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Progress report from LeicesterStephen Ball & Mark Watkins
CAVIAR spectroscopists meeting24 Sept 2009
(Leicester University)
New appointment to Leicester CAVIAR postdoc: Dr Mark Watkins
Research Background:
Laser Spectroscopy (pulsed lasers):– Nanosecond
• Tuneable lasers: Radiant Dyes, Sirah, Jaguar, LaserVision IR OPO, Panther UV/Vis OPO• Pump lasers: Nd:YAG(Continuum), excimer (Spectra-Physik)
– Pico- and Femtosecond• Tuneable solid-state OPO/OPA (TOPAS)• Ti:Sapphire (Spitfire, Mai Tai), Nd:YLF (Evolution and Evolution 30)
Weakly bound clusters:– Aromatic, non-aromatic, atomic chromophores– High resolution spectroscopy: REMPI, ZEKE, MATI, OODR– Small molecule and atomic solvents
Equipment Design– Design, testing, commissioning and operation
New appointment to Leicester CAVIAR postdoc: Dr Mark Watkins
Relevant expertise:
Pulsed valve operation:– Bosch fuel injector valve– General Valve (series 9)
Vacuum apparatus:– High vacuum operation– Turbomolecular pumps, diffusion pumps, roughing pumps– Vacuum instrumentation
Raman spectroscopy (NIR region ~800 nm)– Spectracode instrumentation and CCD imager– Worked industrial patent contracts (Roche, Germany and Santrol, USA)– Developed methods towards real-time mathematical analysis of small (ppt) spectra on large
background
CAVIAR pulsed nozzle apparatus:
Up to now: No dimer signal at 620 nm (v = 5 overtone of hydrogen-bonded stretch)
Not much water monomer signal at 620 nm either
Detection system definitely works!: H2O absorptions when chamber up to atmosphere
NO2 absorption features through nozzle
LED
Nozzle
Spectrograph/CCD camera
Issue #1: v = 5 dimer overtone is v weakSolution: Move to v = 4 overtone around 760 nm
(expected x10 stronger)Progress: Done!LED BBCEAS spectra: 70 nm bandwidth, mirror reflectivity calibration
720 730 740 750 760 770 780 790 8000.99986
0.99987
0.99988
0.99989
0.99990
0.99991
R(
)
Wavelength / nm
Mirror Curve (1200 lines/mm grating, centred at 765 nm) Low resolution spectrum of CO2 “Venus bands”at 782.8 and 789.1 nm
780 790 8005 10
8
0
5 108
1 107
1.5 107
1.102 107
8.324 109
Spectrum fitbase
xCO2 M amount
800775 Xwavelength
10 km path length in 1 m cavity
Issue #2: Spatial overlap of nozzle expansion with light beamSolution: Point nozzle slit expansionProgress: Done!
beampath beampath
Slit width = 12 mmDiameter ~ 350 m
Issue #3: H2O number density in source gas
before: Psat(H2O) = 20 Torr and >1 atm N2 bath gas
Solution: Heated nozzle source ~ 60 Cafter: 150-250 Torr H2O + 0.5-1.0 atm N2
Progress: Heated H2O source built, waiting on thermostat electronics
H2O reservoir
General Valve
thermal bodyheating collar
thermocouple
Issue #4: Temporal overlap of nozzle expansion with light beamCurrent LED-BBCEAS detection methodology is CW
Solution: Pulsed detection methodology: Cambridge BBCRDS systemPulsed laser and clocked CCD camera synchronised to nozzle
Progress: Equipment loan arranged for October
LED-BBCEAS
Pulsed nozzle
Pulsed laser BBCRDS
Pulsed nozzle
Pulsed nozzle: rep rate 20 Hz, 180 – 300 s opening time
Photoacoustic Experiment?
Pulsed IR laser (OPO/OPA)
2400 2500 2600 2700 2800 2900 3000 3100
Inte
nsi
ty
Wavelength / nm
Water vapour spectrum (taken in air)
Timescale:1 – 3 days
Oscilloscope
Sept Oct Nov Dec Jan Feb Mar Apr After
Characterise NIR mirrors (730-780 nm) for = 4 at 755 nm
Finish electronics for heated nozzle source
Optimise slit nozzle conditions for making dimer & for chamber’s pumps
Modification of nozzle design (if necessary)
LED-BBCEAS measurements in the = 4 region
Locate dimer feature
Commission Nd:YAG laser
Experiments with Cambridge BBCRDS detection system
delivery
Characterise IR mirrors (910-1000nm) for = 3 at 960 nm: LED-BBCEAS experiments in the = 3 region
Write up work Shillings et al
Timetable for experimental work @ Leicester