Single-wavelength Laser Research Articles

Switchable and tunable linear cavity erbium-doped fiber laser based on FBGs embedded in Sagnac rings

A switchable and tunable erbium-doped fiber laser with a linear cavity based on fiber Bragg gratings embedded in Sagnac rings is proposed and experimentally verified. Due to the stress birefringence effect and the polarized hole burning effect, which are introduced into the single-mode fiber in the polarization controllers (PCs) by the PCs, the designed laser can achieve seven kinds of laser-states output including three kinds of single-wavelength laser states, three kinds of dual-wavelength laser states and one kind of triple-wavelength laser state. The optical signal-to-noise ratios of the output wavelengths are all higher than 52 dB, and the wavelength shifts are all less than 0.04 nm. Furthermore, the temperature tuning of the wavelength range is also researched, which is about 1.2 nm. Due to advantages, such as low cost, simple structure, easy switching and multiple laser states, the designed laser has great application potential in laser radar, optical fiber sensing and so on.

SVD-based filtering to detect intraplaque hemorrhage using single wavelength photoacoustic imaging.

.Significance: Intraplaque hemorrhage (IPH) is an important indicator of plaque vulnerability. Early detection could aid the prevention of stroke.Aim: We aim to detect IPH with single wavelength PA imaging in vivo and to improve image quality.Approach: We developed a singular value decomposition (SVD)-based filter to detect the nonstationary and stationary components in ultrasound data. A PA mask was created to detect stationary (IPH) sources. The method was tested ex vivo using phantoms and in vivo in patients.Results: The flow and IPH channels were successfully separated in the phantom data. We can also detect the PA signals from IPH and reject signals from the carotid lumen in vivo. Generalized contrast-to-noise ratio improved in both ex vivo and in vivo in US imaging.Conclusions: SVD-based filtering can successfully detect IPH using a single laser wavelength, opening up opportunities for more economical and cost-effective laser sources.

Treatment of Nevus Spilus with dual-wavelength copper vapor laser

Introduction. Speckled lentiginous nevus or Nevus Spilus (NS) is a congenital or acquired melanocytic nevus. NS appears as dark hyperpigmented macules or papules interspersed in the lentigo-like hyperpigmentation patch. Surgical methods for removing NS, primarily on the skin with a thin dermis, are associated with the risk of disruption of its structure or scarring. The use of single wavelength laser irradiation allowed achieving pronounced bleaching of the NS area with such side effects as scars, post-inflammatory hyperpigmentation, and relapses in some cases. Side effects could occur due to the lack of complete blood flow in the microvascular bed near the NS. The study aimed to evaluate the efficacy of NS treatment with a dual-wavelength copper vapor laser (CVL).
 Description of patients and the method of the treatment. Two fair-skinned adult female patients with NS, of medium size and different location, asked to restore the natural colour of the skin in order to get rid of cosmetic defects. NS treatment was carried out using CVL (Yakhroma-Med model, P.N.Lebedev Physical Institute of the Russian Academy of Sciences) during six procedures, an interval of 46weeks. For treatment, we used two-wavelength CVL radiation with average power in the range of 0.60.8W with a power ratio of 3:2 at wavelengths of 511 nm and 578 nm; exposure time: 0.20.3 s. The diameter of the light spot on the skin accounted for 1 mm. Both patients were satisfied with the result of the treatment due to the noticeable blanching of the pigmented skin area after the NS removal. During the following two years, no dark spots or scarring was observed at the NS removal site.
 Conclusion. Treatment of medium-sized NS using two-wavelength CVL radiation made it possible toeliminate the cosmetic defect without side effects.

