Laserstrahlquellen auf Basis eines neuartigen Neodym-dotierten Mischgranats für Wasserdampf-DIAL-Systeme bei 935 nm

For remote sensing of certain trace gases in the atmosphere like water vapor using the Differential Absorption LIDAR (DIAL) technique pulsed single frequency laser sources are required which can be tuned to certain absorption lines of that gas. A special set of four wavelengths between 935.561 and 935.906 nm is beneficial for spaceborne measurements of atmospheric water vapor density distributions according to the studies for the WALES (Water Vapor Lidar Experiment in Space) mission. Today, usually broadband laser media like Ti:Sapphire or frequency converted lasers are used in order to address these wavelengths and to fulfill all remaining beam requirements. In both cases usually frequency doubled and maybe diode pumped Nd:YAG-lasers at 532 nm are used as pump source. Thus both concepts offer only low electro-optical efficiencies and lead to comparatively complex setups, which is not suitable for space applications. Alternatively, specific laser media can be grown that offers direct diode pumping and whose emission wavelengths can be tuned to the application wavelength by the crystal composition. Hereby, generally a more compact and efficient setup is possible. In the context of this work Nd:(Y_{x}Lu_{1-x})_{3}Ga_{5}O_{12} crystals (with 0<=x<=1) were used for the first time in order to address the above-mentioned wavelengths. Thereby, especially the crystal properties relevant for the design of an appropriate laser source are analyzed. This comprises the absorption and emission cross sections, the lifetimes of the upper laser level, the changes of the refraction index with temperature and the heat conductivities for different crystal compositions. This data is used in design studies in order to identify advantageous configurations for stable oscillators and Innoslab-amplifiers. Oscillators based on different crystal compositions are investigated experimentally. Though a composition which emits at 935.7 nm vac. and which allows the addressing of all relevant WALES wavelengths is found. Furthermore, a Nd:YGG-based demonstrator emitting at 935.3 nm in single frequency mode, consisting of an oscillator and an amplifier stage, is implemented and analyzed. Herewith, a pulse energy of 30.5 mJ is obtained at a pulse repetition frequency of 100 Hz, a pulse duration of 52.5 ns, a beam quality of M2<1.4 and a spectral purity of <99.996%. This system is successfully employed at the DLR-IPA for ground based measurements of atmospheric water vapor densities. The maximal optical-to-optical efficiencies (pump light to laser light) are 10% and 3.2% for the oscillator and amplifier, respectively. This first attempt to generate light with that new laser material already comes up to the optical efficiencies and exceeds the spectral quality achieved by the above mentioned state of the art concepts. Moreover, the high efficiencies achieved in oscillators show the potential of these novel laser sources, especially for airborne and spaceborne water-vapor DIAL systems. Here, high efficiencies are a prerequisite for mission feasibility.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2011

Author dc:creator

• Löhring, Jens

Contributors dc:contributor

• Poprawe, Reinhart

• info:eu-repo/classification/ddc/620
• DIAL
• Lidar
• Einmodenlaser
• Diodengepumpter Laser
• Festkörperlaser
• Wasserdampf
• Granat
• Mischkristall
• Impulslaser
• Ingenieurwissenschaften
• Nd:YGG
• Nd:LuGG
• compositionally tuned laser
• mixed garnet laser

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124484%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:63019