Red-emitting Lasers Research Articles

A New Organic Laser Material Design Toward Ultra-Low Amplified Spontaneous Red Emission and Ultra-Bright Electroluminescence.

Significant efforts are dedicated to developing new classes of organic semiconductor materials to achieve electrically pumped lasing. However, further advancements are necessary to understand the relationship between the structure and property for the creation of innovative laser materials with high stability, low triplet yield, ultra-low lasing threshold, and low-efficiency roll-off at ultra-bright electroluminescence. Here, a new design principle is validated for organic semiconductor laser materials, demonstrating simultaneous enhancement in the key figures of merit of low amplified spontaneous emission thresholds (Eth), efficient electroluminescence, and low triplet yields. By applying the Einstein stimulated emission rate equation and Strickler-Berg approximation, Two red-emitting laser dimers of Cibalackrot with different linkers are constructed, leading to giant enhancement (≈250%) in oscillator strengths, and stimulated emission cross-sections. When blended in poly(9,9-dioctylfluorene-alt-benzothiadiazole), the new dimers achieve an ultra-low Eth (4.5±0.3µJcm-2) in the deep red region (λASE=655nm), among the lowest reported for deep-red emitters. Organic light-emitting diodes (OLEDs) utilizing the dimer blend exhibit low-efficiency roll-off under DC mode. Under pulse operation, the OLEDs achieve high current densities (90Am-2) and ultrahigh brightness (≈710000cdm-2). These findings highlight the dimerization design as an excellent platform to advance organic semiconductor laser materials.

Effect of Antimicrobial Photodynamic Therapy on the Tongue Dorsum on Reducing Halitosis and the Duration of the Effect: A Randomized Clinical Trial.

Antimicrobial photodynamic therapy (PDT) is a treatment that is gaining popularity in modern clinical medicine. However, little is known about the effect of PDT alone on reducing oral halitosis and the duration of the effect. This trial examined the effect of PDT on the tongue dorsum on reducing oral halitosis and the duration of the effect. This study was approved by the Ethics Committee of Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, and Okayama University Hospital (CRB20-015), and it was registered in the Japan Registry of Clinical Trials (jRCTs061200060). Twenty-two participants were randomly assigned to two groups: an intervention group and control group. PDT was performed in the intervention group using red laser emission and methylene blue gel on the middle and posterior area of the tongue dorsum. The concentration of volatile sulfur compounds, bacterial count on the tongue dorsum, probing pocket depth, bleeding on probing, and simplified oral debris index score were determined before and 1 week after PDT. The Mann-Whitney U test was used to assess the significance of the differences in each parameter between the two groups. We found that the hydrogen sulfide concentration and bacterial count on the tongue dorsum were decreased in the intervention group, but there was no statistically significant difference between the two groups. These results indicated that performing only PDT on the tongue dorsum may not contribute to reducing halitosis.

Comparison of high power red-emitting diode laser designs for medical applications

A comparison is made between, on the one hand, the red-emitting laser structure currently widely used for medical applications and based on an ultranarrow waveguide layer with a compressively strained QW active layer in it and, on the other hand, the red emitting laser using a broadened asymmetric waveguide structure with a bulk active layer near the p-cladding, proposed by us. It is shown that the proposed design promises substantial improvements over the ultranarrow one including lower series and thermal resistances, and higher catastrophic degradation threshold, while maintaining relatively narrow far field and allowing the typical power required for medical applications to be achieved at lower currents, particularly at elevated temperatures.

Radiation and Emission Phenomena in Combination

Radiation and Emission Phenomena in Combination

Laser performance of high optical quality 4 at.% Pr3+: Sr0.7La0.3Mg0.3Al11.7O19 (Pr:ASL) single crystals.

