Saturation Intensity Research Articles

Plasmonic gold-enhanced GaAs for femtosecond laser generation

Surface plasmon resonance (SPR) can significantly enhance the local electromagnetic fields, facilitating the interaction between light and matter at the nanoscale. However, its ultrafast photonics application in lasers remains unexplored, especially for femtosecond pulsed laser generation. In this work, we investigate the femtosecond pulse generation based on SPR-enhanced nonlinear absorption characteristics in GaAs for the first time, to the best of our knowledge. The gold nanoparticles (GNPs)+GaAs bilayer saturation absorber (SA) decorated on the tapered fiber generates a modulation depth of 2.02% and a saturable intensity of 3.13 MW/cm2. Stable mode-locked pulses can be obtained in an erbium-doped fiber cavity, as demonstrated here. The signal-to-noise ratio (SNR) of the pulses is 75 dB and the shortest pulse duration can reach 384 fs, highlighting the potential of the SPR effect in manufacturing ultrafast optical devices.

Optical spectroscopy of Nd3+-doped cadmium-rich borate glasses for near-infrared laser applications

AbstractThe structural and spectroscopic properties of Nd3+-activated cadmium-rich borate (inverted) glasses are analyzed for near-infrared laser applications. The evaluation of the optimal glass-emitting sample by the Judd–Ofelt (JO) theory revealed JO parameter values of 4.56 × 10–20 cm2 (Ω2), 2.56 × 10–20 cm2 (Ω4), and 3.84 × 10–20 cm2 (Ω6). The Ω2 value, along with the experimental oscillator strength, suggested that the cadmium-rich borate glass could provide a more asymmetrical Nd3+ environment than other borate glasses like lithium-strontium-zinc, sodium-calcium, and lithium-lead-aluminum. In addition, the quality spectroscopy factor (χ = Ω4/Ω6) of 0.67 suggested that the 4F3/2 → 4I11/2 emission could be more suitable for laser applications. The stimulated emission cross-section (σp), theoretical quantum yield (ηQ), gain bandwidth (σp × Δλem), and optical gain (σp × τrad) laser parameters were close to those reported in sodium-calcium-borate, zinc-aluminum-barium-borate, and bismuth-borate glasses, while the non-radiative rate (WNR) and emission intensity saturation (IS) resulted to be lower. The emission spectra, under 808 nm laser excitation, displayed the featured neodymium 4F3/2 → 4I9/2,11/2,13/2 transitions, being the 4F3/2 → 4I11/2 (1058 nm) transition the more dominant one, in agreement with the χ parameter value. Nd3+ contents higher than 1.4 mol% led to emission quenching due to the increment of the cross-relaxation and/or energy migration rate. Such processes, according to the Inokuti–Hirayama model, were mainly mediated by electric dipole–dipole interactions within Nd–Nd clusters.

Para-phenylenediamine Schiff base: highly fluorescent photostable solid-state organic dye

Schiff bases derived from the condensation of primary amines with aldehydes, such as para-phenylenediamine with salicylaldehyde, exhibit unique optical and structural properties ideal for photonic applications. This study synthesizes such a Schiff base, revealing its properties through detailed HNMR1, FTIR, and XRD characterizations. The compound forms a robust π-conjugated structure, showing a fluorescence emission peak at 560 nm and significant absorbance at 380 nm. A spin-coated laser cavity displayed a critical lasing threshold at 1 MW·cm−2, which could be optimized down to 0.6 kW·cm−2. Moreover, the compounds’ acceptor-donor-acceptor configuration raised outstanding nonlinear optical properties, including a substantial two-photon absorption cross-section of 2×10−11 cm ⋅ W−1·GM, enhancing its utility in high-resolution two-photon imaging and advanced photonic applications. Other nonlinear optical characteristics determined during these studies are the saturable absorption-induced nonlinear absorption coefficient (−2×10−11 cm ⋅ W−1), saturation intensity (2.5×1011 W·cm−2), and Kerr-induced nonlinear refractive index (5×10−16 cm2 ⋅ W−1). The combined linear and nonlinear optical properties, supported by sustained emission and minimal photobleaching under intense re-excitation, establish the para-phenylenediamine Schiff base and derivatives as promising materials for high-brightness, photostable organic light emitters, and solid-state lasers.

