1,720,977 research outputs found
Optimal control of phase boundary in a 2-phase Stefan problem by laser heating
No full textThe 2-phase heat control problem by a single laser point input is studied and a method of overcoming the moving boundary problem is introduced. This is achieved by applying a sequence of linear time varying control problems which converge to the single nonlinear problem which can be obtained from the joint moving boundary problems
Intact printing of solid phase materials using femtosecond laser-induced forward transfer technique
No full textLaser-Induced Forward Transfer (LIFT) is an important direct-write technique for printing of materials and devices with micron and sub-micron resolution [1, 2]. In the conventional LIFT technique the material to be printed (the donor) is coated onto a laser-transparent substrate (the carrier). A laser pulse is then focussed at the carrier-donor interface which melts or ablates the donor and transfers it onto a nearby placed substrate (the receiver) as shown in Fig. 1. The inherent disadvantage of the conventional LIFT technique is that the donor acts as its own propellant and hence gets damaged during the transfer. Many complementary LIFT techniques have been developed in recent years to avoid this damage and to achieve an intact transfer of donors in the solid phase such as Dynamic Release Layer (DRL)-LIFT [3], Ballistic Laser-Assisted Solid Transfer (BLAST) [4] and Laser Induced Thermal Imaging (LITI) [5]. A brief overview of these techniques, the successes achieved by them to date, their current challenges and the ongoing work in this field will be presented
Femtosecond laser-induced solid etching (LISE) of silicon and silica
No full textWe present a novel, laser-based microstructuring technique for the etching and deposition of solid materials. This technique, which we call laser-induced solid etching (LISE), utilises the absorption of femtosecond duration laser pulses in a constrained metal film between two bulk substrates, at least one of which is transparent to the laser wavelength. The very rapid pressure increase in the metal film following irradiation is believed to initiate crack-propagation in one or other of the bulk substrates. By spatially shaping the laser beam, the cracking process can be controlled to etch solid chunks of material from the substrates. Using LISE we have etched smooth, micron-scale pits and trenches in silicon and silica. The results will be compared to etched features produced using conventional techniques.A unique feature of LISE is that the material etched from the bulk substrate is removed as a single solid piece and is not shattered, melted, or vaporised by the process. Hence, the etched material can be collected on the other bulk substrate used in the process. In this way, we have deposited micron-scale dots and lines of silica onto silicon and visa-versa. The deposited structures obtained using LISE compare well with those obtained with conventional laser forward transfer techniques. Minimal evidence of melting during the process has been observed, suggesting that LISE may be a useful technique for the forward transfer direct-write of intact solid materials
Cellular modelling of the laser-induced forward transfer of micro - and nano-scale droplets
No full textLaser-Induced Forward Transfer (LIFT) [1] of micro- and nano-scale droplets is a relatively well-understood process experimentally [2,3]. By careful control of the applied laser fluence to just melt through a thin source film (the donor), it is possible to transfer single droplets of the film to a receiver substrate placed nearby. Such droplets can be micron [2] or sub-micron [3] in diameter and have potential applications in plasmonic devices. The process is inherently complex involving laser-induced phase changes (which may be non-thermal on femtosecond timescales), droplet growth from fluid flow in thin molten films, moving boundaries, and the flight dynamics of the droplet during transfer and upon impact at the receiver. At present, a complete model that encompasses all these different phenomena is still lacking. However, an approximate numerical model of the process would be highly desirable so that the various experimental parameters (laser fluence, donor thickness, donor-receiver separation etc.) can be optimised for minimum droplets sizes and close deposit spacing. One method of modelling highly complex processes is to use cellular automata [4]. In a cellular automaton, the spatial domain is split into a regular grid of cells whose states evolve in time according to a set of rules based on the states of neighbouring cells. An advantage of this technique for highly complex systems such as the LIFT of droplets is that rules which reproduce the behaviour of a system can be found without explicit derivation from the underlying physical equations
Laser Induced Forward Transfer (LIFT) using femtosecond laser pulses: laser printing of functional materials
No full textLaser induced forward transfer (LIFT) is a versatile direct-write method for spatially selective printing of a wide range of materials. In the conventional LIFT technique a thin film (usually of thickness < 1 µm) of the material (the donor) to be printed is deposited on top of a substrate (the carrier) which is transparent to the incident laser wavelength. A laser pulse is then focussed/imaged onto the carrier-donor interface which induces the necessary impulsive force to push the donor onto a substrate placed nearby (the receiver) either by melting it (for the case of a sufficiently thin donor) or ablating the top layer (the thick donor case). In this talk, I shall describe our progress to date using femtosecond light pulses for LIFTing, and discuss what we have been able to achieve using sacrificial absorbing layers to provide the impulsive push, pre-machining of the donor, active and passive spatial beam shaping of the laser profile, use of LIFT to print source material for optical waveguide fabrication, and printing of the smallest metallic dots so far (300nm diameter)
Femtosecond laser-induced forward transfer of thin films using a Triazene polymer sacrificial layer and an active carrier
No full textLaser Induced Forward Transfer (LIFT) is a novel direct write technique for material transfer from thin film precursors. In conventional LIFT the material to be transferred is required to act as its own propellant. This requirement is not compatible with the objective of intact material transfer. Recently, UV-absorbing triazene polymers have been reported to be used as sacrificial layers in LIFT experiments. We report the use of these polymers as sacrificial layers at infrared wavelength (800nm) for transferring gadolinium gallium oxide amorphous thin films. A 150 nm thick film was deposited on a 100 nm thick polymer layer by Pulsed Laser Deposition (PLD), to be used as the donor film. Intact thin films were successfully deposited on a silicon receiver kept at a distance of 400nm. The concept of using the carrier in an active role is a completely new and exciting approach for LIFT
Waveguide mode filter fabricated using laser-induced forward transfer
No full textTitanium 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
Laser Induced Forward Transfer (LIFT) using femtosecond laser pulses: laser printing of functional materials
No full textLaser induced forward transfer (LIFT) is a versatile direct-write method for spatially selective printing of a wide range of materials. In the conventional LIFT technique a thin film (usually of thickness < 1 µm) of the material (the donor) to be printed is deposited on top of a substrate (the carrier) which is transparent to the incident laser wavelength. A laser pulse is then focussed/imaged onto the carrier-donor interface which induces the necessary impulsive force to push the donor onto a substrate placed nearby (the receiver) either by melting it (for the case of a sufficiently thin donor ) or ablating the top layer (the thick donor case). In this talk, I shall describe our progress to date using femtosecond light pulses for LIFTing, and discuss what we have been able to achieve using sacrificial absorbing layers to provide the impulsive push, pre-machining of the donor, active and passive spatial beam shaping of the laser profile, use of LIFT to print source material for optical waveguide fabrication, and printing of the smallest metallic dots so far (300nm diameter)
Femtosecond pulsed 244nm versus CW 244nm grating writing in boron codoped germanosilicate optical fibres operating within the one photon absorption regime
No full textWe compare the performances of low intensity (~18 nJ/pulse) femtosecond 244 nm grating writing with that of CW (20 mW) 244 nm grating writing for fixed fluencies. We find no evidence of any improvement using pulsed light with duration commensurate with phonon-assisted relaxation away from the excited state
Femtosecond laser-induced forward transfer (LIFT): a technique for versatile micro-printing applications
No full textThe 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
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