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

2. 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

3. Slit design Previously: rubber seal against slit Leaks! Sticky opening! armature standard valve poppet pin hole orifice 1 1 30mm volume exchangeable slit (100 m 30mm) face plate New design Standard valve with slit attached to face plate: reproducible operation

4. Slit valve performance Ringdown time = 40 s

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

6. Typical cavity parameters Mirror reflectivityAbsorption path length # of passes thru cavity (740-770nm) 10km 15000 10km 66cm 3cm i.e ~ 25 fewer molecules intercepted by light beam

7. H 2 O spectra at reduced pressure H 2 O (~1.5%) in Ar at room temp; P TOTAL = 26 Torr [H 2 O] = 1.3 10 16 molecules cm 3 Stdev(resid) = 2.7 10 9 cm 1 H 2 O (~1.5%) in Ar at room temp; P TOTAL = 106 Torr [H 2 O] = 5.2 10 16 molecules cm 3 Stdev(resid) = 6.2 10 9 cm 1 Comparison with Shillings et at BBCRDS paper

8. 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? 0.01-0.05 Things weve not thought of 0.1 NET 0.1-0.5

9. O 2 spectra at reduced pressure Another (stronger) absorber to put through valve to aid alignment Peak differential cross sections: O 2 = 5 10 24 cm 2 molec 1 at 760nm band head (at our resolution) NO 2 = 3 10 21 cm 2 molec 1 around 745nm O 2 (100%) P TOTAL = 10.2 Torr [O 2 ] = 3.3 10 17 molecules cm 3 Stdev(resid) = 7.2 10 9 cm 1

10. 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…