Laser Output Wavelength Research Articles

MHz sampling rate measurements of N2(A3Σu+) population in a Ns pulse discharge in a heated plasma flow reactor

Abstract Absolute, time-resolved population of a metastable electronic state of molecular nitrogen, N2( A 3 Σ u + , v = 0 ), is measured in a heated plasma flow reactor excited by a ns pulse discharge burst, by tunable diode laser absorption spectroscopy using a distributed feedback laser. Nitrogen or NO–N2 gas mixture in the reactor are heated by a tube furnace maintained at T = 800–1000 K, at pressures of P = 50–300 Torr. A diffuse plasma in the flow channel made of quartz is generated using a repetitively pulsed, double dielectric barrier, ns discharge in a plane-to-plane geometry. N2( A 3 Σ u + ) molecules in the plasma are generated by electron impact excitation of N2 ( B 3 Π g ) and N2 ( C 3 Π u ) states, followed by their cascade quenching. The laser is tuned across an absorption line near 1028 nm in a N2 B 3 Π g , v ′ = 0 ← A 3 Σ u + , v ′ ′ = 0 band at 100 kHz–1 MHz. The laser output wavelength and the absorption signal are measured by an etalon and two high bandwidth detectors. At all operating conditions, the absorption signal is fully resolved in time. The data points are taken every 500 ns–5 μs, with the temporal uncertainty of 50–500 ns, respectively. The data are used to infer the line pressure broadening coefficient and its temperature dependence. This study demonstrates the feasibility of this approach for the time-resolved N2( A 3 Σ u + ) measurements in pulsed hypersonic flow facilities, behind strong shock waves and in hypervelocity expansion flows.

K0.9Rb2.1B8PO16: Design and Synthesis of a Deep-Ultraviolet Nonlinear Optical Crystal with Balanced Performance Derived from π-Conjugated and Non-π-Conjugated Groups.

A new deep-ultraviolet (DUV) nonlinear optical (NLO) material K0.9Rb2.1B8PO16 (KRBPO) has been designed and synthesized by adjusting the B/P molar ratio to 8:1. The KRBPO crystals were synthesized by a flux method and crystallized in noncentrosymmetric (NCS) and polar space group Cc. This compound exhibits a double-layer structure in which the A layer is composed of [B2O5] and [BO4] units and the B layer is formed by interconnected [B3O7] and [BO3] groups, and the two layers are connected by [PO4] tetrahedron. The theoretical calculations and experiments show that the synergistic interaction of π-conjugated and non-π-conjugated units leads to relatively well-balanced NLO properties of the title compound, including moderated SHG (0.7 × KDP), short UV cutoff edge (λcutoff < 190 nm), and a large band gap of 6.16 eV. Specifically, the coplanar arrangement of B-O groups in double-layer makes the KRBPO display a large birefringence (0.075@532 nm) and enables the shortest phase-matched wavelength to reach an important laser output wavelength of 266 nm.

Simultaneous measurement of 13C-,18O-, and 17O- isotopes of CO2 using a compact mid-infrared hollow waveguide gas sensor

A compact gas sensor has been developed for the first time employing a quantum cascade laser (QCL) with a central wavelength of 4.32 μm, combined with direct absorption spectroscopy technology and a hollow waveguide. The sensor could measure the concentrations of four isotopic molecules (16O12C16O, 18O12C16O, 16O13C16O, and 17O12C16O) in CO2 gas simultaneously, thereby obtaining the relative isotope ratios of δ13C, δ18O, and δ17O. By adjusting the incident light path, the anomalous absorption peaks in the system have been effectively suppressed, and a compact feedback function generator has been integrated to ensure control of the laser output wavelength to eliminate the loss of measurement precision caused by wavelength fluctuations. Under the two conditions of free-running and wavelength-controlled, a standard CO2 sample with a concentration of 5 % was measured continuously. The results showed that under wavelength-controlled conditions, the precision of the four isotopic molecule concentration measurements was improved by a minimum of 1.8 times, and the measurement precision could be further improved after filtering. According to the Allan variance analysis, the detection precision for δ13C, δ18O, and δ17O were 0.7 ‰, 0.62 ‰, and 1.58 ‰, respectively, at the optimal integration time of 98 seconds. This study has the potential for respiratory diagnosis to detect simultaneously the values of δ13C, δ18O, and δ17O in exhaled samples.

