John Lopez

Microlenses fabricated by ultraviolet excimer laser irradiation of poly(methyl methacrylate) followed by styrene diffusion.

A new technique of microlens array fabrication based on the use of excimer laser radiation is described. Poly(methyl methacrylate) (PMMA) substrates are treated with many low-energy KrF laser pulses and exposed to styrene vapor. The irradiated material swells, producing spherical microlenses that are stabilized by UV polymerization. The chemistry of this process and the optical quality of the lenses are discussed.

Ultrafast laser with high energy and high average power for industrial micromachining: Comparison ps-fs

Ultrafast lasers present a growing interest for industrial applications such as surface structuring or thin film selective ablation. Indeed, they combine the unique capacity to process any type of material, such as dielectrics, semiconductors or metals, with an outstanding precision and a reduced affected zone. In this paper, we report on results about surface engraving of metals (Al, Cu, Mo, Ni), semiconductor (Si) and polymer (PC) using a picosecond thin disk Yb:YAG-amplifier, which could be used in the picosecond regime as well as in the femtosecond regime by simply changing the seed laser source. In the picosecond regime the oscillator pulses (34ps) can be directly amplified which leads to a quite simple and efficient amplifier architecture. On the other hand, a broadband femtosecond oscillator and a CPA configuration can be used in order to obtain pulse duration down to 900fs. The results obtained with this thin disk laser are compared to ones achieved with two commercial femtosecond lasers respectively based on Yb-doped crystals and fibers, and operating at similar output power levels (up to 15Watt). Finally, we have considered etch rate and process efficiency for both ps-and fs-regimes as a function of average power, of fluence and of intensity.Ultrafast lasers present a growing interest for industrial applications such as surface structuring or thin film selective ablation. Indeed, they combine the unique capacity to process any type of material, such as dielectrics, semiconductors or metals, with an outstanding precision and a reduced affected zone. In this paper, we report on results about surface engraving of metals (Al, Cu, Mo, Ni), semiconductor (Si) and polymer (PC) using a picosecond thin disk Yb:YAG-amplifier, which could be used in the picosecond regime as well as in the femtosecond regime by simply changing the seed laser source. In the picosecond regime the oscillator pulses (34ps) can be directly amplified which leads to a quite simple and efficient amplifier architecture. On the other hand, a broadband femtosecond oscillator and a CPA configuration can be used in order to obtain pulse duration down to 900fs. The results obtained with this thin disk laser are compared to ones achieved with two commercial femtosecond lasers respectiv...

Surface blackening by laser texturing with high repetition rate femtosecond laser up to 1MHz

The interaction between laser pulses and material surface can generate sub-wavelength surface structures named ripples. The used of ultrashort laser pulses avoid thermal effect in the lattice so the structures generated are well preserved and can be observed on various materials as metals, polymers or crystals. With increasing energy deposit, ripples grow to give cone-shape structures named spikes. All these structures are interesting to give special properties to the treated surface as coloration change, improvement of light absorption or modification of wettability properties. These structure generation process is well known for femtosecond Ti:Sa laser with a pulse duration below 100fs and repetition rates in the range of 10 kHz. However, to be relevant for industrial applications, the average power of the laser is a critical parameter. The emergence of new femtosecond Yb doped fiber lasers with pulse duration below 350fs permits an increase of the average power for a few years. We will present our latest results obtained for surface texturation on various metals such as stainless steel, titanium, aluminum and copper with these up to date laser source. We study the influence of the average power and of the repetition rate up to 1000 kHz on the surface structures generated on scanned areas. We obtain light reflexion below 7% on stainless steel and below 5% on titanium from 200nm to 2000nm. The characterizations of the results are done with SEM imaging, optical profilometry and with a spectrophotometer.

High-aspect-ratio microdrilling in polymeric materials with intense KrF laser radiation

UV laser microdrilling of high aspect ratio holes requires a low numerical aperture and intense beam. It does not produce any thermal or mechanical damage on the target. In some particular experimental conditions, it is shown that long deep holes are obtained with reproducible aspect ratio ((Phi) /d approximately equals 600) in a variety of materials. Generally speaking the more absorbing the polymer is, the better is the resolution. However highly absorbing materials exhibit a low ablation rate. These promising results on laser microdrilling can be extended to new applications when beam and target relative movement is computer driven. For instance this approach can applied to cutting micro-objects with complicated shape or machining of fragile or brittle materials.

Study on the influence of repetition rate and pulse duration on ablation efficiency using a new generation of high power ytterbium doped fiber ultrafast laser

Ultrafast laser are well known to provide cold ablation on metals at near-threshold fluence and low repetition rate. However increasing the repetition rate from multi-kHz to MHz may produce a heat accumulation in the target depending on both the scanning speed and the material properties. This potentially leads to two effects: enhanced ablation efficiency as well as increased heat affected zone. To identify potentials and limitations while maintaining highest processing quality is the main objective of this paper and a key issue for many industrial applications. We present some comprehensive results on the influence of both repetition rate and pulse duration on the ablation efficiency. This investigation is performed using a new generation of high power Ytterbium doped fiber ultrafast laser with a tunable pulse duration ranging from 350fs to 10ps and with repetition rate going from 250kHz to 2MHz. The output power is up to 40 watt. The effect of both parameters above on ablation efficiency of Al, Cu and Mo is discussed with respect to removal rate measurement and SEM analysis.

