Quasi-Dammann Grating With Proportional Intensity Array Spots

A quasi-Dammann grating is proposed to generate array spots with proportional-intensity orders in the far field. To describe the performance of the grating, the uniformities of the array spots are redefined. A two-dimensional even-sampling encode scheme is adopted to design the quasi-Dammann grating. Numerical solutions of the binary-phase quasi-Dammann grating with proportional-intensity orders are given. The experimental results with a third-order quasi-Dammann grating, which has an intensity proportion of 3:2:1 from zero order to second order, are presented. (C) 2008 Optical Society of America

Spectral evolution of angularly resolved third-order harmonic generation by infrared femtosecond laser-pulse filamentation in air

We experimentally investigate the evolution of an angularly resolved spectrum of third harmonic generated by infrared femtosecond laser pulse filamentation in air. We show that at low pump intensity, phase matching between the fundamental and third-harmonic waves dominates the nonlinear optical effect and induces a ring structure of the third-harmonic beam, whereas at high pump intensity, the dispersion properties of air begin to affect the angular spectrum, leading to the formation of a nonlinear X wave at third harmonic.

Third harmonic enhancement due to Fano interference in semiconductor quantum well

We investigate the emission spectra of the semiconductor quantum well for few-cycle and sub-cycle pulse exciting. We find that Fano interference may induce third harmonic enhancement. Third harmonic enhancement varies with the magnitude and duration of the incident pulse, and may be enhanced by approximately one order of magnitude for the low intensity region of the sub-cycle incident pulse exciting.

X-shaped third harmonic generated by ultrashort infrared pulse filamentation in air

The authors report the measurement of the angularly resolved spectrum of the third harmonic generated in a femtosecond filament in air and its evolution with increasing pump power. Pumped by a focused infrared ultrashort pulse with a carrier wavelength of 1270 nm, a pulse duration of similar to 20 fs, and pulse energy up to 487 mu J, the generated third harmonic is composed of an on-axis emission and a conical ring emission. When the pump power is sufficiently high, angularly resolved spectra with significant X-like feature could be observed, indicating the formation of nonlinear X wave at third harmonic. (c) 2008 American Institute of Physics.

Ghost imaging with thermal light by third-order correlation

Ghost imaging with classical incoherent light by third-order correlation is investigated. We discuss the similarities and the differences between ghost imaging by third-order correlation and by second-order correlation, and analyze the effect from each correlation part of the third-order correlation function on the imaging process. It is shown that the third-order correlated imaging includes richer correlated imaging effects than the second-order correlated one, while the imaging information originates mainly from the correlation of the intensity fluctuations between the test detector and each reference detector, as does ghost imaging by second-order correlation.

Non-resonant third-order non-linear optical properties of amorphous GeSe2 film

The real and imaginary parts of third-order susceptibility of amorphous GeSe2 film were measured by the method of the femtosecond optical heterodyne detection of optical Kerr effect at 805 nm with the 80 fs ultra fast pulses. The results indicated that the values of real and imaginary parts were 8.8 x 10(-12) esu and -3.0 x 10(-12) esu, respectively. An amorphous GeSe2 film also showed a very fast response within 200 fs. The ultra fast response and large third-order non-linearity are attributed to the ultra fast distortion of the electron orbits surrounding the average positions of the nucleus of Ge and Se atoms. (c) 2005 Elsevier B.V. All rights reserved.

Super-resolution scanning laser microscopy with a third-order optical nonlinear thin film

In a configuration of optical far-field scanning microscopy, super-resolution achieved by inserting a third-order optical nonlinear thin film is demonstrated and analyzed in terms of the frequency response function. Without the thin film the microscopy is diffraction limited; thus, subwavelength features cannot be resolved. With the nonlinear thin film inserted, the resolution is dramatically improved and thus the microscopy resolves features significantly smaller than the smallest spacing allowed by the diffraction limit. A theoretical model is established and the device is analyzed for the frequency response function. The results show that the frequency response function exceeds the cutoff spatial frequency of the microscopy defined by the laser wavelength and the numerical aperture of the convergent lens. The main contribution to the improvement of the cutoff spatial frequency is from the phase change induced by the complex transmission of the nonlinear thin film. Experimental results are presented and are shown to be consistent with the results of theoretical simulations.

Ultra-narrow bandwidth resonant reflection grating filters using the second diffracted orders

In this paper, we design resonant reflection grating filters employing the second diffracted orders as the leaky modes, then analyze the bandwidth of the reflection peak and the electric field distributions inside the wavegude under resonance. The numeric calculation confirms that ultra-narrow resonant reflection peaks can be observed in these structures. At the same time, strong electric field enhancement appears under resonance. It provides a new approach to diversify the resonant reflection filters and may open a new way to the realization of ultra-narrow bandwidth filters. (C) 2008 Elsevier B.V. All rights reserved.

Interaction between the intrinsic second- and third-order optical fields in an Al0.53Ga0.47N/GaN heterostructure

We present an experimental demonstration of the interaction between the intrinsic second- and third-order optical fields in an Al0.53Ga0.47N/GaN heterostructure. The sample was deposited by metal-organic chemical vapor deposition on (0001) sapphire. The nonlinear optical coefficients of the sample, which were measured with a Mach-Zehnder interferometer system, quadratically increase with the applied modulating voltage, indicating the existence of the third-order optical field. The third-order signal was then detected by the Z-scan method and we calculated the built-in dc field on the AlGaN/GaN interface to confirm the strong interaction between the intrinsic second- and third-order optical fields. (c) 2008 American Institute of Physics.

Third-order optical nonlinearities of lead-free (Na1-xKx)(0.5)Bi0.5TiO3 thin films

(Na1-xKx)(0.5)Bi0.5TiO3 (NKBT) (x = 0.1, 0.2, and 0.3) thin films with good surface morphology and rhombohedral perovskite structure were fabricated on quartz substrates by a sol-gel process. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties were investigated by Z-scan technique performed at 532 nm with a picosecond laser. A two-photon absorption effect closely related with potassium-doping content was found in thin films, and the nonlinear refractive index n(2) increases evidently with potassium-doping. The real part of the third-order nonlinear susceptibility chi((3)) is much larger than its imaginary part, indicating that the third-order optical nonlinear response of the NKBT films is dominated by the optical nonlinear refractive behavior. These results show that NKBT thin films have potential applications in nonlinear optics. (C) 2007 Elsevier B.V. All rights reserved.