Output Characteristics Of Laser Research Articles

915 nm pumping kilowatt fiber oscillator with high optical-to-optical efficiency

We demonstrate an all-fiber oscillator with high optical-to-optical efficiency using laser diodes working at 915nm as the pump sources to reduce the demand for thermal management. When the output power of the bidirectional pumped oscillator is 1.16kW, the optical-to-optical efficiency is as high as 75.4%. In this working state, the output characteristics of the oscillator are observed. The Raman suppression ratio is 41.23dB and the beam quality factor Mx2 = 1.14, My2 = 1.29. Analyzing the time trajectory of the highest power output, there are no significant characteristic peaks in the time domain signal and the frequency domain signal, which indicates that the oscillator has good stability.Improving the output characteristics of the 915nm pumping lasers has a positive significance for the application of non-strict ambient temperature control.

Investigation on gain-managed nonlinearity in Mamyshev oscillators

Mamyshev oscillators and gain-managed nonlinear (GMN) amplifiers have the capability to generate high-power sub-50 fs pulses, but their close relationship has not been systematically investigated. In this paper, we numerically study the influence of gain-managed nonlinearity on the laser evolution and output characteristics of the Mamyshev oscillator. The impact of the gain fibre length, as well as the central wavelength and bandwidth of spectral filters on GMN evolution in the laser are investigated. The results indicate that optimizing these cavity parameters can lead to the GMN evolution, which can improve the output peak power by 1.5–4 times in Mamyshev oscillators.

Multivariate optimization effectiveness model of single-longitudinal-mode laser under pre-laser Q-switching regime.

The optimal effectiveness model for optimizing the system parameters was established in this study by combining the optimization function based on the pre-laser Q-switching technique. By introducing boundary conditions to solve the rate equations, the specific process of composite mode selection is analyzed, and the specific pre-laser modulation time interval that enables single-longitudinal-mode laser output is obtained. Furthermore, through the established efficiency evaluation function for single-longitudinal-mode laser output characteristics, with the maximization of single-pulse energy as the objective, an energy efficiency analysis of relevant parameters in the mode selection components is conducted. The model we have established is universal, which can accurately control the pre-laser Q-switching process and reveals the inherent logical relationship of the relevant parameters in composite mode selection. The output characteristics of a single-longitudinal-mode Q-switching laser can be predicted and adjusted under the condition of high pump injection. Both simulation and experimental results confirm the effectiveness of the model.

Ag/MXene as Saturable Absorber for Tm:Ho Co-Doped Q-Switched Fiber Laser.

Q-switched fiber lasers have become reliable light sources for generating high-energy pulses, which can be passively modulated by saturable absorbers with excellent nonlinear optical properties. The composite combining Ag and MXene exhibits a broadband nonlinear response and high modulation depth, making it a promising candidate for saturable absorbers in pulsed lasers. Herein, we demonstrate a Q-switched Tm:Ho co-doped fiber laser centered at 2 µm, where the Ag/MXene composite serves as a saturable absorber to generate pulses. The typical spectrum, pulse train, and radio frequency spectrum of Q-switched pulses were observed, in which the 60 dB signal-to-noise ratio was higher than that of 2 µm Q-switched fiber lasers based on other materials, demonstrating the stability of the output pulses. Additionally, the long-term stability of the laser was evaluated over 2 h, where the well-maintained central wavelength and output power also indicated the robustness of the Q-switched laser. Furthermore, the influence of the pump power on the parameters of Q-switched pulses was also investigated, which is conducive to control the output characteristics of lasers. Specifically, the pulse width of the Q-switched pulse decreased, while the repetition rate, output power, and single pulse energy all increased with the increase in pump power. These experimental results demonstrate the ability of Ag/MXene as a saturable absorber and show its potential for generating high-performance pulses in ultrafast lasers.