CH3NH3PbBr3 as a saturable absorber for infrared passively Q-switched solid-state laser

Perovskite materials are used in the field of lasers and can achieved good results. In this paper, we prepared an organic–inorganic hybridized CH3NH3PbBr3 saturable absorber (SA). Continuous wave (CW) Tm:YAP solid-state lasers with CH3NH3PbBr3-SA successfully obtained pulsed lasing at 1987.5 nm after continuous tuning. In CW mode, the maximum absorbed pump power by the laser was 19.42 W, which corresponds to 0.68 W output power. The central output wavelength of the continuous wave laser was 1989.9 nm. In PQS mode, the output power of laser was 203 mW. Under the condition of maximum repetition frequency of 45 kHz, the narrowest pulse width of the PQS laser were 1.16 μs. Meanwhile, the laser produced a maximum single-pulse energy (4.5 μJ) and a maximum peak power (3.9 W). The beam quality factors (the horizontal/vertical directions) were M2 x = 1.1 and M2 y = 1.39. The CH3NH3PbBr3 was an excellent SA for infrared PQS solid-state lasers, which had a large potential for development applications in the field of lasers.

Cascaded All-Fiber Gas Raman Laser Oscillator in Deuterium-Filled Hollow-Core Photonic Crystal Fibers.

Hollow-core photonic crystal fibers (HC-PCFs) provide an ideal transmission medium and experimental platform for laser-matter interaction. Here, we report a cascaded all-fiber gas Raman laser based on deuterium (D2)-filled HC-PCFs. D2 is sealed into a gas cavity formed by a 49 m-long HC-PCF and solid-core fibers, and two homemade fiber Bragg gratings (FBGs) with the Raman and pump wavelength, respectively, are further introduced. When pumped by a pulsed fiber amplifier at 1540 nm, the pure rotational stimulated Raman scattering of D2 occurs inside the cavity. The first-order Raman laser at 1645 nm can be obtained, realizing a maximum power of ~0.8 W. An all-fiber cascaded gas Raman laser oscillator is achieved by adding another 1645 nm high-reflectivity FBG at the output end of the cavity, reducing the peak power of the cascaded Raman threshold by 11.4%. The maximum cascaded Raman power of ~0.5 W is obtained when the pump source is at its maximum, and the corresponding conversion efficiency inside the cavity is 21.4%, which is 1.8 times that of the previous configuration. Moreover, the characteristics of the second-order Raman lasers at 1695 nm and 1730 nm are also studied thoroughly. This work provides a significant method for realizing all-fiber cascaded gas Raman lasers, which is beneficial for expanding the output wavelength of fiber gas lasers with a good stability and compactivity.

Enhancing sensitivity of trace copper detection based on coupled optoelectronic oscillator

We propose to employ coupled optoelectronic oscillator (COEO) for trace copper detection to achieve an enhanced sensitivity and stability. By replacing the optical source of the traditional OEO with an optical feedback loop, the oscillation frequency is determined by the cavity loop length in conjunction with the laser output wavelength. The sensing head, which is fabricated by inserting a fusion spliced fiber with large lateral offset fusion splicing in a Sagnac loop, act as a wavelength selection component in the laser loop. Hence, the oscillation frequency changes with the varying solution concentration. Benefitting from the matching of the laser loop and the OEO loop, the final oscillation mode is more stable. By comparing the performance of the COEO-based, single-loop and dual-loop OEO-based sensors, the highest sensitivity of 41.1 Hz/(uMol/L) is obtained by the COEO-based sensor. Since the positive feedback of two loops, the single mode oscillation can be implemented without additional devices.

Raman-scattering-assisted noise-like pulse generation in an all-PM NOLM-based mode-locked fiber laser core-pumped by a 978 nm fiber laser

Stable Raman-scattering-assisted noise-like pulse is experimentally demonstrated in an all polarization-maintaining ytterbium-doped ‘nine-shaped’ mode-locked fiber laser based on nonlinear optical loop mirror. The pump source is a self-made single mode 978 nm fiber laser with a maximum output power of 8.45 W. Different pulse states are investigated through dispersive Fourier transform technology. First and second order Raman pulses are generated effectively with only 7.2 m length large-mode-area fiber. Numerical simulation is conducted to investigate the effect of gain fiber length on output laser wavelength. The output spectrum ranges from 980 nm to 1175 nm, the short-wavelength edge almost extends to the 978 nm pump wavelength, which is benefitted from the core-pumping scheme providing extremely high population inversion for gain fiber, as well as the short length YDF of 0.2 m suppressing reabsorption of radiation laser. The polarization extinction ratio is experimentally measured by a spectral subtraction method to be larger than 28 dB at each wavelength between 1010 nm and 1120 nm.

