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Supercontinuum generation in bulk media is not normally observed at the nJ-level pulse energies available from high-repetition-rate femtosecond oscillators. Here, we present results demonstrating how a visible supercontinuum can be produced in bulk orientation-patterned gallium phosphide from 100-MHz 1040-nm femtosecond pulses with energies of up to 32 nJ. High-order parametric gain near 550 nm, seeded by self-phase-modulated spectral sidebands, underpins this new and simple supercontinuum process which yields an output spectrum spanning from the blue/green to the red.

Orientation-patterned gallium phosphide [1] (OPGaP) is a wide-bandgap material enabling two-photonabsorption-free pumping using 1040-nm Yb-lasers, and such OPGaP optical parametric oscillators (OPOs) have been applied in Fourier-transform [2] and dual-comb [3] spectroscopies across the 5–12-μm molecular fingerprint region. Hetero-epitaxial growth of GaP on orientation-patterned gallium arsenide (OPGaAs) templates has been developed [4] , to mitigate issues with GaP substrates, but no nonlinear frequency conversion has yet been demonstrated. Here we report the first efficient frequency conversion in OPGaP-on-OPGaAs. OPGaP layers up to 1.2-mm thick were grown by hydride vapor-phase epitaxy (HVPE) on a 3-inch MBE-grown OPGaAs template. Several multi-grating and fan-out crystals of lengths 1.1 mm and 2.9 mm were diced from the wafer and polished into plane-parallel chips, and a broadband anti-reflection coating was applied to both faces.

We present an eye-safe active FTIR spectroscopy system based on a broadband ultrafast optical parametric oscillator (OPO) operating in the 3.1–3.5-μm wavelength range (where common hydrocarbons display absorption peaks) and capable of acquiring gas absorption spectra from a simple target. We demonstrate that simultaneous quantitative measurement of atmospheric background levels of water and methane is readily achieved by this system, even in the presence of strong absorption from a control cell of 1.5% ethane.

We report for the first time nonlinear frequency conversion—specifically optical parametric oscillation—in OP-GaP layers grown by hydride vapor-phase epitaxy on 3-inch OP-GaAs templates. Continuous tuning with wavelength coverage from 3.9–12 µm was achieved by using stepped and fan-out gratings having periods from 18.0–35.2 µm, which propagated 150 µm of a 1.2-mm-thick layer before overgrowth. Anti-reflection-coated OP-GaP crystals were pumped at 1040 nm with an ultrafast Yb-fiber laser, yielding idler output powers up to 150 mW (60 mW) in spectra centered at a wavelength of 5.6 µm (10.7 µm).

Supercontinuum generation from nanojoule femtosecond lasers is well known in photonic-crystal fibers, channel waveguides, and micro-resonators, in which strong confinement shapes their dispersion and provides sufficient intensity for self-phase modulation, four-wave mixing, and Raman scattering to cause substantial spectral broadening. Until now, supercontinuum generation in bulk media has not been observed at equivalent energies, but here we introduce a new mechanism combining second- and third-order nonlinearities to produce broadband visible light in orientation-patterned gallium phosphide. A supercontinuum from the blue/green to the red is produced from 32 nJ 1040 nm femtosecond pulses, and a nonlinear-envelope-equation model including χ ( 2 ) and χ ( 3 ) nonlinearities implies that high-order parametric gain pumped by the second-harmonic light of the laser and seeded by self-phase-modulated sidebands is responsible.

The broad and slowly varying spectral features of liquids and solids require broadband sources in the mid- to long-wave infrared for their detection and identification. We present here a range of measurements made using uniquely tunable femtosecond optical parametric oscillators, which have enabled stand-off Fourier-transform spectroscopy to be implemented across a large part of the spectral fingerprint region. In this way we have achieved active stand-off detection of liquids on surfaces, of powders and of airborne liquid particles in aerosol form. We discuss the optical parametric oscillator technology, the spectroscopy implementations and the detection capabilities and limitations of the techniques.