Spirometry Results in Children over Five Years Old with COVID-19 at Least Six Months after Discharge

Introduction: Since it is necessary to detect changes in lung function for the follow-up of the patients with respiratory and functional complications caused by COVID-19, in this study, we decided to examine the results of spirometry in children over 5 years old with Covid-19. Methods: In this cross-sectional study, 52 over-five-year-old children, hospitalized due to COVID-19 for at least six past months, were examined. The participants’ demographic information, respiratory symptoms, underlying diseases, severity of COVID-19 according to WHO, severity of lung involvement in CT scan, type of lung involvement, oxygen saturation at admission as well as FEV1, FVC, and FEV1/FVC were collected and analyzed, the results were analyzed using SPSS version 16 software and t-test and Chi-square tests. Results: Of all investigated patients،, 26 were boys (50%) and 38 (73.1%) were 5-12 years old. The minimum age of the children was 5 years and the maximum was 18 years. The mean age of children was 3.41±10 years. The FEV1/FVC ranged from 61% to 79% in five patients (9.6%) and from 80% to 100% in 47 patients (90.4%). The FEV1 was lower than 80% in 28 and higher than 80% in 24 patients. FEV1/FVC had no significant relationship with the participants’ age, gender, clinical manifestations, and disease severity in terms of pulmonary involvement, but it had a significant association with blood oxygen saturation level (P: 0.001). Conclusion: The changes in pulmonary function tests vary in different months following contamination with COVID-19. In the present study, 9% of the patients, who were examined in the sixth month after infection, had abnormal pulmonary function test results. Based on the findings, the pulmonary function test results had no significant relationship with the patients’ age, gender, and clinical symptoms, while it was significantly associated with their blood oxygen saturation intensity.

Mode-locked soliton pulse generation using copper phthalocyanine absorber in long erbium-doped fibre laser cavity

We present the development of a mode-locked erbium-doped fibre laser (EDFL) utilizing Copper Phthalocyanine (CuPc) as a saturable absorber (SA). CuPc exhibits unique optical properties, including its high nonlinear optical response and rapid recovery time. To seamlessly integrate CuPc into the laser cavity, we employed a simple embedding technique within a polymer film. The SA demonstrates a modulation depth of 3.1% and a saturation intensity of 17 MW/cm2. Operating within a pump power range of 90.6 to 122.9 mW, the laser achieves mode-locked operation, producing a soliton pulse train with a fundamental frequency of 1.82 MHz and a pulse width of 6.4 ps at a wavelength of 1561.5 nm. It attains a maximum output power of 13.97 mW and a pulse energy of 7.67 nJ. These results underscore CuPc's potential as a promising material for generating mode-locked pulses, suggesting new avenues in ultrafast laser development for diverse applications.

A spatial hue smartphone-based colorimetric detection and discrimination of carmine and carminic acid in food products based on differential adsorptivity

A novel, portable, disposable, affordable, and environmentally friendly paper-based analytical device (PAD) was designed for on-site determination of carmine and carminic acid. This platform utilized paper test strips with a chitosan coating as an adsorption layer, which was characterized using scanning electron microscope, energy-dispersive X-ray analysis, and water contact angle measurement. Carmine and carminic acid could be efficiently adsorbed on chitosan-coated paper test strips, producing distinct colors that could be captured using a smartphone camera without the need for an elution step. Notably, by utilizing the Hue component of the HSL model, it was possible to differentiate between carmine and carminic acid, confirming their presence in a sample. Furthermore, the color saturation intensity changed in a concentration-dependent manner, allowing for the determination of carmine and carminic acid concentrations in the ranges of 200–800 μg/mL and 20–100 μg/mL, respectively. Additionally, the created test strip could be used to measure the percentage of carminic acid in the presence of carmine. The developed PAD enabled the quantification of carmine in various food samples without the need for reagents or complex equipment. The environmental impact of this method was found to be positive based on assessments using GAPI and AGREE tools.