Intra-cavity photoacoustic spectroscopy dual-gas detection system utilizing dual wavelength fiber laser

An intra-cavity photoacoustic spectroscopy dual-gas detection system using dual wavelength fiber laser has been developed and experimentally demonstrated. The output wavelength of the fiber laser can be tuned within the spectral range of 1520–1600 nm. Using a single fiber laser, the detection of different gases can be easily achieved by changing the wide fiber Bragg grating (FBG) and seed laser. Photoacoustic spectroscopy with the laser intra-cavity technique is employed to achieve high detection sensitivity. The mixture of carbon dioxide (CO2) and acetylene (C2H2) is selected as target gas for evaluating the detection characteristics of the dual-gas detection system. The minimum detection limits (MDLs) of ∼71.82 ppm for monitoring CO2 and ∼924.24 ppb for monitoring C2H2 are realized. The concentrations of CO2 and C2H2 are linearly fitted with the photoacoustic signal, with R-squared values of 0.99859 and 0.99732, respectively, proving the accuracy and robustness of the dual-gas detection system.

Development of a tunable, narrow, and ultraviolet Ce:LiCAF crystal multipass laser amplifier for environmental application

In this paper, the authors present results on the development of both an oscillator and a 4-pass amplifier of ultraviolet and narrow linewidth pulses using a Ce:LiCAF crystal. By using a grating at one end of the laser cavity, the output laser wavelength of the laser can be tuned from 285 nm to 296 nm with a maximum output power of 8 mW at 288.5 nm. Moreover, amplification in a 4-pass amplifier of the Ce:LiCAF laser was investigated theoretically and experimentally. From the results, 49.0 mW amplified pulses can be obtained using a 4-pass amplifier with 7.0 mW power and 3.6 ns pulse duration at 288.5 nm injection, corresponding to an amplifier gain of 7. Furthermore, the angular scattering intensity of some common single-particle aerosols such as black carbon, brown carbon, and polluted water has been studied using the Ce:LiCAF laser. This result can serve as the basis for the multipass laser amplifier’s environmental application, particularly in identifying atmospheric particles.

33.8 W Mid-infrared 2.8 μm Er-doped fiber laser with high optical efficiency

We demonstrate an efficient, high-power single-end-pumped Er-doped ZBLAN (Er:ZBLAN) fiber laser operating at 2.8 μm. A maximum laser power of 33.8 W at a wavelength of 2.87 μm was achieved with an optical efficiency of 26.4 %. A maximum slope efficiency of 32.8 % was obtained, which approaches the Stokes efficiency of the intrinsic Er3+ energy transfer up-conversion process. We examine both experimentally and theoretically, the change in optical efficiency in relation to output coupling ratios, laser wavelength, and pump power. Simulations demonstrate that the Er:ZBLAN fiber laser system exhibits high gain at 2.8 μm, and red-shifting of the laser wavelength results in reduced laser field reabsorption and increased laser efficiency. To the best of our knowledge, this work demonstrates the highest output power generated from a single-end-pumped Er-doped fluoride fiber laser.

Development of methane leakage telemetry system based on tunable diode laser absorption spectroscopy

A methane telemetry system based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) is proposed for the long-range, high-precision, and real-time measurement of methane concentration in coal mine safety production. The output wavelength of the tunable semiconductor laser is controlled to scan at 1654nm (6045.94cm−1) of the methane absorption spectrum. The harmonic signal is obtained by digital phase locking technique, and the effect of light intensity variation on the system measurement results is eliminated by 2f/1f signal processing technique. Through calibration experiment and measurement error analysis, the measurement error of the system is less than 10%, which proves that the device has the advantages of high accuracy.

A good beam quality Ho:GdVO4 laser pumped by thulium‐doped fiber laser at 1940 nm

AbstractWe demonstrate a Ho:GdVO4 solid‐state laser pumped by a thulium (Tm)‐doped fiber laser at 1940nm. In continuous wave mode, a maximum output power of 6.1 W was obtained under the absorbed pump power of 31.9 W with the slope efficiency of 24.3% at the temperature of 18°C. The wavelength of output laser was 2048.53 nm with full width at half maximum of 0.2 nm. In Q‐switched mode, a maximum single pulse energy of 0.94 mJ was obtained with a minimum pulse duration of 7.3 ns at the pulse repetition frequency of 5 kHz, corresponding to a peak power of 129 kW and an average output power of 4.7 W. The beam quality factor of M2 was 1.01 under the maximum absorbed pump power. To the best of our knowledge, 0.94 mJ is the highest single pulse energy in single holmium (Ho) doped GdVO4 laser pumped by Tm‐doped fiber laser at 1940 nm, and 1.01 is the best beam quality factor of M2 in Ho:GdVO4 laser pumped by a Tm‐doped fiber laser.

