Mirrorless Laser Research Articles

In Situ Characterization of Thermal‐Induced Evolution of Structure/Optical Properties of Heterogeneous 3D Chiral Soft Photonic Crystal Polymer

AbstractPolymer stabilized blue phase (PSBP) liquid crystal has aroused wide attention due to its broad temperature range and potential applications in flexible display, multi‐mode monitor, and mirrorless laser based on its well‐compatible stability and multi‐responsiveness, such as electricity, humidity, and temperature. Temperature produces an important effect on the structure/optical properties of PSBP, but there lack of detailed investigation on thermal‐induced deformation and its influence on the optical performance of PSBP. Here, the thermal‐induced evolution of structure/optical properties of PSBP with different polymer content is in situ characterized by variable‐temperature ultra‐small‐angle X‐ray diffraction, Kossel diffraction, and polarized optical microscopy. A restricted deformation of PSBP cubic lattice is revealed by the shift of reflective wavelength and evolution of Kossel diagrams, which is mainly attributed to the thermal‐induced phase transition/separation of non‐polymerized components. The thermal stability of PSBP is improved by increased polymer content based on the limited deformation ability. This work is significant for the design of novel functional material, which paves the way for the preparation of photonic crystal soft materials with high stability and optical quality.

On-demand pitch tuning of printed chiral nematic liquid crystal droplets

Identifying facile means with which to tune the pitch of, and therefore the reflected colour from, chiral nematic liquid crystals (CLC) is of interest for many different photonics applications including optical filters, coloured displays, and mirrorless lasers. Precise control of the pitch of the helix, however, can be challenging. Here, we demonstrate the ability to tune the pitch, and consequently the reflection band, by depositing picolitre volumes of nematic LC into printed CLC droplets with a short pitch. Results are presented that demonstrate mixing of the nematic LC and CLC droplets such that the pitch elongates causing the reflection band located at blue wavelengths (430 nm) to redshift to longer wavelengths. The magnitude of the redshift can be controlled by varying the number of nematic LC droplets deposited into each CLC droplet. We consider the process of diffusion of these two separate mixtures using inkjet printing and showcase how this process of tuning the pitch can be employed to create coloured images in the form of an alphanumeric logo.

Recent Advances in Electro-Optic Response of Polymer-Stabilized Cholesteric Liquid Crystals

Cholesteric liquid crystals (CLC) are molecules that can self-assemble into helicoidal superstructures exhibiting circularly polarized reflection. The facile self-assembly and resulting optical properties makes CLCs a promising technology for an array of industrial applications, including reflective displays, tunable mirror-less lasers, optical storage, tunable color filters, and smart windows. The helicoidal structure of CLC can be stabilized via in situ photopolymerization of liquid crystal monomers in a CLC mixture, resulting in polymer-stabilized CLCs (PSCLCs). PSCLCs exhibit a dynamic optical response that can be induced by external stimuli, including electric fields, heat, and light. In this review, we discuss the electro-optic response and potential mechanism of PSCLCs reported over the past decade. Multiple electro-optic responses in PSCLCs with negative or positive dielectric anisotropy have been identified, including bandwidth broadening, red and blue tuning, and switching the reflection notch when an electric field is applied. The reconfigurable optical response of PSCLCs with positive dielectric anisotropy is also discussed. That is, red tuning (or broadening) by applying a DC field and switching by applying an AC field were both observed for the first time in a PSCLC sample. Finally, we discuss the potential mechanism for the dynamic response in PSCLCs.