Observation of terahertz nonlinear absorption activity in Al2O3

We investigate the terahertz (THz) nonlinear absorption characteristics in a thin Al2O3 crystal using nonlinear THz spectroscopy. A THz saturable absorption performance with a high modulation depth (27.5%) and a relatively low saturable intensity (6.99 µJ/cm2) of Al2O3 is revealed, covering the THz spectrum from 0.1 to 8 THz. The inevitable presence of oxygen vacancies and impurities in Al2O3 single crystal results in the existence of free electrons within the conduction band. The transmission enhancement can be described by the change of the mobility of electrons due to intervalley scattering induced by THz pulses, based on first-principles calculations. Therefore, Al2O3 crystals have promising application potential in mode-locked devices for directly delivering broadband ultrashort THz pulses.

Passively mode-locking fiber laser based on Cr2Si2Te6 saturable absorber

This paper reports on the generation of third-order harmonic mode-locking, double-pulse phenomena, and conventional solitons in an erbium-doped fiber laser using Cr2Si2Te6 as a saturable absorber (SA). The double-balance probing method was employed to examine the nonlinear characteristics of Cr2Si2Te6-SA. Its modulation depth is 2.35 %, and its saturation intensity is 29.74 MW/cm2. We discovered conventional soliton functioning with a center wavelength of 1561.8 nm at a pump power of 34.76 mW. It has a repetition frequency of 6.76 MHz and a signal-to-noise ratio of 45 dB. As the pump power increased, the traditional soliton was able to maintain its existence in the range of 34.76 mW to 80.96 mW. The maximum output power reaches 1.1 mW when the pump power is 80.96 mW, and the maximum single-pulse energy of the conventional soliton is 0.16 nJ. Furthermore, we observed third-order harmonic mode-locking and double-pulse phenomena at pump outputs of 53.65 mW and 71.16 mW. The experimental findings demonstrate the excellent nonlinear effect of the SA based on Cr2Si2Te6. In ultrashort-pulse fiber lasers, Cr2Si2Te6 nanosheets can be employed as an efficient saturable absorption material.

Passively mode‐locked Tm:YAP laser with a V2AlC saturable absorber

AbstractIn this work, a V2AlC‐based saturable absorber (SA) was applied to a 2 μm band passively mode‐locked (PML) laser. The saturation intensity and modulation depth of the V2AlC‐based SA were detected by the I‐scan method, which were 225.05 MW/cm2 and 7.68%, respectively. In the PML mode, an average power of 2.12 W at 1939 nm and a pulse width of 1077 ps at 82.49 MHz were obtained from the Tm:YAP laser. In addition, the laser exhibited a good beam quality factor (M2) which was measured to be less than 1.2. These results will pave the way for the application of V2AlC‐based SA in ultrafast lasers.

Continuous harmonic mode-locked pulsed ultrafast fiber laser based on PtS2 saturable absorber

Saturable absorbers (SAs) play an important role in mode-locked fiber lasers. The search for SAs with excellent modulation properties has become a hot topic in the field of ultrafast photonics. PtS2 is a ideal material for SA due to its suitable band gap and Easily peelable layer structure. We prepared PtS2-SA by liquid-phase exfoliation (LPE) and tapered fiber. Subsequently, we measured the modulation depth of the prepared SA using the two-arm detection method as 6.4%, and the saturation intensity is 4.5 MW/cm2. By varying the input power in the annular cavity, a conventional solitons (CS) with a center wavelength is 1530.3 nm and a repetition frequency of 6.1 MHz was obtained. Continuing to increase the power, a stable second-fourth orders harmonic mode-locked (HML) was obtained. Our work shows that PtS2-SA has excellent modulation in mode-locked fiber lasers. It also proves that PtS2 has good saturable absorption properties and improves the knowledge of research workers about the performance of PtS2. There is hope in future research work to further exploit the output properties of PtS2.

