Purging & cooling of Mira

From the manual :

Cooling water :

• max temperature : 15 C
• min flow rate : 0.3 liter / minute
• pressure : 2 bar

purging with dry N2 :

• Initial purge : 10 CFH
• Later purge : 2 CFH

Purging is especially recommended for operation above 870 nm.
Strong water absorption : between 920 and 970 (high velocity purge needed for several hours to get below 5%).
Other water absorption's : around 761 +/- 5 nm and 820 +/- 5 nm.

Take a look at the aborption spectrum of water in the atmosphere.
From this absorption spectrum, it follows that above 890 nm, the water absorption begins !!