Third-harmonic generation via broadband cascading in disordered quadratic nonlinear media.

We study parametric frequency conversion in quadratic nonlinear media with disordered ferroelectric domains. We demonstrate that disorder allows realizing broadband third-harmonic generation via cascading of two second-order quasi-phase matched nonlinear processes. We analyze both spatial and polarization properties of the emitted radiation and find the results in agreement with our theoretical predictions.

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 pi/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 BaF2 and YVO4 crystals.

Comment on "Generation of 10(11) contrast 50 TW laser pulses".

We argue for a different physical interpretation of the results given in the recent Letter by Chvykov et al. [Opt. Lett.31, 1456 (2006)] in which a double nonlinear crystal scheme for cross-polarized wave generation is analyzed. We discuss the most important factors that explain the origin of the two-crystal scheme's increased efficiency, namely, the Kerr lensing effect and a Gouy phase shift. The position and orientation of the second crystal relative to the first one are unambiguously defined; related effects are illustrated by already published works on the subject.

A two crystal arrangement to fight efficiency saturation in cross-polarized wave generation.

We describe a method that overcomes the observed saturation effect in cross polarized wave (XPW) generation. The previously reported internal efficiencies for XPW generation are known to be limited to around 15% whatever the length of the nonlinear medium and/or the input intensity values are. At the opposite, the theoretical limit had been estimated to be close to 25%. Here we show that using two thin BaF(2) crystals separated at optimum distance the saturation level of XPW generation efficiency can be drastically increased. An internal efficiency of 30% is demonstrated experimentally using two BaF(2) crystals.

Quantitative characterization of aqueous solutions probed by the third-harmonic generation microscopy.

Third-harmonic microscopy is one of the emerging techniques for noninvasive microscopic imaging of biological structures. We use a novel technique for nonlinear optical material characterization and study the effect of different environment and the structural sensitivity of the third harmonic. In particular, a transformation of collagen in solution is observed for the first time using third-harmonic generation. We also study the ultimate limits of the third harmonic to detect micro- and nanoscopic features inside living cells and find that structures as small as 50 nm can be detected using the current level of technology.

Highly efficient blue-light generation from a compact, diode-pumped femtosecond laser by use of a periodically poled KTP waveguide crystal.

We present a simplified, potentially portable, and highly efficient blue-light source from a periodically poled KTP waveguide crystal with a compact femtosecond Cr:LiSAF laser. This light source generates 5.6 mW of blue average output power at 424 nm with 27 mW of incident fundamental in a single-pass extracavity arrangement at room temperature. The overall system efficiency of electrical power to blue light is 0.5%, and the internal second-harmonic generation conversion efficiency is as high as 37%. The slope efficiency of 5.5% pJ(-1) at low pulse energies is, to our knowledge, the highest slope efficiency yet reported for frequency conversion into the blue spectral region.

Polarization rotation induced by cascaded third-order processes.

Intensity-dependent polarization rotation that results from the simultaneous action of two third-order processes, self-phase modulation and four-wave mixing, is observed. The effect is recorded along the fourfold axis of a YVO(4) crystal. The angle of rotation is proportional to the square of the input intensity-crystal length product. This is to the authors' knowledge the first experimental evidence showing that intensity-dependent polarization rotation can be related to the real part of cubic susceptibility.

Cross-polarized wave generation by effective cubic nonlinear optical interaction.

A new cubic 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 observed in BBO crystal. The effect is explained by cascading of two different second-order processes: second-harmonic generation and difference frequency mixing.

Efficient collinear fourth-harmonic generation by two-channel multistep cascading in a single two-dimensional nonlinear photonic crystal.

We investigate efficient fourth-harmonic generation in a single two-dimensional (2D) quadratically nonlinear photonic crystal. We propose a novel parametric process that starts with phase-matched generation of a pair of symmetric second-harmonic waves, which then interact to produce a fourth-harmonic wave that is collinear to the fundamental. We show that this process is more efficient than conventional fourth-harmonic-generation schemes by a factor that reaches 4 at low intensities and discuss how to design and optimize the nonlinear 2D photonic crystals that are implemented in LiNbO(3) and LiTaO(3) .

Phase matching in nonlinear chi((2)) photonic crystals.

We analyze harmonic generation in a two-dimensional (2D) chi((2)) photonic crystal and demonstrate the possibility of multiple phase matching and multicolor parametric frequency conversion. We suggest a new type of photonic structure to achieve simultaneous generation of several harmonics; we also present both general analytical results and design parameters for 2D periodically poled LiNbO(3) structures.

