COL Cover Story:Carbon nanotube mode-locked Cr:YAG laser: High Efficient solution for high-repetition-rate femtosecond source near 1.5 μm
At: 2018/6/21 15:50:53 by admin

The femtosecond (fs) laser source with high average powers andhigh repetition rate (above500 MHz) is very attractive for the applicationslike nonlinear spectroscopyand material processing. The femtosecond lasersource with high pulse peakpower and high repetition rate can increase pulsenumber in unit time. Both thesignal to noise ratio in nonlinear spectroscopyand production of materialprocessing can be substantially improved.

Comparedwith the low-repetition-rate femtosecond laser source, the road to high-average-powerand high-repetition-rate version becomes tough, as it requires moreprecisebalance between nonlinearity of thegain medium, intracavity dispersion and theperformance of saturable absorber. In particular, as smallgain and low thermalconductivity of laser crystal, the Cr:YAG laser is quitesensitive tointracavity gain and loss, and the precise control to theparameters ofsaturable absorber is unavoidable.

Recently,the researchers from the groups of Prof. Fabian Rotermund (KAIST,Korea) and Prof.Guang-Hoon Kim (KERI, Korea) demonstrated a carbon nanotube mode-locked compactfemtosecond Cr:YAG laser with high repetition rate (>500 MHz). Theyfabricated a carbon nanotube(CNT)possessing 0.51% modulationdepth and 28 μJ/cm2 saturationfluence near 1.5 μm. By employing the CNT as saturable absorber mirror(CNT-SAM), they realizedthe 1.5-μm stable mode-lockedoperation of Cr:YAG laser.Tothe best of the groups’ knowledge, the laser provides 147 mWoutputpower and 110 fs pulses with the highest repetition rate among CNTmode-locked Cr:YAG lasers. These results arereported in Chinese Optics Letters (J. W. Kim et al., “550-MHz carbonnanotube mode-locked femtosecond Cr:YAGlaser.” Vol. 16, No. 6, 0614042018).

“Acompact 1.5 μm femtosecond coherentsourcewhich delivers high average output power, short pulse duration andhighrepetition rate simultaneously can provide an efficient solution for avarietyof applications in material processing and nonlinear spectroscopy.” saysFabian Rotermund.

Furtherworkwill be focused on the development of multi-GHz ultra-compact solid-statelasers, mode-locked by carbon nanostructures in variouswavelength ranges.

GraphicdescriptionA schematic and photograph ofcarbon-nanotubemode-locked high-repetition-rate femtosecond Cr:YAG laser. Thecompact Cr:YAGlaser delivers 147 mW output power and 110 fs pulses at 550 MHzrepetition ratenear 1.5 μm.


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