Andrius Marcinkevicius

Femtosecond laser-assisted three-dimensional microfabrication in silica

We demonstrate direct three-dimensional (3-D) microfabrication inside a volume of silica glass. The whole fabrication process was carried out in two steps:(i) writing of the preprogrammed 3-D pattern inside silica glass by focused femtosecond (fs) laser pulses and (ii) etching of the written structure in a 5% aqueous solution of HF acid. This technique allows fabrication of 3-D channels as small as 10mum in diameter inside the volume with any angle of interconnection and a high aspect ratio (10mum -diameter channels in a 100mum -thick silica slab).

80 W, 120 fs Yb-fiber frequency comb

We report on a high-power fiber frequency comb exhibiting linear chirped-pulse amplification up to 80 W and generating 120 fs pulses. By proper matching of the group delay between the fiber stretcher and compressor, a compression ratio of 3100 could be achieved. Carrier envelope offset self-referencing and long-term phase locking to an rf reference is demonstrated, exemplifying the suitability of this system for generating vacuum and extreme-UV frequency combs via enhancement in passive cavities and high harmonic generation.

Application of femtosecond laser pulses for microfabrication of transparent media

Femtosecond laser microfabrication of 3D optical memories and photonic crystal (PhC) structures in solid glasses and liquid resins are demonstrated. The optical memories can be read out from both transmission and emission images. The PhC structures reveal clear signatures of photonic bandgap (PBG) and microcavity formation.

Tailoring and characterization of photonic crystals

Photonic crystals are promising systems for application in the fields of optoelectronics and optical communications. Understanding of their underlying physical principles and techniques for fabrication and characterization has progressed significantly during the last decade. This paper outlines the main achievements in these areas, and gives an overview of various photonic crystal systems, including those fabricated in semiconductors by traditional tools of microelectronics, and those fabricated from glasses, resins and other materials using novel non-traditional techniques.

Application of bessel beams for microfabrication of dielectrics by femtosecond laser

We demonstrate a novel approach to femtosecond microfabrication of transparent dielectrics, which employs nondiffracting Bessel beams instead of the conventionally used Gaussian beams. The main advantage of Bessel beams is the possibility of recording linear photomodified tracks, extending along the lines of nondiffractive beam propagation without sample translation, as would be required for Gaussian beams. Recording of patterns with an aspect ratio of up to 102–103 in vitreous silica using amplified femtosecond Ti:saphire laser pulses is demonstrated.

Femtosecond laser micro-fabrication for tailoring photonic crystals in resins and silica

We report laser micro-fabrication of photonic crystal structures in silica glass and photopolymerizing resins, and present a detailed analysis of their structural and optical properties. Photonic crystals with 2D triangular lattice and 3D diamond lattice in glass are found to exhibit moderately pronounced photonic pseudogaps. Formation of planar microcavity is demonstrated in log-pile 3D photonic crystal, laser micro-fabricated in resin.

Fabrication of 3D interconnected network of microchannels inside silica by femtosecond irradiation and etching

We present, to the best of our knowledge, first demonstration of a direct three-dimensional (3D) microfabrication in the volume of silica glass. The microfabrication was carried out in two steps: 1) recording 3D patterns inside silica glass via silica damaging by focused femtosecond laser pulses (in multishot regime), and sample translation along X, Y, and Z directions; 2) etching the recorded patterns in HF based etchants. Comparative study of chemical etch rates in diluted HF, buffered HF, and a mixture of HF, H2O and HNO3 (P etch) reveals direct evidence of structural and/or stoichiometrical difference between damaged and fresh silica. 3D structures consisting of submicrometer size voxels (smallest optically damaged volume element per shot) were successfully fabricated in the silica glass. The presented technique allows fabrication of 3D channels as narrow as 10 micrometers inside silica, with arbitrary angle of interconnection and high aspect ratio (10 micrometers diameter channels in a 100 micrometers thick silica slab). This approach allows to speed up fabrication, and the resulting 3D structures are optically transparent, which is advantageous for optical characterization (transmission, photoluminescence, Raman scattering, etc.) with spatial resolutions determined by focusing optics.

Stereolithography and 3D microstructuring of transparent materials by femtosecond laser irradiation

We review applications of photopolymerization and photodamage by tightly focused picosecond and femtosecond pulses for the formation of three-dimensional structures. Laser microfabrication of various structures, like surface gratings, 3D optical memory, 2D and 3D photonic crystals, 3D microfluidic systems, etc., are described. Microfabrication by laser irradiation provides new opportunities to realize microstructures and microdevices, highly demanded in a number of fields, e.g., microchemistry, information storage, and photonics. The background of this technique is very simple, and relies on modification of materials by intense, strongly focused laser irradiation. In this highly spatially localized region, the material may become destroyed, solidified from liquid, or otherwise photomodified, and complex structures can be formed from many photomodified regions. Below, we describe techniques, applications, and achievements of laser microstructuring in liquid resins and solid silica glasses.

Subpicosecond optical damaging of silica: time-resolved measurements of the light-induced damage threshold

We investigate damage of purified silica (transmission band down to 160 nm) by sub-ps light pulses having a wavelength of 795 nm. Illumination by 350 fs duration pulses focused by a high numerical aperture NA equals 1.35 microscope objective results in one of the lowest reported values for the single-shot bulk light-induced damage threshold (LIDT) of 5 J/cm2, well below the critical self-focusing power in silica. We have also investigated peculiarities of damage by two coincident laser pulses (duration 440 fs) having power of about 0.5 x LIDT, and linearly cross-polarized to avoid interference effects. The reduction of LIDT in silica is demonstrated for an elevated lattice temperature T equals 400 K, at which the thermal linear/volume expansion coefficient has its maximum. Comparison between the LIDT values obtained from the numeric simulation and experiments demonstrates that the critical density of optically generated free carriers corresponding to LIDT ncr approximately equal to 1021cm-3 is reached during the first half time of the laser pulse illumination (0.2ps).

Femtosecond laser microfabrication of photonic crystal structures by glass damaging and resin photosolidification

We report microfabrication of photonic crystal structures in silica glass and photopolymerizing resins using femtosecond laser pulses, and study their structural and photonic characteristics.