Efficient and accurate parameter extraction for quantum-well DFB lasers: a comprehensive approach integrating multiple mathematical models

This study proposes an efficient and accurate method for parameter extraction of quantum well distributed feedback (DFB) lasers by combining the rate equation model, finite element method, transmission matrix method, and traveling wave model (TWM). By fabricating and measuring the companion Fabry-Perot (FP) lasers, material and structural parameters common with the target DFB laser are extracted efficiently. All the intrinsic parameters of the DFB laser are accurately extracted by integrating multiple mathematical models, and the possibility of multiple solutions is avoided. From the extracted parameters, the output characteristics of the DFB laser are simulated using the TWM. The simulation results agree closely with the experimental results, proving the feasibility and accuracy of the proposed method.

Ultra low RIN, low threshold AlGaInAs/InP BH-DFB laser

This study presents a comparative analysis of DFB lasers based on AlGaInAs/InP heterostructures, exploring the impact of different groove shapes and cavity lengths on laser output characteristics. Leveraging the vertical groove structure, we achieved a remarkable laser output of 90mW at 25°C. Compared to lasers without grooves, this represents a 3.6-fold increase in output power, coupled with an impressively low threshold current of only 4mA. In addition, we conducted a study on the temperature stability of the laser, revealing that even at elevated temperatures of 85°C, the laser maintains an edge mode suppression ratio of over 45dB. This demonstrates the robustness and reliability of the laser over a wide range of operating conditions, further enhancing its suitability for practical applications in diverse environments. Upon packaging the chip into a butterfly shape, we observed a significant reduction in relative intensity noise, with values below -162.8 dB/Hz across the frequency range of 0-40 GHz, while operating at an output power of 3mW. These findings underscore the robustness, reliability, and high-performance capabilities of the developed DFB laser, highlighting its potential for various practical applications.

Design optimization of Yb-doped fiber lasers for operation in radiation environments

AbstractRadiation hardening should be considered for various active fiber systems operated in adverse environments to reduce their sensitivity to complex ionizing radiations. And, architecture optimization through numerical simulation provides an efficient choice. Here, introducing radiation effects into the conventional fiber laser model, a radiation model concerning the design optimization of low- and moderate-power Yb-doped fiber lasers is developed. And, experiments at different radiation levels up to 750 Gy are carried out for validation, demonstrating the ability of this model to correctly simulate the performance of the Yb-doped fiber laser in harsh environments. Then, with this model, impacts of active fiber length, pump scheme, and pump allocation on the output characteristics of Yb-doped fiber lasers are analyzed numerically. And, optimization of Yb-doped fiber lasers are conducted through architecture design. Simulations show that a proper design with relatively short active fiber and dynamic pump allocation can remarkably improve the radiation tolerance of Yb-doped fiber lasers.

3.73 W all-solid-state dual-wavelength Nd:Lu2O3 crystal laser

The laser output characteristics of Nd:Lu2O3 crystals were investigated in detail to obtain a dual-wavelength all-solid-state laser. Using 806 nm LD end-face pumped Nd:Lu2O3 crystals with lengths of 6 mm, a 1076 & 1080 nm laser outputs with a maximum output power of 3.73 W were obtained, with a slope efficiency of 30.4%, an optical-to-optical conversion efficiency of 28.5%, and a power stability of 0.41% for 4 h of continuous measurement. Furthermore, by suppressing the higher-order modes, a high beam quality laser output with beam quality factors of 2.092 and 1.589 in the x and y directions, respectively, and a maximum output power of 1.27 W were obtained. In addition, it was experimentally verified that both wavelengths of the output laser were elliptically polarized.

Passively Q-Switched 1.5- μm Erbium-Doped All-Fibre Laser with Silver Saturable Absorber

This research examines the operation of a passively Q-switched erbium-doped all-fibre laser (EDFL) using a silver (Ag) based saturable absorber (SA) by comparing the output characteristics of the Q-switched laser with those of continuous wave all-fibre lasers. A study was done on how the laser's Q-factor is modified and affects the rate at which pulses are repeated, as well as their output power, width, and energy. The results showed that high-energy Q-switched pulses were successfully generated at the essential 1.5 µm wavelength within the pump power range of 83.6 mW to 171.7 mW, with repetition rates ranging from 33.46 kHz to 77.96 kHz. The EDFL generated a pulse with a width of 4.033 µs and an energy of 2.82 nJ at a pump power of 171.7 mW. The results indicate that Ag may potentially be a good SA for pulse production in the 1.5 µm wavelength area as well as for use in a wide range of applications.