Effect of dephasing on modulation transfer in potassium

In this work, experimental studies on the effect of dephasing on modulation transfer are reported. Here Potassium D1 transition, i.e., 39K 4S1/2(F) → 4P1/2(F/), is used as the medium. The 4 S→4P connection is modified by introducing two independent lasers. The separation between ground hyperfine states 4S1/2(F = 2,1) is almost half of Doppler width (~ 815 MHz). Hence, the two-level connections satisfied by respective lasers are overlapping in nature. In such cases, the existing optical pumping for particular F = 1, 2→ F/ channel influences each other. Further, the D1 transition itself is an open transition, i.e., it does not have any cyclic decay route. Hence, decay from each of the F/=2,1 states can also influence the population in the other F/state. Our pump-probe spectroscopy results clearly show the presence of Four Wave Mixing due to degenerate two-level and Vee (V) coupling, Electromagnetically Induced Transparency (EIT) signals due to single Lambda (Λ) and Double Λ connections. We have studied these signals as a function of dephasing, which is mainly contributed by transit time broadening for two different regimes of pump laser intensities: (i) below and (ii) above saturation intensity level of 4S1/2(F) → 4P1/2(F/) transition. The pump laser is current modulated, and phase-sensitive detection is performed on the probe transmission to study modulation transfer under different values of coherent dephasing. For this purpose, the beam size of the pump laser is varied systematically. This study provides a scope to explore the modulation transfer as a function of transit time broadening, and it may find applications in photonics technology where potassium vapor is used as a medium.

Large-energy operation of an Er-doped fiber laser with ZrGeTe4 saturable absorber

ZrGeTe4 as a layered semiconductor material with good stability and optoelectronic properties, and excellent saturable absorption characteristics, but its application in fiber lasers is still insufficient. In order to explore its application in fiber lasers, we prepared ZrGeTe4-PVA thin film by liquid phase exfoliation and performed a series of characterizations. A modulation depth of 13.15 %, a non-saturated loss of 6.4 %, and a saturation intensity of 5.5 MW/cm2 were obtained. Then used the ZrGeTe4-PVA thin film as the saturable absorber (SA) in an Er-doped fiber laser (EDFL), the large-energy operation could be realized. In the case of a cavity length of 234 m, when the pump power was increased to 1229 mW, a maximum single pulse energy of about 32.72 nJ was achieved, with a repetition frequency of 859 kHz. To the best of our knowledge, this is the highest single-pulse energy achieved in an EDFL based on ZrGeTe4-SA. This experiment shows that the ZrGeTe4 is a promising two-dimensional (2D) material with good nonlinear absorption properties, proving that it is a promising pulse modulation of SA and laying a foundation for its subsequent study in fiber lasers.

Optimization of polarization spectroscopy signal for laser-frequency stabilization

Abstract We experimentally generate polarization spectroscopy (error) signals corresponding to the D2-line hyperfine transitions, F g = 2 → F e = 1 , 2 , 3 of 87Rb, and F g = 3 → F e = 2 , 3 , 4 of 85Rb, and show that the strongest error signals correspond to the closed hyperfine transitions (oscillator strength ∼ 0.7 ), F g = 2 → F e = 3 and F g = 3 → F e = 4 , respectively. We make the generated error signal robust to fluctuations in external parameters by finding optimum values for the vapor cell temperature and pump-probe intensities at two different beam diameters. We further employ these optimized error signals to directly (without the need for frequency/phase modulation) lock the laser frequency—reducing the rms drift/linewidth from ∼ 10 MHz to < 500 kHz, when measured over a ∼ 60 min duration. In addition, by comparing theoretically calculated and experimentally measured error signals for the pump intensities ranging from ∼ 0.1 I sat 0 − 10 I sat 0 (where, I sat 0 ∼ 1.6 mW cm−2 is the two-level saturation intensity for the Rb D2-line transitions), we discuss the applicability and limitations of existing numerical and analytical approaches based on a full multi-level rate equation model for polarization spectroscopy.

