Generation of multiple parallel non-diffractive beams without any disruption of each beam is a challenging task. Here, we report the approach of spatial-spectral modulation for non-disruptive generation of Bessel beam array. Such modulation is realized with a simple beam splitter placed in a Fourier plane of the initial beam. The various designs of the beam-splitter phase mask allow to generate an array of the Bessel beams with various shapes and controlled intensity distribution without mutual interference of each beam. As such, this array formation can enhance quality of glass cutting and increase the throughput of micro-patterning of glass-fine mask required for a new generation high-resolution OLED display.
Requirements on glass manufacturing with exceptionally high mechanical strength triggered development of new laserbased processing methods. Localized modifications produced by ultrashort pulsed lasers are attractive but may lead to micro-crack generation in glass. Aiming to control stresses during volumetric material modifications, we have studied the effect of pulse duration experimentally. Bessel beam shapes with arbitrary conical angles have been generated using a programmable spatial light modulator (SLM), while stresses have been monitored using time-resolved optical transmission and cross polarized microscopy. Pulse duration variation influences mechanical stress in the laser glass interaction, and we found the optimized pulse duration exists in the laser glass machining by pump-probe microscopy.
Diffraction-free Bessel beams have been of great interest for laser processing of transparent materials. Compared to traditional Gaussian beams, the Bessel-Gauss beams has thin focus profile which remains invariant over much longer propagation distances. Achieved in such a way extended depth of focusing in combination with precise energy deposition has opened diverse promising applications in display industry. Here we have analyzed the effect of conical angle on the interaction of Bessel beam with a display panel having multiple organic and inorganic layers on a glass. First, we have shown that experimentally observed thermal damages in display emission area are caused by long Bessel beam tails in contrast to Gaussian beams, where the damages are driven by heat diffusion. Second, we study the role of Kerr effect and arising instabilities in non-linear propagation through the glass substrate. Using numerical simulations and in-situ pump-probe microscopy methods we gain the knowledge of primary steps of energy deposition with high temporal and spatial resolution. At high laser intensities and low numerical aperture, the original Bessel beam profile can be de-stabilized leading to the longitudinal fluctuation of intensity. The laser processing with high conical angle Bessel beams is much more resistant to undesirable beam self-focusing and phase self-modulation effects, which enables us to achieve the regime of optimal laser energy deposition for high-quality glass cutting.
In the present work, we investigate the benefits and the drawbacks in using on dual-wavelength double fs-pulse laser irradiation for fused silica processing. Our purpose of this pump-pump experiment is to tune the electron dynamics in order to optimize energy deposition and then to improve ablated volume. We use green wavelength (515 nm) for the first pulse to enhance photo-ionization and near-infrared (1030 nm) for the second pulse to maximize electron heating and impact ionization. The investigated parameters are pulse-to-pulse delay (up to 20 ps), second pulse duration (1 and 10 ps) and total fluence (up to 20 J/cm²). The results will be discussed in terms of ablated volume and optical transmission. We demonstrate that (i) there is an optimum delay and (ii) the ablation behavior is intermediate between green and near-infrared single pulse irradiation. Our results are supported by a numerical model taking into account electron dynamics and absorbed energy density.
We report on a 100-fs GHz burst laser with up to 100-W average output power. This laser is based on a Tangor femtosecond laser with GHz burst option followed by nonlinear pulse compression in a gas-filled hollow core Kagomé fiber. Combining pulse compression with hollow core fiber transport is an attractive extension for industrial femtosecond lasers. Laser ablation of metals, silicon, and sapphire have been performed with this new laser source in order to study the impact of the ultrashort pulse duration on the laser matter interaction with GHz bursts.
Based on a simplified ablation model using only two parameters to describe a material, we have developed a numerical method of inverse computation to obtain the most judicious laser configurations for a given depth of ablation in a given material. The calculations are carried out for more than one million configurations (pulse energy, pulse rate, spot diameter, scan speed, …). The results are stored and analyzed on demand via multiple input tables. The digital tools are validated for stainless steel, and ablation results will also be presented for other metals (aluminum, titanium) or composite materials (CFRP).
Ultrafast laser glass processing is highly interesting for microelectronics and consumer electronics industries. Indeed, ultrafast laser technology has the unique capacity to produce a high-quality surface or bulk modification in dielectric transparent materials thank to nonlinear absorption. However, there is a need to improve both processing quality and throughput in order to meet the industry requirements. Beam shaping, performed by tuning spatial or temporal intensity profile, polarization, fluence, or any other laser parameters, is a smart and flexible technique to achieve this goal. This work is dealing with double fs-pulse laser irradiation of fused silica. Our purpose is to investigate the benefits and the drawbacks in using single and dual-wavelength double fs-pulse laser irradiation of fused silica. The influence of pulse-to-pulse delay (0 to 5 ps), pulse duration of the second pulse (1 ps to 25 ns) and fluence on both removal rate and optical transmission will be discussed.
