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