Nonlinear Optical Saturable Absorption Properties of 2D VP Nanosheets and Application as SA in a Passively Q-Switched Nd:YVO4 Laser.

Two-dimensional (2D) violet phosphorus (VP) plays a significant role in the applications of photonic and optoelectronic devices due to its unique optical and electrical properties. The ultrafast carrier dynamics and nonlinear optical absorption properties were systematically investigated here. The intra- and inter-band ultrafast relaxation times of 2D VP nanosheets were measured to be ~6.83 ps and ~62.91 ps using the pump-probe method with a probe laser operating at 1.03 µm. The nonlinear absorption coefficient ßeff, the saturation intensity Is, the modulation depth ΔR, and the nonsaturable loss were determined to be -2.18 × 104 cm/MW, 329 kW/cm2, 6.3%, and 9.8%, respectively, by using the Z-scan and I-scan methods, indicating the tremendous saturable absorption property of 2D VP nanosheets. Furthermore, the passively Q-switched Nd:YVO4 laser was realized with the 2D VP nanosheet-based SA, in which the average output power of 700 mW and the pulse duration of 478 ns were obtained. These results effectively reveal the nonlinear optical absorption characteristics of VP nanosheets, demonstrating their outstanding light-manipulating capabilities and providing a basis for the applications of ultrafast optical devices. Our results verify the excellent saturable absorption properties of 2D VP, paving the way for its applications in pulsed laser generation.

The visible nonlinear optical properties and passively Q-switched laser application of a layered PtSe2 material.

Platinum diselenide (PtSe2), a type-II Dirac semi-metal material, is a potential saturable absorber (SA) to generate visible pulsed lasers due to its prominent optoelectronic properties. A high quality PtSe2 thin film was fabricated by combining magnetron sputtering with chemical vapor deposition methods; then, its microtopography was characterized by atomic force microscopy. The saturable absorption properties and electron relaxation time in the visible region were measured via open-aperture Z-scan and femtosecond pump probe technology, respectively. The modulation depth and saturable intensity are 39.9% and 256.6 GW cm-2, respectively. The relaxation time constants were fitted to be τ1 = (1.405 ± 0.024) ps, τ2 = (99.03 ± 0.01) ps, and τ3 = (2.032 ± 0.27) ns. The as-prepared PtSe2 thin film was experimentally applied as a novel SA to achieve a stable passively Q-switched (PQS) Pr:YLF visible laser. A shortest pulse width of 91.8 ns with a maximum repetition rate of 297.6 kHz was obtained. These results demonstrate that the PtSe2 thin film has promising applications in generating visible pulsed lasers.

The energy band structure analysis and 2 µm Q-switched laser application of layered rhenium diselenide.

Layered rhenium diselenide (ReSe2) has triggered strong interest because of its outstanding optical and electrical properties. In this paper, we prepared a high-quality multilayer ReSe2 saturable absorber with a liquid-phase exfoliation method and characterized its saturable absorption properties around 2 µm. During the Q-switching regime, a maximum average output power of 1.7 W was obtained. A shortest pulse width of 925.8 ns was measured and the corresponding single pulse energy and peak power were 17.6 µJ and 19.0 W, respectively. The results indicate that layered ReSe2 is a promising alternative as a nonlinear optical modulator near the 2 µm region.

Two-photon saturable absorption properties and laser Q-switch application of carbon quantum dots.

In this Letter, high-quality carbon quantum dots (C-QDs) with an average size of 15 nm are synthesized by using a solvothermal method. A C-QD saturable absorber mirror (SAM) was prepared, characterized, and employed as an ultrafast optical switch successfully in a 1.0 µm solid-state laser. The saturable absorption effect (at 1 µm) far away from the linear absorption band of the C-QDs could be attributed to two-photon saturable absorption, which has a native characteristic of wavelength selectivity. The modulation depth (ΔT) and saturable energy intensity (ϕs) of the C-QD-SA was measured to be about 4% and 15.34 W/mm2, respectively. By using this SA, a Q-switched Nd:GdVO4 laser at 1 µm were first realized with the shortest pulse width of 66.8 ns and a maximum repetition rate of 1.13 MHz, respectively. The results indicate that C-QDs may found to be a decent carbon SA material for the high-repetition-rate pulsed laser applications.

