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Semiconductor light reveals a rapidly changing limit on coherence

A peer-reviewed experiment and modelling study links the loss of coherent light emission in strongly driven semiconductors to electron scattering that changes with momentum. Longer laser wavelengths produced a steep decline in high-harmonic output. A momentum-dependent calculation explained the measured behaviour better than a fixed lifetime, while an increase predicted from cooling remains a calculation rather than a demonstrated device result.

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The colour of the driving laser changes output

High-harmonic light from strongly driven semiconductors fell steeply as the driving laser’s wavelength increased. A single peer-reviewed Nature Communications study combines measurements with calculations to explain this behaviour through interactions that disrupt coherent electron motion. The investigated materials included atomically thin tungsten disulfide and molybdenum disulfide, with a cadmium selenide comparison.[1]

Across the measured wavelength range, the yield decreased with a power between six and nine. A calculation without dephasing did not reproduce the observations. Giving every electron the same short coherence time could match integrated output, but failed to reproduce the spectral plateau, exposing a difference between fitting total brightness and explaining its distribution.[1]

Scattering depends on where electrons move

The better-performing model allowed electron–phonon scattering to change with momentum. Calculated coherence times ranged from around seventy femtoseconds near one part of the electronic structure to below ten elsewhere. These are extremely short intervals describing the material’s response; a single constant lifetime conceals differences that matter to the emitted spectrum.[1]

A cooling prediction awaits a device test

The calculations suggest that cooling could substantially increase harmonic output by reducing scattering. That predicted improvement was not demonstrated as the performance of a working device. The immediate result is an explanation of measured light and a way to distinguish models, while practical efficiency under other temperatures and operating conditions requires further experimental work.[1]

References

  1. News sourceNature CommunicationsSemiconductor light emission reveals electron-scattering constraints↩1↩2↩3↩4
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