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 Verfasst am: 30. Mai 2023 07:43 Titel: Carbon nanotube films for ultrafast broadband technology |
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Carbon nanotube films for ultrafast broadband technology
Mode-locked sub-picosecond operation of Yb-, Er- and Tm:Ho-doped fiber lasers operating at 1.05 μm, 1.56 μm and 1.99 μm, respectively, is demonstrated using the same sample carbon nanotube-based saturable absorber mirror. A mesh of single-walled carbon nanotubes was deposited on an Ag-mirror using a one-step dry-transfer contact press method to combine broadband saturable absorption and high reflectance properties. The novel fabrication method of the polymer-free absorber and device parameters determined using nonlinear reflectivity measurement are described in detail. To our knowledge the observed operation bandwidth of ~1 μm is the broadest reported to date for a single carbon nanotube-based saturable absorber.Get more news about carbon nanotube film seller ,you can vist our website!
Ultrafast passively mode-locked lasers are of unprecedented interest for a large variety of applications which has led to a recent search for novel, low-cost approaches. Passive mode-locking can be initiated by nonlinear polarization evolution, the Kerr-lens method or saturable absorption [1–3]. Saturable absorption can be generated by e.g. semiconductor saturable absorber mirrors (SESAMs) or various dyes [3, 4]. Recently, new types of saturable absorbers based on single-walled carbon nanotubes (SWCNTs) have been used in fiber and solid-state lasers to initiate mode-locking [5–7]. The CNT-based devices benefit from a fairly simple manufacturing process, offer short absorption recovery times (<1 ps) and reasonable modulation depths [7, 8]. Different SWCNT-absorbers have been reported to mode-lock lasers at wavelength regimes of 1 μm [6], 1.55 μm [5] and 1.9 μm [9]. However, none of the so far demonstrated absorbers have been shown to operate at all of these wavelengths. The operational parameters of a CNT-absorber can be tailored during the fabrication process since its absorption characteristics are determined by the diameter of the nanotubes and details of the structure [10].
SWCNTs were synthesized by thermal decomposition of ferrocene vapor in a carbon monoxide atmosphere [15]. Briefly, the Carbon Nanotube Reactor consisted of a saturator, a water-cooled injector probe, and a heated growth chamber. A 300 cm3/min flow of CO was passed through the saturator filled with a mixture of silicon dioxide and ferrocene powders. This provided the conditions for the CO ferrocene vapor saturation of 0.8 Pa at room temperature. The growth chamber was an alumina tube inserted inside a tube furnace. The flow containing ferrocene vapor was then introduced directly into the high temperature zone of the growth chamber through the water-cooled probe. An additional CO flow (100 cm3/min) was introduced outside the injector probe. The Ferrocene thermally decomposed in the high temperature gradient formed between the injector probe and the ambient reactor temperature. The decomposition leads to supersaturation conditions that result in iron nanoparticle formation. Iron nanoparticles are the catalysts from which the CNTs grow.
3. Absorber design and fabrication
A Saturable Absorber Incorporating NanoTubes (SAINT) was prepared by a room temperature dry-transfer process previously applied to SWCNT-films on polyethylene substrates [14]. A piece of a nitrocellulose membrane filter with a SWCNT-film was placed on a protected Ag-mirror with the SWCNT-film upside down. Then, the mirror and the filter were pressed together at a pressure of 1000 Pa. After the pressing procedure, the membrane filter was peeled off and the SWCNT-film was strongly adhered to the mirror surface. It is worth noting that the SWCNT-film was utilized as-deposited and no purification or dispersion steps were required. When compared to standard wet deposition methods, which may require several time-consuming stages, such as purification, dispersion and filtering, the approach of the SWCNT-film preparation demonstrated here is simple and easily scalable [16].
4. CNT-absorber mirror characterization
The SAINT-film was characterized by scanning and transmission electron microscopy, and optical absorption measurements. SWCNT-network morphology of the SAINT is depicted in the Fig. 1. SEM-imaging reveals up to 20 nm-wide bundles and iron nanoparticles which give large back-scattered electron yield and large contrast in the images. SEM-imaging of the SWCNT-network was performed on the nitrocellulose membrane filter prior to transfer. A sample of SWCNT-film was also transferred to a carbon coated TEM-grid for Carbon Nanotube diameter estimation. A high resolution TEM-image, shown as an inset to Fig. 1, reveals the tube diameter ranging from 1.2 nm to 1.8 nm. |
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