Polarization-induced control of two-photon excited fluorescence in a chiral polybinaphthyl

More than double the fun with two-photon excitation microscopy

For generations researchers have been observing the dynamic processes of life through the lens of a microscope. This has offered tremendous insights into biological phenomena that span multiple orders of time- and length-scales ranging from the pure magic of molecular reorganization at the membrane of immune cells, to cell migration and differentiation during development or wound healing. Standard fluorescence microscopy techniques offer glimpses at such processes in vitro, however, when applied in intact systems, they are challenged by reduced signal strengths and signal-to-noise ratios that result from deeper imaging. As a remedy, two-photon excitation (TPE) microscopy takes a special place, because it allows us to investigate processes in vivo, in their natural environment, even in a living animal. Here, we review the fundamental principles underlying TPE aimed at basic and advanced microscopy users interested in adopting TPE for intravital imaging. We focus on applications in neurobiology, present current trends towards faster, wider and deeper imaging, discuss the combination with photon counting technologies for metabolic imaging and spectroscopy, as well as highlight outstanding issues and drawbacks in development and application of these methodologies.

Polarization modulation of two-photon excited fluorescence in a V-shaped dipicolinate-triphenylamine compound

Polarization modulation of two-photon excited fluorescence in a V-shaped dipicolinate-triphenylamine compound was investigated with 100 fs 800 nm laser pulses. The peak fluorescence intensity versus the input irradiance was measured to meet a square dependence, which offered evidence for two-photon excited fluorescence. The variations of the two-photon excited fluorescence intensity showed strong response to the different polarized incident lights and were tightly dependent on the linearly polarized component of the incident light. Furthermore, the polarization modulation efficiency of the two-photon excited fluorescence had an obvious concentration dependence when the concentration of solution was under 2.5×10(-4)  mol/L. The enhancement of modulation efficiency was attributed to the concentration dependence of the two-photon absorption cross section.

Upconversion luminescence mechanisms of Er3+ ions under excitation of an 800 nm laser

The green/red emission mechanisms of Er³⁺ ions are studied by comparing PL properties upon excitation by CW and fs lasers.

Polarization-induced fluorescence modulation in a self-assembled coordination cage-shaped complex

Polarization-induced fluorescence modulation behavior of a self-assembled coordination cage-shaped complex was investigated using femtosecond laser pulses. The variations of the total two-photon-induced fluorescence (TPF) intensity were found to be strongly modulated by different polarized incident lights and tightly dependent on the linearly polarized component of the excited light. The polarization-induced modulation efficiency of the TPF underwent intensity-dependent decrease, which could be attributed to the two-photon-induced excited-state absorption. The nonlinear absorption behavior of the complex was also studied by performing both femtosecond open aperture Z-scan and nonlinear transmission measurements, which help to better understand the intrinsic optical properties of the molecule and portend its practical applications.

Polarization effect on the two-photon absorption of a chiral compound

In this report, we investigate the polarization effect (linear, elliptical and circular) on the two-photon absorption (2PA) properties of a chiral compound based in azoaromatic moieties using the femtosecond Z-scan technique with low repetition rate and low pulse energy. We observed a strong 2PA modulation between 800 nm and 960 nm as a function the polarization changes from linear through elliptical to circular. Such results were interpreted employing the sum-over-essential states approach, which allowed us to model the 2PA circular-linear dichroism effect and to identifier the overlapping of the excited electronic states responsible by the 2PA allowed band.