Xiaoyu Shi

High performance plasmonic random laser based on nanogaps in bimetallic porous nanowires

A plasmonic random laser is fabricated using gold-silver bimetallic porous nanowires with abundant nanogaps that provide strong feedback or gain channels for coherent lasing from dye molecules. The strong confinement of the nanogaps allows the bimetallic porous nanowire-based random laser, which is pumped by ns pulses, to operate with a very low threshold and extremely low concentrations of Rhodamine 6 G (as low as 0.067 mM). This random laser can be used as a pump source for another coherent random laser based on oxazine. These results provide a basis for studies of coherent random lasing pumped by another random laser.

Cascade-pumped random lasers with coherent emission formed by Ag–Au porous nanowires

A series of sequentially cascade-pumped random lasers is reported. It consists of three random lasers in which the Ag-Au bimetallic porous nanowires play the role of scatterers, and the gain materials are coumarin 440 (C440), coumarin 153 (C153), and rhodamine 6G (R6G), respectively. The random laser with C440 is first pumped by a 355 nm pulsed laser. The emission of C440 pumps the C153, and the emission of C153 pumps the R6G sequentially. Low-threshold coherent emissions from the three random lasers are observed. The cascade-pumped random lasers can be achieved easily with low cost and can be used in applications conveniently.

Coherent plasmonic random laser pumped by nanosecond pulses far from the resonance peak of silver nanowires

Silver nanowires were used to enhance stimulated emission of Rhodamine 6G in a liquid random laser. Low-threshold coherent emission from the nanosecond-pulse-pumped random laser was achieved. Surface plasmonic resonance plays a key role in low-threshold operation of this random laser. The results demonstrate the ability of silver nanowires to enhance the stimulated emission, especially when the emission light from the dye molecules is far from the plasmonic resonance peak. Although the random laser shows different emission spectra in different directions, universal properties of strong interaction among multiple modes under different pump power densities were also demonstrated.

Two-threshold silver nanowire-based random laser with different dye concentrations

The feedback mechanisms of silver nanowire-based random lasers with different concentrations of laser dye rhodamine 6 G pumped by a nanosecond pulsed laser were demonstrated. It was shown that dye concentration greatly impacts on the optical amplification mechanism. At lower or higher dye concentrations, random lasers have a single threshold. At a proper concentration, the system shows transition from incoherent emission to coherent lasing and has two thresholds corresponding to incoherent feedback and coherent feedback, respectively. The corresponding physical mechanism was displayed. Also, the processes of fluorescence, incoherent feedback and coherent feedback were distinguished by the emission spectra in the time domain. The results will supply some guidance to clear the working mechanism of random lasers.

Broadband plasmonic silver nanoflowers for high-performance random lasing covering visible region

Abstract Multicolor random lasing has broad potential applications in the fields of imaging, sensing, and optoelectronics. Here, silver nanoflowers (Ag NF) with abundant nanogaps are fabricated by a rapid one-step solution-phase synthesis method and are first proposed as effective broadband plasmonic scatterers to achieve different color random lasing. With abundant nanogaps and spiky tips near the surface and the interparticle coupling effect, Ag NFs greatly enhance the local electromagnetic field and induce broadband plasmonic scattering spectra over the whole visible range. The extremely low working threshold and the high-quality factor for Ag NF-based random lasers are thus demonstrated as 0.24 MW cm−2 and 11,851, respectively. Further, coherent colorful random lasing covering the visible range is realized using the dye molecules oxazine (red), Coumarin 440 (blue), and Coumarin 153 (green), showing high-quality factor of more than 10,000. All these features show that Ag NF are highly efficient scatterers for high-performance coherent random lasing and colorful random lasers.

Resonance energy transfer process in nanogap-based dual-color random lasing

The resonance energy transfer (RET) process between Rhodamine 6G and oxazine in the nanogap-based random systems is systematically studied by revealing the variations and fluctuations of RET coefficients with pump power density. Three working regions stable fluorescence, dynamic laser, and stable laser are thus demonstrated in the dual-color random systems. The stable RET coefficients in fluorescence and lasing regions are generally different and greatly dependent on the donor concentration and the donor-acceptor ratio. These results may provide a way to reveal the energy distribution regulars in the random system and to design the tunable multi-color coherent random lasers for colorful imaging.

Temporal profiles for measuring threshold of random lasers pumped by ns pulses

The working threshold is an important parameter to assess the performance of cavity-free random lasers. Here, the temporal profile measurement is proposed as an alternative method to determine the thresholds of the surface plasmon based random lasers pumped by ns pulses based on analyzing the delay time (tDelay) and rising time (tR) of the emission signal. The obvious and slight inflection points of the curves of tDelay and tR varying with the pump power density are observed as indicators for the thresholds of random lasing and for the transition of lasing mode, respectively. The proposed method supplies consistent values to those supplied by traditional methods in frequency-domain for the random systems with different gain length. The demonstrated temporal profile approaches are free from the spectrometers and may be as a candidate for measuring the threshold of random lasers in ultrafast optics, nonlinear optics and bio-compatible optoelectronic probes.

Cascade pumped random lasers with coherent emission formed by Ag-Au porous nanowires

A series of sequentially cascade pumped random lasers is reported. It consists of three random lasers, in which the Ag-Au bimetallic porous nanowires play the role of scatterers, and the gain materials are coumarin 440 (C440), coumarin 153 (C153) and rhodamine 6G (R6G) respectively. The random laser with C440 is firstly pumped by 355 nm pulsed laser. The emission of C440 pumps the C153 and the emission of C153 pumps the R6G sequentially. Low threshold coherent emissions from the three random lasers are observed. The cascade pumped random lasers can be achieved easily with low cost, and can be used in applications conveniently.