Laser micro processing of metal and silicon using 100KHZ and 2MHZ ultrafast lasers

Ultrafast laser micromachining has been widely proven to be a high quality, high flexibility process, with numerous potential, industrial applications. Indeed, femtosecond laser is a key technology for micro processing since it combines the unique capability to process any material with a reduced heat affected zone. Low pulse energy is generally required for micromachining (<100µJ). Until recently, a main drawback was the low processing speed due to the limited average power available from ultrafast lasers. Recent advances in commercial ultrafast lasers enables to overcome this limitation since there is a significantly increase of the average power available to the user. However, parallel advances in process development are required to take full advantage of these new capabilities. In this paper, we report on micromachining and engraving of metal and silicon using both crystal-based systems (4W@100kHz) and fiber lasers (15W@2MHz), operating in the picosecond and femtosecond regimes. We obtained removal rate up to 2mm3/min on metal without any burr. Processing speeds greater than 5m/s are reached with smooth and burr-free sidewalls.Ultrafast laser micromachining has been widely proven to be a high quality, high flexibility process, with numerous potential, industrial applications. Indeed, femtosecond laser is a key technology for micro processing since it combines the unique capability to process any material with a reduced heat affected zone. Low pulse energy is generally required for micromachining (<100µJ). Until recently, a main drawback was the low processing speed due to the limited average power available from ultrafast lasers. Recent advances in commercial ultrafast lasers enables to overcome this limitation since there is a significantly increase of the average power available to the user. However, parallel advances in process development are required to take full advantage of these new capabilities. In this paper, we report on micromachining and engraving of metal and silicon using both crystal-based systems (4W@100kHz) and fiber lasers (15W@2MHz), operating in the picosecond and femtosecond regimes. We obtained removal ra...

2D laser induced periodic surface structures with double cross-polarized pulses

We present a systematic study on the generation of 2D surface structures on stainless steel, using double, crosspolarized femtosecond pulses with variable interpulse delay. We demonstrate the combined effect of the interpulse delay and key process parameters in order to obtain periodic structures. The sets of double pulses were produced utilizing a modified Michelson interferometer with interpulse delay varying from -100 ps to +2 ns. The study was carried out with an industrial laser having pulse duration of 350 fs, emitting in the near infrared (λ = 1030 nm), operating at 100 kHz coupled with a Galvo scanner. We evaluate the obtained surface morphology and structure period using SEM characterization and Fourier analysis.

Correlation between ablation efficiency, surface morphology, and multipass capability using a 100-W 10-MHz ultrafast laser

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.

Dash line glass- and sapphire-cutting with high power USP laser

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.

Glass cutting using ultrashort pulsed bessel beams

Glass cutting is a subject of high interest in flat panel display and smart-electronics industries. The key issue is to combine high throughput, low residual thermal load and good sidewall quality. The process must be energy-efficient and material-efficient as well. Among laser-based and diamond tool-based existing solutions, ultrashort pulses (USP) appears as a promising technology. Indeed, USP enables to produce internal modification owing to non linear absorption. Under specific irradiation conditions, this internal modification can lead to a free separation of the two glass parts.In this paper we report on recent investigations dealing with soda lime glass and Sapphire cutting using an USP Bessel beam. In fact, the long and uniform spot of zero-order non-diffractive Bessel beam can be turned into advantage in order to produce an elongated modification along the glass thickness (more than 1 mm long), and to achieve stealth dicing or controlled fracture propagation. The influence of pulse duration, pulse energy, and repetition rate will be discussed in terms of cutting feasibility, extend of heat affected zone and sidewall morphology. The results will be compared to those obtained with Gaussian beams under elongated-spot focusing conditions.Glass cutting is a subject of high interest in flat panel display and smart-electronics industries. The key issue is to combine high throughput, low residual thermal load and good sidewall quality. The process must be energy-efficient and material-efficient as well. Among laser-based and diamond tool-based existing solutions, ultrashort pulses (USP) appears as a promising technology. Indeed, USP enables to produce internal modification owing to non linear absorption. Under specific irradiation conditions, this internal modification can lead to a free separation of the two glass parts.In this paper we report on recent investigations dealing with soda lime glass and Sapphire cutting using an USP Bessel beam. In fact, the long and uniform spot of zero-order non-diffractive Bessel beam can be turned into advantage in order to produce an elongated modification along the glass thickness (more than 1 mm long), and to achieve stealth dicing or controlled fracture propagation. The influence of pulse duration, puls...