Light-shielding film on edges and draft facets of Fresnel lens fabricated by picosecond laser processing

A picosecond laser in spin-cutting mode was used to drill 500μm diameter microholes on 150μm thick aluminium nitride ceramic. The effects of laser processing parameters such as the laser power, scanning speed, and defocus amount on the microhole quality were studied. The results show that as the laser power increases, the inlet and outlet diameters of the holes increase, the taper decreases slightly, and the thickness of the recast layer decreases evidently. The scanning speed has no obvious effect on the diameter and taper of the hole; however, the hole can not be drilled through when the speed is too large. Positive defocus can effectively reduce the taper of the hole. Under 28.5W laser power, 400Hz frequency, 200mm/s scanning speed, and zero defocus amount conditions, high-quality microholes with a taper of 0.85° were obtained.

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Research and Application of Massive Micropores Water-Assisted Picosecond Laser Processing Technology

Chinese Journal of Lasers ◽

10.3788/cjl202047.0302002 ◽

2020 ◽

Vol 47 (3) ◽

pp. 0302002

Author(s):

朱帅杰 Zhu Shuaijie ◽

张朝阳 Zhang Zhaoyang ◽

储松林 Chu Songlin ◽

杨志逸 Yang Zhiyi ◽

张先烁 Zhang Xianshuo ◽

...

Keyword(s):

Laser Processing ◽

Picosecond Laser ◽

Processing Technology

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Residual heat generated during laser processing of CFRP with picosecond laser pulses

Advanced Optical Technologies ◽

10.1515/aot-2018-0001 ◽

2018 ◽

Vol 7 (3) ◽

pp. 157-163

Author(s):

Christian Freitag ◽

Leon Pauly ◽

Daniel J. Förster ◽

Margit Wiedenmann ◽

Rudolf Weber ◽

...

Keyword(s):

Laser Pulse ◽

Heat Affected Zone ◽

Laser Processing ◽

Picosecond Laser ◽

Theoretical Models ◽

Laser Pulses ◽

Groove Depth ◽

Interaction Zone ◽

Heat Accumulation ◽

Residual Heat

Abstract One of the major reasons for the formation of a heat-affected zone during laser processing of carbon fiber-reinforced plastics (CFRP) with repetitive picosecond (ps) laser pulses is heat accumulation. A fraction of every laser pulse is left as what we termed residual heat in the material also after the completed ablation process and leads to a gradual temperature increase in the processed workpiece. If the time between two consecutive pulses is too short to allow for a sufficient cooling of the material in the interaction zone, the resulting temperature can finally exceed a critical temperature and lead to the formation of a heat-affected zone. This accumulation effect depends on the amount of energy per laser pulse that is left in the material as residual heat. Which fraction of the incident pulse energy is left as residual heat in the workpiece depends on the laser and process parameters, the material properties, and the geometry of the interaction zone, but the influence of the individual quantities at the present state of knowledge is not known precisely due to the lack of comprehensive theoretical models. With the present study, we, therefore, experimentally determined the amount of residual heat by means of calorimetry. We investigated the dependence of the residual heat on the fluence, the pulse overlap, and the depth of laser-generated grooves in CRFP. As expected, the residual heat was found to increase with increasing groove depth. This increase occurs due to an indirect heating of the kerf walls by the ablation plasma and the change in the absorbed laser fluence caused by the altered geometry of the generated structures.

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Laser processing of GaN-based LEDs with ultraviolet picosecond laser pulses

10.1117/12.921843 ◽

2012 ◽

Cited By ~ 3

Author(s):

Rüdiger Moser ◽

Michael Kunzer ◽

Christian Goßler ◽

Ralf Schmidt ◽

Klaus Köhler ◽

...

Keyword(s):

Laser Processing ◽

Picosecond Laser ◽

Laser Pulses ◽

Picosecond Laser Pulses

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Laser processing of gallium nitride–based light-emitting diodes with ultraviolet picosecond laser pulses

Optical Engineering ◽

10.1117/1.oe.51.11.114301 ◽

2012 ◽

Vol 51 (11) ◽

pp. 114301 ◽

Cited By ~ 7

Author(s):

Rüdiger Moser ◽

Michael Kunzer ◽

Christian Goßler ◽

Klaus Köhler ◽

Wilfried Pletschen ◽

...

Keyword(s):

Gallium Nitride ◽

Laser Processing ◽

Light Emitting Diodes ◽

Picosecond Laser ◽

Laser Pulses ◽

Light Emitting ◽

Picosecond Laser Pulses

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Compact diffractive optics for THz imaging

Lithuanian Journal of Physics ◽

10.3952/physics.v58i1.3655 ◽

2018 ◽

Vol 58 (1) ◽

Cited By ~ 6

Author(s):

Linas Minkevičius ◽

Simonas Indrišiūnas ◽

Ramūnas Šniaukas ◽

Gediminas Račiukaitis ◽

Vytautas Janonis ◽

...

Keyword(s):

Spherical Surface ◽

Focal Depth ◽

Numerical Aperture ◽

Picosecond Laser ◽

Fresnel Lens ◽

Diffractive Optics ◽

Direct Writing ◽

Thz Imaging ◽

Beam Focusing ◽

Phase Quantization

We present a compact diffractive silicon-based multilevel phase Fresnel lens (MPFL) with up to 50 mm in diameter and a numerical aperture up to 0.86 designed and fabricated for compact terahertz (THz) imaging systems. The laser direct writing technology based on a picosecond laser was used to fabricate diffractive optics on silicon with a different number of phase quantization levels P reaching an almost kinoform spherical surface needed for efficient THz beam focusing. Focusing performance was investigated by measuring Gaussian beam intensity distribution in the focal plane and along the optical axis of the lens. The beam waist and the focal depth for each MPFL were evaluated. The influence of the phase quantization number on the focused beam amplitude was estimated, and the power transmission efficiency reaching more than 90% was revealed. The THz imaging of less than 1 mm using a robust 50 mm diameter multilevel THz lens was achieved and demonstrated at 580 GHz frequency.

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Development of Method Enhanced Laser Ablation Efficiency According to Fine Curvature of the Polymer through the Preliminary Preparation Process Using UV Picosecond Laser

Polymers ◽

10.3390/polym12040959 ◽

2020 ◽

Vol 12 (4) ◽

pp. 959 ◽

Cited By ~ 1

Author(s):

Seung Sik Ham ◽

Ho Lee

Keyword(s):

Laser Processing ◽

Pulsed Laser ◽

Picosecond Laser ◽

Processing Method ◽

New Method ◽

Shielding Effect ◽

Ablation Efficiency ◽

Preliminary Preparation ◽

Ultrashort Pulsed Laser ◽

New Processing

In processes using the ultrashort pulsed laser, the phenomenon that the ablation efficiency is reduced due to the increase of the shielding effect of the generated plume is increasingly caused by the use of the high power and high repetition rate. A new method is needed to prevent a decrease in ablation efficiency in processing using an ultrashort pulsed laser. In this study, the proposed a processing method that can improve the ablation efficiency by providing an efficient escape path of plume, and examine the feasibility of a new processing method. The new method we proposed is a method of laser processing after generating a fine curvature in the polymer as a preliminary preparation. The fine curvature of the polymer produced by the preliminary preparation induces an artificial chimney-like opening along the path of the incident beam during laser processing, thereby enabling the plume to be effectively removed. The experiment for examine the feasibility through a new method was conducted using a 10-picosecond laser of UV wavelength with two optical systems. As a new processing method, when processing with ultrashort pulse laser, it was observed that the ablation efficiency improved.

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