Compact Coherent Light Source Research Articles

Quasi‐Bound States in the Continuum Enhanced Second‐Harmonic Generation in Thin‐Film Lithium Niobate

AbstractThis work reports the second‐harmonic generation (SHG) in a z‐cut thin‐film lithium niobate (LN) under nearly normal‐incident linearly‐polarized pumping. To utilize the largest nonlinear term which is along the out‐of‐plane direction in the z‐cut LN film, the film is patterned with a 2D periodic array to support symmetry‐protected bound states in the continuum (BICs) bearing strong out‐of‐plane electric field component. Enabled by such optical resonances near the BIC condition at the pumping wavelength, significant enhancement in SHG compared to an unpatterned film is observed. This approach, combining transparent thin‐film nonlinear materials with tailored BICs, offers prospects for engineering compact coherent light sources in a broad wavelength range.

Low-threshold, single-mode, and linearly polarized lasing from all organic quasicrystal microcavity.

Organic microcavity lasers based on liquid crystals have attracted substantial attention due to their easy processing, compact volume and excellent tunable properties. However, the threshold of traditional holographic polymer dispersed liquid crystals (H-PDLCs) laser doped with dye is usually as high as several tens of μJ/pulse, which hinders its broad applications. Herein, we demonstrate a low-threshold lasing from quasicrystal based on H-PDLCs. An conjugated polymer poly (2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylene (MEH-PPV) film is coated on the inner surface of glass substrate to dramatically reduce the lasing threshold, which is 20 times lower than that of dye-doped microcavity laser. A low threshold, single-mode, linearly polarized lasing is achieved when the thickness of MEH-PPV film is optimized at 80 nm. Due to its easy fabrication, excellent performance and bio-compatibility, this compact coherent light source may be useful in lab-on-chip applications such as detection, sensing and analyzing, as well as display, optical communications, and other photonic fields.

Colliding ionization injection in a plasma wakefield accelerator

A new scheme of generating high quality electron bunches via ionization injection triggered by an counter propagating laser pulse inside a beam driven plasma wake is proposed and examined via two-dimensional particle-in-cell (PIC) simulations. This scheme has two major advantages: first, the injection distance is easily tunable by varying the launching time or the focal position of the laser pulse; second, the electrons in each injected slice are released at nearly the same time. Both factors can significantly reduce the phase space mixing during the ionization injection process (Xu et al 2014 Phys. Rev. Lett. 112 035003, Xu et al 2014 Phys. Rev. Spec. Top.: Accel. Beams 17 061301, Li et al 2013 Phys. Rev. Lett. 111 015003), leading to very small energy spreads (∼10 keV for slice,∼100 keV for the whole bunch) and very small normalized emittance (∼few nm). As an example, a 4.5 fs 0.4 pC electron bunch with normalized emittance of 3.3 nm, slice energy spread of 13 keV, absolute energy spread of 80 keV, and a brightness of A m−2rad−2 is obtained under realistic conditions. This scheme may have potential applications for future compact coherent light sources.

Optofluidic circular grating distributed feedback dye laser

We demonstrate an optically pumped surface emitting optofluidic dye laser using a second-order circular grating distributed feedback resonator. We present a composite bilayer soft lithography technique specifically developed for the fabrication of our dye laser and investigate a hybrid polymer material system [poly(dimethylsiloxane)/perfluoropolyether] to construct high-resolution Bragg gratings. Our lasers emit single frequency light at low lasing thresholds of 6 μJ/mm2. These optofluidic dye lasers can serve as low-cost and compact coherent light sources that are fully integrated within microfluidic analysis chips and provide an efficient approach to construct compact spectroscopy systems.

Low divergence single-mode surface emitting quantum cascade ring lasers

We describe the fabrication and operation of surface emitting second-order distributed feedback quantum cascade ring lasers. The devices exhibit single-mode emission at a wavelength of 3.95μm with a side mode suppression ratio of 25dB. A linear tuning coefficient of 0.13cm−1∕K is observed. A single longitudinal mode in the ring shaped resonator results in a highly symmetric far-field pattern and a low beam divergence, represented by a full width at half maximum of ∼3°. Based on these characteristics the presented compact coherent light source may find its way into today’s midinfrared spectroscopy applications.