Graphene mode-locked Cr:LiSAF laser at 850  nm

Abstract

We report, for the first time to our knowledge, a mode-locked femtosecond Cr:LiSAF laser initiated with a high-quality monolayer graphene saturable absorber (GSA), synthesized by chemical-vapor deposition. The tight-focusing resonator architecture made it possible to operate the Cr:LiSAF laser with only two 135 mW, 660 nm low-cost single-mode diode lasers. At a pump power of 270 mW, the laser produced nearly transform-limited 68 fs pulses with an average power of 11.5 mW at 850 nm. The repetition rate was around 132 MHz, corresponding to a pulse energy and peak power of 86 pJ and 1.26 kW, respectively. Once mode locking was initiated with the GSA, stable, uninterrupted femtosecond pulse generation could be sustained for hours. The saturation fluence and the modulation depth of the GSA were further determined to be 28 μJ∕cm 2 and 0.62%, respectively. The Cr:LiSAF gain medium, an important member of the class of Cr:colquiriite lasers, has emerged as a versatile solid-state gain medium with broad, tunable emission in the 780-1110 nm wavelength range [1]. Its high emission cross section-fluorescence lifetime product (322 μs × 10 −20 cm 2 ) and high intrinsic slope efficiency (>50%) have made it possible to obtain efficient, low-threshold lasing with the use of widely available low-power, single-mode red pump diodes [1]. The broad emission bandwidth of Cr:LiSAF has further enabled the generation of femtosecond pulses as short as 10 fs [2] and mode-locked tuning over the 800-920 nm wavelength range [3].One disadvantage of the Cr:colquiriites in general and of Cr:LiSAF in particular is the low value of the nonlinear refractive index (0.8 × 10 −16 cm 2 ∕W, four times lower than that for Ti:sapphire [4]), which makes it quite challenging to obtain a sufficient modulation depth via Kerr lens mode (KLM) locking alone. Hence, saturable absorbers and alternative modulation schemes have been proposed recently to improve the long-term stability of the laser during mode-locked operation. For example, semiconductor saturable absorber mirrors (SESAMs) [5] and single-walled carbon nanotubes (SWCNTs) [6] were successfully employed in previous studies to generate mode-locked pulses from Cr:LiSAF lasers with improved long-term stability. In the case of SESAMs, one major drawback is the complexity of the fabrication process. Furthermore, the resonant nature of the quantum well limits the operational bandwidth of the mode-locked laser, making it difficult to obtain pulses with a duration shorter than 25 fs in Cr:LiSAF [7]. In the case of SWCNTs, although the fabrication process is easier and more cost-effective in comparison with that for SESAMs, bandwidth limitations may still arise, depending on the radius distribution of the carbon nanotubes. Furthermore, as the operation wavelength decreases toward the visible, the transmission of the carbon nanotubes increases because of the onset of metallic effects, leading to higher nonsaturable insertion losses [8]. In more recent studies [3,9], our groups further demonstrated the use of a gai...

2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

“…This work promotes the application of graphene and other layered materials in mode‐locked solid‐state lasers. Up to now, plenty of mode‐locked solid‐state lasers using layered materials such as graphene, TMDCs, and BP have been achieved, as shown in Table . It can be seen that these lasers have excellent performance in pulse width, repetition rate, and pulse energy, which is not inferior to similar lasers.…”

Generation of sub-20-fs pulses from a graphene mode-locked laser

“…The GSA used in our experiments was prepared by chemical vapor deposition as described previously [13] and was transferred onto an infrasil substrate. As described in Ref [12], the saturation fluence and recovery time were 28 μJ/cm 2 and 1.6 ps, respectively. Furthermore, previous Raman measurements indicated that a monolayer graphene was deposited on the infrasil substrate [12].…”

“…In an earlier study, pulses as short as 10 fs were generated from a Kerr-lens mode-locked Cr 3+ :LiSAF laser [11]. In our previous study, we demonstrated GSA-initiated mode locking of a Cr 3+ :LiSAF laser for the first time and generated 68-fs pulses at 850 nm [12].…”

Emerging Low‐Dimensional Materials for Nonlinear Optics and Ultrafast Photonics

“…For instance, A Ti: sapphire mode‐locking pulse laser was demonstrated by Baek et al, which generate ultrashort pulse of 63 fs (at 800 nm) with maximum power of 480 mW. A 68 fs laser was reported by Canbaz based on Cr:LiSAF(LiSrAlF 6 ) operating at 850 nm . On the other hand, graphene SAs have also enabled several MIR pulse lasers based on Cr 2+ doped chalcogenide crystals such as ZnS .…”