Second-harmonic tomography of tissues
ABSTRACT A novel noninvasive second-harmonic-generation tomographic method of mapping the structure of animal tissues by use of 100-fs laser pulses at 625nm is described. Subsurface structures were measured with this approach, which is potentially a symmetry-sensitive tool for optical histological reconstruction.
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Conference Paper: Polarization and Second Harmonic Generation in aligned collagen fibersICO-23: Enlightening the future; 08/2014
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ABSTRACT: Taking advantage of the electric field-enhanced second-harmonic generation effect in bulk gallium nitride (GaN) and indium gallium nitride (InGaN) quantum wells, we demonstrated the piezoelectric field distribution mapping in bulk GaN and InGaN multiple-quantum-well (MQW) samples using scanning second-harmonic generation (SHG) microscopy. Scanning SHG microscopy and the accompanying third-harmonic generation (THG) microscopy of the bulk GaN sample were demonstrated using a femtosecond Cr:forsterite laser at a wavelength of 1230 nm. Taking advantage of the off-resonant electric field-enhanced SHG effect and the bandtail state-resonance THG effect, the second- and third-harmonic generation microscopic images obtained revealed the piezoelectric field and bandtail state distributions in a GaN sample. Combined with 720 nm wavelength excited two-photon fluorescence microscopy in the same sample, the increased defect density around the defect area was found to suppress bandedge photoluminescence, to increase yellow luminescence, to increase bandtail state density, and to decrease residue piezoelectric field intensity. Scanning SHG microscopy of the InGaN MQW sample was resonant excited with 800 nm femtosecond pulses from a Ti:sapphire laser in order to suppress SHG contribution from the bulk GaN substrate. Taking advantage of the strong piezoelectric field inside the InGaN quantum well, the wavelength resonant effect, and the electric field-enhanced SHG effect of InGaN quantum wells, resonant scanning SHG microscopy revealed the piezoelectric field distribution inside the wells. Combined with accompanying three-photon fluorescence microscopy from the bulk GaN substrate underneath the quantum wells, the direct correspondence between the piezoelectric field strength inside the quantum well and the substrate quality can be obtained. According to our study, the GaN substrate area with bright bandedge luminescence corresponds to the area with strong SHG signals indicating a higher stained-induced piezoelectric field. These scanning harmonic generation microscopies exhibit superior images of the piezoelectric field and defect state distributions in GaN and InGaN MQWs not available before. Combining with scanning multiphoton fluorescence microscopy, these techniques open new ways for the physical property study of this important material system and can provide interesting details that are not readily available by other microscopic techniques.Scanning 05/2006; 23(3):182 - 192. DOI:10.1002/sca.4950230304 · 1.44 Impact Factor
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ABSTRACT: The microstructural basis for the mechanical properties of blood vessels has not been directly determined because of the lack of a nondestructive method that yields a three-dimensional view of these vascular wall constituents. Here, we demonstrate that multiphoton microscopy can be used to visualize the microstructural basis of blood vessel mechanical properties, by combining mechanical testing (distension) of excised porcine coronary arteries with simultaneous two-photon excited fluorescence and second-harmonic generation microscopy. Our results show that second-harmonic generation signals derived from collagen can be spectrally isolated from elastin and smooth muscle cell two-photon fluorescence. Two-photon fluorescence signals can be further characterized by emission maxima at 495 nm and 520 nm, corresponding to elastin and cellular contributions, respectively. Two-dimensional reconstructions of spectrally fused images permit high-resolution visualization of collagen and elastin fibrils and smooth muscle cells from intima to adventitia. These structural features are confirmed by coregistration of multiphoton microscopy images with conventional histology. Significant changes in mean fibril thickness and overall wall dimension were observed when comparing no load (zero transmural pressure) and zero-stress conditions to 30 and 180 mmHg distension pressures. Overall, these data suggest that multiphoton microscopy is a highly sensitive and promising technique for studying the morphometric properties of the microstructure of the blood vessel wall.Biophysical Journal 11/2004; 87(4):2778-86. DOI:10.1529/biophysj.104.042887 · 3.83 Impact Factor