1.4. How do temperature, humidity etc. affect the laser frequency?

Delta Brechungsindex / Delta temperature (bei 780nm, 35%, 100kPa): -9.07e-7/K
Delta Brechungsindex / Delta pressure (bei 780nm, 25°C, 35%): 2.62533E-6/kPa
Delta Brechungsindex / Delta humidity (bei 780nm, 25°C, 100kPa): -1.14179E-8/%

For the DL 100 that consists of a resonator with a 20.8mm air gap this leads to the following frequency changes with respect to "standard conditions" (780nm, 25°C, 100kPa, 35%):

D Frequency / D temperature: +218MHz/K
D Frequency / D pressure: -631MHz/kPa
D Frequency / D relative humidity: +2,7MHz/%

Typical fluctuations over the course of one day in a lab could be:

D Temperature / day: 2K result in  a frequenzy drift of +440MHz (this does not include frequency shifts by mechanical effects but only the air temperature)
D pressure / day: 0.2kPa (mean variation over day) results in a frequenzy drift of -130MHz, large variation of up to 1kPa are possible as well -> drift of -630MHz (!!)
D relative humidity / day: 5% result in  a frequenzy drift of +14MHz