Electric-field-assisted resonance scanning spectroscopy based on a graphene-on-silicon dual-mode microring

Mid-infrared (mid-IR) microring resonators (MRRs) have been extensively studied for biochemical sensing. However, the temperature fluctuation is an undesirable cross-sensitive effect for refractive index (RI) sensing. Here, we study an electric-field-assisted resonance scanning (EARS) spectroscopic technique based on a graphene-on-silicon dual-mode MRR to overcome this limitation. Specifically, based on the proposed method, we theoretically achieved a RI measuring error of only 2% under a temperature fluctuation of 1 K, which is improved by a factor of ten compared with a single-mode MRR. Moreover, a single-wavelength mid-IR laser is utilized in the technique, significantly simplifying the characterization setup. Also, we discuss the limit of detection and range of measurement of the EARS technique. Our study paves a promising way of developing monolithically chip-integrated mid-IR sensing devices.

Computational Three-Dimensional Imaging System via Diffraction Grating Imaging with Multiple Wavelengths.

This paper describes a computational 3-D imaging system based on diffraction grating imaging with laser sources of multiple wavelengths. It was proven that a diffraction grating imaging system works well as a 3-D imaging system in our previous studies. The diffraction grating imaging system has advantages such as no spherical aberration and a low-cost system, compared with the well-known 3-D imaging systems based on a lens array or a camera array. However, a diffraction grating imaging system still suffers from noises, artifacts, and blurring due to the diffraction nature and illumination of single wavelength lasers. In this paper, we propose a diffraction grating imaging system with multiple wavelengths to overcome these problems. The proposed imaging system can produce multiple volumes through multiple laser illuminators with different wavelengths. Integration of these volumes can reduce noises, artifacts, and blurring in grating imaging since the original signals of 3-D objects inside these volumes are integrated by our computational reconstruction method. To apply the multiple wavelength system to a diffraction grating imaging system efficiently, we analyze the effects on the system parameters such as spatial periods and parallax angles for different wavelengths. A computational 3-D imaging system based on the analysis is proposed to enhance the image quality in diffraction grating imaging. Optical experiments with three-wavelength lasers are conducted to evaluate the proposed system. The results indicate that our diffraction grating imaging system is superior to the existing method.

Microdrilled tapers to enhance optical fiber lasers for sensing

In this work, an experimental analysis of the performance of different types of quasi-randomly distributed reflectors inscribed into a single-mode fiber as a sensing mirror is presented. These artificially-controlled backscattering fiber reflectors are used in short linear cavity fiber lasers. In particular, laser emission and sensor application features are analyzed when employing optical tapered fibers, micro-drilled optical fibers and 50 μm-waist or 100 μm-waist micro-drilled tapered fibers (MDTF). Single-wavelength laser with an output power level of about 8.2 dBm and an optical signal-to-noise ratio of 45 dB were measured when employing a 50 μm-waist micro-drilled tapered optical fiber. The achieved temperature sensitivities were similar to those of FBGs; however, the strain sensitivity improved more than one order of magnitude in comparison with FBG sensors, attaining slope sensitivities as good as 18.1 pm/με when using a 50 μm-waist MDTF as distributed reflector.

Multi-wavelength tunable ring cavity fiber laser incorporated with a Mach–Zehnder interferometer filter based on waist-enlarged fiber bitapers

In this study, a multi-wavelength tunable ring cavity erbium-doped fiber laser based on an all-fiber Mach–Zehnder interferometer (MZI) is proposed and demonstrated experimentally. For the proposed fiber laser, the MZI is composed of two waist-enlarged fiber bitapers, and the free spectral range is 10.8 nm. In the experiment, the length of the gain medium erbium-doped fiber is 4 m, the laser threshold is 40 mW, and a 1556.8 nm single-wavelength laser is generated. When the pump power is 200 mW, the single-wavelength tunable laser can be tuned within the range of 1554.4–1563.5 nm by adjusting the polarization controller (PC). In addition, the wavelength spacing is less than 1.2 nm, the peak power difference is less than 1.1 dB, and the 3 dB linewidth is 0.04 nm. For the proposed fiber laser, four types of dual-wavelength lasing outputs are generated by adjusting the polarization controller, and the wavelength intervals are changed from 0.9 to 8.1 nm. The single-, dual- and triple-wavelength laser power fluctuations are less than 0.15, 0.37, and 0.53 dB, respectively, over a 20 min monitoring period.

