Applied Physics B最新文献

We reported an efficient continuous-wave (CW) and acousto-optically (AO) Q-switched Tm: LuAG laser at 2 μm in-band pumped by a 1.7-µm laser diode for the first time. A maximum CW output power of 7.26 W at 2013 nm was achieved with an incident pump power of 28.2 W, corresponding to a slope efficiency of 38.5% and optical efficiency of 25.6%. With a repetition rate of 1 kHz, a maximum pulse energy of 5.63 mJ and a minimum pulse width of 77 ns were achieved under AO Q-switching regime, corresponding to a calculating peak power of 73.1 kW. Moreover, the M²-factors in x- and y-directions were measured to be about 1.9 and 1.7 at maximum output power, respectively.

We investigate and use the beam propagation method with equivalent input noise for the simulation of narrow-band amplified spontaneous emission (ASE) and signal amplification in continuous-wave Cr²⁺:ZnSe non-waveguiding “bulk” amplifiers with non-saturating signal and ASE in different configurations with weak reabsorption. Both the incident pump at 1901 nm and the signal at 2410 nm were diffraction-limited gaussian beams. We implemented the equivalent input noise as random realizations of one photon per gridpoint, and showed that this leads to one noise photon per mode. Simulation results of between 100 and 6000 realizations were ensemble-averaged to determine the power spectral density of the ASE in a Monte Carlo approach. We validated the approach by comparing results for single-mode and multimode fiber amplifiers to those obtained with well-established fiber amplifier models. We also calculated the beam quality of the ASE, (:{M}_{ASE}^{2}), from its spatial distribution. We found that under some conditions, but not all, (:{{M}_{ASE}^{2}}^{2}) can serve as an estimate of an effective number of ASE modes and, together with the ASE PSD, predict the achievable signal gain. It is also possible to evaluate the PSD per unit solid angle due to spontaneous emission from the input noise seeding, and we found agreement down to the single-photon level.

We investigated a dual-wavelength twin-pulse laser with tunable intensity ratio and pulse interval, pumped by an 808 nm laser diode (LD), using Nd: GdVO₄ and Nd: YVO₄ as laser gain media, in conjunction with a Cr⁴⁺:YAG saturable absorber. A new theoretical model of a dual-wavelength twin-pulse laser based on intracavity gain-switched pumping has been established. The findings of the simulation show that it is possible to accomplish dual-wavelength twin-pulse laser output without gain competition. Moreover, the simulation underscores the capability to fine-tune the intensity ratio and the pulse interval between the two wavelengths. In the experiment, theoretical modeling served as a guide for key parameter settings. Ultimately, dual-wavelength twin-pulse laser outputs at 912 nm & 1064 nm were achieved, with a tunable intensity ratio ranging from 0.8 to 1.4 and an adjustable pulse interval from 18 to 6 ns. The experimental results aligned closely with the simulation outcomes.

A diode-pumped continuous-wave (CW) orthogonally polarized Sm: YAlO₃ (Sm: YAP) orange laser on ⁴G_5/2→ ⁶H_7/2 transition with output power ratio and wavelength tuning was demonstrated. By adjusting the tilt angle of the beam splitter (BS) and the rotation angle of the intracavity Lyot filters, multiple pairs of orthogonally polarized single-wavelength (OPSW) and dual-wavelength (OPDW) lasers were realized. The highest total output power with the OPSW orange laser at 604 nm reached 1.24 W at an absorbed pump power of 9.0 W at 405 nm, resulting in an optical-to-optical conversion efficiency of 13.8% with respect to the absorbed pump power. Besides, maximum balanced output power with the OPDW orange laser at 604 and 610 nm was 0.48 W, resulting in an optical-to-optical conversion efficiency of 10.7% with respect to the absorbed pump power. To the best of our knowledge, it is the first time to achieve Sm: YAP lasers.

In this paper, the nonlinear optical (NLO) properties of two dimensional (2D) CrTe₂-materials in 2 μm were investigated, obtaining with a modulation depth of 6.5% and a saturable intensity of 42 MW/cm², respectively. By using CrTe₂ as a saturable absorber (SA) and operating in a Tm-doped fiber laser system, a stable fundamental mode-locking laser with the pulse width about 0.96 ps and central wavelength of 1907.2 nm has been achieved. Furthermore, multi-pulses and harmonic mode-locking operations also been observed, which indicating the potential of CrTe₂ SA in pulsed laser applications.

Soot formation in flames remains a central topic for both the combustion and atmospheric science communities. Time-resolved laser-induced incandescence (TiRe-LII), an effective optical technique for in-situ and online measurement of soot particle properties in laminar flames, has continued to advance following previous reviews of the LII technique. While the classical TiRe-LII technique focuses on deriving information from temporal decay data, this work reviews its extended applications, such as measuring additional soot particle properties (e.g., the absorption function) in laminar flames. Furthermore, the review highlights recovery strategies for determining primary particle size distributions, emphasizing the adaptability of experimental system design and strategy development to specific experimental conditions. The study concludes that TiRe-LII serves as an effective tool for unveiling the maturity of soot particles, leveraging prior knowledge of input parameters. The article also delves into the uncertainties analysis associated with TiRe-LII. Furthermore, the discussion encompasses advancements and limitations in TiRe-LII measurement, considering various applications scenarios, temporal and spatial resolutions. The article provides a comprehensive outlook on the future of soot particle measurement with TiRe-LII, outlining potential directions for further research and development. This work aims to serve as a valuable resource for practitioners, researchers, and engineers engaged in combustion studies and environmental monitoring.

