Stephan Rapp

Stephan Rapp
Munich University of Applied Sciences | HM · Lasercenter Munich

PhD student

About

36
Publications
7,283
Reads
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426
Citations

Publications

Publications (36)
Article
The ablation rate in double-pulse material processing is strongly influenced by the pulse separation. For pulse separations exceeding 3 ps a significant decrease in ablation volume has been observed. This was attributed to three mechanisms: rarefaction wave interaction, shielding by ablation plume and material re-deposition. Here we present careful...
Article
Full-text available
An ultra-short laser pulse irradiated surface passes through a sequence of physical processes that occur over a wide temporal range, from femtoseconds to microseconds. In this paper for the first time, the complete laser ablation process for industrially relevant metals, aluminium (Al) and stainless steel (AISI 304) is tracked from the initial puls...
Conference Paper
In recent years several works have been investigating the temporal distribution of pulse energy with the aim of maximizing ablation efficiency in terms of energy specific ablation volume by applying double pulses or pulse bursts. Here we study the energy specific ablation volume of double pulses in dependency of increasing pulse separation on alumi...
Presentation
In recent years several works have been investigating the temporal distribution of pulse energy with the aim of maximizing ablation efficiency in terms of energy specific ablation volume by applying double pulses or pulse bursts. Here we study the energy specific ablation volume of double pulses in dependency of increasing pulse separation on alumi...
Presentation
State of the art ultrafast laser systems are capable of delivering fluences up to 100 J/cm^2 when the laser pulses are tightly focused in micro material processing. This fluence value is far above the optimal fluence for processing of metal samples, which ranges between 1.5 J/cm^2 and 15 J/cm^2. An attempt to perform laser processing at the optimal...
Thesis
Full-text available
Ultrakurzpulslaser haben sich als weitverbreitetes Werkzeug in der Lasermaterialbearbeitung etabliert, da sie aufgrund ihrer hocheffizienten Energiedeposition und der dabei auftretenden niedrigen thermischen Materialschädigung präzisen Materialabtrag ermöglichen. Aktuelle Untersuchungen der Metallbearbeitung mit Laserdoppelpulsen haben gezeigt, das...
Article
Several studies on hard tissue laser ablation demonstrated that ultrafast lasers enable precise material removal without thermal side effects. Although the principle ablation mechanisms have been thoroughly investigated, there are still open questions regarding the influence of material properties on transient dynamics. In this investigation, we ap...
Conference Paper
Ultra-short pulsed lasers offer a great potential in precise and efficient material processing. Experimental and theoretical studies on efficiency of laser material processing from metals have demonstrated a high degree of dependency on the laser pulse duration. Within these studies, the investigation of the transient energy deposition in material...
Article
Full-text available
In this paper, we present ultrafast measurements of the complex refractive index for copper up to a time delay of 20 ps with an accuracy <1% at laser fluences in the vicinity of the ablation threshold. The measured refractive index n and extinction coefficient k are supported by a simulation including the two - temperature model with an accurate de...
Article
Full-text available
Ultrashort pulse lasers have been increasingly gaining importance for the selective structuring of dielectric thin films in industrial applications. In a variety of works the ablation of thin SiO2 and SiNx films from Si substrates has been investigated with near infrared laser wavelengths with photon energies of about 1.2 eV where both dielectrics...
Article
Full-text available
Ultrashort pulsed lasers offer a high potential in precise and efficient material processing and deep understanding of the fundamental laser-material interaction aspects is of great importance. The transient pulse reflectivity in conjunction with the transient absorption influences decisively the laser-material interaction. Direct measurements of t...
Article
Full-text available
Numerical simulation reveals the mechanism for pulse duration dependence on laser ablation efficiency
Article
Full-text available
Several investigations of dental tissue ablation with ultrashort pulsed lasers suggest that these lasers enable precise and selective material removal and reduce the formation of micro cracks and thermal effects, when compared to ns-pulses. In this study, two damage mechanisms are presented occurring during ablation of dentin using a laser emitting...
Article
Full-text available
In dental health care, the application of ultrashort laser pulses enables dental tissue ablation free from thermal side effects, such as melting and cracking. However, these laser types create undesired micro- and nanoparticles, which might cause a health risk for the patient or surgeon. The aim of this study was to investigate the driving mechanis...
Article
In the production process of silicon microelectronic devices and high efficiency silicon solar cells, local contact openings in thin dielectric layers are required. Instead of photolithography, these openings can be selectively structured with ultra-short laser pulses by confined laser ablation in a fast and efficient lift off production step. Ther...
