Mechanism and effects of surface morphology on absorption characteristics in ultrashort pulse laser processing of sapphire

Lye, Celescia Siew Mun; Wang, Z. K.; Lam, Yee Cheong

doi:10.1016/j.apsusc.2020.148734

Cited by 11 publications

(7 citation statements)

References 18 publications

(22 reference statements)

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“…Experiment F27D-50 was carried out on a double-side polished sample at 0.1 mm/s scanning speed at 1.13 W. A low repetition rate of 50 kHz was chosen to produce the highest peak power possible; the slowest scanning speed of 0.1 mm/s was chosen for its high energy deposition into the sample, thus giving the best opportunity for nonlinear modification to occur during laser irradiation. In accordance with our recent investigation on sample surface roughness [12], it is to be expected that without the rough exit surface, only cracks were observed on both surfaces of the sample after laser irradiation as shown in Figure 4. Mechanical cleavage was unsuccessful for all samples due to insufficient weakening of the samples.…”

Section: Pulse Energy Nonlinear Absorption Enhancementsupporting

confidence: 92%

“…By simply having a bottom unpolished exit surface in Experiments F27S-50, there was total internal reflection of the laser beam at the exit surface. As discussed in our recent investigation [12], the rough exit surface caused the laser beam to form different angles of incidence at the exit surface. When the angle of incidence of a laser beam exceeds the critical angle, total internal reflection occurs.…”

Section: Pulse Energy Nonlinear Absorption Enhancementmentioning

confidence: 82%

“…With sufficient energy accumulating, nonlinear absorption could occur. Lye et al reported a 40% decrease in transmitted power once the nonlinear absorption threshold has been surpassed, indicating the existence of nonlinear absorption within the sample for laser power exceeding this threshold [12]. With an increase in laser power, more energy is accumulated increasingly at the vicinity of the rough exit bottom surface where total internal reflection occurred.…”

Section: Pulse Energy Nonlinear Absorption Enhancementmentioning

confidence: 99%

“…By dividing the laser pulse energy over more foci, each with a smaller laser spot size, it could potentially reduce the amount of undesirable damage due to energy absorption over a smaller volume of material (i.e., only at the vicinity of the smaller foci). In addition, our recent study has found that with a rough exit sample surface relative to the laser beam, a larger amount of high intensity laser beam could be totally internally reflected at the exit surface [12]. This effectively traps the laser energy within the sample and reduces the amount of light transmission through the sample, resulting in enhanced nonlinear absorption within the samples that is required for laser machining.…”

Section: Introductionmentioning

confidence: 99%

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Multi-Foci Division of Nonlinear Energy Absorption on Ultrashort Pulse Laser Singulation of Sapphire Wafers

2021

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The multi-foci division of through thickness nonlinear pulse energy absorption on ultrashort pulse laser singulation of single side polished sapphire wafers has been investigated. Firstly, it disclosed the enhancement of energy absorption by the total internal reflection of the laser beam exiting from an unpolished rough surface. Secondly, by optimizing energy distribution between foci and their proximity, favorable multi-foci energy absorption was induced. Lastly, for effective nonlinear energy absorption for wafer separation, it highlighted the importance of high laser pulse energy fluence at low pulse repetition rates with optimized energy distribution, and the inadequacy of increasing energy deposition through reducing scanning speed alone. This study concluded that for effective wafer separation, despite the lower pulse energy per focus, energy should be divided over more foci with closer spatial proximity. Once the power density per pulse per focus reached a threshold in the order of 1012 W/cm2, with approximately 15 μm between two adjacent foci, wafer could be separated with foci evenly distributed over the entire wafer thickness. When the foci spacing reduced to 5 μm, wafer separation could be achieved with pulse energy concentrated only at foci distributed over only the upper or middle one-third wafer thickness.

