Ultrafast laser spectroscopy:
Ultrafast laser spectroscopy is basically a spectroscopy method that takes advantage of the ultrashort pulse lasers for the analysis of dynamics on very short time scales (attoseconds or nanoseconds). There are different methods that are used for the examination of charge carriers, molecules, and atoms. Many different processes have been developed, spanning different time scales and photon energy ranges; Some common methods are listed below.
Picosecond-to-nanosecond spectroscopy:
Streak camera:
The duration of the pulses on the nanosecond timescale is very slow and it can be measured through electronic means. Streak cameras translate the temporal profile of the pulses into the spatial profile; That is, the photons arriving at the detector at different times reach different places on the detector.
Time-correlated single-photon counting:
Time-correlated single-photon counting (TCSPC) is basically used to examine how the molecules relax after coming to a lower energy state from an excited state. Since all the molecules present in the sample will throw photons at different times as per their simultaneous excitation, the decomposition must be thought of as having a certain speed instead of happening at specific time intervals after excitation. How long does it take for individual molecules to emit their photons, and then by combining all these data points, an intensity versus time graph can be generated that displays the exponential decay curve typical for these processes. Although, it becomes quite difficult to examine multiple molecules at a particular time.
Instead of this way, excitation-relaxation events of an individual molecule are calculated and then averaged to generate the curve. This method examines the time difference between the release of energy as another photon and the excitation of the sample molecule. One part of the light gets passed through the sample and the other part passes to the electronic as a “sync” signal. The windows optical available in the market are manufactured at flat convex lens factory and research optical company.
The light is then detected and amplified by a photomultiplier tube (PMT). The emitted light signal, as well as the reference light signal, are processed through a constant fraction differentiator (CFD) which eliminates timing jitter. As the pulse is passed through the CFD, a time-to-amplitude converter (TAC) circuit is activated by the referenced pulse. The TAC starts charging a capacitor which holds the signal until the next electrical pulse. In reverse TAC mode, the «sync» signal stops TAC. This data is then processed by an analog-to-digital converter (ADC) and a multichannel analyzer (MCA) to obtain the data output.
