PN: TAS

Question 1

Pump probe method

Answer 1

molecular sys activated with pump pulse and then interrogated bya probe pulse
- optical activation can lead to phase transitions, isomerization, Itramolecular charge transfer (inter and intra), etc
- probe can form dynamic view of system after activation where the temporal delay between activation and interrogration changed sequentially

Question 2

NB to note with rep measurements

Answer 2

New unperturbed sample must be investigated each time else errors

Question 3

NOPA

Answer 3

Non collinearly phase matched Optical paramatric Amplification
- tunable pulses generated
- centre wavlength and band width controlled

pump and seed pulses into BBO, diff freq reasults in generation of idler (not used), amplified seed (signal), depleted pump pulse

4 wave mixing (2x pump at 775nm, 1 from seed,
all 3 spationally separated -> no need for filters -> momentum conservation in phase matching

Question 4

chopper function

Answer 4

Blocks every 2nd pulse so you get 500Hz from the original 1khz pulse rep rate

every 2nd probe pulse is alone w/o pump pusle so that the background can be measured every 2nd pulse

Question 5

discuss movement of sample

Answer 5

can only probe th eu=pumped regions
new smaple each time -> liquid flow cell, solid rotation and movement

Question 6

state of the amplified signal/seed pulse after the NOPA

Answer 6

it is very broad in wavlegnth and short in time
150fs compressed

Question 7

WLG

Answer 7

larger linear chirp
by changing the delay between pump and probe (from NOPA) youcan seectr which portion of WL to amplify

NOPA also generates chirped pulses -> corrected with prism compressor

Question 8

prism compressor

Answer 8

Uncompressed pulsed into 2 prisms at brewster angle (so no reflection) and then pmirror and back

introduce dispersion preferetially to delay the red parts ofpulse

blue light lags behind red, generally blue is more dispresed by prism so give the red a longer path length (go thorugh more of the prism)

double pass -> symmetry -> spatial mode is not destroyed

Question 9

why is the pulses not optically short

Answer 9

the prism correct cannot correct all th echirp from the NOPA if they have large discrepancies

Question 10

wlg

Answer 10

Coherent white light
highly chirped