Applying beam shaping optical components is important in various modern laser micromachining technologies like
drilling holes, scribing, patterning. Typically micromachining systems contain such components like F-theta lenses,
beam expanding and scanning optics like 2- and 3-axis galvo mirror scanners, therefore using of beam shapers require
building of special optical systems combining all optical components. As the beam shaping optics it is suggested to apply
field mapping refractive beam shapers like Shaper having some important features: low output divergence, high
transmittance, extended depth of field, capability to work with TEM00 and multimode lasers, as result providing a
freedom in building various optical systems. De-magnifying of flattop laser beam is realized with using imaging
technique; the imaging optical system to be composed from F-theta lens of scanning head and additional collimating
system to be used right after a Shaper. One of technical tasks in this approach is implementation of compact design of
the collimating part, another task – simple switching between final spot sizes. As a solution it is suggested to apply a
specially designed Beam Shaping Unit, which is based on a Shaper and combination of mirrors, locating between a
laser and a scanning head; the functions of that combined system are: conversion from Gaussian to flattop laser beam
irradiance profile, compact design, alignment features, easy adaptation to a laser and a scanning head used in particular
equipment, stepwise switching between resulting spot sizes.
There will be considered design features of refractive beam shapers and Beam Shaping Unit, examples of optical layouts
to generate flattop laser spots, which sizes span from several tens of microns to millimetres. Examples of real
implementations and results of material processing will be presented as well.
Uniform irradiance distribution of laser spot is highly advisable in various micromachining techniques like scribing, PCB and Through-Silicon Via (TSV) drilling, repair techniques in display making technologies. Scanning over whole working field with using popular 2- and 3-axis galvo mirror scanners is another important part of microprocessing systems. Therefore, combining of beam shaping optics, converting Gaussian to flattop (uniform) laser beam profile, with scanning optical heads is an insistent technical task. To provide flattop irradiance profile it is suggested to apply field mapping refractive beam shaping optics πShaper being characterized by some important features: low output divergence, high transmittance, extended depth of field, capability to work with TEM00 and multimode lasers, as result providing a freedom in building various optical systems. De-magnifying of flattop laser beam can be realized with using imaging technique; the imaging optical system to be composed from F-theta lens of scanning head and additional collimating system to be used right after a πShaper. One of the problems in this approach is implementation of compact design of the collimating part. As a solution it is suggested to apply a specially designed Beam Shaping Unit (BSU) to be installed between a laser and a scanning head and providing: conversion from Gaussian to flattop laser beam irradiance profile, compact collimator design, and functions of laser beam adjustment and adaptation to a laser and a scanning head used in particular equipment. There will be considered design features of refractive beam shapers πShaper and BSU, examples of optical layouts to generate flattop laser spots, which sizes span from several tens of microns to millimetres. Examples of real implementations and results of material processing will be presented as well.
Laser beam shaping systems converting Gaussian to flattop or other irradiance profiles are used in various solar cell manufacturing laser technologies to enhance their performance. Scanning over whole working field with using popular 2- and 3-axis galvo mirror scanners is very often important part of microprocessing systems. Therefore, combining of beam shaping optics with scanning heads is an important technical task in field of solar cells manufacturing. As the beam shaping optics it is suggested to apply field mapping refractive beam shapers πShaper having some important features: low output divergence, high transmittance, extended depth of field, capability to work with TEM00 and multimode lasers, as result providing a freedom in building various optical systems. De-magnifying of flattop laser beam can be realized with using imaging technique; the imaging optical system to be composed from F-ʘ lens of scanning head and additional collimating system to be used right after a πShaper. One of the problems in this approach is implementation of compact design of the collimating part. As a solution it is suggested to apply a specially designed Beam Shaping Unit being based on π Shaper and locating between a laser and a scanning head; the functions of that combined system are: conversion from Gaussian to flattop laser beam irradiance profile, compact collimator design, alignment features, easy adaptation to a laser and a scanning head used in particular equipment. There will be considered design features of refractive beam shapers π Shaper and Beam Shaping Unit, examples of optical layouts to generate flattop laser spots, which sizes span from several tens of microns to millimetres. Examples of real implementations and results of material processing will be presented as well.
We report on a technique for precise hole drilling in optical fibers using tightly focused femtosecond laser pulses. This direct laser writing approach makes it possible to minimize the amount of waveguide material for uncompromised mechanical performance of the fiber. The proof-of-the-principle of the fiber integration into a microfluidic chip is demonstrated. We show that fabricated holes in the waveguides can be used for measurement of absorption coefficient and refractive index changes at 1x10-3 refractive index units and 2 cm-1 for refractive index and absorption changes, respectively. Simple design and integration possibility of laser-fabricated waveguide sensors is prospective for optofluidic applications.