Measurement of radiation induced attenuation in irradiated active fibers using optical frequency domain reflectometry

Radiation induced attenuation (RIA) is a major factor affecting the performance of fiber laser systems operated in adverse environments. To investigate the output characteristics of lasers with irradiated active fibers, measurement of detailed RIA profiles is required. Here, a novel method is proposed to explore the attenuation characteristics of irradiated active fibers using optical frequency domain reflectometry (OFDR), which enables propagation loss measurement by acquiring the spatial-resolved backscattered optical signals. With this technique, the RIA data of Yb-doped fibers (YDFs) under uniform radiation is derived by linear fitting of the OFDR traces. And, conventional optical transmission (OT) method is also exploited for comparison. Analysis show that the measured results of the two approaches are consistent. Then, the capability of OFDR is further verified for non-uniform RIA profile measurement of YDFs. For a pump bleached YDF, an upward parabolic RIA profile is attained by taking derivative of the smoothed polynomial fitting of the OFDR trace. Finally, the impacts of RIA profile on the output characteristics of Yb-doped fiber lasers are examined theoretically with a multiphysics thermal model, further validating the necessity of RIA profile measurement.

Optimization of Dual-Wavelength linear cavity Erbium-Doped fiber laser based on pairs of fiber Bragg gratings

There are few reports in the field of linear cavity dual-wavelength fiber lasers about the laser output characteristics when 3-dB fiber loop mirror (FLM) and Fiber Bragg grating (FBG) are used as full reflective mirrors, respectively. Additionally, there is scarce research on further tuning of the FBG parameters (reflectivity and center wavelength interval) to study dual-wavelength fiber lasers. In this paper, we compare the performances of dual-wavelength lasing outputs between the 3-dB FLM-FBG cavity and the FBG-only cavity in a linear-cavity erbium-doped fiber laser (EDFL) based on the polarization hole burning effect. The results show that the optical signal-to-noise ratios (OSNRs) of the dual-wavelength lasing outputs with the FBG-only cavity are approximately 4 ∼ 5 dB higher than those with the 3-dB FLM-FBG cavity. Furthermore, the lasing output performances based on the FBG-only cavity are compared when the reflectivities of the output-mirror FBGs are the same or different. It is observed that the dual-wavelength laser with the same output reflectivity leads to higher OSNR, slope efficiency, and stability. Moreover, by varying the center wavelength interval of pairs of FBGs in the FBG-only cavity to values of 4 nm, 8 nm, and 12 nm respectively. It is shown that wider intervals result in higher OSNRs but lower laser slope efficiency. Finally, we demonstrate a dual- wavelength linear cavity EDFL operating at room temperature with two lasing wavelengths of 1550 nm and 1562 nm. The laser results in OSNRs around 50.62 dB and 50.93 dB; center wavelength variations of less than 0.030 nm and 0.035 nm; output power fluctuations of less than 0.061 mW and 0.059 mW, respectively.

Effects of tunable circuit parameters on pulsed discharge and input-output characteristics of a XeCl excimer laser

High-pressure, pulsed discharge-pumped XeCl excimer lasers are operating in the ultraviolet range at a wavelength of 308 nm. In this paper, a one-dimensional fluid model coupled to a magnetic pulse compression (MPC) excitation circuit and a laser gain model is established for describing the discharge and laser output characteristics of XeCl excimer lasers. The effects of the peaking capacitor (the terminal of the MPC circuit) on the discharge properties and input-output characteristics are explored. The results reveal that plays a key role in suppressing discharge pulse oscillation, which in turn influences the peak value and duration of the laser pulse. By optimizing the capacitance, a maximum excimer formation efficiency of 6.6% and a maximum laser output efficiency of 5% (output energy of 1.26 J) are obtained when , where is the storage capacitor in the MPC circuit.