Effect of morphology on the optical limiting of BiVO4 films

Precise control over the morphology and crystal structure of semiconductor-based optical materials is essential for optimizing their nonlinear optical properties. Morphological factors significantly affect the material’s interaction with light, influencing nonlinear absorption, harmonic generation, and optical confinement. In this study, the nonlinear optical (NLO) properties and optical limiting (OL) performance of bismuth vanadate (BiVO4) films depending on precursor solution pH condition, powder morphology and weight percentage of the BiVO4 powders in PMMA (10–30 wt.%) were investigated. The BiVO4 powders were synthesized via the hydrothermal method and the effect of precursor solution pH (pH of 1, 7.5 and 12) was investigated on the size and morphology of the BiVO4 powders. BiVO4 films were prepared using the spin coating method utilizing the BiVO4 powders and PMMA. The bandgap values of films were found to change from 3.39 to 3.56 eV depending on the BiVO4 growth solution pH. The nonlinear absorption coefficients (βeff), saturation intensity thresholds (ISAT) and optical limiting (OL) threshold were obtained using the open aperture (OA) Z-scan experiment. It has been observed that the nonlinear absorption and optical limitation performance of the BiVO4 films can be altered by changing the powder morphology and BiVO4 weight concentration. BiVO4 thin films fabricated using a precursor solution pH 12 and weight concentration of 30 wt.% showed the best performance among all fabricated films with the highest nonlinear absorption coefficient (βeff), saturation density threshold (ISAT) and lowest OL threshold value.

Interlayer engineered bilayered V₂O₅ NPs as saturable absorbers for infrared ultrashort pulse generation

Interlayer engineering offers a promising approach to modifying the structure of layered vanadium-based oxides, enhancing their saturable absorption effect and making them a desirable choice for developing infrared wavelength-range photonics devices. This experimental work synthesizes interlayer vanadium pentoxide (V2O5) using hydrothermal techniques to produce an excellent saturable absorber (SA). The interlayer engineering strategy enhances strong saturable absorption and self-defocusing effects in V2O5-based SA, enabling the generation of ultrashort pulses in the infrared region. Their superior nonlinear optical characteristics are demonstrated by a modulation depth of 13.9 % and saturation intensity of 0.42 GW cm−1, respectively. By utilizing a transmission coupling fiber-based V2O5-SA inside an Er-doped fiber laser cavity, a passively Q-switched (PQS) laser with a narrow pulse width of 2.78 μs and signal-to-noise ratio (SNR) ∼50 dB is realized for the first time. Furthermore, we explore a V2O5 NPs-SA long-term stability and high damage threshold. The results not only offer additional proof of the capable potential of interlayer V2O5 as a photo-bleaching absorber for realizing pulsed lasers in the NIR band but also cover the method for advancing their probable applications in optoelectronic devices.

One-step synthesis of superparamagnetic copper alginate gel microspheres (Cu2+-Alg@Fe3O4) using a compression nebulizer

For the application needs of histidine-rich protein separation, this study proposes to prepare a magnetic adsorbent enriched with copper ions and small particle size. Using a compression nebulizer, the magnetic + sodium alginate solution was broken into micrometer-sized droplets and cross-linked and cured with copper ion solution. The magnetic copper alginate microspheres (Cu2+-Alg@Fe3O4) were obtained with an average particle size of 7.1 μm, a magnetic saturation intensity of 36.9 emu·g−1, and a Cu2+ content of 149.2 mg·g−1.The adsorption equilibrium time of the Cu2+-Alg@Fe3O4 microspheres on bovine hemoglobin(BHb) was 90 min, and the maximum adsorption amount was 4318.5 mg·g−1. The Cu2+-Alg@Fe3O4 microspheres also showed stable and good adsorption performance in five cyclic adsorption experiments.

Semi-metallic PtTe2 nanosheets are used as saturable absorbers to generate passive mode-locked pulse laser in the 2 μm band

In passively modulated pulse lasers, the highly stable saturable absorber (SA) used to generate passive pulsed lasers is a necessary core device. In this paper, layered PtTe2 nanosheets were fabricated using a simple, efficient, and low-cost liquid phase exfoliation (LPE) method, and PtTe2-SA devices were prepared by spin coating. Nonlinear optical tests show that the layered PtTe2 nanosheets have good nonlinear saturable absorption characteristics in the 2 μm band, with a modulation depth of 8.2 %, a saturated light intensity of 3.72 MW/cm2, and a non-saturated loss of 9.8 %. We introduced PtTe2-SA devices into Tm3+ doped solid-state laser for the first time, achieving passive mode-locking (PML) operations. In PML operation, a short pulse output of 670.8 ps was achieved. After being exposed to the air for 20 days, it can still produce good pulse output under the same experimental device. The results show that semi-metallic PtTe2 is expected to become a highly stable SA candidate material for pulsed solid-state lasers, which can be used to generate short pulse output in the 2 μm band, providing huge production power in many fields.