Highly sensitive torsion sensor based on a coupled optoelectronic oscillator incorporating nonlinear polarization rotation.

We propose and demonstrate a new, to the best of our knowledge, technique to implement a high-speed and highly sensitive torsion sensor based on a coupled optoelectronic oscillator (COEO) incorporating nonlinear polarization rotation (NPR). The COEO consists of a mode-locked laser loop and an OEO loop. In the laser loop, the NPR effect effectively induces intensity- and wavelength-dependent loss, which acts as a Lyot birefringent fiber filter. When twisting the polarization-maintaining fiber (PMF), the transmission of the filter varies as well as the laser output wavelength. In the OEO loop, the optical source is provided by the output signal of the mode-locked laser. The variation in the optical carrier wavelength changes the time delay and the oscillation frequency of the OEO loop. The oscillation frequency shift is a linear function of the twist angle. Sensitivities of -60.006 Hz/deg over 360° for a 48 cm PMF and -180.996 Hz/deg over 92° for a 22 cm PMF are achieved.

Study on Time-frequency Imaging of Ultrasonic Detection with Phase Shifted Fiber Bragg Grating Sensing

Abstract The influence of the wavelength difference between the laser source and the phase-shifted fiber Bragg grating (PS-FBG) on the intensity of the power demodulation system based on an adjustable laser source was studied experimentally, and the optimum of the output laser wavelength was determined. Then, the research on time-frequency imaging damage identification based on smooth pseudo-Wigner-Ville distribution was carried out. The Time of Flight of the acoustic wave signal was calculated and time compensation was made according to the Wigner-Ville distribution and the Lamb wave dispersion curve. The ultrasonic waves before and after damage were measured with spatially arranged PS-FBGs. The difference signals were processed in a window, and then the time-frequency energy of the normalized difference signal was imaged to assess the damage detection and location. Although the mode and group velocity of ultrasound measured by each fiber grating were different, the accurate location and identification of artificial damage in an aluminum alloy plate was realized by using only three PS-FBGs and a smooth Wigner time-frequency imaging method.

Characterization of infrared free electron laser output profile through sum frequency generation spectroscopy

Infrared free electron laser is a unique broadband tuning IR light source and useful tool to trace the reaction and vibrational energy transfer dynamics. It is essential for the infrared free electron laser debug and optimization to accurately characterize the wavelength and micropulse profile of the infrared free electron laser output. By synchronizing the infrared free electron laser and tabletop femtosecond laser with high precision, infrared free electron laser-sum frequency generation setup, a sum frequency generation spectroscopy setup using infrared free electron laser pulses, is developed. Through sum frequency generation cross-correlation, the infrared free electron laser output wavelength and micropulse duration are measured from the delaytime-dependent infrared free electron laser-sum frequency generation spectra of a ZnS window. The infrared free electron laser-sum frequency generation measured infrared free electron laser wavelength is linearly correlated with the theoretically calculation with the fixed electron beam energy and variable undulator magnetic gaps. And the measured micropulse duration is 2.0 ps@5.25 µm and 2.9 ps@8.35 µm. These results demonstrate the excellent ability of sum frequency generation in the diagnostic and characterization of infrared free electron laser output profile, and the quality of the infrared free electron laser pulse structure.

Stand-off detection of ethanol gas in turbulent state using a 1.7 μm/1.5 μm near-infrared spectroscopy system