In this work, we present the visible laser performance of improved optical quality Czochralski-grown 4 at.% Pr3+-doped Sr0.7La0.3Mg0.3Al11.7O19 (Pr:ASL) single crystals in the deep red (726 nm), the red (645 nm) and the orange (620 nm) range using two different pumping sources. Using a high beam quality frequency doubled Ti:sapphire laser with 1 W output power as pump source, deep red laser emission was reached at a wavelength of 726 nm with 40 mW of output power and a laser threshold of 86 mW. The corresponding slope efficiency was 9%. At 645 nm in the red, up to 41 mW of laser output power were obtained with 15% slope efficiency. Moreover, orange laser emission at 620 nm was demonstrated with 5 mW output power and 4.4% slope efficiency. Using a 10 W multi-diode module as pumping source allowed to obtain the highest output power of a red and deep-red diode-pumped Pr:ASL laser to date. The respective output powers at 726 and 645 nm reached 206 mW and 90 mW.

A super-high brightness and excellent colour quality laser-driven white light source enables miniaturized endoscopy.

A laser-driven white light source promises intrinsic advantages for miniaturized endoscopic illumination. However, it remains a great challenge to simultaneously achieve high brightness and excellent colour rendition due to the shortage of highly efficient and thermally robust red-emitting laser phosphor converters. Here, we designed CaAlSiN3:Eu@Al (CASN@Al) converters with neglectable efficiency loss by tightly bonding all-inorganic phosphor films on an aluminium substrate. A layer-by-layer phosphor converter (LuAG/CASN@Al), i.e., stacking a green-emitting Lu3Al5O12:Ce (LuAG) layer on CASN@Al, was constructed to enhance light conversion efficiency and reduce reabsorption loss under blue laser excitation, which thus produces an excellent white light source with a luminous efficacy of 258 lm W-1 and a colour rendering index of 91. A miniaturized endoscopy with a coupling efficiency twice that of the commercial white LEDs was demonstrated by using the laser-driven white light and showed a central illuminance as high as 52 730 lx, more vivid images and long-term reliability.

Analysis of InGaN-Delta-InN Quantum Wells on InGaN Substrates for Red Light Emitting Diodes and Lasers

Modern multi-color RGB micro-light emitting diode (μLED) displays and digital micro-mirror laser projectors often require the use of both III-V and III-Nitride material systems for different pixel/laser colors. This is due primarily to the conventionally low efficiencies of red emitters based on the InGaN materials system, which is used to create green and blue emitters for RGB displays. The main challenges for InGaN red emitters are the quantum confined stark effect (QCSE) and the difficulty of incorporating high In-content into the active region. In this work, InGaN/InGaN/delta-InN quantum wells (QWs) on InGaN substrates are proposed and demonstrated to show significant enhancement in electron-hole wavefunction overlap ( Γe_hh ) and spontaneous emission radiative recombination rate (Rsp) in the red emission regime. Analysis of InGaN/InGaN/delta-InN QWs with InGaN barriers emitting at 630 nm was performed using a self-consistent six-band $k \cdot p$ formalism. The Γe_hh was shown to increase by more than 230% compared to an InGaN/InGaN QW emitting at 630 nm, leading to significant increases in Rsp and internal quantum efficiency ( ηIQE ). With growth of InN monolayers on InGaN now readily achievable, this novel active region design could pave the way for high-efficiency, native red-emitting InGaN LEDs and lasers.

Frequency doubling of acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded Raman laser for narrow pulse-width 657 nm laser

Frequency doubling of second-Stokes in an acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded self-Raman cavity is demonstrated to achieve a narrow pulse-width red laser. A three-stage bonded YVO<sub>4</sub>/Nd:YVO<sub>4</sub>/YVO<sub>4</sub> crystal is designed by comprehensively considering the improvement of thermal effect, the performance of fundamental frequency laser and Raman conversion, to improve the Raman efficiency and output power. An LBO crystal cut for critical phase matching at room temperature is selected and used as a nonlinear optical crystal for realizing the frequency doubling of second- Stokes wave. Its phase matching angle (<i>θ</i> = 86.0°, <i>φ</i> = 0°) is very close to the non-critical phase matching angle and has a small walk-off angle, which is beneficial to the realizing of the high conversion efficiency of frequency doubling. In the experiment, the beam waist position of the pump light and the repetition frequency of the acousto-optic Q-switcher are optimized. Under an incident pump power of 14.2 W and a repetition frequency of 60 kHz, the highest average output power of 1.63 W and conversion efficiency of 11.5% are obtained for the 657 nm red laser emission. The pulse width of 657 nm red light is 11.5 ns at the maximum output power, which is much narrower than that generated by frequency doubling of ordinary neodymium-doped laser at a waveband of 1.3 μm. The result shows that the frequency doubling of the acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded self-Ramanlaser can take advantage of the pulse-width compression characteristics of Raman process to achieve a narrower pulse-width red light laser output.