Linear cavity erbium-doped fiber laser employing PM-PCF based Sagnac loop comb filter for wavelength tunable laser generation

A wavelength tunable linear cavity erbium-doped fiber (EDF) laser based on Sagnac loop incorporating with polarization-maintaining photonic crystal fiber (PM-PCF) was proposed and demonstrated experimentally. The Sagnac loop was composed of 0.5 m length PM-PCF, 1 × 2 optical coupler with 50:50 splitting ratio, and one polarization controller (PC). For the proposed fiber laser, the working threshold was 35 mW, the 3 m length EDF was used as gain medium, and 0.5 m length EDF was selected as saturable absorber to improve lasers stability. In the experiment, the comb filter effect was generated by Sagnac interferometer, and period was 2.52 nm. When the pump power was 150 mW, single-wavelength tunable laser output was realized within the range of 1528.73–1531.45 nm through adjusting PC, wavelength tuning interval was more than 0.58 nm, power difference was less than 3.681 dB, and signal to noise ratio (SNR) were higher than 31.101 dB. For the designed fiber laser, different groups of dual- and triple-wavelength lasers output were obtained, the power difference was lower than 7.349 and 7.724 dB, and SNR was more than 31.752 and 38.623 respectively. The single-, dual- and triple-wavelength laser stability was test within 20 min, and power and wavelength fluctuation were 3.325 dB and 0.07 nm respectively.

Triple pass laser therapy for recalcitrant facial port wine stains.

Patients with recalcitrant facial port wine stains (rfPWS) can be challenging to manage, often leaving the clinician with difficult decisions for treatment options. 'Triple therapy' consists of using three different laser wavelengths at each treatment setting. The evidence on outcomes is limited as this treatment approach has not been previously reported to the best of our knowledge. Children who received triple therapy at least once for rfPWS, and for whom SIAscopy readings had been taken, were retrospectively identified. SIAscope readings were compared before the first triple therapy treatment and at final the most recent clinical follow-up. The clinical appearance was also assessed using a Visual Analogue Scale comparing clinical photographs taken before triple therapy to those taken at the most recent clinical follow-up. A total of 47 children were identified and included in our review. The SIAscope readings showed an overall significant (p < 0.001) lightening with 39 (83%) showing lightening and 8 (17%) patients showing a darkening. Scores using the VAS also showed improvement with 55% experiencing an improvement in their clinical appearance, 38% showing no visible change and 6% appearing to have worsened. Triple therapy can offer improvement of rfPWS which have failed to respond to single wavelength laser therapy. SIAscopy and VAS scores correlate well in assessing clinical response; however, the added clinical benefit of SIAscopy in vascular laser clinics remains uncertain.

A diketopyrrolopyrrole-based conjugated polymer for efficient photodynamic and photothermal combination therapy under single 808 nm laser irradiation

Photodynamic therapy (PDT) and photothermal therapy (PTT) are two powerful tools to tackle cancer in the biomedical field due to their super tumor ablation efficiency and minimal damage to normal tissue. However, it is still a tricky challenge to combine these two treatment modalities into a single agent for single wavelength laser triggered efficient tumor therapy. Herein, water-soluble nanoparticles consisting of diketopyrrolopyrrole-based conjugated polymer and amphipathic Pluronic F127 were intelligently devised and fabricated, which possessed outstanding optical properties, superb biocompatibility, excellent photostability. Surprisingly, the nanoparticles exhibited moderate singlet oxygen yield (2.34%) and photothermal conversion efficiency (41.5%) under an 808 nm laser illumination, which was in favor of achieving high-performance PDT/PTT combination therapy. Moreover, the evident antitumor effect of the nanoparticles was confirmed by in vitro and in vivo experiments. This work provides a promising approach to rationally design near infrared absorbing organic polymer nanoplatforms for combination cancer therapy.

