RESUMEN

The multi-longitudinal mode high-spectral-resolution lidar (MLM-HSRL) is an effective technique for detecting atmospheric optical characteristics of aerosols. Due to the excessive longitudinal mode numbers, the current MLM-HSRL cannot obtain a well spectral suppression effect, which seriously affects the retrieval accuracy of the optical characteristic parameters. In this paper, a new index called Longitudinal Mode Rejection Ratio (LMRR) has been proposed to evaluate the spectral suppression effect of the MLM-HSRL; a novel mismatch error and mode control (MEMC) technique is proposed to improve the spectral suppression effect of the MLM-HSRL, which contributes to developing the scientific potential of the MLM-HSRL for aerosol remote sensing. Based on our self-developed MLM laser, through controlling the longitudinal mode frequency-pulled shift of the MLM laser, adjusting the total mismatch error, and reducing the longitudinal mode numbers, we realize the LMRR index improved from about 5 to over 30, and the working stability of the system is also promoted by decreasing the longitudinal mode numbers. The experiment well improves the spectral suppression effect and verifies the effectiveness of the proposed MEMC technique. To the best of our knowledge, for the first time, the study addresses the conundrum of the lower spectral suppression effect for the MLM-HSRL. This work would help to provide a powerful support for the high-precision, long-term, and stable operation of the MLM-HSRL in the future.

RESUMEN

A novel implementation of high-spectral-resolution LIDAR based on a passively Q-switched few-longitudinal mode laser (PQFLM-HSRL) is proposed, and the prototype is built for detecting aerosol and cloud characteristics. The spatial-temporal distributions of the aerosol and cloud are continuously observed by the PQFLM-HSRL for the first time, to the best of our knowledge. Based on observation, we present the retrieval results of backscatter coefficient, particle linear depolarization ratio, and LIDAR ratio, and these intensive parameters are used to classify the aerosol and cloud into different types. Particularly, we have observed mix-phased clouds. The resulting aerosol optical depths (AODs) are highly consistent with CE-318, the Sun photometer measurements of the local National Meteorological Station (NMS), which verify the retrieval accuracy and the system stability. In addition, the retrieved AODs also characterize the ambient air quality, which show a high correlation with the measured PM2.5 concentrations. The implementation of the PQFLM-HSRL provides a new method for atmospheric feature detection, which shows superior scientific potential for further study on climate change and environmental health.

RESUMEN

Optical-feedback (OF) cavity ring-down spectroscopy consisting of a linear cavity is developed by employing a continuous wave laser diode (LD) with multi-longitudinal modes. Due to the OF effect caused by the cavity output laser back into the LD, the laser frequency is locked, and the intracavity laser intensity is enhanced. We use different concentrations of NO2 gases to test the apparatus, and the results show good agreement with theoretical values. Owing to the compactness of the laser source and high detection accuracy, the device can be used for detection of low-concentration absorbent gases in the environmental monitoring field.

RESUMEN

One of the key questions in the generation of monodisperse droplets is how to eliminate satellite droplets. This paper investigates the formation and elimination of satellite droplets during the generation of monodisperse deionized water droplets based on a piezoelectric method. We estimated the effects of two crucial parameters-the pulse frequency for driving the piezoelectric transducer (PZT) tube and the volume flow rate of the pumping liquid-on the generation of monodisperse droplets of the expected size. It was found that by adjusting the pulse frequency to harmonize with the volume flow rate, the satellite droplets can be eliminated through their coalescence with the subsequent mother droplets. An increase in the tuning pulse frequency led to a decrease in the size of the monodisperse droplets generated. Among three optimum conditions (OCs) (OC1: 20 mL/h, 20 kHz; OC2: 30 mL/h, 30 kHz; and OC3: 40 mL/h, 40 kHz), the sizes of the generated monodisperse deionized water droplets followed a bimodal distribution in OC1 and OC2, whereas they followed a Gaussian distribution in OC3. The average diameters were 87.8 µm (OC1), 85.9 µm (OC2), and 84.8 µm (OC3), which were 8.46%, 6.14%, and 4.69% greater than the theoretical one (81.0 µm), respectively. This monodisperse droplet generation technology is a promising step in the production of monodisperse aerosols for engineering applications.

