Short optical pulses

The MIDP method may be used to obtain either the relative steady-state populations, or the relative isc rate constants, p, depending on how the system is prepared. If the system is prepared in the steady state, the A (0) values are given by the values. If, on the other hand, it is prepared by a short optical pulse, the A (0) values are proportional to the p values. The expressions are the most straightforward if only one of the... 

Using the building blocks described above, we have built several optical systems on MEMS micro-optical benches. A femtosecond autocorrelator has been constructed to measure the pulse width of extremely short optical pulses (120 femtoseconds has been demonstrated experimentally). A single-chip optical disk pickup head has also been realized. 

Using high resolution time resolved absorption spectra we have been able to observe the time evolution of a nearly monoenergetic population of carriers in a semiconductor, excited with a short optical pulse, to a carrier distribution In which a temperature can be defined. 

The applied field also suppresses the optically written phase grating. However, since we are committed to short optical pulses, we can take advantage of the slow viscous relaxation when the applied field is removed. 

Because of the special properties of the exponential function the light decays with the same time constant r as the population decay. The light decay can be followed by a fast detector connected to fast, time-resolving electronics. If the excited state has a substructure, e.g. because of the Zeeman effect or hyperfine structure, and an abrupt, coherent excitation is made, oscillations (quantum beats) in the light intensity will be recorded. The oscillation frequencies correspond to the energy level separations and can be used for structure determinations. We will first discuss the generation of short optical pulses and measurement techniques for fast optical transients. 

This relationship provides an alternative method to determination of the concentration of the analyte of interest. Specifically, lifetime or decay time measurements can be used in fluorescence based sensors to determine the analyte concentration. These measurements provide better results than steady-state measurements. Time-domain lifetime measurements are typically performed by exciting the sensing element with a short optical pulse which is much shorter than the average fluorophor lifetime. For a single population of fluorophors, the rate at which the intensity decays over time can be expressed as ... 

The time evolution of the fluorescence spectrum of a suitable probe molecule, following excitation by an ultra-short optical pulse, can be used to monitor the dynamic Stokes shift response function... 

To consider the response of an assembly of isolated molecules to a short optical pulse of duration At, the Hamiltonian for the system must be modified as follows ... 

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