The delay on femtosecond laser spectroscopy is done by altering the length of th

Question

The delay on femtosecond laser spectroscopy is done by altering the length of the light path (this is the only way to do this). The speed of light is 3.00 × 108 m/s. Recalling that

1. What is the difference in path length required to measure a time delay of 1 ps?

2. In Marguet and Markovitsi (2005), it was shown that the timescale for the formation of the (6-4) photoadduct was about 2 ms. What isthe length of the pathlength difference required to obtain this? Is this practical to build in the laboratory?

Explanation / Answer

speed(m/s) = distance (m)/time (s)

3 x 108 m/s = distance (m)/1 x 10-12 s

distance (m) = 3 x 108 m/s x 1 x 10-12 s

Difference in path length required is 0.0003 m or 0.3 mm

2) for 2ms the distance should be

speed(m/s) = distance (m)/time (s)

3 x 108 m/s = distance (m)/2 x 10-3 s

distance (m) = 3 x 108 m/s x 1 x 10-3 s

path difference of 6 x 105 m

The only way this can be achieved in a laboratory is by using large number of mirrors and prism. But will be tremdously impractical way to build it. I guess it can still be made possible

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