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Compact wavelength monitor for remote sensing applications suitable to precisely measure the wavelength of individual laser pulses

 

Remote sensing of chemicals in a cloud can be accomplished, for example, with a tunable LIDAR system. The principle is to direct a series of laser pulses with different wavelengths at the cloud and measure the response (amount of reflected, scattered, or transmitted light) for each wavelength. The observed features in the recorded spectra reveal information on the constituents in the cloud. The most informative spectral bands for chemical identification are the wavelengths near 3 and 10um where gas molecules have characteristic vibrational modes that contribute characteristic structure in the spectra. For chemical identification it is essential to have precise wavelength information for each individual laser pulse.

We will describe a compact and fast wavelength monitor that can determine the wavelength of individual laser pulses with a resolution of a few pm. It combines a position sensor with a linear-variable-filter optical coating that converts the wavelength information of the incident light into a spatial intensity distribution on the photo-detector. Differential read-out of the position detector is used to determine the centroid of this distribution. Wavelength change between individual laser pulses is detected as a shift of the centroid of the spatial light distribution on the detector. We tested our wavelength monitor with a wavelength-tunable fiber laser which can produce randomly accessible sequences of laser pulses. The laser emits 100ns long laser pulses at 2kHz with selectable, well-defined wavelengths in the spectral range from 1030 to 1075nm. Such lasers can be used in combination with an OPO to convert the wavelength sequences in the 3um band for remote sensing. Our wavelength detector can measure the wavelength of each individual laser pulse with a resolution better than 10pm over the entire wavelength range.

 
citation

Kiesel, P.; Staudt, T.; Martini, J.; Johnson, N. M. Compact wavelength monitor for remote sensing applications suitable to precisely measure the wavelength of individual laser pulses. Invited paper for SPIE Defense, Security and Sensing; 2013 April 29 - May 3; Baltimore, MD USA.