Two-color multistep cascading and parametric soliton-induced waveguides.

We introduce the concept of two-color multistep cascading for vectorial parametric wave mixing in optical media with quadratic (second-order or chi(2)) nonlinear response. We demonstrate that the multistep cascading allows light-guiding-light effects with quadratic spatial solitons. With the help of the so-called "almost exact" analytical solutions, we describe the properties of parametric waveguides created by two-wave quadratic solitons.

Spatial optical solitons resulting from multistep cascading.

We introduce a novel class of parametric optical solitons supported simultaneously by two second-order nonlinear cascading processes, second-harmonic generation and sum-frequency mixing. We obtain analytical and numerical solutions for three-wave spatial solitons and show that the presence of an additional cascading mechanism can change dramatically the properties and stability of two-wave quadratic solitary waves.

Polarization switching as a result of cascading of two simultaneously phase-matched quadratic processes.

A method of intensity-dependent polarization switching is proposed. The effect is based on simultaneous action of two phase-matched second-order processes in a quadratic medium. Using analytical and numerical techniques, we demonstrate that a single linearly polarized fundamental wave, when it is propagating in such a medium, can efficiently generate a new fundamental wave of orthogonal polarization. The polarization switching is explained by an effective four-wave-mixing process that is performed through second-order cascading.

High-order nonlinear phase shift caused by cascaded third-order processes.

We show, for the first time to our knowledge, that the fundamental beam that participates in the process of third-harmonic generation experiences an additional high-order nonlinear phase shift. The magnitude of the shift is proportional to the square of the pump intensity and the length of the sample and depends on the deviation from the exact phase-matched condition. This phase shift arises from cascaded third-order processes. Its value can exceed the value of the phase shift that originates from inherent fifth-order susceptibility of the nonlinear medium. Its sign is controllable by the sign of the phase mismatch of the third-harmonic generation process.

Asbestos-related rounded atelectasis. Radiologic and mineralogic data in 23 cases.

A retrospective study was conducted in 23 subjects with previous occupational exposure to asbestos and exhibiting rounded atelectasis (RA) on high-resolution computed tomography scan (HRCT scan) to evaluate the retention of asbestos bodies (ABs) using light microscopy in the bronchoalveolar lavage (BAL) fluid or lung parenchyma in such patients. A total of 31 RAs were identified, usually located in the lower (25 RAs) and posterior (23 RAs) parts of the lung. Pleural thickening in contact with the RA was observed in 27 RAs and parenchymal bands were detected in 15 cases. Twelve of the 20 patients who underwent BAL or surgery exhibited significant retention of ABs in BAL fluid or lung tissue. Moreover, a significant retention of ABs was observed in five of nine patients with a history of asbestos exposure but no diffuse pleural thickening on chest radiograph or interstitial opacities on HRCT scan. Patients with RAs and coexisting diffuse pleural thickening and/or interstitial fibrosis should be considered at a higher risk for lung cancer in comparison to patients with isolated circumscribed pleural plaques based on increased AB counts. By contrast, the excess risk of lung cancer is more questionable in patients with only RAs and circumscribed pleural plaques as they may have AB counts either above or below that associated with pleural plaques alone. This emphasizes the need for further follow-up studies to define criteria indicating the need for thoracotomy in these subjects.

Measurement of x((3)) and phase shift of nonlinear media by means of a phase-conjugate interferometer.

We have constructed a new interferometer that uses two phase-conjugate mirrors. This device allows for the measurement of the relative phase shift and the ratio of the nonlinear susceptibilities of materials. We have been able to measure weak reflectivity signals not detectable by normal degenerate four-wave mixing methods. It has been determined that the x((3)) value of colloid semiconductor glass OG530 at 532 nm is 7 x 10(-12) esu.

DIMENSIONS OF PERSONALITY: I. CONJOINT FACTOR STRUCTURE OF GUILFORD AND CATTELL TRAIT MARKERS.

The Work Component Study was administered to high school students and the stability of the structure of the variables of work motivation examined. The strudure found among college students and college trained employees is well developed at the high school level. The relationship of work motivations to personality variables and to aspirations is also dear: However, there is little relationship found between work motivations and status variables of the students or their parents. This was unanticipated and oreates a question regarding the sources of work motivations.