Nonlinear mirror based on cross-polarized wave generation

We present a new type of nonlinear mirror based on the generation of a cross-polarized wave through a nonresonant electronic third-order process. It is characterized by a reflection coefficient that depends on the input intensity. Its behavior results from the interference between the nonlinearly generated cross-polarized wave and a /2 phase-retarded wave. This setup has a lot of advantages: it does not require any phase matching, it is achromatic and suitable for femtosecond pulses, linear losses are easily adjustable, and the overall behavior is predictable. The device has been experimentally tested using BaF 2 and YVO 4 crystals. OCIS codes: 190.0190, 230.4320, 140.4050. Nonlinear mirrors (NLMs) are known to be used for mode-locking (ML) operation in solid-state lasers and also for other applications, e.g., for pulse reshaping and compression and contrast improvement. In general, NLMs can be divided into two groups. The first group is based on ͑3͒ effects: self-induced ellipse rotation in isotropic media, 1,2 the Kerr lens effect, 3 or interference effects in an external cavity with ͑3͒ media. © 2006 Optical Society of America ͑2͒ cascaded processes. 12 Here, we introduce a new type of NLM based on the generation of a linearly polarized wave cross polarized to the input one. The cross-polarized wave (XPW) generation effect is a four-wave mixing process that depends on the anisotropy of the ͑3͒ tensor. The scheme of the XPW-based NLM is shown i

A CALCULATION OF THE PHONON DISPERSION CURVES IN TRIGONAL AND MONOCLINIC SELENIUM WITH THE HELP OF A SINGLE VIBRATIONAL POTENTIAL

We present phonon dispersion curves in trigonal Selenium (chains) and zone center phonons in α monoclinic Selenium (rings) calculated with the same internal force constants. Most of their differences in phonon energies can be explained by intermolecular interactions which in both case promote a tetrahedral neihbouring leaving some danglin bonds in monoclinic Se. Long range forces of the Van der Waals type were neglected in first approximation

Experimental and theoretical investigation of generation of a cross-polarized wave by cascading of two different second-order processes

A nonlinear optical effect in which a linearly polarized wave propagating in a single quadratic medium is converted into a wave that is cross polarized to the input wave is investigated theoretically and observed experimentally in ␤-barium borate crystal. It is proved that this effect is a result of cascading of two different second-order processes. It starts with the generation of an extraordinary second-harmonic wave by type I interaction and is followed by type II difference-frequency mixing between the second-harmonic wave and the ordinary fundamental wave. The experiment was performed (a) for phase-matched type I interaction and non-phase-matched type II interaction and (b) for non-phase-matched type I interaction and phase-matched type II interaction. The observed generation of a cross-polarized wave is to our knowledge the only cubic effect whose first manifestation has been observed in quadratic crystal