The ineffectiveness of antimicrobial photodynamic therapy in the absence of preincubation of the microorganisms in the photosensitizer

Abstract Introduction: Considering its potential as an alternative therapy to combat multiresistant bacteria, photodynamic therapy has been improved and better studied in recent years, and determining its optimized application patterns is important. Objective: This study aimed to evaluate the action of antimicrobial photodynamic therapy mediated by methylene blue in the absence of preincubation of infectious agents in the photosensitizer. Method: Standard strains of Staphylococcus aureus and Pseudomonas aeruginosa were used, which was or was not submitted to two methylene blue concentrations (0.1 μg/mL and 500 mg/mL) applied alone or in combination with a variety of red laser emission parameters (660 nm); in both cases, the streak was performed immediately after mixing between the photosensitizer and the solution containing the bacteria. Results: In the dishes with only methylene blue application neither antibacterial was produced, nor inhibition at the application points of the photodynamic therapy in the case of the bacterium Pseudomonas aeruginosa. However, in the cultures of Staphylococcus aureus in which laser emission was associated with the concentration of 500 mg/mL of the photosensitizer, inhibition was present at the laser application points. Conclusion: The time of exposure to the photosensitizer prior to the application of phototherapy seems to be an essential factor for the optimized action of photodynamic therapy, especially in the case of Gram-negative bacteria.

Compact Two-Color Pr3+-Doped ZBLAN Fiber Lasers

ABSTRACTTwo-color laser simultaneous oscillation in compact trivalent praseodymium ion (Pr3+)-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber lasers is investigated. Fiber pigtails by coating high-reflective visible dielectric films are utilized as fiber mirrors (FMs) to construct compact all-fiber laser cavity. Reflectance/transmittance of FMs is intentionally designed to balance net gains and reduce gain competition of different lasable wavelengths in the constructed fiber lasers. By using two selected FMs with high reflectivity at green-light and low reflectivity at red-light, simultaneous green and red laser emission in all-fiber Pr3+-doped ZBLAN fiber laser is obtained. Moreover, simultaneous orange and red laser emission is also achieved with another selected FM of high reflectivity at orange-light and low reflectivity at red-light. Our work will provide an effective and easy method to construct compact special fiber (e.g.,ZBLAN fiber, chalcogenide fiber) lasers.

10-m 9.51-Gb/s RGB laser diodes-based WDM underwater wireless optical communication.

The availability of the underwater wireless optical communication (UWOC) based on red (R), green (G) and blue (B) lights makes the realization of the RGB wavelength division multiplexing (WDM) UWOC system possible. By properly mixing RGB lights to form white light, the WDM UWOC system has prominent potentiality for simultaneous underwater illumination and high-speed communication. In this work, for the first time, we experimentally demonstrate a 9.51-Gb/s WDM UWOC system using a red-emitting laser diode (LD), a single-mode pigtailed green-emitting LD and a multi-mode pigtailed blue-emitting LD. By employing 32-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) modulation in the demonstration, the red-light, the green-light and the blue-light LDs successfully transmit signals with the data rates of 4.17 Gb/s, 4.17 Gb/s and 1.17 Gb/s, respectively, over a 10-m underwater channel. The corresponding bit error rates (BERs) are 2.2 × 10-3, 2.0 × 10-3 and 2.3 × 10-3, respectively, which are below the forward error correction (FEC) threshold of 3.8 × 10-3.

