BBO Crystal Handling

BBO has a low susceptibility to moisture. The AR coating or the protective coating ( P-coating ) on the crystal faces can protect the faces from moisture to some extent. It is fine to leave the crystal in the  setup for most optics labs with HR =< 40%.  However, we suggest to store the crystal in a desiccator if it will not be used for over > 1 month to prolong the crystal lifetime. Alternatively, a small enclosure (with openings for light) may be built around the crystal with dry nitrogen or air continuously flow into the enclosure. The dry nitrogen/air pressure needs only to be slightly above the atmosphere to keep the small volume around the crystal dry and clean.

BBO is relatively soft and therefore requires precautions to protect the surfaces. 

Cleaning the Crystals

Dust and stains on crystal surfaces can cause scattering/loss of light and can even react with light to damage optical surfaces at a high incident laser power.

You can inspect the crystal surface for dust and stains by holding it near a bright visible-light source. Viewing at different angles helps to see scattering from dust and stains. The crystal surface has to be cleaned if dust and stains are found.

You should perform the following cleaning procedures in a clean, low-dust environment while wearing powder-free gloves or finger cots.

1. Blowing off the crystal surface

A canister of compressed N2/clean air or a blower bulb (http://www.adorama.com/GTRABS.html ) should be first used to blow off dust and other loose contaminants. If a dry nitrogen line is available in the lab, an air gun can also be used  to blow away dust particles. Blow off the surface gently. Do not blow off the crystal itself from your hand !

2. Drop and Drag Method

Hold the crystal so that the crystal surface is horizontal and slightly above your fingers. Take a fresh, clean sheet of lens tissue and place it on the crystal.  Make sure the lens tissue can be drawn across the crystal surface. Next place a small drop of pure isopropyl alcohol (IPA) on the lens tissue on top of the crystal surface. The weight of the solvent will cause the lens tissue to come into contact with the crystal surface. Slowly but steadily drag the damp lens tissue across the crystal surface being careful not to lift the lens tissue off of the surface. Continue dragging the lens tissue until it is off of the surface.

The amount of the solvent can be adjusted for various crystal size so the lens tissue is kept damp for the entire drag but there is not any visible trace of solvent on the crystal surface after the drag is finished. Inspect the surface and repeat if necessary, but only use each sheet of lens tissue once.

If the crystal surfaces are still “dirty” after the above cleaning procedures, the surfaces might have been damaged. Please contact us for rework of the crystals.