Organic Printed Core–Shell Heterostructure Arrays: A Universal Approach to All‐Color Laser Display Panels

A universal approach is demonstrated for realizing dual‐wavelength lasing in organic core–shell structured microlaser arrays, which show great promise in serving as all‐color laser display panels. By alternately printing hydrophilic and hydrophobic laser dye solutions on preprocessed substrates, precisely patterned core–shell heterostructure arrays were obtained. The spatially separated core and shell independently function as optical resonators to support dual‐wavelength tunable lasing in each heterostructure. Such a general method enables to flexibly control the lasing wavelength of the core–shell microlasers across a wide spectral range by systematically designing the gain media. Using as‐prepared microlaser arrays as display panels, full‐color laser displays were achieved with a color gamut much larger than that of standard RGB space. These results provide insights for design concepts and device construction for novel optoelectronic applications.     

Organic Printed Core–Shell Heterostructure Arrays: A Universal Approach to All-Color Laser Display Panels

A universal approach is demonstrated for realizing dual-wavelength lasing in organic core–shell structured microlaser arrays, which show great promise in serving as all-color laser display panels. By alternately printing hydrophilic and hydrophobic laser dye solutions on preprocessed substrates, precisely patterned core–shell heterostructure arrays were obtained. The spatially separated core and shell independently function as optical resonators to support dual-wavelength tunable lasing in each heterostructure. Such a general method enables to flexibly control the lasing wavelength of the core–shell microlasers across a wide spectral range by systematically designing the gain media. Using as-prepared microlaser arrays as display panels, full-color laser displays were achieved with a color gamut much larger than that of standard RGB space. These results provide insights for design concepts and device construction for novel optoelectronic applications.     

A low-threshold, high-efficiency microfluidic waveguide laser

This communication describes a long (1 cm), laser-pumped, liquid core-liquid cladding (L2) waveguide laser. This device provides a simple, high intensity, tunable light source for microfludic applications. Using a core solution of 2 mM rhodamine 640 perchlorate, optically pumped by a frequency-doubled Nd:YAG laser, we found that the threshold for lasing was as low as 22 muJ (16-ns pulse length) and had a slope efficiency up to 20%. The output wavelength was tunable over a 20-nm range by changing the ratio of solvent components (dimethyl sulfoxide and methanol) in the liquid core.     

Analytical applications of laser moding caused by intracavity absorption

A continuous CO₂ laser with a reflecting mirror can operate at several wavelengths simultaneously. If an organic vapor is introduced into a separate cavity in the laser optical path, the laser will sometimes mode rapidly causing some lasing lines to diminish to zero and others to become enhanced; this has been observed even for very low amounts (10^-5 g) of organic gases. Laser intercavity absorption spectroscopy depends on overlap of a vibrational—rotational line of a sample with a laser transition line. The absorption by the sample greatly affects the laser wavetrain at that particular wavelength and interferes with the lasing action. The technique is not based on Beer's law, and the detection limits observed are orders of magnitude better than those of conventional infrared absorption spectroscopy. Two laser systems were used and various organic gases were studied. When a totally reflecting mirror which permitted free moding was used, the detection limits found were 0.14 μg, 0.95 μg and 0.60 μg for vinyl chloride, propylene, and ethylene, respectively. When a grating was used as the rear cavity optics restricting the wavelengths of the laser lines, the detection limits were 140 μg, 94 μg, 63 μg and 0.26 μg for vinyl chloride, propylene. ethylene and ethyl chloride, respectively.     

Liquid-crystal-droplet optical microcavities

ABSTRACT

The use of liquid-crystal droplets as optical microcavities and lasers is reviewed and possible applications are discussed. Liquid-crystal droplets are prepared by simple methods that enable scalable production since their internal structure is formed by self-assembly. Light is trapped in droplets due to total internal reflection on the surface due to refractive index mismatch or because of a photonic bandgap structure in cholesteric liquid crystals (CLCs). Light confinement gives rise to a variety of optical modes and by employing a fluorescent dye end external optical pumping, lasing can be achieved. Liquid-crystal-droplet cavities are largely tunable by applying an electric field or a temperature change. Such cavities can be used as temperature and chemical sensors, and tunable light sources and filters in future integrated soft photonic circuits.     

Laser emission in a 3D nanoporous polymer replica of amorphous blue phase III

Wide‐temperature polymer stabilized cubic blue phases (BPI and BPII) facilitated the emergence of practically feasible band‐edge BP lasers. However, the mysterious “blue fog” amorphous BPIII always remained elusive in terms of its applicability to photonic devices due to its random amorphous structure devoid of photonic bandgaps and due to the difficulty in effectively identifying and stabilizing it for practical applications. We present the first photonic device based on amorphous BPIII by demonstrating that a three‐dimensional BPIII polymer scaffold or template, when infiltrated with liquid crystal and laser dye, forms a system where random lasing action is generated due to multiple scattering events occurring in the nanoporous and disordered polymer replica of BPIII. This study represents a facile approach for the development of photonic devices which favorably exploit unique polymer network morphologies for laser emission. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 551–557     

