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We report on a noniterative method for coherent diffractive imaging based on a specially designed multipinhole (MP) plate. We demonstrated that the complex amplitude of the wavefront penetrating through an MP plate inserted between the specimen and the detector plane can be directly extracted from the Fourier transform of a single far-field diffraction intensity pattern without need of any iterative algorithm. A form of scanning diffractive imaging based on a rotatable MP plate is also demonstrated, which provides a feasible approach for lensless diffractive imaging of complex-valued objects.

We made a theoretical investigation on the top-hat-beam Z scan when the nonlinear media possess third- and fifth-order nonlinearities simultaneously. A high-accuracy method was proposed to allow the determination of the nonlinear refraction coefficients related to the third- and fifth-order effects. We also reconfirmed the common procedure for dividing the contributions of the third- and fifth-order effects to the nonlinearity in the top-hat-beam Z-scan measurements; the results indicated that the common procedure can be still employed for the determination of the third-order nonlinearity, whereas it is inapplicable for the fifth-order nonlinearity. We investigated experimentally, as a test, the nonlinear refraction of a Disperse Yellow 7 thin film by using the top-hat-beam Z-scan technique, with 35-ps-duration pulses at a 1064-nm wavelength.

We report a theoretical study of the Z-scan technique by using quasi-one-dimensional slit beams for characterizing third-order optical nonlinearity. We verify that the sensitivity of this Z-scan scheme is roughly the same level as top-hat beams and is greatly higher than Gaussian beams by a factor of approximately 2.5. This scheme should have the capability to measure less than a λ/500 wave-front distortion at least. Numerical formulas obtained in theory allow direct estimation of nonlinear refraction and absorption coefficients from the normalized peak–valley transmittance difference measured. Some salient features are also discussed. This Z-scan scheme is also demonstrated experimentally.

An idea of an optimal annulus structure phase mask with helical wavefront is suggested; the resulting helical mode can be focused into a very clear optical vortex ring with the best contrast. Dependences of the optimal annulus width and the radius of the optical vortex ring on topological charge are found. The desired multi-optical vortices as the promising dynamic multi-optical tweezers are realized by extending our idea to the multi-annulus structure. Such multi-optical vortex rings allow carrying the same or different angular momentum flux in magnitude and direction. The idea offers flexibility and more dimensions for designing and producing the complicated optical vortices. For the Gaussian beam illumination, the optimal spot size, which ensures the high energy/power efficiency for generating the best contrast principal ring is also found.

We present a method for controlling the efficiency of direct third-harmonic generation in quasi-periodic optical superlattices by means of the electro-optic effect. The calculated results manifest that this method is extremely efficient for achieving high efficiency of direct third-harmonic generation in predesigned quasi-phase-matched coupled parametric processes and is feasible at any given fundamental intensity. In addition, we demonstrate that the electro-optic control approach is significantly better than the temperature-control method.

We present a simple and efficient technique for evaluating the optical losses of a planar film by use of a quasi-waveguide configuration and a prism film coupler configuration. The technique can separate two contributions to optical loss: that from the surface scattering caused by the roughness of surface and that from volume losses including volume scattering and volume absorption.

Quasi-phase matching facilitates the phase matching of any parametric interaction by setting an appropriately modulated period. We propose a dual-periodic structure that is used in the construction of a frequency-conversion device. For example, we have designed and fabricated such a dual-periodic structure in a LiTaO3 crystal. Using a fundamental source at 1.064 µm, we obtained ultraviolet radiation at 355 nm and green radiation at 532 nm simultaneously by frequency tripling and frequency doubling the fundamental source. Theoretically, this idea can be further extended to the design of a multiperiodic structure for achievement of more quasi-phase-matched processes in a single optical superlattice.