SATURATION DIVING WITH HELIOX TO 350 METERS OBSERVATION ON HEARING THRESHOLD, BRAINSTEM EVOKED RESPONSE AND ACOUSTIC IMPEDANCE

Four divers were compressed to 350 m to observe changes in hearing threshold, brainstem evoked response and acoustic impedance. The divers experienced no tinnitus, impairment of bearing, earache daring compression. Examination showed that the threshold of tower frequency range of hearing was elevated because of the masking effect of the noise in the hyperbaric chamber. Changes in waveform and latency of brainstem evoked response were due to changes in sound wave transmission affected by the chamber pressure and a poor ratio of signal to noise in the hyperbaric environment with heliox. All these changes were transient After leaving the chamber, the hearing threshold and brainstem evoked response returned to normal. Besides, there were no changes in tympanogram, acoustic compliance and stapedius reflex before and after diving. This indicated the designed speed of compression and decompression in the experiment caused no damage to the divers' acoustic system, and the functions of their Eustachain tubes, middle and inner ears were normal during the diving test

Q-switched Er-doped fiber laser with low pumping threshold using graphene saturable absorber

We propose a Q-switched Er-doped fiber laser （EDFL） with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol （PVA） thin film as a passive saturable absorber （SA）. The SA is fabricated from graphene flakes, which is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulfate aqueous solution. The flakes are mixed with PVA solution to produce a thin film, which is then sandwiched between two ferrules to form a SA and integrated in the EDFL ring cavity to generate a stable Q-switched pulse train. The pulse train operates at 1560 nm with a threshold pump power of 7.4 roW. At maximum 1480 nm pump power of 33.0 roW, the EDFL generates an optical pulse train with a repetition rate of 27.0 kHz and pulse width of 3.56/as. The maximum pulse energy of 39.4 nJ is obtained at a pump power of 14.9 roW. This laser can be used as a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.

Robust YAG:Ce single crystal for ultra-high efficiency laser lighting

At present,solid-state laser-driven lighting fabricated with blue laser diode(LD)and phosphor has been greatly developed in high-power lighting applications.The major obstacle is the luminescence saturation threshold of the fluorescence conversion material(YAG:Ce).In this work,we successfully prepared a series of high-quality and robust YAG:Ce single crystals.With high quantum efficiency(QE=92%),regular crystal structure and high thermal conductivity,the single-crystal has excellent ability to deal with high radiation flux and thermal accumulation generated by high power.Matching the single-crystal with the laser,the luminous efficiency up to 274 lm/W and saturation threshold of 12 W/mm^(2) were obtained.In addition,the influence of Ce doping concentration and sample processing conditions on the indicators in laser-driven white lighting was systematically studied.The results are of great significance and are believed to promote the development of solid-state laser-driven lighting.