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.
"Second Harmonic Generation (SHG) is a particular form of multiphoton microscopy providing information of structures with local anisotropy . SHG signal allows microscopic imaging and provides information not available with regular techniques. "
"However, there is a lack of studies on the retinal cell densities at different eccentricities in chickens, using multiphoton imaging techniques. The development of femtosecond lasers as excitation sources allowed the development of multiphoton (or nonlinear) microscopy techniques, including two-photon excitation fluorescence (TPEF) and second-harmonic generation (SHG), which present high resolution and 3D imaging capabilities [18,19]. The basic principle underlying these techniques is that for tightly focused ultrashort laser pulses, the photon density is high enough to induce multiphoton absorption within the focal volume, providing intrinsic optical sectioning. "
[Show abstract][Hide abstract] ABSTRACT: The structure and organization of the chicken retina has been investigated with an adaptive optics multiphoton imaging microscope in a backward configuration. Non-stained flat-mounted retinal tissues were imaged at different depths, from the retinal nerve fiber layer to the outer segment, by detecting the intrinsic nonlinear fluorescent signal. From the stacks of images corresponding to the different retinal layers, volume renderings of the entire retina were reconstructed. The density of photoreceptors and ganglion cells layer were directly estimated from the images as a function of the retinal eccentricity. The maximum anatomical resolving power at different retinal eccentricities was also calculated. This technique could be used for a better characterization of retinal alterations during myopia development, and may be useful for visualization of retinal pathologies and intoxication during pharmacological studies.
"Since the introduction of the scanning second-harmonic generation (SHG) microscopy technique by Gannaway and Sheppard in 1978, a scanning SHG microscope was used to obtain microscopic images of nonlinear materials including KD*P (Gannaway and Sheppard 1978), lithium niobate (Gannaway and Sheppard 1978), lithium triborate (Gauderon et al. 1998), and nonlinear poled polymers (Vydra and Eich 1998), as well as animal tissues (Freund et al. 1986; Guo 1996, 1997). Just like scanning two-photon fluorescence microscopy (Denk et al. 1990), scanning SHG microscopy can provide high axial/depth discrimination without a confocal aperture due to the quadratic dependence of the SHG signals on the laser intensity. "
[Show abstract][Hide abstract] 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.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.