Article
Full-text available
In the production process of microelectronic devices and high efficiency solar cells, local openings in thin dielectric layers are required. Instead of photolithographic, laser based processing enables to open these dielectric layers locally in a low-cost mass production step. In this work, thin silicon nitride layers deposited on planar silicon wa...
Article
Full-text available
In recent years, several applications for the laser ablation of thin metal films from the glass substrate side have been studied.In this case, the laser pulse transmits through the glass substrate, the metal film absorbs the pulse, and the energy is confined at the molybdenum-glass interface. The ablation mechanism is called confined laser ablation...
Article
Full-text available
Ultra-short pulse lasers can be applied for fast and precise structuring of thin passivating SiO2 films on the surface of high efficient Si solar cells. This single pulse ablation reaction is investigated over the whole reaction time ranging from ps to mu s by pump-probe microscopy. Results show ultra-fast reflectivity changes of the Si after 1 ps...
Conference Paper
Maskless patterning of biocompatible sensor chips consisting of a Ta2O5/Pt/glass layer system can be realized by ultrashort laser pulse ablation allowing fast and precise structuring. Here, a 650 fs laser at a center wavelength of 1053 nm is used at a peak fluence of 5 J/cm2. It was observed, that a greater diameter of the Pt film (400 nm) is ablat...
Conference Paper
The transient behavior of the laser lift-off of thin molybdenum films, initiated by glass substrate side irradiation with a 660 fs laser pulse, is investigated in the picosecond range. For this purpose, a pump-probe microscopy setup is utilized to measure the transient relative reflectivity change in the center of the irradiated spot at the molybde...
Article
Full-text available
For the monolithic serial interconnection of CIS thin film solar cells, 470 nm molybdenum films on glass substrates must be separated galvanically. The single pulse ablation with a 660 fs laser at a wavelength of 1053 nm is investigated in a fluence regime from 0.5 to 5.0 J/cm2. At fluences above 2.0 J/cm2 bump and jet formation can be observed tha...
Article
Full-text available
A femtosecond laser is used for selective structuring of biocompatible sensorchips consisting of a Ta 2 O 5 /Pt layer system on glass substrate. It was observed, that for low fluences the Ta 2 O 5 can be selectively lifted-off from the Pt, while high fluences enable a removal of both layers. The underlying physical effects are investigated by pump-...
Article
Full-text available
Ultra-short-pulse laser irradiation of thin molybdenum films from the glass substrate side initiates an intact Mo disk lift off free from thermal effects. For the investigation of the underlying physical effects, ultra-fast pump–probe microscopy is used to produce stop-motion movies of the single-pulse ablation process, initiated by a 660-fs laser...
Article
Full-text available
Ultrafast pump-probe microscopy is a common method for time and space resolved imaging of short and ultra-short pulse laser ablation. The temporal delay between the ablating pump pulse and the illuminating probe pulse is tuned either by an optical delay, resulting in several hundred femtoseconds temporal resolution for delay times up to a few ns, o...
Conference Paper
Full-text available
Laser lift-off processes have been observed during structuring CIS thin film solar cells with ultra-short laser pulses, if a Mo film on glass is irradiated from the glass substrate side. To investigate the underlying physical effects, ultrafast pump-probe microscopy is used for time-and space resolved investigations. The setup utilizes a 660 fs-las...
Conference Paper
Export Date: 7 October 2012, Source: Scopus, Article in Press
Article
Full-text available
A biocompatible sensor chip consists of a 200 nm conducting platinum layer between a glass substrate and a 200 nm tantalum pentoxide layer as insulator on top. The irradiation of the biochip from the Ta2O5 side with ultra-short laser pulses ( 660 fs) at a wavelength of 1053 nm leads to a selective ablation of the Ta2O5 layer from the platinum. The...
Article
Laser lift-off processes have been observed during structuring CIS (copper-indium-diselenide) thin film solar cells with ultra-short laser pulses, if a thin molybdenum film is irradiated from the glass substrate side. To investigate the underlying physical effects, ultrafast pump-probe microscopy was used to record the transient behavior of the sin...
Conference Paper
Laser lift-off processes have been observed during structuring CIS (copper-indium-diselenide) thin film solar cells with ultra-short laser pulses, if a thin molybdenum film is irradiated from the glass substrate side. To investigate the underlying physical effects, ultrafast pump-probe microscopy was used to record the transient behavior of the sin...
Conference Paper
A biocompatible sensor chip consists of a 200 nm conducting platinum layer between a glass substrate and a 200 nm tantalum pentoxide layer as insulator on top. The irradiation of the biochip from the Ta2O5 side with ultra-short laser pulses (660 fs) at a wavelength of 1053 nm leads to a selective ablation of the Ta2O5 layer from the platinum. The a...

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