Self‐Steering Lasing System Enabled by Flexible Photo‐Actuators with Sandwich Structure

AbstractWith the flourishing development of artificial intelligence, lasing with tailored features generated by photonic crystal (PhC) lasers has been playing a more important part in the optics field and in potential applications of self‐control, light detection and ranging, telecommunications, and holography imaging. As an information vehicle, the optical beam's maneuverability is influenced by the working wavelength, direction, and efficiency of the laser. Liquid crystal (LC)‐based mirrorless lasers are widely investigated in manipulating the tuning of emission wavelength. Realizing fast self‐steering of the laser beam to tune the emission direction is challenging because of the limitation on the complex and expensive inorganic fabrication and circuit design. In this work, a self‐steered lasing from a defect‐mode sandwich film composed of photomechanical deformable azobenzene cholesteric LC elastomer (CLCE) PhC layers and an isotropic gain interlayer is demonstrated. On the basis of the great light‐deformability of the CLCE, the output single‐mode lasing emission of the sandwich‐film laser can be steered quickly by UV irradiation in a wide angular tuning range of ≈±57°. This flexible, portable, and durable laser system with controllable beam‐steering and mechanical robustness is envisioned to open a gate for autonomous vehicles, self‐sustaining machines, and optical devices with the core feature of photomechanical conversion.

Synthesis, TD-DFT, and optical properties study of a chromeno-quinoline (acceptor) and mirror-less laser action enabled by energy transfer from a conjugated-polymer (Donor)

Structurally interesting chromeno-quinolines were constructed via the cyclization reaction of O-propargylated naphthaldehyde and substituted anilines in good yields. We explored compound methyl-chromenoquinoline (MCQ) in detail for its optical properties using Time-dependent density-functional theory (TD-DFT) and experimental studies. The conjugated-polymer (CP) Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(2,5-p-xylene)] or [(ADS145UV or PFOPX)] was studied as donor. The TD-DFT implied that MCQ is a fluorescent compound with well-defined highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) structure at −5.327 eV and −1.836 eV, respectively, with an energy gap of 3.49 eV in toluene captivity. The TD-DFT-based model and experimental study showed an energy gap of 3.326 eV and 3.351 eV, respectively, and the deviation was 0.025 eV. The experimental studies of MCQ showed solvent-dependent fluorescence peak shifted from 445 ± 2 nm to 538 ± 2 nm for dielectric constant ranging from 0.01 (hexane) to 10.2 (water). Despite the good optical properties, MCQ produced a weak laser-induced fluorescence (LIF) and not produce amplified spontaneous emission (ASE) to any pump energy of 3rd harmonic from Nd:YAG laser (5 ns, 355 nm). When PFOPX of concentration 500 nM (500 μL) was added to MCQ of 506 mM (3.5 mL) concentration, the LIF suddenly improved tenfold due to efficient Fluorescence resonance energy transfer (FRET) process. At the optimal concentration of PFOPX (670 nM) in MCQ solution, the spectrum changed dramatically. The spectrum has five peaks with a LIF in the background, where peaks around 393.5 nm and 417.3 nm attribute to the oligomer; 438.7 nm attributed to a combined fluorescence of PFOPX and MCQ; 466.4 nm, and 493.1 nm corresponding to MCQ. Analysis shows that the peaks at 440 nm (partly) and 493 nm were ASE from MCQ.

Programmable Engineering of Sunlight-Fueled, Full-Wavelength-Tunable, and Chirality-Invertible Helical Superstructures.

Dynamic control of motion at the molecular level is a core issue in promoting the bottom-up programmable modulation of sophisticated self-organized superstructures. Self-assembled artificial nanoarchitectures through subtle noncovalent interactions are indispensable for diverse applications. Here, the active solar renewable energy is used to harness cholesteric liquid crystal (CLC) superstructure devices via delicate control of the dynamic equilibrium between the concentrations of molecular motor molecules with opposite handedness. Thus, the spectral position and handedness of a photonic superstructure can be tuned continuously, bidirectionally, and reversibly within the entire working spectrum (from near-ultraviolet to the thermal infrared region, over 2 μm). With these unique horizons, three advanced photoresponsive chiroptical devices, namely, a mirrorless laser, an optical vortex generator, and an encrypted contactless photorewritable board, are successfully demonstrated. The sunlight-fueled chirality inversion prompts facile switching of functionalities, such as free-space optical communication, stereoscopic display technology, and spin-to-orbital angular momentum conversion. Motor-based chiroptic devices with dynamic and versatility controllability, fast response, ecofriendly characteristics, stability, and high efficiency have potential to replace the traditional elements with static functions. The inexhaustible natural power provides a promising means for outdoor-use optics and nanophotonics.