EFFECT OF LOW-INTENSITY RED LASER ON GROWTH OF STAPHYLOCOCCUS AUREUS AND SENSITIZING EFFECT OF PHOTODITAZIN

Study the effect of laser emission in the red spectrum on growth of methicillin- sensitive. and methicillin-resistant strains of Staphylococcus aureus, as well as photodynamic effect of photosensitizer photoditazin. Effect of light of semiconduc- tor red laser (X 660 nm, 100 mW/cm2) at 30,'60, 90 and 180 J/cm2 on growth of S. aureus colonies was determined. Time of exposure 5; 10, 15 and 30 minutes. In certain series of experiments bacterial cells were sensitized in advance by a Water. solution of photoditazin at a concentration of5xl0-6 M. Red laser emission was established to cause a pronounced suppression of bacterial growth. This effect on standard S. aureus strain only took place dur- ing use of relatively high exposure doses (180 J/cm2). Photosensitivity of methicillin-resistant strain turned out to be significantly higher: bacteriostatic effect of red light was noted already at the dose of 60 J/cm2. Treatment of bacterial cells with photoditazin in advance signifi- cantly enhanced growth-inhibiting effect of laser light.

Watt-level red-emitting diode lasers and modules for display applications

Red-emitting lasers for display applications require high output powers and a high visibility. We demonstrate diode lasers and modules in the red spectral range based on AlGaInP with optical output powers up to 1 W and a nearly diffraction limited beam. These high-luminance light sources based on tapered lasers are well suited for laser TVs and projectors for virtual reality simulators based on the flying spot technology. Additionally, we developed diode lasers with internal distributed Bragg reflector (DBR) surface gratings. These DBR tapered lasers and master-oscillator power-amplifiers based on DBR ridge-waveguide lasers and tapered amplifiers feature high power, single mode emission with coherence lengths up to several meters, which are suitable for the next-generation 3D displays based on holography.

Crystalline Waveguide Lasers in the Visible and Near-Infrared Spectral Range

This paper summarizes our recent results on crystalline waveguides and waveguide lasers fabricated by the femtosecond-laser writing technique. Highly efficient waveguide lasers emitting in the near infrared spectral range based on ytterbium and neodymium doped Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> with slope efficiencies above 70% and continuous wave output powers of more than 5 W were demonstrated. Furthermore, pulsed laser operation of passively Q-switched Yb:YAG and Nd:YAG wavequide lasers was achieved by incorporating the saturable absorber Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG in a monolithic setup. Based on fs-laser written curved structures in Yb:YAG, efficient curved waveguide lasers could be demonstrated. Also, waveguide lasers in the visible spectral range were investigated. We achieved laser emission in the green, orange, red and deep-red spectral region and could demonstrate output powers of more than 1 W with waveguides based on praseodymium doped materials. Additionally, switchable and dual wavelength operation between the orange and red laser emission was achieved. By utilizing the nonlinear crystal KTiOPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> as substrate material for fs-laser inscription, nonlinear waveguides were realized. With these devices, efficient second harmonic generation into the blue and green spectral range was achieved.

Kinetics of fluorescence properties of Eu3+ ion in strontium-aluminium-bismuth-borate glasses

Eu3+ doped strontium-aluminium-bismuth-borate glasses with the chemical composition (50–x)B2O3+20Bi2O3+7AlF3+ 8SrO+15SrF2+xEu2O3 (where x=0.1 mol.%, 0.5 mol.%, 1.0 mol.% and 1.5 mol.%) were prepared by the conventional melt quenching technique. Structural properties of the prepared glasses were analysed through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Raman spectral techniques. Thermal stability of glass was analysed by differential thermal analysis (DTA) curve. Photoluminescence characteristics were studied using excitation, emission spectra and decay curves of Eu3+ doped strontium-aluminium-bismuth-borate glasses. The Judd-Ofelt (J-O) intensity parameters, Ωλ (λ=2, 4 and 6) were obtained using emission spectra and was used to identify the nature of Eu3+ ions with their surrounding ligands. Using J-O parameters the transition probabilities (A), stimulated emission cross-sections σE p, branching ratios (βR) and radiative lifetimes (τmeas and τcal) were evaluated for the 5D0→7FJ (J=0, 1, 2, 3 and 4) transition of Eu3+ ions in the present glasses. The decay profiles were found to be non exponential for all the concentrations and the measured lifetimes (τmeas) were obtained from the decay profiles. The higher values of A, σE p, βR and quantum efficiency (η) for 5D0→7F2 emission transition at 617 nm confirmed the present glass was as active medium for red laser emission applications.

