Laser-induced photoelectron emission is well studied and important for many applications, including the photocathodes of free electron lasers, bright X-ray sources, ultrafast electron microscopy and nanoelectronics. However, the effects of laser wavelength on photoemission and quantum efficiency have not been systematically studied.
Yang Zhou and Peng Zhang performed a comprehensive theoretical analysis of photoemission from metal surfaces due to laser illumination ranging from ultraviolet wavelengths of 200 nanometers to near-infrared wavelengths of 1200 nanometers.
Using a quantum model that can study the photoemission of arbitrary laser wavelengths and cathode work functions, they analyzed photoemission mechanisms and current density, as well as quantum efficiency, for this range of wavelengths. They found the electron emission mechanism varies depending on the laser wavelength, laser intensity and DC bias field.
The calculations showed quantum efficiency can be nonlinearly increased through electron heating produced by intense sub-picosecond laser pulses, emphasizing the importance of laser heating. Quantum efficiency increased the most at laser wavelengths where the cathode work function was close to an integer multiple of the laser photon energy.
The authors validated their model with previous experimental results. Their results could help guide the development of highly efficient and bright photoelectron sources.
“We hope our work gives a better understanding of photoemission mechanisms, and provides insights into the design of photocathodes for higher efficiency, higher brightness electron sources,” Zhang said.
Next, the authors will apply their model beyond a one-dimensional flat surface, to more geometrically complex photoemitters. They will also explore non-metal cathode materials, such as semiconductors or novel two-dimensional materials.
Source: “Quantum efficiency of photoemission from biased metal surfaces with laser wavelengths from UV to NIR,” by Yang Zhou and Peng Zhang, Journal of Applied Physics (2021). The article can be accessed at https://aip.scitation.org/doi/full/10.1063/5.0059497.
