Broadband Nonlinear Optical Response of Colloidal Carbon Nanohorns

Carbon-based nanomaterials, like single- or multiwalled carbon nanotubes (CNT), fullerenes or graphene, were intensively studied by many different groups during the last decades. They show excellent electrical, thermal and... [ view full abstract ]

Carbon-based nanomaterials, like single- or multiwalled carbon nanotubes (CNT), fullerenes or graphene, were intensively studied by many different groups during the last decades. They show excellent electrical, thermal and mechanical properties, which make them suitable for a wide variety of applications. Many of these materials have been found to show also a strong nonlinear optical (NLO) behavior.

Carbon nanohorns (CNH) are a relatively unknown subclass of carbon-based nanomaterials. They consist of single-walled carbonic tubes with a conical end and typically assemble to spherical aggregates of 50 – 100 nm in diameter and larger agglomerates up to several micrometers (Fig. 1).

Fig. 1: SEM-images of CNH at different magnifications.

In this work, a comparative study on the NLO response of suspended CNH and MWCNT is presented. Nonlinear (NL) transmittance and scattering phenomena were investigated using nanosecond laser pulses at 532 nm and 1064 nm. The NLO properties of MWCNT suspensions are well studied and it is generally believed that NL scattering dominates their NLO characteristics.  

Our investigations reveal a strong NLO effect in CNH suspensions, much stronger than in the benchmark material MWCNT (Fig. 2). To ascertain the contribution of NL scattering within the NL attenuation process, angle dependent measurements of the scattered light at different energy levels were performed (Fig. 3). It turned out that the NL behavior of CNH suspensions at 532 nm near the NL onset can be attributed to NL absorption, since only a weak scattering signal was observed. Towards higher energy levels, absorption-induced scattering increases strongly. In contrast to that, at 1064 nm the NL performance is dominated by NL absorption in the complete NL range. NL scattering plays only a minor role even at high input energies. Our results indicated CNH as a promising candidate for optoelectronic devices, such as optical limiting applications. 

Fig. 2: Nonlinear transmittance as a function of the input laser energy and input fluence of suspended CNH and MWCNT at 532 nm (left) and 1064 nm (right).

Fig. 3: Nonlinear scattering of suspended CNH and MWCNT at 532 nm (top) and 1064 nm (bottom) at three different energy levels.