Guide t o Handling & Cleaning Research Optics

1. Guide to Handling & Cleaning Research Optics Farshid Manoocheri

2. Handling Optics Hold an optic only by its edge Never touch an optic with your bare hands Always use a clean, lint-free cloth, latex gloves or finger cots Never touch the surface of an optic, even with gloves or finger cots.

3. Handling Optics • Never lay an optic on a dirty • or an uncovered surface • Place an optic on top of • several sheets of lens tissues • or optical cloth • When not in use • Cover your optics • store them in a dry , dust-free area

4. Cleaning Optics

5. Every cleaning method has risk of damage • Should you remove an optic from its mount? • If the optic is intended to be removable • Take the optic out from its mount and clean • Bonded optics should be cleaned carefully with its mount • Prepare the area first • Provide a soft landing • Use edge restraints • Pour cleaning solution onto the optic • Do not dip the tissue into solution

6. Identifying the contaminant • Know your Optic and Your Enemy Before cleaning • Know your optic • Is it soft or hard? • Durable surface finish? • Identify the contaminant(s) • Particulates • Thin film • both • Determine what is clean enough • Establish and document a standard of cleanliness • Match the cleaning method to the contaminant and the optic

7. Common Contaminants and their sizes

8. Prevention of thin film contamination • Never touch an optical surface with your bare fingers. Oil creeps! • Physically remove all machinery or isolate it so that airborne oil can not circulate to optics • Use clean room techniques to filter air streams used to clean optics • Avoid using cooled optical surfaces at temperatures below ambient Oil films can coat particles, making them extremely difficult to remove.

9. Safety Consideration for Common Solvents • Safety Hazards • Toxcity • Flammability • Reactivity • Attack the optical material • Potential as an irritant Do not rely on odor as a guide - Check exposure limits for any solvent you use - Aceton is well detectedbelow exposure limit - Some materials are detected well in excess of limit Alcohols High Flammability, Low Reactivity

10. Chemical Attack on Optical Glasses Chemicals leach materials out of surface Fused silica glass is resistant to all except to Hydrofluoric acid BK7 glass can be damaged by climate, alkalin solutions • Typical visible surface changes: • No change • Scarred surface but no color change • Interference colors • Whitish staining • White coating Some UV transmitting ”Black Glasses” are fogged by moisture in the air. Do not leave these exposed to the atmosphere for long periods of time.

11. Chemical Attack on Optical Glasses Finger prints etch into the optics if exposed to UV light long enough Enclose your optics Consider coating them with a protective coating.

12. Ensure that the cleaning agent will not harm your optics

16. Routine Cleaning Procedure • Essential Materials for Routine Cleaning: • Latex gloves or finger cots ( Be careful with Acetone) • Clean , well-lit working area • Optical cleaning cloth • Lens tissues and pads • Dust bulb or source of clean filtered air • A bright inspection light (microscope illuminator or flsh light • Suitable solvents (never use Alcohol for Aluminum coated optics) • Solvent dispensers

17. Drag Wipe Method • Suitable for • Removing dust • Fresh fingerprints • Thin contaminant films Remove loose particulates by blowing or brushing Drop one or two drops of the cleaning solvent directly on the optic Drape a clean piece of lens tissue on the wetted surface Drag the tissue across the surface gently Repeat a few times steps 2-4 until optic is clean Do not reuse solvent or lens tissues

18. Dielectric Coated Optics • Found in: • Reflectors • Beam splitters • Windows • Filters • Very thin layers , i.e. <1 µm in thickness • Place the optic with the surface to clean facing up • Remove any surface dust • Or use strippable coating to remove surface dirt • Inspect with your light to ensure complete removal of loose particulates • Use the Drag-Wipe Cleaning Method to remove any film contaminants

19. Strippable Cleaning & Protective Coating • Strippable coatings can clean & protect • Non-metallic coated optics • Uncoated optics • Use it for uncoated glass types and plastics: • Fused silica • BK7 • Borosilicate • Soda lime • Prevents • Contamination • Scratches • Digs • Use it for • Shipping • Storage • During experiment set-ups

20. Strippable Cleaning & Protective Coating II 2. Wait for the coating to cure about 15 minutes for smal optics or until entire surface looks cloudy. 3. Peel coating off with an adhesive backed lable. (White envelope lables work well) Pour coating in the centre & use a bristle brush to evenly coat the surface

21. Strippable Cleaning & Protective Coating III • Tips • If lable does not peel off the coating • Chill the optic in a refrigerator for a few minutes before using the adhesive lable • Do not remove an uncured film, this will not remove the contaminant • To clean a small mirror or laser rod, • Wrap a lable around the periphery, up to the face to be cleaned • Apply the coating to the faces • After curing unroll the lable first

22. Cleaning Metallic Reflectors & Soft Optics • Metallic reflectors reuire special care in cleaning • Can be easily damaged • Soft, bare metal coatings canot be contact cleaned • Diffraction gratings uncoated metal mirrors, etc. • If metal is overcoated (typical) • Can clean with gentle cleaner or acetone using Drag-Wipe method Remove large particles ( brucsh, dust bulb, dry clean nitrogen) Use the Drag-Wipe method Except for chrome, most bare metals are very soft. Do not contact clean If you have no choice then Remove dust Pour acetone (or suitable fluide from the optic vendor Dry with nitrogen

23. Cleaning Interference Filters • UV-VIS Narrowband filters are sealed sandwich structures • The rim seal can be damaged by aggressive solvents • Breaking the seal will greatly shorten the useful life of the filter • . • If absoulutely necessary to clean, then • Use Drag-Wipe method with mild solvents • Strart from a small spot in the centre • Use gentle circural movement toward outer edge • Repeat

24. Other cleaning methods Scrub (for hard optics) Heat the solvents Use more agressive solvents Ultrasonic cleaning Vapor degreasing Plasma cleaning UV/Ozone cleaning Repolish the surface Etch the surface Not all cleaning methods are usable on every optic. Know your optic before implementing any cleaning procedure.

25. Ultrasonic cleaning For heavily soiled optics that can withstand detergents and/or distiled water

26. Storing Optics and Disposal of Chemicals • All optics should be stored when Not in use • Wrap the opic carefully in well cushioned packaging. • Use lens tissue and then bubble wrap • Use opic boxes with dividers • Do not use general purpose tissues or Chemi-wipes • Store in a clean, dry, moderate temperature enviornment (eg. Dry cabinet in our corridore in the basement) Store easily stained materials with sensitive coatings in a drawer with desiccant (Gels) 3. Mark optic boxes with ”Fragile” stickers

27. Disposal Check the latest version safety instructions to ensure that you are following the regulations relevant for the cleaning solvents you use