A robust and inexpensive all optical switch with chiral nematic liquid crystal

A switchable photonic band gap with optical addressing is demonstrated. The switch can tune over a broad wavelength range (about 80 nm) without deformation and degradation with high reproducibility. The material is a mixture of reactive and nonreactive mesogens, azo dye molecules and chiral dopant. The mixture of reactive monomers and nonreactive mesogens leads to a robust polymer template filled with nano-droplets. Due to a photo-induced phase transition, the edges of the bandgap shift to shorter wavelengths after illumination. Three concentrations of reactive monomers are investigated. The features of the device are interesting for several emerging applications: all optical photonic switches, lab-on-a-chip devices, and switchable optical devices such as sensors, reflectors, diffraction gratings, polarizers, shutters, notch- and band-pass filters, reflective displays, mirror-less tunable lasers and modulators.

Light Disorder as a Degree of Randomness to Improve the Performance of Random Lasers

The operation of random lasers (RLs) is possible due to multiple light scattering, which provides optical feedback inside the gain medium. No conventional optical cavity is required for the operation of RLs and, therefore, RLs provide the best evidence to defy the conventional view that disorder is an unwanted phenomenon when present in physical systems. Mirrorless lasers demonstrate that the degree of disorder, associated with the spatial distribution of scattering particles, is the main factor responsible for generating a light source with low spatial coherence; this is reason why RLs are so attractive for modern imaging systems. Here, we demonstrate how to optimize the performance of typical diffusive RLs by exploiting a different degree of randomness in the system, which is loaded onto an induced disorder in the transverse intensity and wave-vector distributions of the light pattern that pumps the random-lasing medium. Quantitative analyses show that the RL's intensity emission and threshold fluence can be optimized by more than 20 times, when excited by an optical field presenting a random spatial-intensity distribution, with high speckle contrast, becoming an efficient methodology to induce high photon degeneracy in RLs required for high sensitivity applications.

TD-DFT Simulation and Experimental Studies of a Mirrorless Lasing of Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)

In this work, we investigate the TD-DFT simulation, optical, and mirrorless laser properties of conjugated polymer (CP) Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)], also known as (PFO-co-PPV-MEHB) or ADS125GE. TD-DFT calculations were performed for three monomer units with truncated tails using time-dependent density functional theory (TD-DFT) calculations. The calculations showed a highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) structure and a very high oscillator strength of 6.434 for the singlet-singlet transition at 374.43 nm. Experimentally, the absorption and fluorescence spectra were examined at various concentrations in verity of solvents, such as benzene, toluene, and hexane. The experimental results obtained in hexane were comparable with theoretical UV-VIS spectra calculated under vacuum. Amplified spontaneous emission (ASE) spectra peaked at approximately 509 nm for CO PFO-co-PPV-MEHB in solution and were obtained at suitable concentrations and pump energies. Additionally, the photochemical stability of this CP and coumarin (C510) were compared. Time-resolved spectroscopy (TRS) studies with a sub-nanosecond resolution were performed for the CO under various pump energies. These results showed the excited state dynamics and single-pass optical gain of CO PFO-co-PPV-MEHB.