Efficient and systematic parameter extraction based on rate equations by DFB equivalent circuit model.

The conventional direct parameter extraction method generally suffers from cumbersome due to redundant experiments. An efficient and systematical parameter extracting solution is proposed based on an equivalent circuit model of distributed feedback (DFB) lasers. The successfully built circuit model includes the necessary intrinsic parameters in the rate equations and the extrinsic parameters to provide a better approximation of the actual laser. This method is experimentally verified through a DFB laser chip measurement of electronic and optical performance under the same conditions. Finally, the nine intrinsic parameters in the rate equations and five extrinsic parameters in the model are efficiently extracted using this technique from a set of experimental characteristics of a DFB laser chip. Modeled and measured results for the laser output characteristics exhibit good agreement when the extracted parameters are used. The method is versatile for other semiconductor lasers that can be modeled using rate equations. Comparison with simulation results of published laser models further validates the reliability of the presented model and extraction method.

High repetition rate π-polarized 1084 nm passively Q-switched Nd:MgO:LiNbO3 laser based on 888 nm thermally boosted pumping

We report a high-repetition-rate π-polarized 1084 nm passively Q-switched (PQS) Nd:MgO:LiNbO3 (Nd:MgO:LN) laser under 888 nm thermally boosted pumping. The 888 nm pumping is selected based on Nd:MgO:LN crystal absorption and energy level properties. Under 813 nm pumping, the continuous wave (CW) 1084 nm average output power (AOP) increased to 2.85 W. After that, 1084 nm is suppressed and gradually disappears as the pump power increases. At the same time, the 1093 nm AOP increases, and 4.4 W of 1093 nm laser is obtained. In contrast, under 888 nm pumping, the CW 1084 nm laser AOP of 5.16 W is obtained. The thermally boosted pumping can eliminate quantum defects caused by conventional 813 nm pumping non-radiative transitions and suppress unmatched σ-polarized 1093 nm output. Moreover, the Cr4+: YAG is replaced into the resonant cavity as the output mirror to obtain 1084 nm pulsed laser output. AOP with different initial transmission (T0) on laser output characteristics is measured under the compact resonant cavity structure. Finally, an AOP of 3.52 W pulsed laser with a repetition rate of 24.43 kHz and the highest peak power of 5.26 kW is obtained when T0 = 87 %, and the absorbed pump power is 20.87 W. The optical conversion efficiency is 16.87 %, and the slope efficiency is about 29.38 %.

Improved two-mode dynamic model for external-cavity quantum cascade lasers under strong optical feedback

In this paper, we propose an improved model for describing the dynamical behavior and mode selection mechanism of an external-cavity quantum-cascade laser (EC-QCL) when subject to strong optical feedback. Theoretical analysis including the dynamical effective reflectivity model, two-mode rate-equation model and Lang-Kobayashi equations are employed to carry out the laser output characteristics under the multiple feedback effects. A main aspect of the model is that the excess mirror loss caused by the EC effective reflectivity is incorporated into the laser dynamical equations as a nonlinear dynamical variable. Because of accounting the multiple round-trip feedback terms in the EC effective reflectivity, the analysis is valid for the arbitrary feedback regimes from weak to strong levels. Besides the stationary characteristics, the model accurately predicts the dynamical competition between the fundamental laser-cavity mode and the desired EC mode that reflected strongly by external diffraction grating. The results are in well agreement with theoretical and experimental data reported earlier for the EC-QCLs.

