1. Femtosecond Laser Micromachining of BioMEMS BioMEMS Lab Mechanical and Aerospace Engineering University of Texas Arlington

2. Comparison of Micromachining Processes ProcessResolution  m Surface Roughness  m Side Effects Mechanical1006.3-1.6Burring, requires polishing EDM1004.75-1.6Electrode wear, rough finish, slow and unclean process Chemical Etch2506.3-1.6Undercutting LIGA51-2Synchrotron source: very expensive Nd: YAG Laser501Redeposition Excimer Laser5 > 1  m (nm range) Recast Layer, aspect ratios Ti:sapphire Ultrafast Laser < 1nm rangeHigher power ranges may require vacuum environment

3. Laser Micromachining Process

4. Advantages of Laser Micromachining Non-contact machining Very high resolution, repeatability and aspect ratios Localized heating, minimal redeposition No pre/post processing of material Wide range of materials: fragile, ultra-thin and highly reflective surfaces Process can be fully automated

5. Effect of Laser Micromachining Process Parameters Process ParametersEffect Wavelength, Focal length of lens Feature size Beam shape (Gaussian/square wave) Feature shape Beam energy, Pulse width Size of heat affected zone Depth of focusAspect ratio Vacuum or inert gas environment Amount of redeposition, size of recast layer

6. Characteristics of Femtosecond Laser Micromachining Very high peak powers in the range 10 13 W/cm 2 provide for minimal thermal damage to surroundings Very clean cuts with high aspect ratios Sub-micron feature resolution Minimal redeposition Possible to machine transparent materials like glass, sapphire etc

7. Ultrashort Pulses vs. Long Pulse Micromachining Ti: sapphire,120fs a) air b) vacuum c) Nd:YAG, 100ns Courtesy: Sandia National Labs Extremely short pulses provide for minimal thermal damage to surroundings

8. Femtosecond Laser System at BioMEMS Lab Spectra Physics Hurricane Femtosecond Ti: sapphire Laser Pulse width: 106fs Wavelength range: 750nm-850nm Average energy: 1mJ/pulse Beam profile: Gaussian Polarization: linear, horizontal

9. Femtosecond Laser Micromachining (Preliminary Experimental Testbed)

10. Additional Equipment for Femtosecond Laser Micromachining Ultra-high precision 3-axis linear stage assembly by Aerotech Inc. Ultrafast High Energy Beam Attenuator by Newport Corporation. Power Meter by Scientech Inc. 2GHz Oscilloscope by Hewlett Packard Under development 10 -3 Torr, 1m 3 Vacuum Chamber with inert gas and electrical and power ports Fully automated multiple lens changer LabView based control environment

11. Preliminary Experimental Results (a)Array of shots (b) Thru-hole drilled after 33 shots at a pulse energy of 14μJ Micromachining in 18μm Thick Aluminum Foil

12. Single Shots in 18μm Thick Aluminum Foil Focal position Off-focal position Preliminary Experimental Results

13. Thru-holes Drilled in 25μm Thick Brass Foil 56μJ/pulse 27μJ/pulse Preliminary Experimental Results

14. Ablation Rate vs. Energy Density in 18  m Thick Aluminum Foil

15. Optimization of Pulse Energy Required to Drill Thru-Holes

16. Femtosecond Laser Bonding of Optically Transparent Materials Explore femtosecond laser bonding of optically transparent PMMA or glass to a substrate Automatic lens changer will be used to study the effect of variable focal length on the bond strength

17. Laser Intensity Distribution in PMMA Focal length of 9mm Focal length of 40mm

18. Through the Thickness Intensity Distribution of Transmitted Laser Beam in PMMA Focal length of 9mm Focal length of 40mm

19. Automation of Laser Micromachining Process

20. Conceptual Solid Model of Laser Micromachining Setup