Heinz Paul Huber

Munich University of Applied Sciences | HM · Department of Applied Sciences and Mechatronics

Accurate simulations are paramount for deepening our understanding of ultra-short pulse laser ablation, a complex process involving non-equilibrium thermal and material transport on time-scales spanning several orders of magnitude. In response to this need, we propose a novel approach that enhances the use of a commercially available tool for multi...

To understand the dynamics of ultrashort-pulse laser ablation, the interpretation of ultrafast time-resolved optical experiments is of utmost importance. To this end, spatiotemporally resolved pump-probe ellipsometry may be utilized to examine the transiently changing dielectric function of a material, particularly when compared to two-temperature...

We draw comparisons between the ablation and damage mechanisms that occur for both film and substrate irradiation using atomic force microscopy, scanning electron microscopy, and pump-probe reflectometry. For substrate irradiation, energy absorbed at the film-substrate interface creates a confined energy situation, resulting in a photomechanical li...

We draw comparisons between the ablation and damage mechanisms that occur for both film and substrate irradiation using atomic force microscopy, scanning electron microscopy, and pump-probe reflectometry. For substrate irradiation, energy absorbed at the film-substrate interface creates a confined energy situation, resulting in a photomechanical li...

In the present study, we investigated the dynamics of a femtosecond (fs) laser induced bio-printing with cell-free and cell-laden jets under the variation of laser pulse energy and focus depth, by using time-resolved imaging. By increasing the laser pulse energy or decreasing the focus depth thresholds for a first and second jet are exceeded and mo...

Active and Redox‐Sensitive Colloidal Nanoclusters In article number 2206485, Stephan Barcikowski, Heinz Paul Huber, and co‐workers track microparticle laser fragmentation processes all along the timescale from picoseconds to milliseconds. They discover the unprecedented efficiency to yield ultrasmall particles, exceeding current laser synthesis’ pr...

Applications of nanoparticles in medicine, energy, catalysis, or additive manufacturing demand the development of nanoparticle production methods that are offering material and solvent versatility, high purity, morphology, and size control, together with industrial-scale production capabilities. Pulsed laser ablation in liquids is a technique that...

Pulsed laser fragmentation of microparticles (MPs) in liquid is a synthesis method for producing high‐purity nanoparticles (NPs) from virtually any material. Compared with laser ablation in liquids (LAL), the use of MPs enables a fully continuous, single‐step synthesis of colloidal NPs. Although having been employed in several studies, neither the...

In the context of current state of the art, understanding the laser ablation efficiency decrease for pulse durations exceeding the mechanical relaxation time of a few ps remains a pending research question. A heuristic approach may be used to reveal the role of effective penetration depth on ablation efficiency. Extending familiar contributions of...

Laser ablation in liquids is a highly interdisciplinary method at the intersection of physics and chemistry that offers the unique opportunity to generate surfactant-free and stable nanoparticles from virtually any material. Over the last decades, numerous experimental and computational studies aimed to reveal the transient processes governing lase...

Nanofillers are added to polymeric insulating materials in order to modify the electrical, mechanical and thermal properties. This study investigates silicone rubber filled with hydrophilic and hydrophobic silica nanoparticles with respect to their resistance to laser ablation and to arc discharges, as well as their mechanical properties. The laser...

Femtosecond laser pulses have been successfully used for film-free single-cell bioprinting, enabling precise and efficient selection and positioning of individual mammalian cells from a complex cell mixture (based on morphology or fluorescence) onto a 2D target substrate or a 3D pre-processed scaffold. In order to evaluate the effects of higher pul...

The interaction of ultrashort laser pulses above the ablation threshold of thin-film indium tin oxide (ITO) is examined with pump-probe microscopy. We are able to observe photomechanical spallation at delay times of hundreds of picoseconds, which plays a stronger role near the ablation threshold of 0.17 J/cm2. A phase explosion may also be observed...

The ablation efficiency during laser processing strongly depends on the initial and transient reflectance of the irradiated material surface. This article reports on the transient relative change of the reflectance ΔR/R of stainless steel during and after ultrashort pulsed laser excitation (800 nm, 40 fs) by spatially resolved pump–probe reflectome...

In this work, we investigate single-pulse laser ablation of bulk stainless steel (AISI304), aluminium (Al) and copper (Cu) and its dependence on the pulse duration. We measured the reflectivity, ablation thresholds and volumes under the variation of pulse duration and fluence. The known drop of efficiency with increasing pulse duration is confirmed...

Tissue engineering requires the precise positioning of mammalian cells and biomaterials on substrate surfaces or in preprocessed scaffolds. Although the development of 2D and 3D bioprinting technologies has made substantial progress in recent years, precise, cell‐friendly, easy to use, and fast technologies for selecting and positioning mammalian c...

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...

In recent years, high entropy alloy research has experienced increased interest and it was found that some of these materials have extraordinary properties. High entropy alloys also show an increased damage resistance to high-energy particle irradiation, mainly due to effects caused by the increased configuration entropy. So far, no detailed studie...

The laser matter interaction of alloys, like industrial relevant stainless steels, with ultra-short pulsed (usp) lasers has been widely discussed. However, a new approach to alloy design, High Entropy Alloys (HEAs), is currently in the focus of many studies. HEAs show promising properties for technical applications. One of the most investigated HEA...

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...