Ultra-fast laser in micromachining have a reputation of highest precision and quality, which justifies additional invest in numerous applications. However, deficits in the synchronization of the positioning of beam deflection device and laser triggering -in particular at high repetition rates- still lead to defects like overtreatment due to the inertia of the mirrors of galvanometer scanners or path deviations at complex shapes. This in turn has led to an increasing demand of advanced pulse to pulse control for precise laser energy deposition. Two recent innovations have the potential to overcome these current limitations. Firstly, the scan ahead feature allows to calculate the actual beam position in acceleration and deceleration mode. According to the precise position feedback the control needs to adjust the repetition rate of the laser source e.g. at rectangular corners of a scan trajectory. Therefore, the pulse on demand feature at the laser interface is obligatory to dynamically adjust the pulse to pulse delay in order to accomplish constant energy deposition at any programmed scan pattern. We have put these two innovations to a test by combining an Excelliscan from Scanlab with an UV Tangor laser from Amplitude to validate the synchronization and constant pulse separation at various scan speeds and geometrical patterns. Applications trials like engraving with scan speed are presented in comparison to conventional scanning techniques to demonstrate the benefit of the fast synchronization and pulse on demand technologies.
Translating the high available power for current industrial lasers in the 100 to 500 W range into high throughput micro-processing is of high importance for future industrial applications. High repetition rates and/or high energies can lead to detrimental thermal effects on the sample and degrade the process quality even using ultrafast lasers. New processing strategies are therefore required to take full advantage of the laser available power. Programmable spatial light modulators (SLM) can bring flexibility while maintaining a high spatial resolution compatible with complex optical functions like multi spots or user defined beam profiles. They enable specific laser characteristics, that can change during the process. The recent technological progress in LCOS based systems, enables high optical transmission greater than 95 %, but also high average power handling up to at least 100 W of laser power. However, the dependence of SLM shaping performance on laser bandwidth places specific requirement when using ultrafast lasers. We will present phase map optimization strategies dedicated to specific industrial applications.
Glass processing is a subject of high interest for electronics, watch and consumer electronics industries. The femtosecond laser has unique capacity to produce a high-quality surface or bulk modification in dielectrics transparent materials thanks to nonlinear absorption. Temporal pulse shaping seems to be a smart and flexible solution to further increase the efficiency of this tool. Indeed, since the lifetime of free electrons in the conduction band is about few picoseconds, it is possible to improve ablation efficiency of dieletrics using a double pulse laser irradiation. The principle is to use the first pulse to promote electrons into the conduction band meanwhile the second one induces the ablation of the target material. This study deals with double femtosecond laser pulse radiation of fused silica in order to tune both ablation threshold and removal rate. The time delay between the two pulses is set from 0 to 5 ps owing to a delay line. The results are discussed in terms of optical transmission and ablation efficiency. Our ultrafast laser operates at 1030 nm and has a pulse duration of 480 fs.
Nowadays the relevance and the robustness of ultrafast lasers are well established for many industrial applications. Indeed this laser technology combines the unique capacity to process any type of material with an outstanding processing precision and a minimal heat affected zone. The key issue is to combine high throughput, low residual thermal load and good processing quality. Thanks to high average power and high repetition rate it is possible to achieve high throughput providing that the operating parameters are precisely tuned to the application, otherwise heat accumulation and heat affected zone may appear, leading to detrimental effects such as burr, uncontrolled melting and metal oxidation. In this paper we report on high-throughput laser ablation of metals using a 100W- and 10MHz- ultrafast laser. Target materials were stainless steel, Copper, and Aluminum. Operating parameters such as fluence, repetition rate and scanning velocity have been considered. Results are discussed in terms of ablation efficiency, surface morphology, multipass and upscaling capabilities. Different behaviors between materials are also discussed. We observe that pulse-to-pulse pitch and delay are key parameters that must be taken into account in order to define relevant process windows for each material. The use of polygon scanner instead of galvo scanner enables us to reduce the thermal load along the laser trajectory. The point is not to avoid heat accumulation but to take advantage of this phenomenon as long as the target material can stand the thermal load without detrimental effects on the processing quality.