A three-layer egg-configurated Bragg microcavity of polyglycerol coated cholesteric-liquid-crystal encapsulated by hollow-glass-microsphere

ABSTRACT

This letter reports the optical pumped lasing behaviours of a three-layer Bragg resonance cavity consisting of dye-doped cholesteric liquid crystal (DDCLC) microdroplet, polyglycerol-2 and hollow glass microsphere. The function of PG2 is to control the parallel anchoring of the liquid crystal (LC) molecules on the surface of the LC microdroplet. The whispering-gallery mode (WGM), radial Bragg (photonic bandgap, PBG) mode and Bragg WGM (BWGM) are observed in DDCLC microspheres with different helical pitches and LC refractive indices. The formation mechanisms of six types of lasing emission conditions are analysed in detail. The study results present the prospect of controlling the output mode of the laser. Furthermore, such solid shell-based DDCLC microspheres have outstanding potential applications in miniaturised 3D Bragg lasers, sensors, and integrated and tunable optical devices.     

New glass ceramics: an effective conjunction of wet chemistry synthesis and sintering

A glass with CdS nanoparticles was used simultaneously as a matrix for Ce-doped garnet and a yellow-red phosphor to prepare luminescent glass ceramics for the sources of white light. CdS nanoparticles compensate for the unbalanced Ce³⁺ emission spectrum of the composite material due to the addition of a red component. The synthesized composite material can be a tunable light converter due to altered luminescence spectra by changing the sintering conditions and excitation wavelength     

Effect of the Wavelength of the Laser Beam on the Response of an Evaporative Light Scattering Detector

Abstract

The effects of the wavelength of the laser beam on the response of an evaporative light scattering detector (ELSD) are discussed. Data characterizing the response of the detector and its dependence on the sample size have been collected for six solutes, using a pulsed dye laser as light source. The experimental results suggest that there is little influence of the wavelength on the intensity of the scattered light. On the other hand, the noise decreases in proportion to the wavelength of the incident light beam. Thus, the detection limit (at constant value of the signal to noise ratio) decreases with decreasing wavelengths. The performance of the ELSD improves when a short wavelength is used.     

A Photoisomerization‐Activated Intramolecular Charge‐Transfer Process for Broadband‐Tunable Single‐Mode Microlasers

Miniaturized lasers with high spectral purity and wide wavelength tunability are crucial for various photonic applications. Here we propose a strategy to realize broadband‐tunable single‐mode lasing based on a photoisomerization‐activated intramolecular charge‐transfer (ICT) process in coupled polymer microdisk cavities. The photoisomerizable molecules doped in the polymer microdisks can be quantitatively transformed into a kind of laser dye with strong ICT character by photoexcitation. The gain region was tailored over a wide range through the self‐modulation of the optically activated ICT isomers. Meanwhile, the resonant modes shifted with the photoisomerization because of a change in the effective refractive index of the polymer microdisk cavity. Based on the synergetic modulation of the optical gain and microcavity, we realized the broadband tuning of the single‐mode laser. These results offer a promising route to fabricate broadband‐tunable microlasers towards practical photonic integrations.     

Multiphoton ionization: a method for characterizing molecular beams and beam reaction products

The technique of multiphoton ionization is applied to Na₂ in an effusive and a supersonic beam to characterize the internal state distribution of this molecule. A tunable dye laser is swept through the wavelength region of the Na₂ BX system and positive ions are counted as a function of laser wavelength. Multiphoton ionization involving a real intermediate state is also used to characterize the BaCl product formed in the beam-gas reaction Ba + HCl. This detection system can combine mass spectrometry with laser spectroscopy for the identification and characterization of beam species. Advantages and drawbacks are discussed.     

基于DFB型半导体激光器的腔增强吸收光谱研究

The Cavity enhanced absorption spectroscopy based on a tunable DFB diode laser (TDL-CEAS) was described. A brief introduction of cavity enhanced absorption spectroscopy development and experimental scheme was given, the effective absorption path of the medium in the optical cavity was interpreted from the way of Fabry Perot cavity. It is pointed out that the main reason why CEAS has high detection sensitivity is that the medium in the cavity can get a long absorption path. A tunable DFB diode laser which center wavelength is 1.573 μm was used as the light source, and an optical cavity which consists of two high reflectivity mirrors (near 1.573 μm, R about 0.994) separated at a distance of 34 cm was used as the absorption cell. Laser radiation was coupled into the optical cavity via accidental coincidences of laser frequency with the cavity mode when scanning the cavity and the laser. An absorption spectrum of carbon dioxide near 1.573 μm was obtained and a detection sensitivity of about 1.66×10-5 cm-1 was achieved. It is experimentally demonstrated that the CEAS is a highly sensitive and high resolution spectrum technology, and it has the advantage of simple experimental setup and easy operation.     

