Matthew E. Anderson

Measuring vortex charge with a triangular aperture

We measure the charge of vortex beams (up to ±7) via diffraction in a triangular aperture. We also apply this technique for measuring femtosecond vortices and non-integer vortices. The results compare favorably with numerical modeling.

Ultra-large field-of-view two-photon microscopy

We present a two-photon microscope that images the full extent of murine cortex with an objective-limited spatial resolution across an 8 mm by 10 mm field. The lateral resolution is approximately 1 µm and the maximum scan speed is 5 mm/ms. The scan pathway employs large diameter compound lenses to minimize aberrations and performs near theoretical limits. We demonstrate the special utility of the microscope by recording resting-state vasomotion across both hemispheres of the murine brain through a transcranial window and by imaging histological sections without the need to stitch.

Simplified spectral phase interferometry for direct electric-field reconstruction by using a thick nonlinear crystal.

We propose and demonstrate a novel implementation of spectral-shearing interferometry (SSI) for reconstructing the electric field of ultrashort pulses by utilizing asymmetric group velocity matching in a long nonlinear crystal. The proposed configuration eliminates the requirement for a linearly chirped auxiliary pulse that is in common in all existing SSI methods, relying on nonlinear conversion to produce a spectral shear.

Measuring ultrafast pulses in the near-ultraviolet using spectral phase interferometry for direct electric field reconstruction

Abstract A novel version of spectral phase interferometry for direct electric field reconstruction (SPIDER) based on parametric downconversion is demonstrated. This process is used to completely characterize low-energy, ultrashort optical pulses in the near-ultraviolet region of the spectrum.

Measuring the topological charge of ultrabroadband, optical-vortex beams with a triangular aperture

A simple technique for determining the topological charge of supercontinuum optical vortices is presented. The spatial dispersion inherent to generating broadband vortices with a single forked grating is compensated with a double-pass arrangement from a single spatial light modulator. The vortex charge is determined by inspecting the diffraction pattern through a triangular aperture. It is shown that the topological charge is constant, and can be consistently measured, across a wide range of colors.

Experimental realization of the devil’s vortex Fresnel lens with a programmable spatial light modulator

We present a unique method for experimentally generating multiple vortices by way of a devils vortex lens combined with a Fresnel lens using a spatial light modulator. These lenses have the multifocal properties of fractal zone plates combined with the orbital angular momentum of a spiral phase plate and can be tailored to fit within a small space on an optical bench. Results are presented alongside numerical simulations, demonstrating the robust nature of both the experimental method and the predictive power of the Huygens-Fresnel wavelet theory.

Measuring ultrashort optical pulses in the presence of noise: an empirical study of the performance of spectral phase interferometry for direct electric field reconstruction

We have measured the performance of a real spectral phase interferometry for direct electric field reconstruction (SPIDER) apparatus operating under suboptimal conditions. We analyzed the errors in SPIDERs measurements of the temporal phases and intensities of 50-fs ultrashort laser pulses as a function of the additive noise in the detected signal. It was found that SPIDER performs exceptionally well, particularly in the case of additive noise. Specifically, a signal with 10% noise yields a pulse that has a mere 2% error in its intensity profile and a phase that differs from the nominal value by 0.2 rad. Furthermore, we quantified SPIDERs performance with limited detector resolution and as a function of signal averaging.

Two-photon absorption and blue-light-induced red absorption in LiTaO3 waveguides

Two-photon absorption and blue-light-induced red absorption (BLIRA) is demonstrated in lithium tantalate (LiTaO3) waveguides with ultrashort laser pulses. The blue transmission is modeled for hyperbolic-secant-squared pulses of blue light and is shown to be heavily attenuated by two-photon absorption. The blue light also generates traps for red light, which are absorbed through single-photon interactions. Over 50% red absorption is observed. The blue pulse energy dependence of BLIRA is shown to follow recent theoretical models that rely on two different physical mechanisms depending on the temporal overlap of the pump and probe pulses. The time dependence of BLIRA is explored experimentally and is shown to fit well to a stretched-exponential model. Finally, we investigate the effects of pulse shaping and find that, over our range of pulse durations, the amount of BLIRA is relatively insensitive to pulse shape.

Single-iteration compression of femtosecond laser pulses

We demonstrate a technique for correcting arbitrary spectral-phase aberrations in a single iteration with no reference pulse. By utilizing spectral-phase interferometry for direct electric field reconstruction and a programmable liquid-crystal spatial light modulator, we have achieved compression of complex pulse shapes from nearly picosecond extent down to 70 fs.

Vortex Interference Effects From A Segmented Spatial Light Modulator And A Supercontinuum Source

We generate optical vortices from the supercontinuum output of an ultrafast laser interacting with a micro-structured fiber. Using a spatial light modulator, single and multiple vortices are generated, controlled and made to interfere.