Stretchable Freestanding Films of 3D Nanocrystalline Blue Phase Elastomer and Their Tunable Applications

AbstractGiven that it is a potential medium for 3D manipulation of photons in the forward‐looking technology of quantum optics, nonlinear optics, electronics, nanomaterials, and bionics, 3D photonic crystal (PhC) is a promising material of strategic significance and has great impact on scientific development. Blue phase (BP), a liquid crystalline mesophase with unique nanoscaled 3D PhC features, has been shown to contain significant potential values in fundamental studies and technological applications. However, thus far, the environmental stability of BP devices remains a puzzling issue of material exploitation. Therefore, in this study, stretching‐tunable BP elastomer (BPE) photonic bandgap (PBG) free‐standing films are fabricated via full photopolymerization. The BPE films exhibit benefit‐specific features, including sharp PBG with high reflectivity and flexible tunability in the visible region, high thermal stability, and good mechanical ductility and resistance in chemicals. These properties are attributed to the pre‐developed, fully‐reactive mesogenic materials employed, which show BP states in a wide temperature range, including room temperature. Additionally, mirrorless laser applications with flexible tunability are also realized in this study. The freestanding BPE film can be used as a prototype instrumentality to promote the future development of multifunctional intelligent applications in lasers, sensors, displays, intelligent lightings, lidars, micro‐robots and antennas.

Role of Vitamin D Antiviral Plants and Precaution in COVID-19

Energy concentration is essential to create compact, efficient microfluidic optical devices. Polyethylene glycol (PEG) is a suitable fluid for this purpose with its bipolarity (molecular dissolvability), nonvolatility, and high index of refraction (waveguiding). Its distinguished feature is a bistability in the phase transition process; i.e., a mixture of two PEG types (molecular weight: 300 and 2000), for example, takes both the liquid and solid phases in the temperature range of 2�??38 °C. One can use this phase transition to pause a sample flow at a specific position in microchannels. The bistability also realizes a rewritable signboard with a PEG droplet array, since both the clear (liquid) and milk-white (solid) states are stable at room temperature. The strong scattering in the solid phase is useful to confine a light beam (photonic localization). Mirrorless lasers, which have been studied extensively with microdroplets, can be constructed with dye-dispersed PEG, since the confined fluorescence induces a stimulated emission. A bistable laser emission has been demonstrated in the phase transition process of the microfluid. The light confinement is also useful to enhance the absorbance of inorganic materials, which hardly absorb excitation or probe light particularly in a microchannel. Chemists have recently developed organic-inorganic hybrid phosphors with an enhanced excitation efficiency. Spectroscopic analysis of these hybrids needs time-resolved measurements, since both rapid and slow processes occur in organic ligands and metal ions. The time-space conversion spectral measurement is suitable for microfluidic devices, since a nanosecond resolution is attainable with no need for a large pulsed laser.

Single‐Crystalline Optical Microcavities from Luminescent Dendrimers

AbstractMicrocrystallites are promising minute mirrorless laser sources. A variety of luminescent organic compounds have been exploited along this line, but dendrimers have been inapplicable owing to their fragility and extremely poor crystallinity. Now, a dendrimer family that overcomes these difficulties is presented. First‐, second‐, and third‐generation carbazole (Cz) dendrimers with a carbon‐bridged oligo(phenylenevinylene) (COPV2) core (GnCOPV2, n=1–3) assemble to form microcrystals. The COPV2 cores align uni/bidirectionally in the crystals while the Cz units in G2‐ and G3COPV2 align omnidirectionally. The dendrons work as light‐harvesting antennas that absorb non‐polarized light and transfer it to the COPV2 core, from which a polarized luminescence radiates. Furthermore, these crystals act as laser resonators, where the lasing thresholds are strongly coupled with the crystal morphology and the orientation of COPV2, which is in contrast with the conventional amorphous dendrimers.

Single-Crystalline Optical Microcavities from Luminescent Dendrimers.

