Jess M. Gunn

Quantitative investigation of the multiphoton intrapulse interference phase scan method for simultaneous phase measurement and compensation of femtosecond laser pulses

Femtosecond pulse characterization and compensation using multiphoton intrapulse interference phase scan (MIIPS) [Opt. Lett.29, 775 (2004)] was rigorously tested. MIIPS was found to have 3 mrad precision within the 90 nm bandwidth of the pulses. Group-velocity dispersion measurements of glass and quartz provided independent accuracy tests. Phase distortions from high-numerical-aperture objectives were measured and corrected using MIIPS, an important requirement for reproducible two-photon microscopy. Phase compensation greatly improved the pulse-shaping results through a more accurate delivery of continuous and binary phase functions to the sample. MIIPS measurements were possible through the scattering of biological tissue, a consideration for biomedical imaging.

The MIIPS method for simultaneous phase measurement and compensation of femtosecond laser pulses and its role in two-photon microscopy and imaging

A number of nonlinear imaging modalities, such as two-photon excitation and second harmonic generation, have gained popularity during the last decade. These, and related methods, have in common the use of a femtosecond laser in the near infrared, with the short pulse duration making the nonlinear excitation highly efficient. Efforts toward the use of pulses with pulse duration at or below 10 fs, however, have been a great challenge, in part due to the fact that shorter pulses have been found to cause greater sample damage. Here we provide a brief review of the MIIPS method for correction of phase distortions introduced by high numerical aperture objectives and the introduction of simple phase functions capable of preventing three-photon induced damage, reducing autofluorescence, and providing selective probe excitation.

Ultrashort optical pulse propagation in metal nanoparticle covered dielectric surfaces

We characterize the behavior of optical pulse propagation in surfaces covered with silver metal nanoparticles and quantify the dispersion introduced as the pulse propagates.

Measurement of Dispersion Properties of Silver Nanowires Used as Plasmon Waveguides

Surface plasmon waves created by shaped femtosecond pulses are used to control the two-photon induced plasmon emission of silver nanoparticles. A quantitative measurement of the dispersion properties of surface plasmon waveguides is given.

Properties of Two-Photon Induced Emission from Dendritic Silver Nanoclusters

The emissive properties of dendritic silver thin films due to two-photon excitation are explored. Emission is observed to occur at points more than 40 µm from the focal spot, and is polarization dependent.

Two-Photon Induced Emission From Silver Nanoparticle Aggregates on Thin Films and in Solution

The coupling of incident electromagnetic radiation with surface plasmons on nanoscale dendritic metal particles has been observed to cause localization of the electromagnetic field, or ‘hot spots’. This has led to observed enhancements of nonlinear optical processes, including surface-enhanced Raman scattering (SERS), second harmonic generation (SHG), and multiphoton photoemission [1]. These effects are reportedly strongest in aggregates that have a fractal nature.

Remote two-photon emission from dendritic silver nanoclusters

Silver nanoparticles have been known to enhance local electromagnetic fields and therefore many optical processes, including surface-enhanced Raman scattering, second harmonic generation and multiphoton photoemission [1]. Dendritic silver nanoparticle clusters, which have a fractal nature, can behave as antennas that focus the electromagnetic field into “hot-spots” – extremely localized regions of enhanced electromagnetic fields (see Fig. 1). Recent theoretical work indicates that patterned silver nanoparticle structures could be created to enhance a field with nanometer resolution [2].

Quantitative phase characterization and compensation by multiphoton intrapulse interference phase scan (MIIPS)

Accurate and reproducible research in the field of femtochemistry requires both the measurement and then subsequent correction of phase distortions inherent in femtosecond laser pulses. Spectral phase distortions, which are introduced by the transmission of an ultrashort laser pulse through a lens, optical fiber, or microscope objective, or by interaction with an optical surface such as a dielectric mirror, have a negative effect both on the ability to carry out and the ability to reproduce experiments in which pulse duration is of importance, or nonlinear optical processes are utilized. This chapter presents a quantitative study on the ability of multiphoton intrapulse interference phase scan (MIIPS) to both characterize phase distortions with better precision and reproducibility than other established methods, and to correct them to obtain transform-limited pulses. The MIIPS method provides accurate phase retrieval and phase correction at the sample. These are important functions for reproducible femtosecond laser pulse experiments, especially those involving nonlinear optics. The MIIPS setup can also be used to deliver accurate synthetic wavefunctions at the sample as would be required for laser control experiments.

Selective Two-Photon Imaging of a Biological Sample

The use of phase shaping to selectively enhance the excitation of dyes in biological samples is shown. Resulting images show high contrast without the use of filters or tuning the laser.

Compensation of phase distortions introduced by high objectives on sub-10 fs pulses

The ability of MIIPS to characterize and compensate for the high distortion experienced by a sub-10 fs laser beam passing through a high NA microscope objective is explored.