Tunable erbium-doped-fiber laser based on the Double-Superimposed Fiber Bragg Gratings

Multi-wavelength D-SIFBG has the advantages of small size, wavelength interval and flexible reflectivity, so it is suitable for tunable EDFL. Therefore, a single wavelength tunable EDFL based on multi-wavelength D-SIFBG is proposed. The pump source of the laser is a 980 nm semiconductor laser, and the resonator is composed of SIFBG1 with a reflectivity higher than 91% and SIFBG2 with a reflectivity higher than 87%. The gain medium is erbium-doped fiber. Based on gain equalization technology, stable single-wavelength tunable laser output is obtained at room temperature. The test results show that the 3 dB line width is less than 0.020 nm, the optical signal-to-noise ratio is more than 60.4 dB, the central wavelength shift and maximum output power fluctuation are less than 0.004 nm and 1.25 dBm respectively, and the maximum tunable range is 5.796 nm. The single-wavelength laser output from this multi-wavelength laser has good stability.

THE 308-nm EXCIMER LASER: AN XCEPTIONAL TREATMENT MODALITY IN VITILIGO- A CASE SERIES

Objective: Vitiligo is a common depigmenting condition that carries a high psychosocial morbidity and social stigma. Present treatment modalities for vitiligo like topical corticosteroids, immunomodulators, phototherapy with psoralens plus UVA radiations and broadband or narrowband UVB radiation phototherapy requires many months of treatment with not so promising results. The excimer laser comprising of a targeted phototherapy with single wavelength laser light is a new treatment option which may be time efficient and a better treatment option in terms of repigmentation in management of vitiligo.

Visualizing Synaptic Multi-Protein Patterns of Neuronal Tissue With DNA-Assisted Single-Molecule Localization Microscopy.

The development of super-resolution microscopy (SRM) has widened our understanding of biomolecular structure and function in biological materials. Imaging multiple targets within a single area would elucidate their spatial localization relative to the cell matrix and neighboring biomolecules, revealing multi-protein macromolecular structures and their functional co-dependencies. SRM methods are, however, limited to the number of suitable fluorophores that can be imaged during a single acquisition as well as the loss of antigens during antibody washing and restaining for organic dye multiplexing. We report the visualization of multiple protein targets within the pre- and postsynapse in 350–400 nm thick neuronal tissue sections using DNA-assisted single-molecule localization microscopy (SMLM). In a single labeling step, antibodies conjugated with short DNA oligonucleotides visualized multiple targets by sequential exchange of fluorophore-labeled complementary oligonucleotides present in the imaging buffer. This approach avoids potential effects on structural integrity when using multiple rounds of immunolabeling and eliminates chromatic aberration, because all targets are imaged using a single excitation laser wavelength. This method proved robust for multi-target imaging in semi-thin tissue sections with a lateral resolution better than 25 nm, paving the way toward structural cell biology with single-molecule SRM.

Folate-targeted Pluronic-chitosan nanocapsules loaded with IR780 for near-infrared fluorescence imaging and photothermal-photodynamic therapy of ovarian cancer