Microcrystallites are promising minute mirrorless laser sources. A variety of luminescent organic compounds have been exploited along this line, but dendrimers have been inapplicable owing to their fragility and extremely poor crystallinity. Now, a dendrimer family that overcomes these difficulties is presented. First-, second-, and third-generation carbazole (Cz) dendrimers with a carbon-bridged oligo(phenylenevinylene) (COPV2) core (GnCOPV2, n=1-3) assemble to form microcrystals. The COPV2 cores align uni/bidirectionally in the crystals while the Cz units in G2- and G3COPV2 align omnidirectionally. The dendrons work as light-harvesting antennas that absorb non-polarized light and transfer it to the COPV2 core, from which a polarized luminescence radiates. Furthermore, these crystals act as laser resonators, where the lasing thresholds are strongly coupled with the crystal morphology and the orientation of COPV2, which is in contrast with the conventional amorphous dendrimers.

Temperature activated mirror-less laser action from a hole-transport conjugated-polymer

A plethora of experimental reports and evidences from recent times have collectively taken efforts in developing a novel mirror-less laser. Breakthrough in Conjugated polymer lasers unravel numerous attractive research direction over the last decade. The present study experimentally demonstrated a temperature-activated/controlled amplified spontaneous emission (ASE) in a hole-transport conjugated polymer (HTCP) Poly[N,N’-bis(4-butylphenyl)-N,N’-bis(phenyl)-benzidine] [poly-TDP (4B)]. The poly-TDP (4B) dissolved in toluene under wide range concentration. The solution of different concentration was pumped with an Nd:YAG (355 nm) laser. For temperature lower than 37 °C, the poly-TDP (4B) did not produce ASE, but for the 40 °C, the ASE is observed. Furthermore, the output energy of the ASE is dependent on the temperature of the solution. The ASE output energy attains maximum at a temperature of 78 °C, and then the output falls drastically. The time-resolved spectroscopy studies showed the temperature responsiveness of the HTCP poly-TDP (4B) in the sub-nanosecond time domain. The temperature-dependent laser action is due to reversible dimerization property of the poly-TDP (4B), and it is rare.

Femtosecond laser direct writing of few-mode depressed-cladding waveguide lasers.

We report on mirrorless laser operation of Nd:YVO4 single- and double-cladding waveguides fabricated by femtosecond laser direct writing. Fundamental- (LP01) and high-order-mode (LP03, LP05) guiding and lasing have been observed in waveguides with different geometries and sizes. Double-cladding waveguides exhibit good guiding and lasing performance via inheriting advantages respectively from individual single cladding. As a result, continuous-wave lasing with a threshold as low as 59 mW is obtained, depending on the optical feedback provided only by Fresnel reflections at the waveguide end faces. By using few-layer graphene as saturable absorber, passively Q-switched operation in fabricated waveguides is also achieved.

Mid IR hollow core fiber gas laser emitting at 4.6 μm.

Emission at 4.6μm was observed from an N2O filled hollow core fiber laser. 8-ns pump pulses at 1.517μm excited a vibrational overtone resulting in lasing on an R and P branch fundamental transition from the upper pump state. At optimum gas pressure of 80Torr, photon conversion efficiency of 9% and slope efficiency of 3% were observed from a mirrorless laser. The laser threshold occurred at absorbed pump energy of 150nJ in a 45-cm long fiber with 85μm core diameter. The observed dependence of the laser output on gas pressure was shown to be a result of line broadening and relaxation rates.

Opto-chemical and laser properties of FLTX1, a novel fluorescent tamoxifen derivative, and its potential applications in breast cancer photodynamic chemotherapy