Considering that the stand-off detection of ethanol gas is significant for monitoring ethanol-free occasions, we propose and experimentally demonstrate a 1.7 μm/1.5 μm near-infrared spectroscopy system. Then based on the generated laser signals and the system, the ethanol gas and ethanol solution was stand-off detected and researched. Firstly, we measured the absorption characteristics of ethanol solution in the near-infrared band for wavelength selection. Secondly, the Tm-doped fiber laser in the system was achieved based on a ring cavity and a customized FBG; its output laser wavelength was 1728.45 nm. The linewidth of the 1.7 μm band signal was about 0.18 nm and the side mode suppression ratio (SMSR) was about 57 dB. Thirdly, ethanol gas and ethanol solution were stand-offs detected using the established 1.7 μm/1.5 μm near-infrared spectroscopy system. The concentration of ethanol solution was measured by 1.7 μm band laser, and the R-Square of the linear fit was 0.98. However, the concentration of ethanol gas in a turbulence state cannot be easily measured due to scintillation. Therefore, we detected the ethanol gas a turbulence state using a 1.7 μm/1.5 μm dual-band system, R-Square of the linear fit was 0.83 when the power jitter variance was 2.35. the experimental results offer a technical reference for stand-off detection of ethanol gas.

Accurate Modeling of Distributed Bragg Reflector Laser Power and Wavelength Using Gaussian Process Regression

Distributed Bragg reflector (DBR) lasers are widely used in many physics experiments. However, regarding the power and frequency control of DBR lasers, obtaining complete and accurate output characteristics is challenging due to the need for general and accurate quantitative models. In this study, we propose and validate a method based on Gaussian process regression to quickly and accurately establish the DBR laser output power and wavelength model. Two models are developed to describe the output power, wavelength, input current, and temperature. The findings show that our power model explains the laser’s power change from the current threshold to the maximum value more precisely, with a root mean square error (RMSE) of 0.16921 mW, less than one-fifth of that of the classic power model. Moreover, our wavelength model is feasible for accurately describing the laser wavelength with a RMSE of 4 × 10−4 nm. This study can improve DBR laser power and frequency control efficiency and precision.

Optofluidic R6G microbubble DBR laser: A miniaturized device for highly sensitive lab-on-a-chip biosensing

In this work, we propose a miniaturized optofluidic bio-sensor based on organic Rhodamine 6G optofluidic microbubble distributed Bragg reflector (R6G OMB DBR) laser and investigate its performance using a 3-D finite difference time domain (FDTD) simulation method. For this aim, lasing characteristics are precisely calculated and then exploited to scrutinize the capability of the proposed bio-laser in bio-sensing. The designed laser is pumped with a 532 nm Nd: YAG laser and operates at a wavelength of 561.1 nm. The threshold pump energy density and quality (Q)-factor of this single-mode microlaser are 3.6 μJ/mm2 and 4.28 × 104, respectively. The results declare that the presence of Polio virus-like-particles (VLPs) leads to a spectral redshift in the laser output wavelength while decreasing its output intensity. The obtained sensitivity and intensity sensitivity of the proposed bio-sensor are 1377 nm/RIU and 0.98 × 104%/RIU, respectively. Therefore, the proposed miniaturized device shows proper lasing characteristics as well as high abilities in real-time lab-on-a-chip (LOC) bio-sensing applications.

Wavelength-tunable multi-point pump semiconductor disk laser based on an intra-cavity transmission grating

We report a wavelength-tunable multi-point pump scheme of the semiconductor disk lasers (SDLs). By designing an external cavity of SDL with an intra-cavity transmission grating, multiple pump gain regions share the same resonator. The effect of the intra-cavity grating on the output laser power, wavelength, and beam quality was investigated. The emission wavelength could be tuned over a bandwidth of ∼18 nm. With multi-point pumping, we achieve the laser output power with almost no loss, and further improvement is limited by the thermal effect. The changes in the beam are due to the mode selectivity by the intra-cavity grating.

High-Precision Semiconductor Laser Current Drive and Temperature Control System Design.

To solve the problem in which the output power and wavelength of semiconductor lasers in fiber optic sensing systems are easily affected by the drive current and temperature, a high-precision current drive and temperature control system was developed in this study. The embedded system was used to provide a stable drive current for the semiconductor laser through closed-loop negative feedback control; moreover, some measures, such as linear slow-start, current-limiting protection, and electrostatic protection, were adopted to ensure the stability and safety of the laser's operation. A mathematical model of the temperature control system was constructed using mechanism analysis, and model identification was completed using the M sequence and differential evolution (DE) algorithms. Finally, the control rules of the fuzzy proportional integral differentiation (PID) algorithm were optimized through system simulation to make it more suitable for the temperature control system designed in this research, and the accurate control of the working temperature of the semiconductor laser was realized. Experimental results showed that the system could achieve a linearly adjustable drive current in the range of 0-100 mA, with an output current accuracy of 0.01 mA and a temperature control accuracy of up to 0.005 °C.