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Resonance Enhanced Multi Photon Ionization and Detection ofHyperthermal Oxygen Reacting with A lated !ar on

Tino Woodburn

March 2013

Abstract for Laser Applications by Dr. Rufus Cone

R M!" #Resonance nhanced Multi !hoton "oni$ation% is a techni&ue that uses laser

li'ht to e(cite s)all )olecules or ato)s to inter)ediate states and ioni$e the) *ithin the sa)e

pulse of li'ht. The resonant electronically e(cited inter)ediate states are sti)ulated as &uic+ly

as picosecond. Thus a fe* nanosecond laser pulse *ith hi'h enou'h intensity is sufficient to

ioni$e the )olecule, this can be a )ore than a t*o photon absorption techni&ue. R M!" can

'i-e spectroscopic infor)ation such as rotational states and hi'h Rydber' state that are not

achie-able *ith sin'le photon )ethods. Dependin' on *hat the ener'y le-els are bein' probed

certain *a-elen'ths )ust be used. The laser in use is a D /000 Continuu) Dye Laser usin'

DCM dye doubled to 31 *hich e(cite the C #carbon )ono(ide% )olecule. ecause the laser

is not in a(is *ith the interaction re'ion !ellin roca pris)s and )irrors to ali'n the laser

throu'h a *indo* into a -acuu) cha)ber. The dye laser is pu)ped by a !o*erlite d34

56A7

*hich also uses a nonlinear optical crystal to use the second har)onic of 832n). The

hyperther)al o(y'en is obtained by detonation of 2 *ith a C 2 laser *ith *att9pulse. A $inc

selenite *indo* and a 'old )irror are used in con:unction *ith a -acuu) cha)ber to create a

pulsed bea) of 'round state ato)ic o(y'en # triplet p%. The carbon is ablated by a ;urelite

d 34 56A7 laser tripled to 38< n) or an e(ci)er laser usin' +rypton fluoride *hich lasin' at

2


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Introduction:

What is ;pectroscopy> The study of )olecular structure and dyna)ics throu'h the absorption,)ission, and scatterin' of li'ht

http599***.pci.tu bs.de9a''eric+e9!C


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products. This procedure beca)e +no*n as Resoncance nhanced Multi !hoton "oni$ation

#R M!"% ?. Che). !hys. = , 1


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-. The Wa-eMaster )easures the *a-elen'th of both CW and pulsed lasers

of any repetition rate. The *a-elen'th can be displayed in 7@$,

*a-enu)bers, or nano)eters *ith -acuu) and air readin's a-ailable.

-i.

c. Ali'n)ent

i. Location, Location, Location

d. Ti)in' and delays

i. Ti)in' is essential to all the sinners and saints but *hen tryin' to

deter)ine the )echanics and ener'y of ato)s collidin' *ith each other it

is on a co)pletely different le-el. This ti)in' ta+es ti)e and a 'ood

understandin' of all the processes 'oin' on in the syste). Iirst *e *ill

i)a'ine the apparatus. The 800 psi pulse of )olecular o(y'en )ust be

released around 1 3Js before the C 2 laser is fired #if the laser is fired

too early there *ill not be enou'h o(y'en to absorb the ener'y of the

laser pulse and the copper cone *ill be catastrophically da)a'ed%. The

C 2 laser has a pulse len'th of K2.8 Js dependin' on the )i(ture of 'as.

"f the laser is fired )icro second too late the pulse of o(y'en *ill be

ahead of the focused laser bea) )eanin' a portion of the o(y'en

)olecules *ill not be bro+en into ato)ic o(y'en 'i-in' lo*er yields of the

C product. The laser ablation of the carbon rod needs to happen

)icroseconds before the pulse of carrier 'as #ar'on% en'ulfs the ablated

carbon carryin' the carbon into the reaction re'ion. oth of these pulses

of 'as the ato)ic o(y'en #a plas)a *hich is tra-elin' )uch faster than


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the ori'inal pulse of o(y'en, ther)al -s. hyperther)al% and the ablated

carbon bein' carried by ar'on )ust )eet in the reaction re'ion directly

belo* the ion optics in the sa)e ti)e and space as the fre&uency

selected laser that *ill e(cite the C )olecule to a )etastable state

+no*n as a Rydber' state and then co)pletely strip the )olecule of the

e(cited electron all in the sa)e -ery short pulse of li'ht. This ion, C 4 is

then accelerated to to*ard the detector by the ion optics. The detector

)ust be s*itch on and then off at the correct ti)e to 'i-e a ti)e sliced

-elocity i)a'e.

The delay is chosen to be lon' enou'h to allo* suficient product density to build up prior to thedetection step, but also su ciently short to ensure that the product distribution is nascent at theinstant of detection and that no post reacti-e collisions ha-e occurred #i.e., under sin'le collisionconditions%. The delay )ust also be short enou'h to ensure that prod ucts for)ed *ith thehi'hest -elocities do not escape the probe laser interaction re'ion before they can be ionised#i.e., fly out is a-oided%.Dr. ass !hD.Thesis ora.ox.ac.uk/objects/uuid:ea381f05-6a68-435f-91d6.../THES S0!

ii.

iii. Ti)in' is essential as *e ha-e *ell learned if you *ant to 'uess at the

ti)in' of ato)s and electrons you need to consult @eisenber', T N

10 3< ? s. Meanin' if you are 'oin' to 'uess you need to be *ithin 10 3

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