A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation, photonic crystal fiber

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Differential Optical Absorption Spectroscopy를 이용한 대기오염 측정 및 분석

The three-dimensional global wind field is the most important remaining measurement needed to accurately assess the dynamics of the atmosphere. Wind information in the tropics, high latitudes, and stratosphere is particularly deficient. Furthermore, only a small fraction of the atmosphere is sampled in terms of wind profiles. This limits our ability to optimally specify initial conditions for numerical weather prediction (NWP) models and our understanding of several key climate change issues. Because of its extensive wind measurement heritage (since 1968) and especially the rapid recent technology advances, Doppler lidar has reached a level of maturity required for a space-based mission. The European Space Agency (ESA)'s Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) Doppler wind lidar (DWL), now scheduled for launch in 2015, will be a major milestone. This paper reviews the expected impact of DWL measurements on NWP and climate research, measurement concepts, and the recent advances in technology that ...

LIDAR-MEASURED WIND PROFILES The Missing Link in the Global Observing System

Atmospheric lidar techniques for the measurement of wind, temperature, and optical properties of aerosols rely on the exact knowledge of the spectral line shape of the scattered laser light on molecules. We report on spontaneous Rayleigh–Brillouin scattering measurements in the ultraviolet at a scattering angle of 90 °o n N 2 and on dry and moist air. The measured line shapes are compared to the Tenti S6 model, which is shown to describe the scattering line shapes in air at atmospheric pressures with small but significant deviations. We demonstrate that the line profiles of N2 and air under equal pressure and temperature conditions differ significantly, and that this difference can be described by the S6 model. Moreover, we show that even a high water vapor content in air up to a volume fraction of 3:6 vol:% has no influence on the line shape of the scattered light. The results are of relevance for the future spaceborne lidars on ADM-Aeolus (Atmospheric Dynamics Mission) and EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer). © 2010 Optical Society of America OCIS codes: 280.3640, 280.1310, 290.5830, 300.6390.

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Spontaneous Rayleigh-Brillouin scattering of ultraviolet light in nitrogen, dry air, and moist air.

A mobile Rayleigh Doppler lidar based on double-edge technique is developed for mid-altitude wind observation. To reduce the systematic error, a system-level optical frequency control method is proposed and demonstrated. The emission of the seed laser at 1064 nm is used to synchronize the FPI in the optical frequency domain. A servo loop stabilizing the frequency of the seed laser is formed by measuring the absolute frequency of the second harmonic against an iodine absorption line. And, the third harmonic is used for Rayleigh lidar detection. The frequency stability is 1.6 MHz at 1064 nm over 2 minutes. A locking accuracy of 0.3 MHz at 1064 nm is realized. In comparison experiments, wind profiles from the lidar, radiosonde and European Center for Medium range Weather Forecast (ECMWF) analysis show good agreement from 8 km to 25 km. Wind observation over two months is carried out in Urumqi (42.1°N,87.1°E), northwest of China, demonstrating the stability and robustness of the system. For the first time, quasi-zero wind layer and dynamic evolution of high-altitude tropospheric jet are observed based on Rayleigh Doppler lidar in Asia.

/pdf/mid-altitude-wind-measurements-with-mobile-rayleigh-doppler-36gxfxi64l.pdf

Mid-altitude wind measurements with mobile Rayleigh Doppler lidar incorporating system-level optical frequency control method

We report on the development of a 1579 nm pulsed fiber laser source with high peak-power, intended to be used as a lidar source for CO 2 monitoring from space. We first discuss water-vapor sensitivity of spaceborne CO 2 measurements by lidar and point the interest of the 1579 nm wavelength with that respect. Then we detail the current development status of the pulsed fiber laser source.

/pdf/1579-nm-fiber-laser-source-for-spaceborne-monitoring-of-3acrebgf6m.pdf

1579 NM Fiber Laser Source for Spaceborne Monitoring of Carbon Dioxide

We present a theoretical, numerical and experimental assessment of the impact of speckle on a dual electro-optic frequency comb (EOFC) based system for integrated path differential absorption (IPDA) measurements. The principle of gas concentration measurements in a dual EOFC configuration in the absence of speckle is first briefly reviewed and experimentally illustrated using a C2H2 gas cell. A numerical simulation of the system performance in the presence of speckle is then outlined. The speckle-related error in the concentration estimate is found to be an increasing function of the product between the roughness of the backscattering surface and the EOFC line-spacing. As this product increases, the speckle-induced power fluctuations in the comb lines are no longer correlated to each other. To confirm this, concentration measurements are conducted using backscattered light from two different surfaces. Experiment results are in very good agreement with numerical simulations. Though detrimental for IPDA measurements, it is finally shown that decorrelation of speckle noise can be advantageously exploited for surface characterization in a dual EOFC configuration. 

EOFC-based IPDA lidar: assessment of speckle issues

Development of gas sensing Lidars for industrial and climate issues

Fiber technology has led to new lidar architectures. We present some of the recent developments on pulsed coherent beam combining lidar, airborne true air speed sensors and gas sensing spectroscopy using supercontinuum laser.

Atmospheric fiber lidars

Connaissez-vous les deux principales techniques LIDAR qui permettent de mesurer à distance le profil de concentration d’un gaz ? Elles possèdent des bases physiques et des exploitations différentes, ainsi que des avantages et des inconvénients spécifiques. 

Nicolas Cézard

Papers

1579 NM Fiber Laser Source for Spaceborne Monitoring of Carbon Dioxide

EOFC-based IPDA lidar: assessment of speckle issues

Development of gas sensing Lidars for industrial and climate issues

Atmospheric fiber lidars

Mesure des gaz atmosphériques par LIDAR