Iain G. Cormack

Ultrashort pulse characterisation with SHG collinear-FROG

We outline criteria for fast and accurate acquisition of collinear FROG (CFROG) trace and how it can be transformed into the more traditional noncollinear FROG trace. The CFROG has an intrinsically simple geometry that provides greater versatility as well as the ability for built-in delay calibration and enhanced error-checking. The procedure, based on data processing, allows conventional SHG-FROG retrieval algorithms to be used. This technique is tested numerically and experimentally giving excellent results. This work represents an attractive alternative to the traditional, more complex non-collinear FROG technique while, at the same time, extending its use to experiments where collinear geometry is imposed.

Measurement of electric field by interferometric spectral trace observation.

We present a new methodology that obtains, in an analytical way, the complex electric field of ultrashort pulses. This methodology is based only on Fourier analysis of the frequency components of spectrally resolved interferometric collinear autocorrelations. We present an experimental demonstration of this technique and the results are compared with the conventional second-harmonic generation frequency-resolved optical gating technique.

Starch-based second-harmonic-generated collinear frequency-resolved optical gating pulse characterization at the focal plane of a high-numerical-aperture lens

We report the use of starch as an ideal nonlinear medium with which to perform collinear frequency-resolved optical gating measurements of ultrashort pulses at the focal plane of a high-numerical-aperture (NA) lens. We achieved these measurements by simply sandwiching starch granules (suspended in water) between two coverslips and placing them within the focal plane of a high-NA lens. The natural nonlinear characteristics of starch allow the correct phase matching of pulses at the focal plane of a high-NA lens at different wavelengths. This elegant arrangement overcomes all the complexity and problems that were previously associated with pulse characterization within a multiphoton microscope.

Simultaneous analytical characterisation of two ultrashort laser pulses using spectrally resolved interferometric correlations

In this paper we discuss in detail the underlying theory of a novel method that allows the characterizing of ultrashort laser pulses to be achieved in an analytical way. MEFISTO, (measuring the electric field by interferometric spectral trace observation) is based on a Fourier analysis of the information contained in a spectrally resolved interferometric correlation and can be applied to both situations: the characterization of an unknown pulse (MEFISTO) or to the simultaneous characterization of two different unknowns pulses (Blind-MEFISTO). The theoretical development and experimental practical implications are discussed in both situations.

Cavity resonances in finite plasmonic chains

The authors report on the observation of cavity resonances along finite gold nanoparticle chains which, unlike continuous gold nanowires, lead to a high field concentration at their extremity. The mode signature has been assessed by probing the local field bound to the metal with two-photon luminescence spectroscopy. Simulations based on the Green dyadic method corroborate a good agreement with the measurements and bring further insight to the physics involved.

MEFISTO characterization of broadband pulse from a single mode fiber for in situ nonlinear microscopy

The generation of controlled broadband pulses using output pulsed of a Ti:sapphire laser traveling through a bending insensitive single mode fiber. A pair of prisms is used to control the chirp of the pulses from the fiber. A simple technique to increase the available bandwidth of the pulses from a Ti:sapphire laser is proposed. The pulses are characterized using a nonlinear microscope.

Neuronal fillopodia respond to distant femtosecond pulses

In this paper, we show that the neuronal fillopodia can detect and respond to the presence of focused femtosecond laser light at a distance, an effect that does not occur when CW illumination is used. Control and manipulation of axonal growth is of extreme importance in the field of neurosciences as it could lead to advances such as in-vivo nerve regeneration or arbitrary patterning of neural circuits.

In situ, starch-based backwards SHG for MEFISTO pulse characterization in multiphoton microscopy

In this paper an ideal approach for pulse characterisation within a multiphoton microscope is demonstrated. This methodology will be used for shaping the pulses with an spatial light modulators (SLM) and to study the influence of arbitrary phase profiles, specifically with large bandwidth pulses, on nonlinear imaging of the biological samples.

Archaeophotonics:Lasers Unveil the Past

Scientists use two-photon absorption fluorescence to recover written information on Roman relics and solve a 2,000-year-old mystery.

Comparison of iterative and non-iterative retrieval from few-cycle interferometric FROG traces

We carefully compared pulse characterization methods for few-cycle pulses, using transform-limited sub-7-fs oscillator pulses and chirped amplified pulses. The non-iterative MEFISTO method is found capable of determining all major properties of these challenging test pulses.