Study On The Weak Signal Detection Technique In The Pump-probe Ultrafast Spectroscopy

Ultrafast laser pump-probe technology is used for study on the optical parametric variation of excited sample with the delay time of the probe light pulse and the pump light pulse changing, by recording the change of probe light after the probe light through the sample with the time interval of arriving at the sample between the probe light pulse and the pump light pulse changing. Ultrafast time-resolved transient absorption spectroscopy, as a commonly used ultrafast laser pump-probe technique, is a powerful tool to study the material state energy relaxation process of excitation. In traditional ultrafast laser pump-probe technology, what is recorded in experiment is the change in absorbance of the sample to probe light absorption. Due to the integration time is long, two adjacent signal, the pump light and no-pump light, respectively include hundreds or thousands of light pulses, when the output energy of the laser is fluctuating with time, there will be large differences in background. In particular, when the absorbance of sample to probe light is relatively small, the random fluctuation in the output power of the laser will give a great influence to the signal. This creates a great impact on the detection of test signal and the accuracy and effectiveness of experimental data.First of all, this article introduces the traditional ultrafast time-resolved transient absorption experiment system and the transient absorption spectroscopy. Combining with ultrafast time-resolved transient absorption experiments principle and the random fluctuation in the output energy of the laser, we analyze the source of experimental deviation in experiment. We propose a new weak signal detection experimental program in the pump-probe ultrafast light spectroscopy, then in order to show the advantage of experimental program raised in issue, we make a theoretical simulation to it and compare it with the traditional Experimental program.Furthermore, combining the weak signal detection improved experimental program in the pump-probe ultrafast light spectroscopy and the related experimental experience, we set up the weak signal detection experimental system in the pump-probe ultrafast light spectroscopy. Using the the weak signal detection improved experimental system in the pump-probe ultrafast light spectroscopy to measure the carotenoid sample, comparing the experimental result with the experimental result from traditional experimental system, to show the advantage of experimental program set up in improving the signal to noise ratio of the experimental data.Finally, using the weak signal detection improved experimental system in the pump-probe ultrafast light spectroscopy to measure the quantum dot sample,to show the advantage of experimental program set up in measuring the weak signal sample.In this paper, we analyze the source of experimental deviation in the traditional ultrafast time-resolved transient absorption experiment system and propose the weak signal detection improved experimental program in the pump-probe ultrafast light spectroscopy which can reduce the experimental deviation, then we use it to measure the transient absorption spectroscopy of weak signal sample. We offer a new method to reaserch the excited states of the weak signal sample for researchers.