Micro-machining of transparent materials with. nano, pico and femtosecond lasers

Transcription

1 Micro-machining of transparent materials with nano, pico and femtosecond lasers - a review M.R.H. Knowles Oxford Lasers Ltd., Unit 8, Moorbrook Park, Didcot, Oxon OX11 7HP.

2 1. Motivation Applications & Markets 2. Laser processing of transparent media 3. Examples 4. Conclusions

3 There is good reason to believe that the impact of photonics in the 21 st Century will be as significant as electronics was in the 20 th or steam in the 19 th. Lord Sainsbury QE2 Conference 13 th July 2006

4 Photonic Applications Rely on transparent media Processing of transparent media on milli & micro & nano scale is increasingly important. Transparent media encountered in Photonics include glass, fused silica, sapphire, PMMA, polycarbonate

5 Photonic Applications Displays TV, PC, mobile phones Sensors healthcare, security, industrial Lighting LEDs, OLEDs Energy solar cells Communications high bandwidth fibre optics

6 Photonic Markets 150 billion for components & enabled products in billion estimate for 2015 If the 1970s 1980s saw the birth of laser processing of metals, the 1980s 1990s the breakthrough h of laser applications in electronics and semiconductors then it seems will be the era of growth into processing of transparent photonic materials.

7 Laser Processing of Transparent Media Definition of transparent lets visible light through laser processing with UV & IR would seem good choice also ultrafast (ps & fs) lasers Restrict t this talk to UV and ultrafast t lasers

8 Laser Processing of Transparent Media The penetration to which a laser pulse interacts with material is determined by optical and thermal penetration L = L op + L th In dielectrics optical penetration dominates over thermal and for long pulses (>ns) strongly depends on wavelength. UV lasers <300nm 266nm Nd 255nm CVL 248nm KrF 193nm ArF 157nm F 2

9 Laser Processing of Transparent Media Ultra-fast t Lasers High intensity rips electrons out of the lattice. Resulting ions repel each other and cause a Coulomb explosion. Coulomb explosion is a non-thermal ablation mechanism. Wavelength of laser becomes less important as pulses become shorter

10 Examples Fibre Bragg Gratings - inscription of grating structure in fibres - telecoms, sensors, fibre lasers Fibre structuring - milling & drilling of fibres - medical devices, sensors, telecoms Micro-fluidics Display & Solar Lighting - milling & drilling glass or polymers - lab-on-chip - ablation of thin films - structuring of transparent electrical circuits - ablation thin films & sapphire dicing

11 Fibre Bragg Gratings inscription of grating structure in fibres modification of the refractive index in a periodic manner induced refractive index modulation in the fibre core achieved by exposing fibre to modulated UV beam satisfying Bragg condition means a single can be selected, ideal as filters in optical networks telecoms, sensors, fibre lasersuv

12 Fibre Bragg Gratings 2 methods used to produce FBGs UV Laser Beam Phase mask Cylindrical Lens Optical Fiber Overlap Region From Light Source -1 Order Interferometer Phase Mask a UV Laser Beam c b C ylin drical L ens x z Phase Mask +1 Order d y Optical Fiber To OSA Overlap Region easy to use harder to align fixed flexible, omit zero order independent of source coherence requires good source coherence high n using both methods 12

13 Fibre Bragg Gratings Optical microscope image of grating written using 255nm Lucent Photosil graded d index B/Ge co-doped d fibre Grating period of 1 m Outer Cladding Inner Cladding Core 13

14 FBG filters for use in DWDM Systems GHz Reflec ction (db) ission (db) Transmi GHz Wavelength (nm) Fiber Type - FibreCore 1250/1550 Laser Power - 300mW at 255nm Phase Mask - uniform 1550nm Apodised - gaussian, super gaussian Reflectio n (db) ion (db) Transmiss Scanning mm -40 Reflectivity- > -25dB Wavelength (nm) 14

15 Fibre Bragg Gratings Method 3 Direct write inscription using femtosecond laser. Optical microscope image of grating written using 1030nm fs laser Aston University, Photonics Group 15

