Abstract
Single-wall carbon nanotubes (SWNTs) are promising materials for saturable absorbers (SAs) in mode-locked lasers. However it has been widely recognized that the degradation of optical properties of film-type SWNTs used in femtosecond mode-locked lasers limits the achievable long-term stability of such lasers. In this paper, we study the degradation of optical properties of SWNT-SA fabricated as sandwich type using HiPCO SWNTs with an Er-doped all-fiber laser. The thresholds of laser pump power are examined to avoid the damage of the SWNT-SA. Based on the proposed analysis, it is shown that all-fiber laser pulses of 300 fs pulse width, 3.85 mW average output power, 211.7 MW/cm² peak intensity and 69.9 MHz repetition rate can be reliably generated without any significant damage to the SWNT-SA film.
Highlights
Demands for research on carbon nanotubes (CNTs) have significantly increased due to their superior physical and chemical properties since the discovery in 1991 by Iijima [1]
A mode-locked Er-doped fiber laser was presented with a sandwich-type single wall carbon nanotubes (SWNTs) saturable absorber (SA)
It was newly shown that the Single wall carbon nanotubes (SWNTs)-SA can be graphitized by the laser-heating over the threshold power causing the film surface damage, which is consistent with the known fact of the multi-wall carbon nanotubes films
Summary
Demands for research on carbon nanotubes (CNTs) have significantly increased due to their superior physical and chemical properties since the discovery in 1991 by Iijima [1]. Single wall carbon nanotubes (SWNTs) have several advantages over the semiconductor SA mirrors (SESAMs) such as low saturation intensity, faster recovery time, broad spectral range, large third-order nonlinear susceptibilities and easy fabrication [5]. Cho et al were successfully generated 115 fs pulse width, 202 mW average output power at 89 MHz with SWNT-SAs using bulk optics [6]. W, Song et al suggested a vertically aligned SWNT-SA for the evanescent field interaction of propagating light and achieved a 1.02 ps pulse with 250 mW output average power [10].It turns out that the structure of CNTs may change under certain laser conditions [11, 12]. Graphitization of SWNTs film is verified based on the changes of the optical micrographs, Raman spectra, and SEM images before and after the irradiation with a laser
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