Article

# Primary spherical aberration in two-color (two-photon) excitation fluorescence microscopy with two confocal excitation beams.

National Institute of Physics, University of the Philippines, Diliman, Quezon City 1101, Philippines.

Applied Optics (Impact Factor: 1.69). 07/2003; 42(17):3398-406. DOI: 10.1364/AO.42.003398 Source: PubMed

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**ABSTRACT:**We analyze the influence of residual two-photon excitation (2PE) in two-color (two-photon) optical beam induced current (2CE-OBIC) generation in wide band gap semiconductor samples. 2CE-OBIC generation is accomplished with two confocal excitation beams of separation angle θ and wavelengths λ1 and λ2 where λe-1=λ1-1+λ2-1, λe=hc/Eb, h is the Planck’s constant, c is speed of light in vacuum, and Eb is the energy band gap. Because the conduction band of the sample is a continuum, at least one excitation beam would also contribute an undesirable 2PE-OBIC signal that degrades the signal-to-noise ratio of the measured 2CE-OBIC response and broadens the effective OBIC distribution in the sample particularly when θ≠0 or π. We show that the deleterious effects of crosstalk are reduced by a careful selection of λ1 and λ2 and the relative excitation beam intensities. λ1 and λ2 should be chosen to minimize the ratio of the two-photon absorption coefficients (β1,β2) to the 2CE absorption coefficient β12 or at least satisfy the constraint: β1+β2⩽β12. Keeping the two excitation intensities equal is beneficial only when β1=β2. Otherwise, it is advantageous to bias the intensity ratio towards the wavelength with a lower 2PE absorption coefficient.Optics Communications 02/2007; 270(2):139-144. · 1.54 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Optical-beam induced current (OBIC) is generated in blue light-emitting diode samples (peak emission wavelength=480 nm) via two-color (two-photon) excitation using the second- (502.9 nm) and third-order (635.9 nm) Stokes beam outputs of a hydrogen Raman shifter that is pumped by the 355 nm pulsed output (5.4 ns pulsewidth) of a 10 Hz Nd:YAG laser. Two-color OBIC generation happens only in sample regions where the two focused Stokes beams overlap in both space and time. We have verified the direct proportionality of the two-color OBIC signal with the product of the individual Stokes beam intensities as well as the localized nature of two-color OBIC generation in the common focal volume of the two confocal excitation beams.Optics Communications 02/2005; 246(1):117-122. · 1.54 Impact Factor -
##### Article: Axial resolution in two-color excitation fluorescence microscopy by phase-only binary apodization

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**ABSTRACT:**We study the effect of a kind of binary phase-only filters, the Toraldo filters, in two-color excitation fluorescence microscopy. We show that by simple insertion of a properly designed Toraldo filter in one of the illumination arms the axial resolution of the system is significantly improved. Specifically, the main peak of the point spread function is narrowed by 22% along the axial direction.Optics Communications 02/2005; 4230. · 1.54 Impact Factor

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