I am developing a pump probe spectroscopy. I know that I have to find the time zero before starting the experimental part (measurements) but I don't know how to do it. My idea is to use a ZnO sample and send the pump and the probe at the same time. I have to move the delay line and the time at which I see the signal of absorption, is defined as the delay time? Is it like this? Thank you.
In pump-probe experiments, you have two beams the pump and the probe that are usually incident on the same spot on the sample. You either have the delay line in the path of the pump or the path of the probe. By changing the position of the delay line you change the time delay between the pump and the probe.
Depending upon the kind of measurement you do (reflectivity, absorption, etc) as you keep changing the delay line and move from a negative time delay to zero to positive times there will be a sharp increase in the signal. Once you find this sharp increase, go back in smaller steps till you find the starting point of this sharp increase and this will be your time zero.
Thank you, Aswathi, for this answer. I measure the transmission of the sample.
If the probe is a supercontinuum of white light, will we observe different pics of the signal? if yes, how can you define the time zero?
If you are measuring transient absorption with a white light supercontinuum, I suppose you are measuring a 2D array of intensities as a function of wavelength and time delay. At each wavelength that is supposed to have a peak, you can see a sharp rise. This onset of the sharp rise is your time zero for that wavelength. The time zero will be only shifted by 100s of fs to a few ps for different wavelengths due to something called chirp. Chirp is basically the difference in the time that different wavelengths take to reach the sample. This doesn't affect the dynamics of the material, only the time zero and can be corrected for.
You can compress the laser pule in spacial to improve the chirp to have the consistent time zero for different wavelengths.
A pair of Gratings can compress a white light of laser pulse, and a pair of prisms is as well too. The gratings can cover a wide wavelength range for compression, while it causes a big loss of laser power; in contrast, the prisms have less power lost but cover a narrower wavelength range.
If the probe pulse is a white light, the time zero is not the same in different wavelength. Ususally, we call it zero shift. This data need to be measurement by Kerr effert, which neet two polarizing film and a polar transparency liquid. With this data, you can match it with zhe transient absorption spectroscopy near the time zero, and then, correct the zero shift.
Thank you for your answers.
Miaomiao Zhou what do you mean about "If the probe pulse is a white light, the time zero is not the same in different wavelength." ? please.
For me, the time zero is related to the moment where a change in the transmission of the sample is observed.
- Badges
- Science topic
- Similar topics
- Correction