13' Other Miniaturization Tools

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13. Other Miniaturization Tools
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Theoretical background for Laser Machining
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Laser wavelength

• For short-wavelength radiation ( 200 ?), direct
  photochemical bond breaking plays an important
  role
• At longer wavelengths ( gt 300 nm), the single
  photon energy is not sufficient for bond
  breaking two photon or multiphoton avalanche
  effect processes must be considered.

Laser spot size

• Smallest spot obtainable is about half
  wavelength of the light used

Average Laser Beam IntensityLaser spot size

• W/cm2 (in open air with highly collimated beam
  106 W/mm2).
• W J/pulse duration (sec).
• I 2P / (pW02 ) P total
  power in watts
• W0 Gaussian beam radius the radius at
  which the intensity decreased to 1/e2
  of its value on the axis.

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Depth of Focus

• ? the wavelength of the radiation
• M2 the beam mode parameter
• d0 (mm) the diameter of the beam at the
  focusing line.
• f the focal length of the lens

Laser Pulse Length
Long pulses

• Pulse duration 8 ns, energy 0.5 mJ
• The laser pulse duration is longer than the the
  heat diffusion time
• Adequate for welding
• Undesirable for micromachining

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Short Pulses

• Femto second laser 5 10 GW intensity 1014
  W/cm2 at the workspot
• The duration of laser pulse is less than the
  heat diffusion time.
• Adequate for micromachining

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