2637.5 nm Mid-infrared SrWO4 Raman laser intracavity-pumped by an actively Q-switched Ho:YAG laser

We first report a 2.6 µm mid-infrared SrWO4 Raman laser, intracavity-pumped by an actively Q-switched Ho:YAG laser. The 2122 nm fundamental laser was generated from the Ho:YAG laser, which was resonantly pumped by a 1908 nm continuous wave Tm:YLF laser. Based on the stimulated Raman scattering effect of SrWO4 crystal, the fundamental wavelength of 2122 nm was converted into the Raman wavelength of 2637.5 nm, corresponding to the Raman shift of 921 cm−1. The output characteristics of SrWO4 Raman laser were investigated at various repetition frequencies. The maximum average output power was 720 mW at the 6.6 W absorbed pump power and 4 kHz repetition frequency. The maximum single pulse energy and peak power were 196 μJ and 10.9 kW at the 5.6 W absorbed pump power and 3 kHz repetition frequency, respectively. The pulse Raman laser near 2.6 µm has potential applications in material processing, spectroscopy, remote sensing, and nonlinear frequency conversion.

Influence of saturable absorber parameters on the hybrid mode-locking performance of fiber lasers

In this paper, we numerically study the influence of saturable absorber parameters, namely, modulation depth, recovery time, and saturation energy, on the performance of an ultrafast fiber laser that is mode-locked by a hybrid scheme of a saturation absorber (SA) and a nonlinear polarization rotation (NPR). Maps of mode-locked states related to intracavity wave-plates are created to evaluate the operation of hybrid mode-locking under different modulation depths of the SA. Along with the improvement of modulation depth of the SA, the mode-locked pulse results from a combination effect of the SA and NPR. The numerical analysis reveals that the SA parameters can significantly impact the pulse profile, peak power, and operation state. Moreover, they can also impact the selection of NPR mode-locked points, resulting in variation in stable single pulse output. A higher modulation depth can suppress the unstable multiple pulses’ operation and convert them into harmonic mode-locked pulses. The obtained results indicate that the selection of appropriate SA parameters can effectively improve the output characteristics of hybrid mode-locked fiber lasers.

Investigation of the multi-spectral line output characteristics of a multi-atmospheric CO2 pulsed laser

We have investigated the multi-spectral line output characteristics of a CO2 pulsed laser at multi-atmospheric pressure. The pulse waveforms, wavelengths, and energies of the output spectral lines and the small-signal gains of the full spectrum were measured at 3, 4, and 6 atm. To explain the experimental results and predict the output at higher pressure, a modified six-temperature multi-frequency dynamic model of the regular and sequence band lines was developed. The output spectrum varying from the 10P to 9R band with the increase of pressure was studied theoretically and experimentally. In addition, the gains of the 9R(16), 9P(16), 10R(16), and 10P(16) lines at 3 to 14 atm were simulated and measured, providing insights into variation regulation of the four band gains as pressure increases.

Order controllable enhanced stimulated Brillouin scattering utilizing cascaded diamond Raman conversion

We report on the design and operation of a laser, which outputs wavelengths in the 1.2 and 1.5 μm ranges by leveraging two non-linear processes of stimulated Raman scattering and stimulated Brillouin scattering in diamond. By precisely controlling characteristics of the laser resonator formed around the diamond crystal, we are able to selectively control the onset of each non-linear process so as to tailor laser output characteristics both in way of wavelength and output power. This work demonstrates the high degree of flexibility and power-handling capacity of diamond for wavelength conversion of common laser wavelengths (such as 1064 nm as used in this work) and the generation of a span of discrete wavelengths (with up to eight cascaded orders being demonstrated in this work).

The role of saturable absorbers thickness in the Q-switching of the erbium-doped fiber laser

A passively Q-switched Erbium (Er3+) doped fiber laser (EDFL) based on a ZnO saturable absorber (SA) prepared using a pulsed laser deposition (PLD) technique is demonstrated. The in-situ monitoring of the thickness in the PLD system enabled the control of the SA’s thickness during the growth. The thickness of the SA was varied and the output characteristics of the fiber laser with all thicknesses are compared. This study reveals that the performance and efficiency of an EDFL including pulse repetition rates, pulse duration, pulse energy, peak power, stability, and signal-to-noise ratio can be improved by varying the thickness of the SA. Based on the thickness of the SA, the optimized results are also presented. These findings suggest that the thickness control of the SA film grown directly on the fiber ferrule facilitates much-improved EDFL that has potential applications in pulsed laser sources.