Pumping optical power

Pth is the pumping optical power necessary to reach threshold and is linearly proportional to the threshold generation rate of excitons, Gth- Thus, if the introduction of an analyte causes the overall relaxation rate (732) to change then the quenched laser power becomes... 

This review describes some of the recent developments in materials which exhibit enhanced two-photon absorption that can initiate photopolymerization or up-converted emission. Various optical methods including femtosecond time-resolved pump-probe experiments to characterize the two-photon properties are discussed. Finally, the applications of two-photon processes to optical power limiting, up-converted lasing, 3-D data storage, 3-D micro-fabrication, two-photon fluorescence microscopy and bio-imaging, and two-photon photodynamic therapy are presented. 

An approach to full spectroscopic near-field imaging in the IR range was presented by Michaels et al. [62], whose illumination-mode a-SNOM set-up was based on a Ti sapphire-pumped optical parametric amplifier (OPA) coupled into a tapered fluoride glass optical fiber. The OPA system provides tunable broadband IR radiation with output powers in the miUi Watt range. After passing the thin film sample, the transmitted fight is collected by a Cap2 lens and coupled into a monochromator with a detector array. Broadband illumination with a bandwidth... 

The 632.8 nm helium-neon (HeNe) laser is also very popular for Raman spectroscopy because it is small, portable, mature, and very inexpensive. The resulting Raman wavelengths are well matched to the optimum sensitivity of charge-coupled device (CCD) detectors. HeNe lasers used for Raman spectroscopy typically deliver 5-30 mW of optical power. Sometimes they also sporadically deliver a weaker laser-like beam at 650 nm that can cause a huge line in the Raman spectrum at 418cm. The 650nm radiation is due to an intracavity pumped laser Raman transition. 

Typical optical power output levels in standard singlestripe diode lasers are on the order of several milliwatts. These power levels are adequate for many commercial applications that use diode lasers, such as fiber communications, optical discs, etc. However, for many other applications, such as optical pumping, optical time-domain re-flectometry, laser radar, and nonlinear optics, these power levels are not sufficient. 

Synchronously Pumped Optical Parametric Oscillator. Optical parametric oscillators (OPOs) were first used in the mid-1960s as an alternative to dye lasers for generating coherent radiation tunable over a wide wavelength region [204, 205]. It is only recently, however, that OPOs have become a practical reality with the advent of new high-quality, nonlinear optical materials and high-power, mode-locked pump sources [206-211]. 

This layer provides the necessary structural support and electrical and optical excitation for the sensor to operate. It includes such devices as LEDs, optical fibers, lasers, power supply and electrical driver circuitry included in a robust package. The development of this sensor layer involves understanding the basic properties of optoelectronic and microelectronic materials and devices for low-power, efficient and high speed devices. Power consumption is a major issue here since the conversion from electrical to optical power for subsequent pumping of the sensing layer is one of the least efficient processes in the integrated system. 

Small probed regions down to 1-2 pm are possible using microscope lenses. Lasers can supply as much pump power as needed to compensate for weaker signals, but a limit is reached when sample heating or nonlinear optically induced processes become significant. 

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