Mid-infrared resonant ablation of PMMA

Laser ablation proved to be a reliable micro-fabrication technique for patterning and structuring of both thin film and bulk polymer materials. In most of the industrial applications ultra-violet (UV) laser sources are employed, however they have limitations such as maintenance costs and practical issues. As an alternative and promising approach, mid-infrared resonant laser ablation (RIA) has been introduced, in which the laser wavelength is tuned to one of the molecular vibrational transi-tions of the polymer to be ablated. Consequently, the technique is selective in respect of processing a diversity of polymers which usually have different infrared absorption bands. In this paper, we present mid-infrared resonant ablation of PolyMethyl MethAcrylate (PMMA), employing nanosec-ond laser pulses tunable between 3 and 4 microns. This RIA nanosecond laser set-up is based on a commercial laser at 1064 nm pumping a singly resonant Optical Parametric Oscillator (OPO) built around a Periodically-Poled Lithium Niobate (PPLN) crystal with several Quasi-Phase Matching (QPM) periods. RIA has been successfully demonstrated for structuring bulk PMMA, and selective patterning of PMMA thin films on a glass substrate has been implemented

Mid-infrared resonant ablation for selective patterning of thin organic films

The fast growing market of organic electronics, including organic photovoltaics (OPV), stimulates the development of versatile technologies for structuring thin-film materials. Ultraviolet lasers have proven their full potential for patterning single organic layers, but in a multilayer organic device the obtained layer selectivity is limited as all organic layers show high UV absorption. In this paper, we introduce mid-infrared (IR) resonant ablation as an alternative approach, in which a short pulse mid-infrared laser can be wavelength tuned to one of the molecular vibrational transitions of the organic material to be ablated. As a result, the technique is selective in respect of processing a diversity of organics, which usually have different infrared absorption bands. Mid-IR resonant ablation is demonstrated for a variety of organic thin films, employing both nanosecond (15 ns) and picosecond (250 ps) laser pulses tunable between 3 and 4 microns. The nanosecond experimental set-up is based on a commercial laser at 1064 nm pumping a singly resonant Optical Parametric Oscillator (OPO) built around a Periodically-Poled Lithium Niobate (PPLN) crystal with several Quasi-Phase Matching (QPM) periods, delivering more than 0.3 W of mid-IR power, corresponding to 15 mu J pulses. The picosecond laser set-up is based on Optical Parametric Amplification (OPA) in a similar crystal, allowing for a comparison between both pulse length regimes. The wavelength of the mid-infrared laser can be tuned to one of the molecular vibrational transitions of the organic material to be ablated. For that reason, the IR absorption spectra of the organic materials used in a typical OPV device were characterized in the wavelength region that can be reached by the laser setups. Focus was on OPV substrate materials, transparent conductive materials, hole transport materials, and absorber materials. The process has been successfully demonstrated for selective thin film patterning, and the influence of the various laser parameters is discussed

Ultrafast DPSS laser interaction with thin-film barrier stacks

The fast growing market of organic electronics, including organic light emitting diodes (OLEDs), stimulates the development of versatile technologies for structuring thin-film materials. Ultrafast diode-pumped solid-state (DPSS) lasers have proven their full potential for patterning transparent conductors, but only few studies report on interaction with thin-film barrier layers. Indeed, in the case of flexible organic applications, thin-film barrier layers consisting of inorganic and sometimes inorganic/organic multi-layers are usually used for protection. This severely restricts the selection of suitable laser patterning conditions, as damaging the barrier stack will result in moisture and oxygen ingress, leading to accelerated device degradation. In this paper we present picosecond laser processes for selective patterning conductive polymers like poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), without damaging the barrier, as well as for selective patterning the top encapsulation, without damaging the anode or cathode contacts. Careful examination using optical profilometry, SEM and chemical surface analysis reveals the importance of the laser wavelength (1064nm, 532nm, 355nm), pulse duration, pulse frequency, pulse energy, spot size, laser fluence, and pulse overlap. The fundamental laser material interaction is discussed for thin-film material stacks, and the material removal is believed to be driven by photomechanical and photochemical processes. After optimisation of the individual processes, the development of generic subtractive laser processes for industrial OLED manufacturing is discussed, with focus on process quality and speed