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Section: Pulse Energy Nonlinear Absorption Enhancementsupporting

confidence: 92%

Section: Pulse Energy Nonlinear Absorption Enhancementmentioning

confidence: 82%

Section: Pulse Energy Nonlinear Absorption Enhancementmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multi-Foci Division of Nonlinear Energy Absorption on Ultrashort Pulse Laser Singulation of Sapphire Wafers

2021

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“…Sapphire material is becoming increasingly used in high-end product manufacturing, electronics and semiconductors as well as the aerospace, military, and medical fields [1][2][3]. However, due to the difficulty of processing hard and brittle materials, it is necessary to improve traditional processing to meet the application requirements of hard and brittle materials [4][5][6]. The processing difficulty is mainly reflected in reducing the surface roughness of hard and brittle materials and improving the processing efficiency.…”

Section: Introductionmentioning

confidence: 99%

Mechanism and Experiment Study of Non-Contact Ultrasonic Assisted Grinding

Huang

Zhong

et al. 2021

Actuators

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Ultrasonic-assisted grinding processing can effectively reduce the surface roughness and enhance the processing efficiency in the processing of hard and brittle materials. However, the most common ultrasonic assisted grinding is a type of contact ultrasonic grinding where the grinding tool directly contacts the workpiece, which means that it is necessary to accurately control the pre-pressure of the grinding tool on the workpiece. The control of pre-pressure will inevitably increase the complexity of the grinding device, and it is easy to wear the workpiece because of improper pre-pressure control. In this paper, a non-contact ultrasonic grinding method is proposed and the machining mechanism of non-contact ultrasonic grinding is revealed. The resonant frequency of the ultrasonic vibration system and vibration amplitude of the grinding tool working face were simulated and experimentally tested, respectively. Then, the experiment of non-contact ultrasonic grinding of a sapphire wafer was carried out. The result showed that non-contact ultrasonic grinding of the sapphire wafer could reduce the surface roughness by 48.6%. Compared with traditional contact grinding of sapphire wafer under certain pre-pressure conditions, the experimental results show that non-contact ultrasonic grinding has better effects in reducing surface roughness, improving processing efficiency, and improving the quality uniformity of the workpiece machining surface.

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Influence of Polymer Surface Roughness on the Fractions of Transmitted, Reflected and Absorbed Energy in Operation of Laser Transmission Welding

Genna,

Leone,

Moretti

et al. 2024

Lasers Manuf. Mater. Process.

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The study of energy fractions plays a fundamental role in laser joining operations: from their knowledge, it is possible to calculate the amount of laser beam energy that is effectively available during the formation of chemical and physical bonds, and how much energy is dissipated. This study examines semi-crystalline polymers of polyamide 6.6 (PA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and polypropylene (PP), semitransparent to light radiation, with the aim of studying the influence of surface roughness on the distribution of energy fractions, and in particular on the reflection portion. For this purpose, polymeric samples with different surface finishing were prepared and characterized by profilometric analysis. Subsequently, an experimental setup was implemented to directly measure the transmitted ratio, obtaining the reflected energy fraction from the Beer-Lambert law, and the absorbed ratio by energy balance. The results showed a decrease in the power transmitted by polymers subjected to surface treatment, due to an increase in the reflection fraction, a phenomenon particularly evident for PET, for which the reflection share increased from ~ 0.5% to ~ 15.3%, following P240 treatment. A lower influence was verified for PA and especially PTFE, due to a lower influence of the treatment on surface morphology. On the basis of the experimental results, it is hypothesised that roughening the lower section of the irradiated polymer could allow an increase in the total internal reflection fraction, favouring the joint at the interface point. Graphical Abstract

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Mechanism and effects of surface morphology on absorption characteristics in ultrashort pulse laser processing of sapphire

Cited by 11 publications

References 18 publications

Multi-Foci Division of Nonlinear Energy Absorption on Ultrashort Pulse Laser Singulation of Sapphire Wafers

Multi-Foci Division of Nonlinear Energy Absorption on Ultrashort Pulse Laser Singulation of Sapphire Wafers

Mechanism and Experiment Study of Non-Contact Ultrasonic Assisted Grinding

Influence of Polymer Surface Roughness on the Fractions of Transmitted, Reflected and Absorbed Energy in Operation of Laser Transmission Welding

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