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Basic optics lab skills. Optics care, types of optics, alignment tricks. Optics care. Don’t let it get dirty in the first place Not all optics can be cleaned Probability of damage exists with each cleaning attempt Never touch coatings -- easy to say, hard to do -- improve with practice

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basic optics lab skills

Basic optics lab skills

Optics care, types of optics, alignment tricks

optics care
Optics care

Don’t let it get dirty in the first place

  • Not all optics can be cleaned
  • Probability of damage exists with each cleaning attempt

Never touch coatings -- easy to say, hard to do -- improve with practice

  • Handle only by edges
  • Have clean hand or wear gloves
  • If touched, clean immediately -- oils chemically attack coatings

Don’t let dust collect

  • Dust is abrasive -- tends to scratch during cleaning
  • Don’t let optics lie face up
    • Dust tends not to collect on vertical surfaces
      • why are most optical setups table-top instead of wall-mounted
    • Ex: set temporarily unused optics on edge
      • optics on edge may fall and be scratched
      • usually smaller problem than dust
optics cleaning
Optics cleaning
  • Compressed gas
    • sensitive optics
    • loosely bound dust
  • Drag and wipe
  • Lens tissue held by hemostat

Let solvents do the work

  • Methanol -- general purpose
  • Acetone -- better organic solvent, toxic
    • excellent as vapor degreaser
    • can dissolve optics glues
  • Isopropanol -- non-toxic, safe for most optics glues
  • Soapy water -- tough, water based dirt
    • Ex: flood in room above or sewer line breaks above optical table
  • De-ionized water -- use as rinse after soapy water -- follow with methanol
types of optics
Types of optics

Passive

  • Mirrors
  • Beamsplitters -- partially reflecting mirrors
  • Lenses and lens assemblies
  • Polarizing elements

Active

  • Modulators -- acousto optic, electro optic
  • Liquid crystals -- shutters, spatial light modulators (SLM)
  • Gain media -- lasers
  • Nonlinear optical elements
  • Samples under study
  • Detectors -- photodiodes, power meters
alignment tricks
Alignment tricks

General

  • Fix beam height on table -- always keep ruler handy
    • Ex: six inches -- usually high enough
    • Reduces 3-D alignment problem to 2-D problem
    • Polarization rotation issues avoided
    • Allows more stable, fixed height mounting
      • can do sensitive experiments w/o floating table
  • Mirrors
    • Tilt angle important -- use tilt plate mount
    • Position less important -- but stay away from edge -- 1.5 beam diameters
  • Lenses
    • Position important -- use translation mount
    • Angle less important -- but can cause aberrations
  • Other, more complicated elements
    • Better to show than tell
long term alignment
Long-term alignment

Use irises

  • Laser beam has position and angle - 4 dimensions
    • two mirrors give enough degrees of freedom
    • two irises needed to define
  • Divide complex setups into sub-assemblies
    • 2 mirrors, 2 irises are 1st elements in each sub-assembly
  • Can use servo control to stabilize
    • replace irises with position sensing diodes
    • many commercial devices incorporate
    • build one here ?

Iris

Iris

Optical

sub-assembly

Mirror

Mirror

Input

mirror mounts
Mirror mounts
  • Tilt plate
    • plate thickness, spring stiffness, contact smoothness
  • All not alike
    • test with laser and long room

Prefer 3/8 -- 1/2 ”

Mount plate

groove

Adjust

screw

Support

plate

Mount

plate

Hard, smooth inserts

dimple

flat

lens mounts
Lens mounts

Translation mounts

  • less critical than mirror mounts
  • long focal lengths -- large translation gives small alignment change
  • short focal lengths -- spatial filters and microscopes
    • all spatial filter designs flawed
mirror and lens mounts
Mirror and lens mounts
  • Magnetic base -- easy to change setup
  • Fixed standard height -- more stable
experimental technique
Experimental technique
  • Most people either Type 1 or 2
    • depends on personality
  • Type 1
    • Quick setup -- try right away
    • If not successful -- fix something, try again
    • Repeat forever
  • Type 2
    • Methodical setup
    • Works 1st (or 2nd) time
    • Takes forever before 1st attempt
  • Best approach
    • Start with type 1
    • If not successful after several attempts -- do type 2
  • Easier to say than do
    • Difficult for both personalities
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