We present a resonantly diode pumped Tm:YAG laser, operating at 2036 nm, wavelength-stabilized using a volume Bragg grating. This laser takes advantage of resonant diode pumping at 1.69 ({upmu })m to achieve efficient emission in the high atmospheric transmission spectral region near 2 ({upmu })m. Despite operation on the wing of the emission spectrum, an output power of up to 4.6 W was obtained with a slope efficiency of 49%. In a Q-switched regime, output pulses with an energy of 0.8 mJ and a duration of 360 ns were achieved with performance constrained by the chosen components. The results highlight the potential of compact resonantly diode-pumped 2 ({upmu })m Tm(^{3+}) laser systems for applications requiring efficient wavelength-specific sources, such as LIDAR and atmospheric sensing.

Due to their controllable optical path length and flexible adjustment of optical nonlinearity, multipass cells (MPCs) have emerged as an effective platform for investigations of strong-field nonlinear optics with few-cycle pulses. Prior compression schemes frequently employed hollow core fibers. Propagation in these fibers is effectively single transverse mode, which greatly simplifies numerical modeling. Here we tackle the problem of transverse-multimode nonlinear propagation in solid-state MPCs, employing a suitably expanded unidirectional pulse propagation equation. Our numerical investigation reveals a peculiar spatiotemporal optical wave breaking mechanisms, which is intricately linked to energy transfer dynamics from the fundamental to higher-order modes. This intermodal energy reallocation results in mode-specific pulse compression, depending on the energy in each mode. Remarkably, this process induces a rapid expansion of the beam size, which leads to a mitigation of adverse thermal effects. Our study provides deeper theoretical insights into multimode nonlinear propagation in solid-state MPCs. The observed spatiotemporal phenomena as well as the observed energy transfer dynamics offer valuable guidance for the design and application of MPCs in pulse compression.

A novel analytical technique for the level detection of cryogenic liquids like liquid nitrogen using wave theory and employing a Gaussian beam, a zeroth-order Bessel-Gauss (BG) beam, and a radially polarized Bessel-Gauss (RPBG) beam is presented here. At first, this wave theory-based analytical model is shined by the Gaussian (G) beam, and the observations are validated with the already reported experimental data. The obtained results are in good concurrence with the experimental findings presented by J. E. Antonio-Lopez et al. in the year 2011. With this validation of the proposed theory, this idea next extended to the utilization of Gaussian, BG, and RPBG beams as input sources for the proposed structure. The performance of this sensor with the change in refractive index according to the cryogenic temperature and the level of liquid nitrogen is investigated using the propagation of these beams inside the sensor structure. A comparative assessment has also been presented utilizing the Gaussian and non-Gaussian beams. By irradiating the RPBG beam, the discerned sensitivity is 4.517 dB/°K, 18458.8 dB/RIU, 9.759 dB/cm, and 0.176 dB/nm, with a resolution of 5.5 × 10⁻⁷ RIU. This is 3.8 times more sensitive than the published ray theory-based publications till date that are based on the Gaussian beam. Due to its better sensing performances, with the ease of fabrication processes, the proposed sensing technology opens new avenues to develop high-performance fiber optic-level sensors with the scope of multiple input sources for physical, biological, and chemical sensing in cryogenic environments.

The present paper reports on the design, fabrication, and characterization of an 8-tube inhibited-coupling guiding hollow-core photonic crystal fiber (IC-HCPCF) capable of guiding both the beam emitted from an Yb:YAG laser at the fundamental wavelength of (lambda =1030 text{nm}) and its second harmonic at (lambda =515 text{nm}). By controlling the strut thickness of the glass capillaries to approximately (362 text{nm}), the transmission of laser radiation at both wavelengths was possible with low losses. Optimizing the outer diameter of the glass capillaries mitigates the bending-induced increase of the confinement loss at the wavelength of (515 text{nm}) without compromising the optical performance of the fiber at the wavelength of (1030 text{nm}). Experimental results confirm the near to diffraction-limited beam quality (left({M}^{2}<1.15right)) of the laser beams exiting the fiber at both operational wavelengths. Operating in the first transmission band at the wavelength of (1030 text{nm}), the calculated chromatic dispersion is (1.02 text{ps}/(text{nm}bullet text{km})), despite a diameter of the hollow core of (40 mu text{m}). At the wavelength of (515 text{nm}) this value amounts to (0.62 text{ps}/(text{nm}bullet text{km})). The measured losses are (27.5pm 0.3 text{dB}/text{km}) at the wavelength of (515text{ nm}) and (25.7pm 0.7 text{dB}/text{km}) at the wavelength of (1030text{ nm}), which is comparable to the loss of state-of-the-art IC-HCPCFs with tubular cladding structures. The measured bending-induced increase of the confinement losses confirms the potential of the proposed approach for flexible, low-loss guiding of ultrashort laser pulses at the two wavelengths using a single fiber. This gained flexibility can significantly enhance the options for wavelength selection in laser material processing applications.