Electrically tunable organic vertical-cavity surface-emitting laser

An electrically tunable organic vertical-cavity surface-emitting laser (VCSEL) is demonstrated and characterized. A lasing wavelength tunability of Δλ = 10 nm with 6 V actuation is shown for a red laser emission tuned between λ = 637 nm and λ = 628 nm. Wavelength tuning of the VCSEL structure is enabled by electrostatic deflection of a reflective flexible membrane that is suspended over an air gap and a dielectric mirror, forming a 3λ lasing cavity. The lasing gain medium consists of an evaporated organic thin film coated on a reflective membrane, which is then additively placed over a patterned substrate containing the dielectric mirror to fabricate an array of air-gap-VCSEL structures, each 100 μm in diameter. Beyond the electrostatic actuation of these tunable lasers, the VCSEL array geometry also has the potential to be used as pressure sensors with an all-optical remote excitation and readout and a pressure sensitivity of 64 Pa/nm in the demonstrated configuration.

Multiple polarization orange and red laser emissions with Pr:BaY₂F₈.

We investigated the polarization of continuous-wave laser emission in the orange region, at 607 nm, and in the red region, at 639 nm and 643 nm, from a Pr:BaY2F8 (Pr:BYF) crystal, pumped by a 445 nm laser diode. We achieved linearly polarized emission along two optic axes of the crystal by changing its orientation with respect to the pump. Simultaneous emission of two orthogonal linear polarizations was observed in the orange region, at the same wavelength, and in the red region, with concurrent emission from the two separate lines.

Visible red, NIR and Mid-IR emission studies of Ho3+ doped Zinc Alumino Bismuth Borate glasses

Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with different concentrations of Holmium were prepared by conventional melt quenching technique. The glassy nature of these glasses has been confirmed through the XRD spectral measurements. The FTIR spectra recorded for undoped glass revealed the information related to the functional groups involved in the host glass. Optical absorption, excitation and photoluminescence spectra of these glasses have been recorded at room temperature. The Judd–Ofelt theory has been applied successfully to characterize the absorption spectra of the ZnAlBiB glasses. From this theory various radiative properties such as radiative transition probability (AR), radiative lifetimes (τR), branching ratios (βR) and spectroscopic quality factor (χ) for the prominent emission levels 5F5→5I7, 5F5→5I8 and 5I7→5I8 have been evaluated. The photoluminescence spectra revealed the quenching of luminescence intensity beyond 1.0mol% of Ho3+ ion concentration in ZnAlBiB glasses. To investigate the lasing potentiality of 5F5→5I7, 5F5→5I8 and 5I7→5I8 transitions, the effective band width (Δλp) and the stimulated emission cross-section (σse) were determined. The CIE chromaticity co-ordinates were also evaluated from the emission spectra for all the glasses to understand the suitability of these materials for visible red laser emission in principle.

Solvent-free fluidic organic dye lasers

We report on the demonstration of liquid organic dye lasers based on 9-(2-ethylhexyl)carbazole (EHCz), so-called liquid carbazole, doped with green- and red-emitting laser dyes. Both waveguide and Fabry-Perot type microcavity fluidic organic dye lasers were prepared by capillary action under solvent-free conditions. Cascade Förster-type energy transfer processes from liquid carbazole to laser dyes were employed to achieve color-variable amplified spontaneous emission and lasing. Overall, this study provides the first step towards the development of solvent-free fluidic organic semiconducting lasers and demonstrates a new kind of optoelectronic applications for liquid organic semiconductors.

Nonresonant Surface-Enhanced Raman Scattering of ZnO Quantum Dots with Au and Ag Nanoparticles

Pronounced 10(4)-fold enhancement of Raman scattering has been obtained for ZnO nanocrystals on substrates coated with 50 nm Ag nanoparticles under nonresonant excitation with a commercial red-emitting laser. This makes feasible beyond 10(-18) mole detection of ZnO nanocrystals with a commercial setup using a 0.1 mW continuous wave laser and can be purposefully used in analytical applications where conjugated nanocrystals serve as Raman markers. For Au-coated surfaces the enhancement is much lower and the heating effects in the course of Raman experiments are pronounced.