2.9 micron laser source for use in the two-photon/laser-induced fluorescence detection of atmospheric OH

摘要

A tandem Raman laser has been constructed using a 1.06 $mu Nd:YAG laser as the fundamental pump source to generate a backward propagating stimulated Raman (D$-2$/ gas) source near 1.5 $mu (185 mJ/pulse), which in turn is used to generate a second backward propagating stimulated Raman (CH$-4$/ gas) source near 2.9 $mu@. This 2.9 $mu Raman Laser can now produce 18 mJ of near diffraction limited output energy. The anticipated sensitivity of a TP-LIF OH sensor using this mid-IR source would give signal limited (i.e. background free) limits of detection of 1.4 $MUL 10$+5$/ OH/cm$+3$/ under boundary layer conditions, and 5.5 $MUL 10$+4$/ OH/cm$+3$/ under free troposphere conditions for a five minute signal integration period. This level of performance coupled with the techniques nonperturbing nature (i.e. direct measurement) and freedom from both interferences and background would allow reliable tropospheric OH measurements to be obtained under virtually any ambient condition of current interest, including interstitial cloud sampling.