Herein, we report the fabrication of a nanotherapeutic platform integrating near-infrared (NIR) imaging with combined therapeutic potential through photodynamic (PDT) and photothermal therapies (PTT) and recognition functionality against ovarian cancer. Owing to its NIR fluorescence, singlet oxygen generation and heating capacity, IR780 iodide is exploited to construct a multifunctional nanosystem for single-wavelength NIR laser imaging-assisted dual-modal phototherapy. We opted for loading IR780 into polymeric Pluronic-F127-chitosan nanoformulation in order to overcome its hydrophobicity and toxicity and to allow functionalization with folic acid. The obtained nanocapsules show temperature-dependent swelling and spectroscopic behavior with favorable size distribution for cellular uptake at physiological temperatures, improved fluorescence properties and good stability. The fabricated nanocapsules can efficiently generate singlet oxygen in solution and are able to produce considerable temperature increase (46 °C) upon NIR laser irradiation. Viability assays on NIH-OVCAR-3 cells confirm the successful biocompatibilization of IR780 by encapsulating in Pluronic and chitosan polymers. NIR fluorescence imaging assays reveal the ability of folic-acid functionalized nanocapsules to serve as intracellular contrast agents and demonstrate their active targeting capacity against folate receptor expressing ovarian cancer cells (NIH-OVCAR-3). Consequently, the targeted nanocapsules show improved NIR laser induced phototherapeutic performance against NIH-OVCAR-3 cells compared to free IR780. We anticipate that this class of nanocapsules holds great promise as theranostic agents for application in image-guided dual PDT-PTT and imaging assisted surgery of ovarian cancer.

Wavelength switchable all-fiber mode-locked laser based on nonlinear multimode interference

We report a switchable single wavelength and dual-wavelength all-fiber ultrafast mode-locked lasers based on nonlinear multimode interference (NL-MMI) effect of graded-index multimode fiber (GIMF). The saturable absorber (SA) used in the laser is composed of tapered fiber-GIMF-tapered fiber. The use of tapered fibers not only reduces the dependence on the length of GIMF, but also simplifies the fabrication of SA. The modulation depth of the SA was measured to be 9%. By adjusting intra-cavity loss and the polarization controllers properly, traditional switchable single wavelength and dual-wavelength mode-locking can be realized. Meanwhile, a single wavelength harmonic soliton molecule mode-locking can be observed, and the central wavelength with the same modulation period can be switched between 1558 nm and 1531 nm. Such a switchable harmonic soliton molecules mode-locked laser with wide wavelength intervals could be useful in measuring chemical reactions, and has rarely been reported.

Single-wavelength tunable erbium-doped fiber laser based on electron beam lithography inscribed varied-period plane diffraction grating

A single-wavelength tunable erbium-doped fiber laser based on varied-period plane diffraction grating for angle sensing measurement was proposed and experimentally demonstrated; the designed grating was fabricated through line-by-line electron beam lithography (EBL) and reactive ion etching. The proposed grating was used as fiber laser wavelength selector, and its line density was varied from 950 to 590 L/mm over the device, according to the designed linear density function, and the device was coated with an aluminized surface. Two ports of 3 dB fiber coupler were used to connect the grating and an optical spectrum analyzer respectively. The inscribed grating length and width were 80 × 10 mm. For the proposed fiber laser, the working threshold was 130 mW, as the incident light angle was increased from 20 to 22.5° in 0.5°, the single-wavelength laser shifted from 1529.47 to 1532.99 nm, and angle sensitivity to be 1.42 nm/° with linearity of 0.998. The laser 3 dB linewidth was less than 0.05 nm and SNR was more than 16.28 dB. During 10 min of monitoring, the laser power fluctuation was less than 0.928 dB.

Three-wavelength optical sensor for measuring distributed mass concentrations of aerosols from stationary sources.

Stationary source emissions of key industries, such as thermal power plants, have become the central consideration in environmental protection programs. Existing photoelectric sensors at stationary sources usually use a single wavelength laser to measure the total mass concentration of the particulate matter, bearing inherent errors due to the changing particle size distribution (PSD). However, the total mass concentration cannot comprehensively estimate the air pollution caused by the stationary sources. Therefore, it is required to measure both the mass concentration and PSD of the aerosols emitted by the stationary sources, based on which we can get a distributed mass concentration. To implement this, in this study, we designed a novel three-wavelength photoelectric sensor and tested its performance. Results showed that the prototype correctly determines the mean particle size and standard deviation of the PSDs and consequently adjusts the coefficient for measuring the mass concentration from light intensity, providing a comprehensive assessment of the pollutants.