Tuning the lasing wavelength of dye-doped chiral nematic liquid crystal by fluid flow

The influence of hydrodynamic flow on the lasing wavelength and stability of the laser emission average power of a dye-doped chiral liquid crystalline (DDCLC) structure is studied. Multiple lasing peaks at equidistant wavelengths are observed, which are originating from multiple domains that are induced by the hydrodynamic flow of the DDCLC. A simultaneous blue shift over 4 nm for all lasing peaks is observed after increasing the flow velocity to 0.3 mm/s for cells with a thickness of 10 μm. It is observed that the CLC flow dramatically increases the stability of the laser emission compared to conventional cells because dye bleaching and LC molecular reorientation due to pumping beam is reduced.     

Blue‐to‐Orange Color‐Tunable Laser Emission from Tailored Boron‐Dipyrromethene Dyes

A series of meso‐substituted boron‐bipyrromethene (BODIPY) dyes are synthesized and their laser and photophysical properties systematically studied. Laser emission covering a wide visible spectral region (from blue to orange) is obtained by just changing the electron donor character of the heteroatom at position 8. The additional presence of methyl groups at positions 3 and 5 results in dyes with a photostability similar to that of the unsubstituted dye but with much improved efficiency. Correlation of the lasing properties of the different dyes to their photophysical properties provides inklings to define synthetic strategies of new BODIPY dyes with enhanced efficiency and modulated wavelength emission over the visible spectral region.     

Tunable fiber laser and fiber amplifier based photoacoustic spectrometer for trace gas detection

A new wavelength modulated photoacoustic spectrometer based on a near-infrared tunable erbium doped fiber laser (TEDFL) and an erbium doped fiber amplifier (EDFA) is first developed for trace gas detection. This sensor has been applied to the detection of ammonia using a first longitudinal resonant photoacoustic cell with double absorption optical path (L = 20 cm) and lock-in harmonic detection technique. The minimum detectable limit of 3 parts-per-billion volume (signal-to-noise ratio = 1) and response time of approximately 1 min is achieved at room temperature and atmospheric pressure with 100 ms time constant and 500 mW optical power at the 1531.7 nm transition line.     

Phonon Scattering by Externded Defects in Polycrystalline Graphene

Phonon scattering by static stress fields created by grain boundaries (GBs) in graphene was studied with the deformation potential method. This method provides exact analytical expressions for phonon mean free paths as a result of scattering by GBs with arbitrary geometries in the Born approximation. Two regimes, k^–1 and k^–3, of the mean free path behavior are discovered in the limit of small momenta. The first (dislocation) regime is realized for open configurations in polycrystalline graphene, while the second regime is realized for closed configurations and Stone-Wales defects in pure graphene. The mean free path does not depend on k for any GB in the short-wave limit (large k). Thermal conductivity in graphene with GBs was calculated using the Callaway model which considers both normal phonon processes and umklapp processes. The contribution from these defects to the thermal conductivity is shown to exceed substantially the contribution from point defects and vacancies in a wide range of temperatures.     

Influence of nanoparticles on elastic and optical properties of a polymeric matrix: Hypersonic studies on ethylene-vinyl alcohol copolymer-titania nanocomposites

High resolution Brillouin spectroscopy (HRBS) backscattering elastic data in nanocomposites of ethylene-vinyl alcohol copolymer (EVOH) and TiO₂ nanoparticles present anomalous dependence with concentration, while Young’s modulus and microhardness data show the expected behaviour. When performing HRBS with the 90A scattering geometry to asses the effective elastic constant, the expected behaviour for low concentration of TiO₂ nanoparticles is again obtained. This unusual disagreement can be solved assuming that the inclusion of TiO₂ nanoparticles induces anomalous refractive index behaviour at the applied laser wavelength for the different EVOH-TiO₂ nanocomposites. Comparison with experimental elastic and optical data obtained in isotactic-polypropylene-TiO₂ nanocomposites proves that EVOH-TiO₂ nanocomposites show an unusual optical behaviour at the laser wavelength, possibly due to a singular bonding between the EVOH polymer and the TiO₂ nanoparticles.     

Speckle observation of pulsed laser-induced dynamics in a guest-host smectic A liquid crystal system

Abstract

Using a pulsed, pump-probe experimental arrangement, we have investigated the speckle generated by a 100 μm path length cell of smectic A liquid crystal 4-cyano-4′-octylbiphenyl doped with 0·1 wt% dichroic dye. Upon irradiation, the guest-host system undergoes a phase transition from an initially transparent condition to a scattering state. We show that the statistical theory of speckle can be used to describe the evolution of scattering domains and estimate an rms refractive index variation of 0·0021 within the irradiated region for one case. Dynamic response as a function of molecular anchoring conditions was also investigated.     

An Experimental Study of Phase Transition in Water and Nitrobenzene Using Light Scattering from a Helium Neon Laser∗

Abstract

A light scattering experiment was conducted in water and nitrobenzene to test the behavior of these two materials as they were made to undergo phase transition. A helium-neon laser was used as the radiation source. The coefficient of the optical absorption and contribution of scattered and absorbed light are computed from the measured transmitted light intensity at different temperatures. These measurements show that the creation and collapse of bubbles due to the laser heating cause more discontinuities in water than in nitrobenzene. Thus, there is indication of a higher order transition in water than in nitrobenzene.

From this study it is concluded that low power density laser irradiation can be used to gain an understanding of bubble dynamics in a liquid.