Tamoxifen is the most common antiestrogen used in the chronic treatment of breast cancer. In these cells, it mainly binds to intracellular receptors (estrogen receptor alpha, ERα) and antagonizes the binding of its cognate ligand, 17β-estradiol, thereby preventing uncontrolled hormone-dependent cellular proliferation and growth. In the last decade, in our laboratories we have developed and characterized different tamoxifen derivatives, including a novel fluorescent tamoxifen conjugate: FLTX1. FLTX1 is formed by the covalent binding of tamoxifen to a common fluorescent biomarker NBD. This new prodrug was originally designed as a fluorescent biomarker to localize intracellular targets, which not only keeps the pharmacological activity of tamoxifen but also adds a luminescent functionality. Strikingly, the quantum efficiency of FLTX1 is so high that laser emission has been obtained as an emerging property. In this review, we will show its laser properties under three different configurations. First, as amplified spontaneous emission or mirrorless laser; second, through the evanescent field of WGMs of a ring resonator around an optical fiber; and finally as random laser in uterine tissues impregnated with the prodrug.Further, we observed another emergent property for FLTX1: this molecule, but not tamoxifen alone or NBD, was able to generate reactive oxygen species (ROS) upon irradiation. This property is extremely interesting as FLTX1 might be used for photodynamic therapy. Under this paradigm, FLTX1 would act as a sensitizer in ERα-overexpressing cells (which feature the most prevalent form of hormone-dependent breast cancer), causing cell death in ERα+ cells but reducing damage to other non-cancer (healthy) cells or surrounding tissues. We show here time resolved fluorescence results that suggest molecular aggregations, which could explain the subsequent generation of ROS. This is an original cancer therapy strategy that combines the pharmacological properties of a new tamoxifen derivative and its laser dye features with a highly selective photodynamic therapy.

Bias‐Polarity Dependent Bidirectional Modulation of Photonic Bandgap in a Nanoengineered 3D Blue Phase Polymer Scaffold for Tunable Laser Application

AbstractTransferring self‐assembly liquid‐crystalline blue phase structure to polymers is emerging as a promising bottom‐up strategy in the nanofabrication of 3D photonic materials and devices. Here a polymer scaffold in blue phase I structure is fabricated with cubic symmetry and its potential application is demonstrated as an electrically tunable mirrorless laser by refilling the scaffold with laser dye‐doped nematic liquid crystal mixture. The templated blue phase exhibits immense thermal stability and sensitive responsive behavior to external electric fields with blueshift of the reflection band under negative bias voltage whereas redshift under positive bias. Moreover, bias‐polarity dependent bidirectional tuning of the laser emission with wavelength range of about 48 nm is achieved in the study. The nanoengineered 3D polymer scaffold with splendid electrical tunability might provide impetus for the preparation of functional hybrid materials and novel device architectures, which have diversified potential applications in reflective full‐color displays, tunable optical devices, and photonic integrated circuits.

Nonlinear spectral singularities and laser output intensity

The mathematical notion of spectral singularity admits a description in terms of purely outgoing solutions of a corresponding linear wave equation. This leads to a nonlinear generalization of this notion for nonlinearities that are confined in space. We examine the nonlinear spectral singularities in arbitrary transverse electric (TE) and transverse magnetic (TM) modes of a mirrorless slab laser that involves a weak Kerr nonlinearity. This provides a computational scheme for the determination of the laser output intensity I for these modes. In particular, we offer an essentially mathematical derivation of the linear-dependence of I on the gain coefficient g and obtain an explicit analytic expression for its slope. This shows that if the real part η of the refractive index of the slab does not exceed 3, there is a lower bound on the incidence angle θ below which lasing in both its TE and TM modes requires η to be shifted by a small amount as g surpasses the threshold gain. Our results suggest that lasing in the oblique TM modes of the slab is forbidden if the incidence (emission) angle of the TM mode exceeds the Brewster’s angle.

Pump angle and position effects on laser emission from quasicrystal microcavity by nine-beam interference based on holographic polymer-dispersed liquid crystals

ABSTRACTWe demonstrate pump angle and position effects on lasing from all organic quasicrystal fabricated by nine-beam interference. The output wavelengths of lasing are experimentally investigated with different pump angles. The underlying mechanism is explained by the photonic band edge simulated by finite-difference time-domain method. Additionally, the position effect on lasing is also demonstrated, and the emission characteristics of lasing are studied. The mirrorless laser is featured by low cost, and simple fabrication, which enables quasicrystal based on holographic polymer-dispersed liquid crystal an all organic miniature lasing devices.