Ariel R. Libertun

Polarization selective computer-generated holograms realized in glass by femtosecond laser induced nanogratings

We demonstrate polarization selective computer-generated holograms (PSCGH) for visible light operation fabricated in glass by a femtosecond laser. For this purpose we create arrays of tailored microwaveplates by controlling the laser formation of nanogratings embedded in fused silica. A birefringent cell-oriented encoding method adapted to the characteristics of the physical writing process is proposed and implemented. According to this method, each cell contains a micro-waveplate with controlled phase retardation and orientation. A detour of each microwaveplate, combined with the orientation of its principal optical axis, simultaneously realizes a different phase function for each polarization. PSCGHs are attractive for integration with other free-space and guided-wave devices embedded in glass.

Quantitative phase microscopy through differential interference imaging

An extension of Nomarski differential interference contrast microscopy enables isotropic linear phase imaging through the combination of phase shifting, two directions of shear, and Fourier space integration using a modified spiral phase transform. We apply this method to simulated and experimentally acquired images of partially absorptive test objects. A direct comparison of the computationally determined phase to the true object phase demonstrates the capabilities of the method. Simulation results predict and confirm results obtained from experimentally acquired images.

Highly coherent light at 13 nm generated by use of quasi-phase-matched high-harmonic generation

By measuring the fringe visibility in a Youngs double pinhole experiment, we demonstrate that quasi-phase-matched high-harmonic generation produces beams with very high spatial coherence at wavelengths around 13 nm. To our knowledge these are the highest spatial coherence values ever measured at such short wavelengths from any source without spatial filtering. This results in a practical, small-scale, coherent, extreme-ultraviolet source that is useful for applications in metrology, imaging, and microscopy.

Quantitative structured-illumination phase microscopy

We introduce a quantitative phase imaging method for homogeneous objects with a bright field transmission microscope by using an amplitude mask and a digital processing algorithm. A known amplitude pattern is imaged on the sample plane containing a thick phase object by placing an amplitude mask in the field diaphragm of the microscope. The phase object distorts the amplitude pattern according to its optical path length (OPL) profile, and the distorted pattern is recorded in a CCD detector. A digital processing algorithm then estimates the objects quantitative OPL profile based on a closed form analytical solution, which is derived using a ray optics model for objects with small OPL gradients.

Calibration of a phase-shifting DIC microscope for quantitative phase imaging

Phase-shifting differential interference contrast (DIC) provides images in which the intensity of DIC is transformed into values linearly proportional to differential phase delay. Linear regression analysis of the Fourier space, spiral phase, integration technique shows these values can be integrated and calibrated to provide accurate phase measurements of objects embedded in optically transparent media regardless of symmetry or absorption properties. This approach has the potential to overcome the limitations of profilometery, which cannot access embedded objects, and extend the capabilities of the traditional DIC microscope, which images embedded phase objects, but does not provide quantitative information.

Design of fully spatially coherent extreme-ultraviolet light sources

We demonstrate experimentally that, in order to generate fully spatially coherent extreme-ultraviolet (EUV) beams using high-harmonic generation, it is necessary to guide the driving laser beam over long interaction lengths in gas-filled hollow waveguides. Numerical simulations show that, in propagating the laser through a long plasma-filled guide, the laser beam forms a stable eigenmode with uniform spatial phase, even at very high levels of ionization. This results in a compact, highly spatially coherent, EUV source useful for applications in EUV metrology, microscopy, interferometry, and holography.

QSIP: phase imaging made possible in a bright field microscope

Quantitative structured-illumination phase microscopy (QSIP) uses a conventional bright field microscope to quantitatively measure the optical path length profiles of homogenous phase-only objects. The illumination in QSIP is structured with a predetermined pattern by placing an amplitude mask in the field diaphragm of the microscope. From the image of the amplitude mask, a numerical algorithm implementing a closed form analytical solution calculates the objects optical path length profile. In this paper, we investigate the accuracy of the numerical algorithm used and show that it can be made arbitrarily accurate by using numerical optimization. We then analyze the effect of the systems numerical aperture (NA), and show that QSIP can be used with a wide range of NAs for objects with small phase gradients, and can be used with relatively lower NAs for objects with large phase gradients.

Coherent imaging of laser-plasma interactions using high-harmonic EUV Light

We demonstrate that light generated using high-harmonic conversion in waveguides has very high spatial coherence at 30 nm and 13nm. Using this light source, we demonstrate EUV images of the explosion of a micron-size water droplet illuminated by an intense femtosecond laser using an all-reflective, double-multilayer mirror setup and a CCD camera as an image recording device.

Novel functionality of three-dimensional nanostructured devices fabricated with femtosecond pulse laser

The optical properties of modulated three- dimensional periodic structures called computer generated volume holograms are studied and different encoding techniques are proposed. The structures are fabricated using femtosecond laser pulses to modify the refractive index in the volume of dielectric materials.

Structured-Illumination Quantitative Phase Microscopy

We propose a quantitative phase microscope that is essentially a bright field transmission microscope with two simple modifications: an amplitude mask is introduced in the field diaphragm and a post processing algorithm retrieves the phase.