Ultrathin cavity strengthens frequency-doubled light by balancing optical losses
A thin semiconductor between gold layers produced stronger light at twice the incoming frequency in a peer-reviewed laboratory experiment. The cavity balances incoming coupling against internal loss. Its largest enhancement was measured against a monolayer, which differs in material thickness; a separate equal-thickness comparison also showed improvement. High illumination eventually damaged the top gold layer.
Science··Midday
Gold layers tune an ultrathin optical cavity
A 55-nanometre layer of molybdenum disulfide between gold layers concentrated incoming light and strengthened emission at twice its frequency. This frequency doubling, called second-harmonic generation, was measured in a peer-reviewed laboratory experiment. Film thickness set the resonance condition, while a semitransparent gold cap adjusted exchange with the outside light field. Matching that exchange to internal optical losses reduced reflection and increased the field stored inside the semiconductor.[1]
More active material contributes to the strongest gain
The largest reported enhancement, about 119,000 times the second-harmonic signal of a monolayer reference, compared samples with different semiconductor thicknesses. It therefore combines the cavity effect with the larger amount of active material. A separate comparison against an unstructured film of equal thickness also showed enhancement. Closing the cavity further reduced reflected incoming light, improving separation of the converted signal from the background. These are optical measurements of the tested structures, rather than a system-wide energy-efficiency figure.[1]
Stronger illumination reaches a material limit
At lower illumination, the harmonic output followed the expected quadratic relationship with incoming power. At higher power the closed cavity departed from that behaviour, and eventually the top gold layer suffered laser damage. The architecture was made through thin-film deposition and transfer, without lithographic patterning. Its simple layered construction offers a route to strengthening nonlinear optical processes, but the high-power departure and observed damage constrain how much light the tested device can accept.[1]
