Polygon Scanning

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작성자 lvitech 댓글 0건 조회 251회 작성일 20-03-12 14:54

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POLYGON SCANNING


The novel NST approach deflects the incoming laser beam by means of a multifaceted mirror or polygon. The one-dimensional large field f-Theta optics keeps the spot focused on the substrate.



By nature rotating scanners are one dimensional scanners. They produce a scanned line and to obtain a 2D scanning system a secondary linear motion is required. The direction of the secondary motion is perpendicular to the line scanned by the polygon scanner. This is synchronized in speed with the latter rotational speed to obtain a line by line scan of the target surface. Since the polygon is rotating at a constant speed, in contrast to the back and forward motion of the galvo mirror scanners, a higher number of scanned lines per second over a larger area can be realized.



Combining a linear stage movement with the one-dimensional f-Theta lens enables the construction of a simple yet very performant system. The reflective f-Theta system is fully telecentric and highly linear. Telecentricity provides for constant light matter interaction across the scan. The impeding beam is circular, constant in size and constant in peak intensity across the scan. Due to the mirror based optics the scan grid shows no pincushion distortion and no error compensation tables are required to achieve accuracy better than 5 μm. The LSE170A system demonstrates its performance over a scan line of 170 mm.



The LSE controller is the heart of the set-up. The controller is controlling the position of the laser beam and takes care of the fine time synchronization between the rotating polygon, the laser pulsing and material transport. The ‘image’ data or laser pulsing pattern is prepared in a black and white bitmap (a windows.bmp) file. The highest repetition accuracy in spot positioning is delivered through proprietary SuperSync controls.



The system controller is controlled by a set of operator defined parameters. The operator sets the laser repetition rate, the horizontal (fast direction) pulse spacing and vertical (slow direction) line spacing. It is this parameter set that controls the actual dimension of the scribed bitmap and sets the laser writing speed.




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FULL TELECENTRIC OPTICS


Polygon scanning is well known in the graphic art industry but still very new in advanced micromachining using high power ultrafast pulsed lasers. Utilizing a polygon scanner demands, just like galvo based scan heads, more than the deflector itself.

Current scanning solutions for high precision processing with uniform spot size need a f-Theta Telecentric lens. Processing larger formats – usually above 50 to 80 mm – will lead to more expensive optics or a step & repeat approach with increased stitching complexity. This scanning approach proves to be less cost efficient when processing at high density and limited speeds.

NST solutions maximizes throughput on small & large formats without compromising processing accuracy.




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SUPERSYNC SYNCHRONIZATION FOR LASERS


When scan speeds improve pulse timing becomes more crucial. Operating a laser at e.g. 1 MHz introduces a writing time uncertainty of 1 µs. At a scan speed of e.g. 50 m/s this timing uncertainty results in a position jitter of 50 µm.

To handle the timing jitter Next Scan developed proprietary SuperSync controls enabling high scan speeds without compromising
spot placement accuracy. The SuperSync option reduces position jitter for MOPA laser system architectures
by a factor of 10 to 50 (repetition accuracy <3 µm standard deviation).




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SPECIAL FEATURES





icon-list.png What is the focal length of your LSE ?
Do not use the classical formulas to calculate focused spot size, they do not work with our mirror optics. Our data sheet shows what spot sizes are possible.
To calculate your spot size = spot size nominal x M^2 x (6/input beam size)



icon-list.png I need to set up a grid as your controller requires a bitmap file. What is the required resolution I need ?
The spot size and overlap determine the spot separation or grid resolution:
Spot separation = Spot size x Overlap
Resolution = 1 / Spot separation



icon-list.png HOW DO I CALCULATE THE REQUIRED SCAN SPEED ?
Scan speed = Spot separation x Pulse Repetition Rate



icon-list.png HOW MUCH LASER POWER DOES MY APPLICATION NEED ?
Average power = Pulse energy x Pulse Repetition Rate






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