By adapting a laser scanning microscope with a titanium sapphire femtosecond pulsed laser and transmission optics, we are able to produce live cell images based on the nonlinear optical phenomenon of second harmonic generation (SHG). Second harmonic imaging (SHIM) is an ideal method for probing membranes of living cells because it offers the high resolution of nonlinear optical microscopy with the potential for near-total avoidance of photobleaching and phototoxicity. The technique has been implemented on three cell lines labeled with membrane-staining dyes that have large nonlinear optical coefficients. The images can be obtained within physiologically relevant time scales. Both achiral and chiral dyes were used to compare image formation for the case of single- and double-leaflet staining, and it was found that chirality plays a significant role in the mechanism of contrast generation. It is also shown that SHIM is highly sensitive to membrane potential, with a depolarization of 25 mV resulting in an approximately twofold loss of signal intensity.

High-resolution nonlinear optical imaging of live cells by second harmonic generation

Recent progress in the development of high power fibre lasers will be reviewed, and the prospects for scaling output powers to well beyond the hundred watt level, whilst maintaining diffraction-limited beam quality will be discussed

High power fibre lasers

Intrinsic, three-dimensionally resolved, microscopic imaging of dynamical structures and biochemical processes in living preparations has been realized by nonlinear laser scanning fluorescence microscopy. The search for useful two-photon and three-photon excitation spectra, motivated by the emergence of nonlinear microscopy as a powerful biophysical instrument, has now discovered a virtual artist's palette of chemical indicators, fluorescent markers, and native biological fluorophores, including NADH, flavins, and green fluorescent proteins, that are applicable to living biological preparations. More than 25 two-photon excitation spectra of ultraviolet and visible absorbing molecules reveal useful cross sections, some conveniently blue-shifted, for near-infrared absorption. Measurements of three-photon fluorophore excitation spectra now define alternative windows at relatively benign wavelengths to excite deeper ultraviolet fluorophores. The inherent optical sectioning capability of nonlinear excitation provides three-dimensional resolution for imaging and avoids out-of-focus background and photodamage. Here, the measured nonlinear excitation spectra and their photophysical characteristics that empower nonlinear laser microscopy for biological imaging are described.

Multiphoton fluorescence excitation: New spectral windows for biological nonlinear microscopy

Recent advance of emerging low-dimensional materials for vector soliton generation in fiber lasers

Narrow-bandgap materials possess the intriguing optical-electric properties and unique structures, which can be widely applied in the field of photonics, energy optoelectronic sensing and biomedicine, etc. Nowadays, the researches on nonlinear optical properties of narrow-bandgap materials have attracted extensive attention worldwide. In this paper, we review the progress of narrow-bandgap materials from many aspects, such as background, nonlinear optical properties, energy band structure, methods of preparation, and applications. These materials have obvious nonlinear optical characteristics and the interaction with the short pulse laser excitation shows the extremely strong nonlinear absorption characteristics, which leads to the optical limiting or saturable absorption related to Pauli blocking and excited state absorption. Especially, some of these novel narrow-bandgap materials have been utilized for the generation of ultrashort pulse that covers the range from the visible to mid-infrared wavelength regions. Hence, the study on these materials paves a new way for the advancement of optoelctronics devices.

Chun-Yang Ma

Papers

Generation, optimization, and application of ultrashort femtosecond pulse in mode-locked fiber lasers

Generation and Categories of Solitons in Various Mode-locked Fiber Lasers