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Selective fluorescence suppression for two spectrally overlapping fluorophores that undergo simultaneous two-photon absorption from identical femtosecond pulses through precise control in relative timing and polarization of the exciting pulse-pair.

Using femtosecond pump-probe thermal lens (TL) spectroscopy, we show that the effect of isotope substitution can be monitored through a modulation of TL signals in binary liquids showing the important of molecular properties on TL.

Confocal microscopy, one of the modern day fluorescence laser-scanning microscopic techniques, is suffered from having sufficient out-of-focus signal. On the other hand, in multiphoton microscopy ultrafast laser pulses are commonly used to circumvent low multiphoton absorption cross-sections of common fluorophores; due to broad overlapping two-photon absorption (TPA) spectra of fluorophores and large spectral bandwidth of a short pulse, simultaneous excitation of many fluorophores is common demanding selective excitation of individual fluorophores if required. Addressing the first issue, our recent work has shown that ultrafast one-photon pulsed illumination leads to increased signal-to-noise ratio by controlling the fluorophore photo-physics.1-2 Considering TPA, we have demonstrated that photo-thermal corruption due to pulse pile-up effect is largely solvent-mediated and a rather slow process which can be taken care of by simple intensity modulation of a pulse-train.3-4 We have recently shown how precise delay between pair of ultrafast pulses can lead to possible selective excitation in microscopy.5 We have also demonstrated how gigantic peak-power of a femto-second laser pulse (with rather low average power) leads to stable optical trapping of latex nano-particles which is otherwise impossible with continuous-wave excitation (at the same average power).6 All these cutting-edge topics will be discussed in the presentation.1. A K De and D Goswami, J. Fluorescence, 19, 931 (2009).2. A K De and D Goswami, J Microscopy, 233, 320 (2009).3. A K De and D Goswami, J. Fluorescence, 19, 381 (2009).4. A K De and D Goswami, J. Microscopy, 235, 119 (2009).5. A K De and D Goswami, J. Biomed. Opt., in press.6. A K De, D Roy, A Dutta and D Goswami, Appd. Opt., 48, G33 (2009).