Raman Spectra of SF6Decomposed Characteristic Products Based on Density Functional Theory

SF6decomposition product analysis is one of the most convenient and efficient methods to diagnose the potential faults of SF6insulated electric equipment in the early stage. Based on SF6decomposition characteristic gas analysis, the operation state of SF6insulated power equipment can be judged by on-line monitoring, so as to ensure its normal operation. Raman spectrum analysis technology can realize the nondestructive detection of gas samples with a single wavelength laser. It has excellent applicability and high efficiency for the detection of SF6decomposition characteristic components. In this paper, molecular configurations of CF4, CO, H2S, SO2were obtained by B3LYP functional that based on density functional theory (DFT), and the Raman frequency and intensity characteristics were calculated by 6-31G (2df, p) basis group. The results were compared with National Institute of Standards and Technology (NIST) standard frequencies and it was found that the optimized configuration has no virtual frequency. The characteristic peaks of CO, CF4, SO2and H2S that were identified by Raman spectrum are respectively 2221.11, 908.97, 1175.24 and 2688.82 cm-1, which are basically consistent with the corresponding NIST standard values. This study not only shows that the Raman spectrum of SF6decomposition products calculated by B3LYP functional function is reliable, but provides a reference for the quantitative detection of SF6decomposition products based on Raman spectrum.

Gold nanoparticle-based nanoprobes with enhanced tumor targeting and photothermal/photodynamic response for therapy of osteosarcoma

AbastractPlasmonic nanomaterials, especially a wide variety of gold nanoparticles, demonstrate great potential for theranostics of cancer. Herein, a gold nanotriangle with CD133 and hyaluronic acid on its surface loaded with a near-infrared photosensitizer was prepared for enhanced photodynamic/photothermal combined anti-tumor therapy. CD133 and hyaluronic acid provide the nanoprobe with dual tumor targeting, while the hyaluronic acid also protects photosensitive drugs from photodegradation. Thus, the nanoprobe has enhanced photothermal/photodynamic effects. This integrated treatment strategy significantly enhanced photodynamic/photothermal destruction of osteosarcoma cells. In addition, this treatment, induced by mild irradiation with a single wavelength laser, inhibited tumor growth in an osteosarcoma mouse model. These results indicate that this systemic treatment strategy can achieve enhanced anti-tumor therapeutic effects through active tumor targeting and protection of the loaded drugs.

Diode-pumped wavelength-switchable visible Pr&lt;sup&gt;3+&lt;/sup&gt;:YLF laser and vortex laser around 670 nm

Here we developed a novel wavelength-switchable visible continuous-wave (CW) Pr³⁺:YLF laser around 670 nm. In single-wavelength laser operations, the maximum output powers of 2.60 W, 1.26 W, and 0.21 W, the maximum slope efficiencies of 34.7%, 27.3%, and 12.3% were achieved with good beam qualities (<italic>M</italic>² &lt; 1.6) at 670.4 nm, 674.2 nm, and 678.9 nm, respectively. Record-high output power (2.6 W) and record-high slope efficiency (34.7%) were achieved for the Pr³⁺:YLF laser operation at 670.4 nm. This is also the first demonstration of longer-wavelength peaks beyond 670 nm in the ³P₁→³F₃ transition of Pr³⁺:YLF. In multi-wavelength laser operations, the dual-wavelength lasings, including 670.1/674.8 nm, 670.1/679.1 nm, and 675.0/679.4 nm, were obtained by fine adjustment of one/two etalons within the cavity. Furthermore, the triple-wavelength lasings, e.g. 672.2/674.2/678.6 nm and 670.4/674.8/679.4 nm, were successfully demonstrated. Moreover, both the first-order vortex lasers (LG₀⁺¹ and LG₀^-1 modes) at 670.4 nm were obtained by off-axis pumping.