PERTURBATIVE EFFECTS ON THE LOWEST EXCITED STATES OF ANTHRACENE STUDIED BY TWO-PHOTON EXCITATION SPECTROSCOPY

Exciton excited states of CuCl nanoparticles dispersed in NaCl matrix have been investigated by means of two-photon excitation and two-step IR transient absorption. In the two-photon excitation spectra, there appears a distinct absorption edge. As the particle radius decreases from 6.3nm to 1.6nm, the edge energy increases by about 0.15eV, more than twice as large as that of the lowest 1S state. The fast decay component of the IR transient absorption under pulsed excitation of the lowest 1S exciton shows a broad band which shifts from 0.2 to 0.4eV as the radius decreases from >10nm to 1.4nm. These absorption edge and band are ascribed to the nP-like Rydberg excited states of the confined excitons. The large energy shift indicates that the weak confinement which is typically valid for the lowest 1S exciton state in CuCl nanoparticles is no more applicable to these excited states. Their spectra and confinement effect are discussed in comparison with theoretical prediction.

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Two-photon excitation microscopy in cellular biophysics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136684 ◽

1995 ◽

Vol 53 ◽

pp. 62-63

Author(s):

David W. Piston ◽

Brian D. Bennett ◽

Robert G. Summers

Keyword(s):

Confocal Microscopy ◽

Laser Beam ◽

Duty Cycle ◽

Excited Electronic State ◽

Input Power ◽

Two Photon ◽

Simultaneous Absorption ◽

Photon Excitation ◽

Very High ◽

Two Photon Excitation

Two-photon excitation microscopy (TPEM) provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging and photochemistry. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10-5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

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Two-photon excitation fluorescence microscopy in living systems

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100146618 ◽

1993 ◽

Vol 51 ◽

pp. 154-155 ◽

Cited By ~ 1

Author(s):

David W. Piston

Keyword(s):

Confocal Microscopy ◽

Fluorescence Microscopy ◽

Singlet State ◽

Excited Electronic State ◽

Input Power ◽

Two Photon ◽

Simultaneous Absorption ◽

Photon Excitation ◽

Very High ◽

Two Photon Excitation

Two-photon excitation fluorescence microscopy provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In our fluorescence experiments, the final excited state is the same singlet state that is populated during a conventional fluorescence experiment. Thus, the fluorophore exhibits the same emission properties (e.g. wavelength shifts, environmental sensitivity) used in typical biological microscopy studies. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10−5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

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