We report the results of our investigation of the second harmonic generation (SHG) green pulse generation with an active, quasi-Q-switched-mode-locked (QML) fiber laser based on subharmonic cavity modulation. First, we investigate the working principle of the quasi-QML pulse generation technique, based on subharmonic cavity modulation through analytical calculation. We show that the stable QML-like pulse generation by subharmonic cavity modulation is induced by phase-locked interference of a large number of subharmonic modulation-induced frequency components within a cavity. Next, we experimentally realize a 1064 nm quasi-QML fiber laser with an ytterbium (Yb)-doped fiber ring cavity incorporating an acousto-optic modulator. Finally, using the implemented quasi-QML laser, we experimentally show that the use of 1064 nm quasi-QML pulses could result in the increase of the SHG conversion efficiency in a MgO:PPLN, compared to the use of continuous mode-locked (ML) pulses. For our particular experimental configuration, we could readily achieve a noticeable SHG efficiency increase of 8% by using quasi-QML pulses with a subharmonic order of 80, compared to continuous ML pulses.

We propose an optimum Q-switching profile for complete suppression of the multi-peak phenomenon (MPP) without loss of pulse energy in an actively Q-switched ytterbium (Yb)-doped fibre laser. Most of the previously demonstrated approaches to suppress MPP have been based on adjusting of the rise time, and these rely on the assumption that the switching profile of the Q-switch has a trapezoidal temporal shape with a linear leading edge. These approaches leave one fundamental question as to whether or not there exists an optimum leading edge profile other than a simple linear one for complete suppression of MPP without loss of pulse energy. Through comparison among four different leading edge profiles. i.e. linear shape, sinusoidal function shape (increasing slope), sinusoidal function shape (decreasing slope), and composite function shape profiles, the proposed leading edge shape of a sinusoidal function (increasing slope) is shown to be capable of achieving complete suppression of MPP without loss of pulse energy under particular rise time conditions. It is shown that the use of a sinusoidal function (increasing slope) with a rise time of approximately 11 times the cavity round-trip time allows for the complete suppression of MPP without pulse energy loss in an exemplary, Q-switched, Yb-doped fibre Fabry-Perot laser.

This study addresses the challenge of trapping nanoscale biological particles using optical tweezers without the photothermal heating effect and the limitation presented by the diffraction limit. Optical tweezers are effective for trapping microscopic biological objects but not for nanoscale specimens due to the diffraction limit. To overcome this, we present an approach that uses optical anapole states in all-dielectric nanoantenna systems on distributed Bragg reflector substrates to generate strong optical gradient force and potential on nanoscale biological objects with negligible temperature rise below 1 K. The anapole antenna condenses the accessible electromagnetic energy to scales as small as 30 nm. Using this approach, we successfully trapped nanosized extracellular vesicles and supermeres (approximately 25 nm in size) using low laser power of only 10.8 mW. This nanoscale optical trapping platform has great potential for single molecule analysis while precluding photothermal degradation.

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We experimentally demonstrate the trapping of nanoscale supermeres using a nonradiating anapole mode. All-dielectric anapole improves electric field enhancement with negligible heat dissipation, allowing low-power near-field trapping.