Light excitation regime

In 1931 in her doctoral dissertation supervised by Max Bom, Maria Goppert-Mayer proposed the concept of the simultaneous absorption of two photons by a molecular system in one elementary action,(English translation Ref ). This prediction was based on the principles of the quantmn theory of radiation " as well as the concept of the intermediate energy level. Based on the formalism of summation over all eigenstates of the system, Maria Goppert-Mayer derived an expression for the two-photon absorption probability which, however, occurred to be too low to be experimentally observed in the incoherent light excitation regime. Hence, the unquestionable experimental confirmation took over thirty years. ... 

Overwhelmingly, the published research on Raman-based biofluid analysis uses excitation in the near-infrared regime in order to reduce fluorescence. Standard linewidth-narrowed diode lasers at 785 or 830 nm are most common. As noted in Chap. 1, several hundred milliwatts of multiple-spatial mode light can routinely be obtained from diode lasers, making them economical choices... 

At potentials near the photocurrent onset (roughly Fn,), a spiked response is seen with a characteristic overshoot when the light is turned off. At positive potentials near the plateau regime (again for the specific illustrative case of an n-type semiconductor), the response reverts to a rectangular profile that mimics the excitation waveform. Intermediate response patterns manifest at potentials in between. 

Perhaps more challenging from both experimental and modeling perspectives is the -excitation case. Primary electron-hole pair separation occurs in the subnanosecond or picosecond time domain and light pulses with temporal resolution of 10 s (or better) are required. However, both nanosecond and picosecond light pulses have been employed [110 127] and although the analysis has been mostly confined to the slower (nanosecond) decay regime in the photocurrent (or photovoltage) transients, the rise-time domain has also been analyzed (see, e.g.. Ref. [256]). 

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