Infrared indicators


CHARGEABLE IR INDICATORS

Chargeable IR indicators comprise an energy storing phosphor. Under infrared irradiation the stored energy is released as visible light. The charging respectively the storage of energy is also done by visible light. However, the charging light needs to have a shorter wavelength than the emitting light. The emission of visible light stimulated by infrared radiation causes a discharge. Thus, occasional recharging is necessary. The discharge speed depends on IR intensity.

An advantage of the chargeable IR indicator is the almost linear dependency of the excited emission on the IR intensity. Furthermore, we have to emphasize the relative high sensibility of this type of indicator. In the dark, the currents of IR fluorescent diodes minor to 1 mA are still detectable without problem.

CONVERTING IR INDICATORS

Converting IR indicators directly convert IR radiation to visible light without further energy supply. The multi-photon processes obeys a square law dependence of the emission on the IR intensity.

An advantage of the converting IR indicators is, apart from the extremely simple usability, the constancy and reproducibility of the emitted light.

It is mainly used for detecting and continuous observation of higher IR intensities as produced by power IR luminescent diodes, IR laser diodes or other IR lasers.

INVERTING IR INDICATORS

Inverting IR indicators emit visible light during and after UV irradiation. When irradiated by IR light this luminescence diminishes or extinguishes depending on the IR intensity. The UV stimulation strength during IR irradiation widely controls the sensitivity of this type of indicator. If only the phosphorescence after UV stimulation is used, the sensitivity will be greatest because of its integrating effect. A limit is given here only by the finite duration of phosphorescence.

An advantage of the inverting IR indicators is the large range of sensitivity along with the possibility to use it either as integrating or continuous IR detector. This combines the advantages of the chargeable IR indicators with those of the converting IR indicators.

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