Match beam inversion of geoacoustic parameters from towed hydrophone streamer array data

183-194<span style="font-size:9.0pt;font-family: " times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">The study estimates geoacoustic parameters of the sediment by inversion of acoustic data acquired from seismic hydrophone streamer array.  Inversion is performed by beamforming technique as the data is pertaining to shallow water and there is no prior information on the sediment type and the profiles of subbottom sediment layers. Initially, the estimates of sediment speed are obtained from critical angle derived from beamformer output by conventional beamforming. The sediment speed is used to set the parameter search bounds for further inversion by beamforming technique. The search bounds for density and compressional attenuation coefficient is set accordingly. The feasibility of inversion is understood by undertaking synthetic runs followed by inversion of field data. The beam cutoff angles are determined from the beampattern and the arrivals pertaining to the sea bottom.  The geoacoustic model comprises of a water column, two sediment layers and a sediment half space.  The inversion results of field data sets are compared with results obtained by modal inversion. The results show negligible variation in estimated sound speed indicating similar sediment type. The sediment density and compressional attenuation coefficient exhibits lesser sensitivity toward inversion process<span style="font-size: 11.0pt;font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">.</span

Fabrication of a laser patterned flexible organic light-emitting diode on an optimized multilayered barrier

The fast-growing market of organic electronics stimulates the development of versatile technologies for structuring thin-film materials. Ultraviolet lasers have proven their full potential for patterning organic thin films, but only a few studies report on interaction with thin-film barrier layers. In this paper, we present an approach in which the laser patterning process is optimized together with the barrier film, leading to a highly selective patterning technology without introducing barrier damage. This optimization is crucial, as the barrier damage would lead to moisture and oxygen ingress, with accelerated device degradation as a result. Following process optimization, a laser processed flexible organic LED has been fabricated and thin-film encapsulated and its operation is shown for the first time in atmospheric conditions

Ultrafast laser patterning of organic/ inorganic thin-films for OLED / OPV applications

In organic electronics (OLED / OPV) fabrication, thin-film layers consisting of inorganic or inorganic-organic multilayered stack are crucial. Process optimization is challenging as the damage on the barrier layer can lead to the moisture and oxygen penetration into the stack resulting in degradation of the device. Various inorganic and organic thin films on a glass / inorganic-organic barrier substrates are patterned using 355 nm, 532 nm and 1064 nm picosecond laser pulses. The laser pulse interaction with thin films / barrier using static single pulse (determining thresholds) and dynamic patterning, has been optimized in terms of energy, frequency and pulse overlap

Excimer laser patterning of PEDOT : PSS thin-films on flexible barrier foils: a surface analysis study

Selective laser patterning of thin organic films is an important aspect in the roll-to-roll production of organic electronic devices such as organic light emitting diodes (OLEDs). An excimer laser is well suited for the patterning and structuring of polymer thin films as their UV absorption is significant. Selective removal of a transparent conducting polymer PEDOT:PSS (poly(3,4-ethylene dioxythiophene):polystyrene sulfonate) on a multilayered (inorganic-organic-inorganic) barrier and a flexible PEN (polyethylene napthalate) substrate has been studied using a KrF excimer laser. The ablation craters were characterized with electron microscopy and profilometry. For the first time, chemical surface analysis of the patterned area was performed with Time-Of-Flight Static Secondary Ion Mass Spectrometry (TOF-S-SIMS), providing a detailed insight of the surface composition after laser ablation and plasma post-treatments. ©2013 Elsevier B.V. All rights reserved