Leicester lab study CAVIAR spectroscopy meeting at UCL 30 th April 2010 Stephen Ball & Mark Watkins

Heated source Water reservoir heater Hot = 50 C P sat (H 2 O) at 50 C = 0.2 Atm P sat (H 2 O) at 20 C = 0.02 Atm Valve heater Hotter ~ 80 C No more condensation in valve

Slit design Previously: rubber seal against slit Leaks! Sticky opening! armature standard valve poppet pin hole orifice mm volume exchangeable slit (100 m 30mm) face plate New design Standard valve with slit attached to face plate: reproducible operation

Slit valve performance Ringdown time = 40 s

Clean pumping system Mist filter Foreline trap Eliminates oil contamination on optics – cavity now maintains ringdown time for days

Typical cavity parameters Mirror reflectivityAbsorption path length # of passes thru cavity ( nm) 10km km 66cm 3cm i.e ~ 25 fewer molecules intercepted by light beam

H 2 O spectra at reduced pressure H 2 O (~1.5%) in Ar at room temp; P TOTAL = 26 Torr [H 2 O] = molecules cm 3 Stdev(resid) = cm 1 H 2 O (~1.5%) in Ar at room temp; P TOTAL = 106 Torr [H 2 O] = molecules cm 3 Stdev(resid) = cm 1 Comparison with Shillings et at BBCRDS paper

Water dimer signal? Heated water reservoir heater: P sat (H 2 O) ~ 0.2 Atm cf 0.02 Atm at 20 C 10 Lines around 740nm are weaker than band centre, 10 yet oscillator strength (H 2 O) 2 H 2 O (…depends if rotational cooling narrows dimer bands) Mole fraction of dimer in source? Things weve not thought of 0.1 NET

O 2 spectra at reduced pressure Another (stronger) absorber to put through valve to aid alignment Peak differential cross sections: O 2 = cm 2 molec 1 at 760nm band head (at our resolution) NO 2 = cm 2 molec 1 around 745nm O 2 (100%) P TOTAL = 10.2 Torr [O 2 ] = molecules cm 3 Stdev(resid) = cm 1

Where now? Marks contract finishes today Engineering, technical side & spectroscopic method => as good as it can be for this experiment Leicester CAVIAR end date = 30/10/2010 (No cost extension to synchronise with other groups?) BBCRDS OK to say in Leicester over the summer Vacuum chamber available until at least Oct Steve wants to do experiments…