D.P. Banks

Nanodroplets deposited in microarrays by femtosecond Ti:sapphire laser-induced forward transfer

The authors present the deposition of nanoscale droplets of Cr using femtosecond Ti:sapphire laser-induced forward transfer. Deposits around 300nm in diameter, significantly smaller than any previously reported, are obtained from a 30nm thick source film. Deposit size, morphology, and adhesion to a receiver substrate as functions of applied laser fluence are investigated. The authors show that deposits can be obtained from previously irradiated areas of the source material film with negligible loss of deposition quality, allowing subspot size period microarrays to be produced without the need to move the source film.

Shadowgraphic studies of triazene assisted laser-induced forward transfer of ceramic thin films

The laser-induced forward transfer process of solid ceramic donor materials (gadolinium gallium oxide and ytterbium doped yttrium aluminium oxide) was studied using triazene polymer as a sacrificial layer by means of a time-resolved nanosecond-shadowgraphy technique. The dependence of the ablation dynamics and quality of the ejected donor material on the laser fluence and thickness of the sacrificial and donor layers were investigated and discussed.

Triazene photopolymer dynamic release layer-assisted femtosecond laser-induced forward transfer with an active carrier substrate

Discs of solid material have been forward transferred from thin films on transparent carrier substrates using femtosecond Ti:sapphire laser-induced forward transfer (fs-LIFT) with a triazene polymer dynamic release layer (DRL). The fluence threshold for fs-LIFT was found to be only ≈20% of the DRL ablation threshold at the laser wavelength. This decrease is attributed to ultrafast shock-wave generation in the constrained polymer layer under femtosecond irradiation being the driving force for fs-LIFT with the polymer DRL. The result is very different from the nanosecond regime, where the LIFT threshold is observed to be slightly above the polymer ablation threshold. White-light continuum generation in a carrier substrate is observed and its influence on the fs-LIFT process is discussed.

Femtosecond Laser-Induced Forward Transfer (LIFT): A Technique for Versatile Micro-Printing Applications

Laser-induced forward transfer (LIFT) method exists as a relatively simple and versatile additive surface micropatterning technology. Material is transferred from a supported thin film to a receiver substrate by irradiating the rear side of the film with a single laser pulse. Typically transfer is effected either through melting through of the source film or by ablation of the film at a constrained interface with a resultant pressure build-up propelling a piece of the film to the receiver. Both of these processes have inherent advantages and disadvantages; by melting the source film during transfer, sub-laser spot size features can be produced, but the choice of available materials is reduced and control of deposit morphology is limited. Ablation-driven transfer is less material selective but resultant deposits are typically broken during transfer and scattered over relatively large areas.

Influence of optical standing waves on the femtosecond laser-induced forward transfer of transparent thin films

The effects of the formation of an optical standing wave during femtosecond laser-induced forward transfer of transparent films is analyzed using a numerical interference model. The dependence of the intensity distribution on a number of easily controllable experimental parameters is investigated. Results of the model are compared to experimental studies of the transfer of gadolinium gallium oxide (GdGaO) with a polymer sacrificial layer. The model allows us to explain the observed variation in deposit morphology with the size of the air gap, and why forward transfer of the GdGaO was possible below the ablation thresholds of polymer and oxide.

Waveguide mode filters fabricated using laser-induced forward transfer

Titanium in-diffused lithium niobate index-tapered waveguides have been fabricated using laser-induced forward transfer technique for mode-filtering applications. Details of their fabrication, losses and transmission characterization are presented.

Fibre Bragg fabrication in germanosilicate fibres with 244nm femtosecond laser light

The ability to fabricate strong and extraordinarily stable Bragg gratings in any type of fibre using femtosecond laser light has attracted much interest in the recent past. The induced index change has been attributed to glass densification brought about by nonlinear multiphoton ionisation resulting in bond breaking, local melting and rapid cooling occurring after optical breakdown by the high-energy femtosecond light.In this paper, a preliminary comparative study between fibre Bragg grating fabrication in germanosilicate fibre using 244nm femtosecond source with a repetition rate of 250kHz and 200fs pulse duration and a 244nm CW frequency doubled argon-ion source is presented. The reflectivities achieved in both cases were close to identical for similar writing fluences, as were the isochronal annealing profiles. This indicated that despite the very high repetition rate used, the collective heat generated by the femtosecond radiation plays no role in the compaction of the glass matrix. The index change observed in this case is a result of single photon absorption into known defect centres - the laser intensity was insufficient to excite the glass band edge leading to glass compaction. No qualitative difference in index change between CW and short-pulse excitation of these defects is found.The ability to fabricate strong and extraordinarily stable Bragg gratings in any type of fibre using femtosecond laser light has attracted much interest in the recent past. The induced index change has been attributed to glass densification brought about by nonlinear multiphoton ionisation resulting in bond breaking, local melting and rapid cooling occurring after optical breakdown by the high-energy femtosecond light.In this paper, a preliminary comparative study between fibre Bragg grating fabrication in germanosilicate fibre using 244nm femtosecond source with a repetition rate of 250kHz and 200fs pulse duration and a 244nm CW frequency doubled argon-ion source is presented. The reflectivities achieved in both cases were close to identical for similar writing fluences, as were the isochronal annealing profiles. This indicated that despite the very high repetition rate used, the collective heat generated by the femtosecond radiation plays no role in the compaction of the glass matrix. The index change o...