[Investigation of noise hazards and hearing status of workers in outdoor quarries].

OBJECTIVE: To investigate the noise hazards in open quarries and to provide a basis for further control of noise hazards. METHODS: An investigation was performed during 2010 to 2011 among all open quarries in Deqing County of Zhejiang Province, China. The investigation included basic information of the quarries, the occupational health situation and noise intensity at the workplace, and the hearing loss of workers exposed to noise in quarry enterprises. The hearing test results were evaluated based on the Diagnostic criteria of occupational noise-induced hearing loss (GBZ 49-2007). RESULTS: A total of 25 enterprises with open quarries were investigated, of which only 30.4% (17/56) workplaces met the national standard. The median noise level was 92.5 dB (A). Fifty-four (10.6%) out of 508 workers in the 25 enterprises were diagnosed with binaural hearing loss in the initial physical examination, with 18.3% (93/508) under surveillance. The rate of normal hearing among crushing workers, mechanists, drilling workers, and blasting workers ranged between 27.6% and 41.4%, which was significantly lower than that among workers exposed to slight noise hazards (80.0%) or other workers (63.7%) (P < 0.05). With increasing working years, the binaural hearing loss of crushing workers became serious. CONCLUSION: Serious occupational noise hazards existed in most jobs in open quarries, with crushing workers, mechanists, drilling workers, and blasting workers most seriously jeopardized. Among crushing workers, those working in the first-line or unprotected second?line positions suffered more than the others. Further measures should be taken by the supervision department and the enterprises to control the noise hazards in open quarries.

[Comparative investigation of hearing injury in workers exposed to punching machine noise and to steady state noise].

OBJECTIVE: To compare the difference of effects on hearing injury between punching machine noise and steady state noise. METHODS: The subjects of present study were 100 workers, included 38 workers exposed to punching machine noise from forging shops and 62 workers exposed to steady state noise from drawbench or abrasive dust workshops. The individual noise dosimetries were used to detect noise that workers exposed, and cumulative noise exposure (CNE) was then calculated. On the basis of GBZ 49-2007, the worker hearing was tested, and the results were assessed. RESULTS: There were no differences of CNE between group exposed to punching machine noise and group exposed to steady state noise. The hearing loss rate (55.3%) at high frequency in workers exposed to punching machine noise was significantly higher than that (32.3%) in workers exposed to steady state noise (P < 0.01). CNE and the hearing loss rate at high frequency showed dose-response relationship (P < 0.01). CONCLUSION: when the exposure levels of workers were similar, the hearing injury induced by punching machine noise may be significantly higher than that induced by steady state noise.

[Low back pain prevalence of female workers in flat-grained veneer wood industry].

OBJECTIVE: To study the low back pain(LBP) and its cause on female workers in flat-grained veneer wood industry. METHODS: Bending posture was analyzed by observation and the prevalence of low back pain was investigated by physical examination and questionnaire among 299 female workers. RESULTS: The prevalence of fatigue compliant in selecting, remending and sticking workers was 68.8%, 66.7% and 59.0%, respectively, which mainly involved in the part of low back. The prevalence of low back pain in selection (53.8%) and remending (58.7%) workers was higher than that in sticking workers (30.1%), which was in accordance with the tenderness between L4/L5 or L5/L6 and on the psoas major. Posture analysis indicated that the biggest bending range of selecting and remending workers (80 degrees ) was larger than that of sticking workers (60 degrees ), as well as the daily bending times[(4396+/-817), (1696+/-286), (1094+/-476)] and the time they kept bending[(6.5+/-0.6), (6.2+/-1.3), 4.5+/-0.9) h]. CONCLUSION: Bending posture is common among female workers especially those who work in selecting and remending and might be the major causes for the high prevalence of LBP in flat-grained veneer wood industry.