Abstract
Laser induced white light emission was observed from porous graphene foam irradiated with a focused continuous wave beam of the infrared laser diode. It was found that the intensity of the emission increases exponentially with increasing laser power density, having a saturation level at ca. 1.5 W and being characterized by stable emission conditions. It was also observed that the white light emission is spatially confined to the focal point dimensions of the illuminating laser light. Several other features of the laser induced white light emission were also discussed. It was observed that the white light emission is highly dependent on the electric field intensity, allowing one to modulate the emission intensity. The electric field intensity ca. 0.5 V/μm was able to decrease the white light intensity by half. Origins of the laser-induced white light emission along with its characteristic features were discussed in terms of avalanche multiphoton ionization, inter-valence charge transfer and possible plasma build-up processes. It is shown that the laser-induced white light emission may be well utilized in new types of white light sources.
Highlights
The bright white light emission was observed from graphene foam placed in vacuum and irradiated with an IR laser diode
In the case of irradiation with two laser beams, the total LIWE intensity of graphene foam was a sum of the intensities of the used laser sources
It was observed that the temperature of LIWE graphene foam was relatively low, which is much less than could be predicted from the black body emission estimation of the lighting temperature
Summary
In the course of LIWE experiments it was found that the intense white lighting occurs only from the spot of the focused laser beam illuminating the front of the graphene foam surface (Fig. 1b). The spot of incident focused laser beam observed at the highest LIWE intensity was determined to be 0.05 cm[2] It means that with the decrease of the laser fluence, the parameter n cannot be directly associated with the number of absorbed photons, but should be rather correlated with the electron density in avalanche ionization[28,29].
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