The rapidly developing semiconductor industry demands constant innovations in optoelectronic imaging of semiconductor integrated circuits to keep up with continuing device scaling. It was recently shown that two-photon laser-assisted device alteration (2pLADA) can deliver precision fault isolation. Here we describe an investigation into the influence of the incident light polarization on the 2pLADA spatial resolution. Linear polarization provides a highly confined but elliptical focal spot, while circular polarization diminishes the lateral resolution but benefits from a symmetrical focal spot. Radially polarized light potentially provides the highest lateral imaging resolution in all directions at the expense of the longitudinal resolution. By comparing 2pLADA results obtained using linear, circular and radial polarizations we show that certain polarizations have advantages in particular applications. Therefore a polarization optimized 2pLADA tool can achieve a sufficiently high performance to isolate faults of transistors separated by as little as 100 nm and maybe smaller.

Laser two-photon polymerization (LTPP) has been widely reported as a tool for three-dimensional micro/nanofabrication. Femtosecond lasers are employed to form nanostructures in photosensitive resins with subwavelength resolution. We demonstrate high throughput large scanning area LTPP system based on linear motor driven stages combined with Yb:KGW high repetition rate (312.5 kHz) amplified laser as irradiation source (515 nm second harmonic’s wavelength). Femtosecond green light can be focused to a smaller diffraction limited spot and provides higher structuring resolution comparing to commonly used Ti:sapphire lasers (operating at NIR wavelengths) used for LTPP. Additionally, shorter irradiation wavelength enables to process more of widely used photosensitive materials. The system capacitates production of nanostructures having 200 nm lateral resolution with high repeatability. By modifying focusing optics there is a possibility to scale up the fabrication: reduction of resolution results in shortening of fabrication time. The system enables formation of 3D structures with size varying from tens of microns to tens of millimetres. Most of the materials commonly used for photopolymerization technology (various blends of acrylates, hybrid organic–inorganic materials, and epoxy resins) are well suitable for processing with the constructed LTPP system. Keywords: two-photon absorption, laser processing, photopolymerization, micro/nanofabrication, three-dimensional structures, tissue engineering

Laser Two-Photon Polymerization (LTPP) is a technique enabling formation of 3D nanostructures in photosensitive resins with sub-wavelength resolution and unmatched flexibility. However, controllable fabrication of sub-100 nm features by this technique is still a challenge. Self-polymerization, also known as non-local polymerization, is considered to be promising in this ultra-high resolution structure formation. Recent observation of fragile self-polymerized fibres with diameter within tens of nanometres (nano-fibres) encourages the use of self-polymerization to produce nanometre scale structures other than fibres and to define the conditions for controllable fabrication. “X”-shaped polymerized supports are used as rigid structures to produce suspended self-polymerized features of different nature (shape and dimensionality) in-between the walls of “X”. By laser writing lines parallel to the substrate and perpendicular to the long symmetry axis of “X” under different conditions, selfformation of periodic nano-fibres (diameter

Comparison of high-resolution sub-surface microscopy shows that illumination with linear polarization resolves an edge with resolutions of 95 nm and 120 nm, depending on E-field orientation, while radial polarization achieves a resolution of 98 nm.

We investigate different linear effects that appear in the light beam propagation behind a three-dimensional woodpile photonic crystal. On one hand we report and analyse experimental observation of narrow and well collimated laser beam formation behind the photonic crystal. We show that this collimation depends on the input laser beam focusing conditions. On the other hand we also report the first theoretical and numerical observation double imaging formation behind the photonic crystal. That conclusion comes from the idea that the spatial dispersion possess multiple branches (Bloch branches), generally of different curvatures, for a fixed frequency.

We report and analyze experimental observation of the formation of a narrow, well collimated laser beam at optical frequency behind the woodpile photonic crystal fabricated using a femtosecond laser multi-photon polymerization technique. We show that the collimation depends on the input laser beam focusing conditions. We discuss the experimental results and give theoretical interpretation.

Three-dimensional photonic crystals with woodpile structure are demonstrated to exhibit collimation of light beams behind the photonic structure. Woodpile structure photonic crystals with longitudinal modulation periods in a range of 7.4 – 7.8 µm, and transverse periods of 1 µm were fabricated using laser multi-photon polymerization technique in a negative-tone photoresist. As expected from theoretical predictions, the beams propagating along the axis of period variation collimate behind the crystal, which is a first experimental observation of the phenomenon.