High diffraction efficiency metal-dielectric grazing incidence grating for laser linewidth narrowing

Grazing incidence gratings (GIGs) are diffractive optical components used in pulsed narrowband tunable lasers. To narrow the output linewidths of external-cavity semiconductor lasers further, a metal-dielectric GIG with high diffraction efficiency and high groove density was designed and fabricated. The grating was optimized using a combination of the Fourier modal method and the particle swarm optimization algorithm. When transverse-magnetically-polarized light at a wavelength of 650 nm was incident at a grazing angle of 89°, the theoretical diffraction efficiency of the -1st order light reached 68%, which is three times higher than that of traditional gratings. A rectangular grating with a groove density of 2800 gr/mm was fabricated using holographic exposure and scanned reactive ion beam etching techniques, and its diffraction efficiency was measured. The experimental results confirmed the excellent performance of the metal-dielectric GIG, indicating its potential for applications, including narrow-linewidth lasers, optical communications, and spectral analysis.