With the development of high average power, high repetition rate, industrial ultrafast lasers, it is now possible to achieve a high throughput with femtosecond laser processing, providing that the operating parameters are finely tuned to the application. Femtosecond lasers play a key role in these processes, due to their ability to high quality micro processing. They are able to drill high thickness holes (up to 1 mm) with arbitrary shapes, such as zero-conicity or even inversed taper, but can also perform zero-taper cutting. A clear understanding of all the processing steps necessary to optimize the processing speed is a main challenge for industrial developments. Indeed, the laser parameters are not independent of the beam steering devices. Pulses energy and repetition rate have to be precisely adjusted to the beam angle with the sample, and to the temporal and spatial sequences of pulses superposition. The purpose of the present work is to identify the role of these parameters for high aspect ratio drilling and cutting not only with experimental trials, but also with numerical estimations, using a simple engineering model based on the two temperature description of ultra-fast ablation. Assuming a nonlinear logarithmic response of the materials to ultrafast pulses, each material can be described by only two adjustable parameters. Simple assumptions allow to predict the effect of beam velocity and non-normal incident beams to estimate profile shapes and processing time.
Glass cutting is a subject of high interest for flat panel display and consumer electronics industries. Among laser-based, water jet-based and diamond tool-based existing solutions, ultra-short pulses (USP) appear as a promising technology since this laser technology has the unique capacity to produce highly localized bulk modification owing to non-linear absorption. The cutting using USP lasers could be performed either by full ablation which is slow and generates a lot of dust, by controlled fracture propagation which is slow as well and may lead to path deviation, by stealth dicing which produces rough sidewalls, or by self-breaking induced by in-volume laser irradiation. The laser treatment is often continuous which is not necessary to perform glass cutting and may lead to over-exposure. In this paper we report on single pass glass and sapphire cutting using an USP laser (20W @200kHz or 8W@2MHz) using dash line laser treatment along the cutting trajectory. In-volume energy deposition was done along the glass thickness owing to a Bessel beam. The results will be discussed in terms of sidewall profile and roughness, path deviation, rim sharpness, energy dose and feed rate. Dash line treatment enables to tune the energy deposition and to produce the cutting effect but with a narrower heat affected zone, a better sidewall quality and a more accurate trajectory control of the cutting path.
We investigated the effect of burstmode with nanosecond (ns) time delay between subpulses on sodalime glass volume machining. We observed in tight focusing configuration that the use of burstmode with ns time delay between subpulses does not increase the absorption efficiency and does not bring a significant effect on the heat affected zone diameter with respect to single pulse mode. On the contrary in loose focusing configuration the use of burst mode allows increasing the aspect ratio of the heat affected zone without extra energy absorption. This effect is highly interesting for filamentation glass cutting applications.
We report on vortex-assisted femtosecond direct laser writing (DLW) in silver-containing phosphate glasses with
complex light fields endowed with optical phase singularities. This allows us to engrave complex patterns showing
sub-wavelength dimensions. The associated linear and nonlinear optical properties show remarkably correlated
but distinct spatial distributions. The creation of a perennial buried electric field leads to an efficient electric-
field induced second harmonic generation. The magnitude and distribution of such buried field is also considered
to actively drive the pattern topology of the fluorescent silver clusters. Using DLW with phase and amplitude
engineered beams, we demonstrate a promising approach to control both fluorescent and nonlinear responses
below the diffraction limit.
The nonlinear absorption character determines a high potential of ultrafast laser pulses for 3D processing of transparent
materials, particularly for optical functions. This is based on refractive index engineering involving thermo-mechanical,
and structural rearrangements of the dielectric matrix. Challenges are related to the time-effectiveness of irradiation,
correct beam delivery, and the influence of material properties on the exposure results. Particularly for light-guiding
applications it is suitable to master positive refractive index changes in a time-efficient manner, considering that the
result depends on the deposited energy and its relaxation paths. To address these challenges several irradiation concepts
based on adaptive optics in spatial and temporal domains were developed. We review here some of the applications from
various perspectives. A physical aspect is related to temporal pulse shaping and time-synchronized energy delivery tuned
to material transient reactions, enabling thus a synergetic interaction between light and matter and, therefore, optimal
results. Examples will be given concerning refractive index flip in thermally expansive glasses by thermo-mechanical
regulation and energy confinement by nonlinear control. A second engineering aspect is related to processing efficiency.
We give insights into beam-delivery corrections and 3D parallel complex photoinscription techniques utilizing dynamic
wavefront engineering. Additionally, in energetic regimes, ultrafast laser radiation can generate an intriguing nanoscale
spontaneous arrangement, leading to form birefringence and modulated index patterns. Using the birefringence
properties and the deriving anisotropic optical character, polarization sensitive devices were designed and fabricated. The
polarization sensitivity allows particular light propagation and confinement properties in 3D structures.
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