게시판 최근논문

[Editor's Pick] Current Optics and Photonics Vol. 7 no. 6 (2023 December)

사무국 hit 482 date 2023-12-22

Femtosecond Mid-IR Cr:ZnS Laser with Transmitting Graphene-ZnSe Saturable Absorber

Won Bae Cho1 *, Ji Eun Bae2, Seong Cheol Lee2, No Soung Myoung3, and Fabian Rotermund2

 

Current Optics and Photonics  Vol. 7 No. 6 (2023 December) pp. 738-744
DOI: https://doi.org/10.3807/COPP.2023.7.6.738 

 

 

Fig. 1  Optical transmission of high-quality monolayer graphene saturable absorber (G-SA) and photos of the G-SAs developed on CaF2 and ZnSe substrate (inset). (a) Graphene transferred onto CaF2 substrate. (b) Graphene transferred onto ZnSe substrate.

 

Keywords: Cr:ZnS, Graphene-ZnSe, Mid-infrared laser, Passive mode-locking, Saturable absorber
OCIS codes: (140.4050) Mode-locked lasers; (140.7090) Ultrafast lasers; (160.4236) Nanomaterials; (160.4330) Nonlinear optical materials


Abstract
Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF2 and ZnSe. Using the graphene-SA based on CaF2, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF2 with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.