Few-layer NbTe2 nanosheets-based saturable absorber for generating 176 fs pulse at 1 μm in ultrafast fiber laser

Ultrafast fiber lasers play an increasingly vital role in diverse fields of science and industry. In this study, a novel NbTe2 nanosheet-based saturable absorber (SA) was prepared by using liquid phase exfoliation and flame brush technology for the first time. Using a twin balance measurement system, the nonlinear optical absorption property was checked. It was found that the fabricated NbTe2 nanosheets-based SA has excellent saturable absorption properties with a large modulation depth of 5.3 %, a very high saturation intensity of 1.11 GW/cm2, and a low non-saturation loss of 63.6 %. After inserting the NbTe2 nanosheets-based SA into a ring-cavity ytterbium-doped fiber laser (YDFL), a stable soliton mode-locking state was achieved. A 176-fs ultrafast soliton pulse train was successfully generated at 1029.76 nm with the repetition rater of 3.097 MHz. Thanks to the unique and very high saturation intensity of NbTe2 nanosheets, the proposed YDFL system achieved a maximum peak power of 96.3 kW and a single pulse energy of 14.09 nJ under 370 mW pump power. These findings indicate that NbTe2 nanosheets have great potential for generating ultra-short optical pulses with higher peak power in mode-locked fiber lasers.

High average power passively Q-switched 2-μm laser with Mo0.5W0.5S2 as a saturable absorber

Two-dimensional transition metal dichalcogenides (TMDs) with remarkable nonlinear properties, like MoS2/WS2 and the ternary compound Mo0.5W0.5S2, have attracted a lot of attention. The field has made use of the nonlinear characteristics of all-solid-state lasers. The liquid-phase exfoliation method was used in this work to create Mo0.5W0.5S2 nanosheets. At 2 μm, the nonlinear absorption characteristics of Mo0.5W0.5S2 were examined and the results showed a saturation intensity of 1.56 MW/cm2 and a modulation depth of 5.2%. A high-power passively Q-switched Tm:YAP laser with an average output power of 3.20 W and a brief pulse width of 633 ns was produced using the Mo0.5W0.5S2 nanosheet as a saturable absorber. According to the results, Mo0.5W0.5S2 has the potential to produce pulsed lasers with high peak and average powers that operate at about 2 μm.

Instant in situ highlighting of latent fingerprints by a green fluorescent probe based on aggregation-induced emission

Fluorescence sensing of latent fingerprints (LFPs) has gained extensive attention due to its high sensitivity, non-destructive testing, low biotoxicity, ease of operation, and the potential for in situ visualization. However, the realization of in situ visualization of LFPs especially with green emission and rapid speed is still a challenge. Herein, we synthesized an amphibious green-emission AIE-gen TPE–NI–AOH (PLQY = 62%) for instant in situ LFP detecting, which integrates the excellent fluorescence properties of naphthalimide (NI) with a hydrophilic head and the AIE character as well as the donating property of tetraphenylethene (TPE). TPE–NI–AOH in ethanol/water binary solvent was used as an environmentally friendly LFP developer and achieved in situ green-fluorescence visualization of LFPs. The fluorescence signal achieves its 60% saturated intensity in 0.37 s and nearly 100% in 2.50 s, which is an instant process for the naked eye. Moreover, level 3 details and super-resolution images of LFPs could be observed clearly. Besides, the TPE–NI–AOH developer could be stored for at least 6 months, suitable for long-term storage. This instant in situ highlighting method does not require post-processing operations, providing a more convenient, rapid, and efficient detection method of LFPs. This work would inspire the further advancement of fluorescent sensors for fingerprint imaging.