We report on surface structuring of sapphire, silicon carbide, and silicon by femtosecond laser pulses in multipulse
irradiation mode. The formed ripples on the flat surface or on the vertical walls with hierarchical structures
whose feature sizes are ranging from the irradiation wavelength down to ~ 50 nm are prospective templates for
surface enhanced Raman scattering after coating with plasmonic metals. We study complex patterns of fine
ripples with periods Λr, as small as λ/Rp, where Rp (see manuscript) 3 - 5. The mechanisms suggested for such Rp values
are discussed: temperature and density of breakdown plasma, angle of incidence, mechanism of second harmonic
generation (SHG) and absorption. Predictions of the surface and bulk models of ripple formation are compared
with experimental values of Rp-factor. We propose a model of ripple formation on the surface, which is based on
the known in-bulk sphere-to-plane formation of breakdown plasma in the surface proximity. In semiconductor
4H:SiC normal ripples with periods 190 and 230 nm were recorded with 800 nm and 1030 nm fs-laser pulses
respectively. We show that the period of ripples is defined by the dielectric properties of crystalline (solid) phase
rather than the molten phase in the case of silicon. Generation of SHG on the surface of sample and plasma
nano-bubbles are discussed: surface-SHG is found not important in ripples' formation as revealed by comparative
study of periods on Al2O3 and TiO2 at 800 nm wavelength of irradiation. We propose that ripple periodicity is
pinned to the smallest possible standing wave cavity (λ/n)/2 inside material of refractive index n.
Femtosecond laser micromachining of grooves in the SiO2 coated crystal silicon is investigated using 300 fs laser pulses
at a center wavelength of 1030 nm. A novel chirped pulse amplified femtosecond Yb:KGW laser source (Pharos, Light
Conversion, Lithuania) with high pulse repetition rate of 1- 350 kHz and high average power up to 8 W is employed. The
ablation depth of grooves as a function of pulse repetition rate, number of passes over the same groove, and the light
polarization relative to the cutting direction is investigated. Different scanning algorithms as well as influence of the focal
plane height relative to the sample are investigated.
We show experimentally, and interpret theoretically the conical and multiconical emission of optical parametric
oscillators with seed injection in monolithic mini-cavities. We show the tunability of the conical emission angle, the
switching between different resonant cones, and simultaneous emission on different cones, depending on the pump angle
as well as on the length of the resonator.
Polymethyl methacrylate (PMMA) is a versatile polymeric material that is well suited for fabrication of many commercial
optical components: lenses, fibers, windows, phase waveplates and others. Our focus is achromatic zero-order waveplates
made of anisotropic PMMA which can be used to modify the state of polarization of electromagnetic radiation. Such
waveplates have a broad range of application in devices where polarized radiation is used. For example, when tunable lasers
are used or when spectropolarimetric measurements are performed, one needs an achromatic waveplate providing a specific
retardation in a wide wavelength range. Herewith anisotropic properties of PMMA subjected to one-axis stretching are
analyzed and the technology for manufacturing such achromatic and super-achromatic, one-axis-stretched PMMA
waveplates is described. This technology excludes any mechanical processing of waveplate component surfaces. Technical
characteristics of achromatic and super-achromatic waveplates manufactured of PMMA including results of laser-induced
damage threshold (LIDT) measurements are discussed below.
We present a novel technique for engraving microscopic 2D patterns in one step with a UV pulsed laser by means of a versatile programmable approach. The laser beam is divided to an expanded low energy signal beam which is spatially modulated by a LCD modulator and a higher energy pump beam with a plane homogeneous wave front. Both beams are superposed in a highly magnesium doped photorefractive lithium-niobate crystal where an energy transfer towards the weaker signal beam takes place. The spatially modulated and amplified signal beam is then de-magnified and imaged onto the surface where the image has to be engraved. The need for the coherent amplifier rises out of the fact that LCDs are unable to withstand the high energy throughput required for etching. The combination of the amplifier with the amplitude modulator leads to a faster and more flexible solution than laser marking with pixel-by-pixel raster-scan, or fixed mask projection mode. Such a technique can thus be applied to identify valuable items by imprinting a smart and personalized 2D code onto its surface.
Theoretical studies on cavity transverse nonlinear dynamics have shown the possibility of exploiting the self-organizing properties of light response in the form of periodic patterns and cavity solitons. While very few experimental confirmations exist - only in macroscopic systems - we report on the first experimental results obtained in bulk and multi-quantum-well AlGaAs microresonators. These systems combine the advantage of : a monolithic character deriving from their well-controlled epitaxial growth conditions, a variety of nonlinear optical properties near the band gap edge, and a high Fresnel number. We review the general properties of semiconductor microresonators that lead to optical self-organization, emerging from the interplay between the dispersive or saturable absorptive nonlinearities and transverse mechanisms such as light diffraction and carrier diffusion. We show the first observation of periodic rolls, rhombs and hexagons patterns, stress the strong interaction of these patterns with the transverse fluctuations of the cavity thickness. Finally, we present the observation of precursor forms of cavity solitons, and evidence the strong thermal contribution they involve.
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