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We measured the temporal dynamics of wavefront aberrations in a beam produced by a commercial ultrafast high-power laser with a research-prototype real-time Hartmann--Shack wavefront sensor. Measurements were performed at two different temporal rates for a 7 mm diameter. Results showed that changes in the wavefront aberrations were always lower than 1%. The main contribution to the total root-mean-square (RMS) wavefront error was due to the effects of low order aberrations (defocus and astigmatism), which persisted even after cavity realignment. The potential improvement in the beam quality after correction of the different aberration modes was also shown. Real-time measurements of laser aberrations while modifying cavity parameters might be a useful tool to improve the beam quality. OCIS codes: 140.0140, 010.7350, 220.1010, 320.7090.

Retinal images of approximately 1[degrees] of visual field were recorded with a homemade scanning laser ophthalmoscope. The benefit of using a nonlinear registration technique to improve the summation process when averaging frames, rather than a standard approach based on correlation, was assessed. Results suggest that nonlinear methods can surpass linear transformations, allowing improved contrast and more uniform image quality. The importance of this is also demonstrated with specific polarization measurements to determine the degree of polarization across an imaged retinal area. In such a context, where this parameter of polarization is extracted from a combination of registered images, the benefit of the nonlinear method is further increased. OCIS codes: 100.2000, 100.2980, 110.5405, 170.5755, 330.7327.

The existence of evanescent optical waves is usually demonstrated by the observation of transmitted light in frustrated total-internal-reflection experiments that make use of two closely spaced prisms. The main characteristic of a monochromatic evanescent plane wave is the exponential decay of its amplitude in the direction perpendicular to its surface of generation. This decay, however, is not what is seen in the usual experiments when the gap between the prisms is small. Only when the gap is sufficiently large does it gradually approach the exponential dependence. We use a different technique that uses a local probe to reveal the presence of an evanescent wave. The results come closer to the ideal of the exponential decay of the wave amplitude, and the presence of the evanescent wave can be seen directly, making it a suitable demonstration for pedagogical purposes. [DOI: 10.1119/1.1564811]

Radiation and collection characteristics of four different near-field optical-fiber probes, namely, three uncoated probes and an aluminum-coated small-aperture probe, are investigated and compared. Their radiation properties are characterized by observation of light-induced topography changes in a photosensitive film illuminated with the probes, and it is confirmed that the radiated optical field is unambiguously confined only for the coated probe. Near-field optical imaging of a standing evanescent-wave pattern is used to compare the detection characteristics of the probes, and it is concluded that, for the imaging of optical-field intensity distributions containing predominantly evanescent-wave components, a sharp uncoated tip is the probe of choice. Complementary results obtained with optical phase-conjugation experiments with the uncoated probes are discussed in relation to the probe characterization.

Second-harmonic scanning optical microscopy in reflection is used to image at room temperature individual GaInP/GaAs microstructures formed on a GaAs (001) substrate. Second-harmonic images of individual microstructures are recorded along with first-harmonic images for four combinations of polarizations of the pump and second-harmonic radiation with different pump wavelengths in the range of 720–920 nm. We observe different second-harmonic images for different polarization configurations and their evolution when changing the pump wavelength. Comparing the dependencies of the second-harmonic signal from the bare sample surface with those related to the microstructures, we conclude that the second-harmonic radiation detected when illuminating the microstructures originates from the substrate at short wavelengths and directly from the microstructures at ∼900 nm of the pump wavelength. The appearance of the second-harmonic images for different polarization configurations is used to discuss the nonlinear properties of the investigated microstructures. [ABSTRACT FROM AUTHOR]

GaInP/GaAs microstructures formed on GaAs substrate is imaged. The appearance of second-harmonic images is used to discuss the nonlinear properties of the microstructure.