RESUMEN

Resonate frequency and cell constant of photoacoustic spectrum system are usually calibrated by using standard gas in laboratory, whereas the resonate frequency and cell constant will be changed in-situ, leading to measurement accuracy errors, caused by uncertainties of standard gas, differences between standard and measured gas components and changes in environmental condition, such as temperature and humidity. As to overcome the above problems, we have proposed an on-line atmospheric oxygen-based calibration technology for photoacoustic spectrum system and used in measurement of concentration of carbon dioxide in atmosphere. As the concentration of atmospheric oxygen is kept as constant as 20.96%, the on-line calibration for the photoacoustic spectrum system can be realized by detecting the swept-frequency and peak signal at 763.73 nm. The cell of the PAS has a cavity with length of 100 mm and an inner diameter of 6 mm, and worked in a first longitudinal resonant mode. The influence of environmental temperature and humidity, gas components on the photoacoustic cell's performance has been theoretically analyzed, and meanwhile the resonant frequencies and cell constants were calibrated and acquired respectively using standard gas, indoor air and outdoor air. Compared with calibrated gas analyzer, concentration of carbon dioxide is more accurate by using the resonant frequency and cell constant calculated by oxygen in tested air, of which the relative error is less than 1%, much smaller than that calculated by the standard gas in laboratory. The innovation of this paper is that using atmospheric oxygen as photoacoustic spectrum system's calibration gas effectively reduces the error caused by using standard gas and environmental condition changes, and thus improves the on-line measuring accuracy and reliability of the photoacoustic spectrum system.

RESUMEN

A parameter x is introduced to characterize the strength of thermal lens spherical aberration, whose influences on resonator's stable zones are analyzed theoretically. Some new and helpful results are obtained. For symmetrical plane-plane cavity, spherical aberration has just influence on the back edge of stable zone. For asymmetrical plane-plane cavity, spherical aberration has influence on the back edges of the two stable zones and the front edge of the second stable zone. Effects of transverse mode collapsing to TEM00 mode and stable zones separation of different order's transverse modes are pointed out, which is the foundation of TEM00 mode output power scaling for solid state laser oscillator. Influences of parameters such as resonator's long arm length, short arm length, and pump beam radius on the extent to which of stable zones separation of different order transverse modes are discussed. An experimental setup of a high power diodes dual-end pumped Nd:YVO4 TEM00 mode laser oscillator is built up and investigated experimentally. 51.2 W TEM00 mode output power in CW operation is achieved with an optical-to-optical efficiency of about 50% and beam quality factor M2 being 1.2.

Asunto(s)

Láseres de Estado Sólido , Óptica y Fotónica , Oscilometría/métodos , Algoritmos , Conductividad Eléctrica , Electroquímica/métodos , Diseño de Equipo , Tecnología de Fibra Óptica , Lentes , Microscopía Electrónica de Transmisión/métodos , Modelos Estadísticos , Fibras Ópticas , Temperatura

RESUMEN

A large aperture fused silica tapered fiber phase conjugate mirror is presented with a maximum 70% stimulated Brillouin scattering (SBS) reflectivity, which is obtained with 1 kHz repetition rate, 15 ns pulse width and 38 mJ input pulse energy. To the best of our knowledge, this is the highest SBS reflectivity ever reported by using optical fiber as a phase conjugate mirror for such high pulse repetition rate (1 kHz) and several tens of millijoule (mJ) input pulse energy. The influences of fiber end surface quality and pump pulse widths on SBS reflectivity are investigated experimentally. The results show that finer fiber end surface quality and longer input pulse widths are preferred for obtaining higher SBS reflectivity with higher input pulse energy. Double passing amplification experiments are also performed. 52 mJ pulse energy is achieved at 1 kHz repetition rate, with a reflected SBS pulse width of 1.5 ns and a M(2) factor of 2.3. The corresponding peak power reaches 34.6 MW. Obvious beam quality improvement is observed.

Asunto(s)

Tecnología de Fibra Óptica/instrumentación , Láseres de Estado Sólido , Fibras Ópticas , Oscilometría/instrumentación , Amplificadores Electrónicos , Diseño de Equipo , Análisis de Falla de Equipo/instrumentación , Tecnología de Fibra Óptica/normas , Oscilometría/normas , Dispersión de Radiación

RESUMEN

In end-pumped Nd:YVO4 amplifiers, beam quality improvement is obtained both in theory and in experiments. A theoretical model of gain-guided laser amplifier is developed by comprehensively considering thermal effect, gain guiding and gain saturation effect. Several key parameters of the amplifier are discussed such as the input beam quality, the beam filling factor between input beam and pump beam, the ratio between input power and pump power, and the length of laser crystal. The theoretical results are confirmed by the experiments.