero imbalance depending on the sign of the phase mismatch.

Photofield emission from a tipped silicon photocathode in IR with a new picosecond Nd–YAG laser at a frequency of 100 MHz

Tipped silicon photocathodes are tested with the IR wavelength (1.064micronmeter) Full-size image (<1 K) of a new lock-mode Nd–YAG laser. The impulse width of 30 ps is repeated at a frequency of 100 MHz at a power of 122 W. A quantum yield of 2.5×10−3 is obtained in a DC gun using the best continuous emission field of 20 MV/m for the photofield emission current. The ratio of the photofield emission current to the field emission current (dark current) is more than 104. A previous experiment with the second harmonic of a Nd–YAG at 10 Hz gave 700 pC per pulse of 35 ps width with a quantum yield of 10−5 at the threshold emission field of 7.5 MV/m.

Interactions of Type II vectorial spatial solitary waves in materials with quadratic non-linearity

We present analytical, numerical and experimental results of the interactions between Type II vectorial spatial solitary waves (QSSW) in second-order non-linear media. We show that the outcome of the interaction can be changed from beam coalescence to steering, crossing or repulsion through a non-coherent control (i.e. the control does not rely on the relative phase between the interacting QSSW). We also provide experimental evidence that both quasi-elastic and inelastic collision between QSSW are feasible in second order non-linear media, depending on the relative velocity of the interacting QSSW. We determine (analytically, numerically and experimentally) the critical transverse velocity for elastic collision to be observed, when the fundamental frequency component of the two interacting beams are orthogonally polarized at the input face of the non-linear crystal.

Collisions between two-dimensional quadratic spatial solitons in PPLN

Self-guided waves that can be excited in quadratic nonlinear media have been extensively studied for their potential applications in ultra-fast all-optical processing. We have previously reported the use of solitary waves collision in a KTP crystal to experimentally demonstrate all-optical switching of IR picosecond pulses. Up to now, the intensity required to obtain self-trapping of a beam remained at a high level. This has been due to the lack of nonlinear crystals which combine the attributes of a large nonlinearity and phase-matching capability at experimentally convenient wavelengths. The availability of Periodically Poled Lithium Niobate can circumvent this difficulty. 2D spatial solitary waves in PPLN have been predicted theoretically and simulated numerically. In this communication we will report their experimental observation and for the first time their interaction in a 15mm long crystal. Then we will compare solitary wave behavior in KTP and PPLN, in particular self-trapping intensity threshold versus phase mismatch. We will also compare experimental data with the reslut of our computations modeling. In a last part we will show our first experimental result about 2D quadratic soliton collision in a PPLN crystal. Finally we will discuss the advantages of choosing PPLN to realize all- optical devices using solitary wave interactions.

Generation and interactions of two-dimensional vectorial second-order spatial solitary waves

We review recent experimental, theoretical and numerical results dealing with the generation and the interaction of solitary waves in second-order nonlinear crystals. Particular emphasis is devoted to the issues related to the collisions between two-dimensional type II second-order solitons of orthogonal polarization in a KTP crystal. We report the experimental evidence that both quasi elastic and inelastic collision (when two solitons at input merge into a single one at output) are feasible, depending on the relative transverse velocity of the interacting beams.

Propagation autoguidée soliton lors de la génération de second harmonique dans un cristal de PPLN

We report what are to our knowledge the first observation and characterization of quadratic spatial solitons in periodically poled lithium niobate (PPLN). Using an Nd:YAG (1064 nm) source, we observed self-trapped solitary-wave propagation over more then six diffraction lengths as a result of the cascaded quadratic non linear process. Low-threshold operation was measured for the quasi-phase-matched PPLN structure designed for frequency doubling.

Nouvelle méthode de blocage passive des modes longitudinaux d'une cavité laser par rotation de polarisation dans un cristal doubleur de fréquence

Blocage en phase des modes, longitudinaux dun resonateur laser par commutation de polarisation dans un cristal doubleur de frequence. Cette etude a ete menee en regime de pompage continu dans des cristaux de Nd:YAG et de Nd:YVO4. Des impulsions de 3 picosecondes avec des frequences de repetition de 1GHz a 100MHz pour une puissance moyenne comprise entre 700mW et 4W ont ete obtenues. La meme etude realisee en regime declenche avec un milieu laser Nd:YAG a permis dobtenir des impulsions de 25ps pour une energie par impulsion superieur a 100μj.