After a short overview of the historical development of the Cu(In, Ga)Se2 (CIGS) thin film solar cell and its special features, we give an overview of the deposition and optimization of the p-type CIGS absorber as well as the subsequent n-type buffer layer and the molybdenum back contact. Developments to increase efficiency by optimizing the implem...

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...

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...

In this study, we compare different laser systems used for the synthesis of nanoparticles. The productivity and ablation efficiency of laser ablation of gold in water and in air are determined for three pulsed laser systems with comparable pulse energy but different pulse duration and repetition rate. All experiments are performed in a fluence rang...

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...

Although green femtosecond lasers provide outstanding quality and wide processing windows for monolithic interconnection of the individual cells in organic photovoltaic (OPV) modules, they are hardly used in commercial applications, due to cost reasons. In this work, a process has been developed that allows the monolithic interconnection in OPV mod...

Ultrashort pulsed lasers have gained widespread use in laser material processing applications, as they enable precise ablation due to their highly efficient energy deposition and low thermal damage. Recent investigations using double laser pulses for metal ablation with temporal spacing in the region of a few picoseconds (ps) have shown that the la...

We consider expansion, break off, and flight of 10 nm molybdenum film deposited onto glass support. These events are initiated by action of subpicosecond laser pulse onto film. Approximations for two-temperature equation of state and electron–ion coupling parameter are developed. Heat conduction is unimportant because film is ultrathin and because...

We consider expansion, break off, and flight of 10 nm molybdenum film deposited onto glass support. These events are initiated by action of subpicosecond laser pulse onto film. Approximations for two-temperature equation of state and electron--ion coupling parameter are developed. Heat conduction is unimportant because film is ultrathin and because...

Lithium-ion batteries are widely used as energy storage devices due to their high energy density and versatile applicability. Key components of lithium-ion batteries are electrically isolated electrodes and a liquid electrolyte solution which enables ion transport between the electrodes. Laser structuring of electrodes is a promising approach to en...

In this study, we report on femtosecond (470fs) laser pulse ablation and modification of solution processed single-walled carbon nanotube (SWCNT) networks sprayed on oxidized silicon and polyimide substrates. Taking advantage of the small heat affected zone of the femtosecond pulse regime we demonstrate precise and selective laser processes, that a...

Ultrashort laser pulses are widely used for the precise structuring of semiconductors like silicon (Si). We present here, for the first time, a comparative study of experimentally obtained and numerically simulated two-dimensional ablation profiles based on parameters of commercially relevant and widely used near-infrared and diode pumped femtoseco...

Here, we describe a method for producing locally micro-structured fiber Bragg gratings (LMFGB) by fs-laser machining. This technique enables the precise and reproducible ablation of cladding material to create circumferential grooves inside the claddings of optical fibers. From initial ablation experiments we acquired optimized process parameters....

Laser-induced cell transfer has been developed in recent years for the flexible and gentle printing of cells. Because of the high transfer rates and the superior cell survival rates, this technique has great potential for tissue engineering applications. However, the fact that material from an inorganic sacrificial layer, which is required for lase...

Time-lapse video. Time-lapse series of B16F1 cells after femtosecond laser-induced transfer. (AVI)

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...

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...

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...

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...

A new fabrication method for a locally micro-structured fiber Bragg grating (LMFBG) is proposed and demonstrated. With this new type of LMFBG, simultaneous sensing of compressive force and temperature is possible. The LMFBG consists of a circumferential groove of ∼86 μm length and ∼27 μm depth in the middle of a type I FBG. Direct femtosecond (fs)...

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...

A locally micro-structured fiber Bragg grating (LMFBG) was manufactured by forming a circumferential groove in the middle of a type I fiber Bragg grating (FBG). The groove was directly ablated using a fs-laser and had a length of 86μm, a depth of 27μm and steep side walls. Due to the precisely machined geometry of the structure the reflection spect...

An automated fs-laser machining procedure was developed to engrave circumferential grooves into the cladding of optical fibres. The grooves are positioned centrally to type I fibre Bragg gratings (FBG) and form locally micro structured FBGs. The grooves realized so far were ~30μm deep and were 48 μm to 200 μm long. These devices show the occurrence...

A theoretical approach using ab initio calculations was applied to study the interaction of an ultrashort laser pulse with the metal alloy Fe0.72Cr0.18Ni0.1 (AISI 304). The electronic structure was simulated by taking into account the chemical and magnetic disorder of the alloy by the coherent potential approximation implemented in a fully relativi...

Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient,...

Time dynamics of thin plasma disk generation and ablation dynamics in SiOx film on silicon are examined by femtosecond laser pump and probe experiments. Quantized etching, nanovoids and blisters are revealed on half-wavelength interference period.

Automated laser beam focus positioning for precise work piece alignment is highly important in laser processing. Ideally, the laser used for processing of the work piece should also be used for focus finding. For this a confocal camera can be used in front of a galvanometric scanner and objective. However, in typical laser processing applications t...

The production and characterisation of a micro-structured FBG force sensor is described. Employing femtosecond laser micro machinery a circumferential ditch of about 30 μm depth and 40 μm width is engraved in the clad of an optical fibre at the centre of a 3 mm long type I fibre Bragg grating (FBG). The purpose of the structure is the enhancement o...

Numerical simulation reveals the mechanism for pulse duration dependence on laser ablation efficiency

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...

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...

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...

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...