16 Fibre Structuring Drilling or milling of features to create features that : interface/export the fibre photons to other devices (photodiodes) allow fibre photons to access a chemical for spectroscopic analysis Bilumen catheter, hole drilled using 248nm KrF ns laser Industrial Applications of Laser Micromaching M. C. Gower (2000), Optics Express, 7(2) pp

17 Fibre Structuring Milling using 1030nm femtosecond laser Laser and vision set-up View of fibre, showing fibre core from vision system Grooves milled into fibre Aston Universtiy, Photonics Group

18 Micro-Fluidics Microfluidics / BioMEMS becoming an important tool for analytical chemistry Glass, Polymers,Silicon channels, mixers, reservoirs, diffusion chambers, integrated electrodes, pumps, valves chips 1-50 cm 2, channel width and depth μm fluid volumes handled μl Other etching techniques: acid, photolithography, p DRIE Laser Micromachining: fast, simple, flexible, cheaper, ideal for rapid prototyping

19 Optical Beam Delivery Direct Writing Mask Projection Laser Laser Focal Plane Image Plane Mask Projection Technique Direct Writing Method (No mask used) Resulting Channel Profile

20 UV Nanosecond Results (255nm) in Glass Channel with cracking Small process window with ns

21 UV Nanosecond Results (193nm) in Glass Bottom of channel Excellent surface Channel with cracking Small process window with ns

22 UV Nanosecond Results (266nm) in PMMA

23 ps Laser Results - Fused Silica Partially optimized results Scan Velocity = 100 mm/s Line pitch = 1 m 5 μm = 355nm PRF = 50kHz Av. Pwr = 250mW Spot Size = 15 m Fluence = 3 J/cm 2 Surface Roug ghness, Ra [μm m] Laser Milled Depth [μm] Best Ra~0.434 μm

24 ps Laser Results - Fused Silica ess, Ra [μ μm] Sur rf.roughn Surface Roughness vs Fluence Scan Velocity = 1 mm/s Line pitch = 5 m = 3 m = 355nm PRF = 10kHz Spot Size = 2 m Ave.Pow er [mw] Ra 1.03 m at t80j/ J/cm 2 Ra 0.6 m at 40 J/cm 2 Fluence plays important role in surface roughness

25 Femtosecond Results (100fs, 780nm) Glass Dimitris Karnakis 1, MRH Knowles 1, KT Alty 2, M.Schlaf 2 & HV Snelling 2 Comparison of Glass Processing using High Repetition Rate Femtosecond (800nm) and UV (255nm) Nanosecond Pulsed Lasers Photonics West 2005

26 Microfluidic Channels for Liquid Sample Manipulation Flow restrictor (8 parallel (8 parallel 8 µm wide 8 µm channels) channels) 60µM MB BodipyFL in 0.1M acetic acid/50%meoh To grounded plate From CE channel Electrokinetic flow channels flow channels 1µM 1µM rhodamineb B 0.1M in 0.1M acetic acetic acid/20% id/20%m MeOH Hydrodynamic flow channel Device made in D263 glass (no dopants) with UV ns Copper laser (255nm) Dimitris Karnakis 1, MRH Knowles 1, KT Alty 2, M.Schlaf 2 & HV Snelling 2 Comparison of Glass Processing using High Repetition Rate Femtosecond (800nm) and UV (255nm) Nanosecond Pulsed Lasers Photonics West 2005

27 Glass & Sapphire Cutting 255nm ns laser (5eV) 0.2mm thick borosilicate bandgap ~4eV 0.43mm thick sapphire bandgap ~8eV 27

28 Sapphire substrate dicing for Blue LEDs V-I curve shows no effect on component Data courtesy of Institute of Photonics, University of Strathclyde, Glasgow, UK 28

29 Sapphire substrate dicing 266nm ns laser Requires high power & high pulse freq for high throughput 2.5 Sapphire etch rate 2 etch rate ( m/pulse) Fluence (J/cm 2 ) 29

30 Summary Laser processing of transparent materials is an increasingly important field, supporting several growing markets. Ultrafast lasers often produce the best quality results but are still a new technology. UV ns lasers produce acceptable results in many transparent materials