Cw Optical Resonance Transfer Lasers (ortl)

Wavelength-agile, single and multiline laser radiation has been obtained from a subsonic gas flow system which is optically pumped with a multiline chemical laser. This optical resonance transfer laser (ORTL) concept was first demonstrated on the 10.6pm DF/C02 system in 1976, Since then, several IR laser pumped molecular lasers have been demonstrated. The pump laser is either a cw HF or DF chemical laser. Two classes of ORTL have been developed : interand intramolecular ORTLs. The demonstrated intermolecular systems include : 10.6 pm DF/CO~ , 10.8 pm DF/N20, 4.1 pm DF/HBr, 3.8pm HF/DF and 3.85pm HF/HCN. The intramolecular ORTLS include 2.9pm BF/HF and 3.9pm DF/DF. Demonstration experiments and the kinetics of ORTL systems will be described. 1.0 Introduction characteristics including large vibrational excitation, high small signal gain, nondissociative CW HF/DF chemical lasers are efficient but they are excitation and wavelength agility. In this paper, multi-band, multi-line lasers with large density the recent developments on the ORTL technology will and J-dependent gain variations in the active presented. medium. This is due to the supersonic mixing of fuels, the heat generated during the chemical 2.0 ORTL Kinetic Considerations excitation reaction processes and the rapid deactivation processes associated with hydrogenfluorides. Elaborate engineering efforts are required to efficiently extract the available power to produce an output beam with good optical quality for specific applications. Recently, an Optical Resonance Transfer Laser (ORTL) concept has been developed in which the chemical laser is used strictly as an optical pump source where good beam quality is not required. On the other hand, an output with good beam quality is easily achievable from an ORTL medium because it is a subsonic flow system with minimum external disturbance and no chemical reaction and mixing in the active medium. Several ORTL systems have been demonstrated and they can be classified into two categories: the 1 intermolecular ORTL including 10.6pm DF/C02 , 2 3 10.8pm DF/N20 , 4.lpm DF/HEr , 3.8pm HF/DF~, and 4 3.9pmHF/HCN ;and the intramolecular ORTL including 6 2 . 9 ~ HF/HF~ and 3.9pm DF/DF . These demonstrations have illustrated several advantageous ORTL In an intermolecular ORTL, there are three components in the flowing ORTL medium: the donor, the acceptor and the helium diluent. A DF or HF chemical laser serves as the resonant pump source to excite the donor molecules (DF or HF) in the ORTL cell. The vibrational excitation energy in the donor is transferred via rapid near resonance V-V collisions to the acceptor molecule which then becomes the active laser molecule. Lasing in C02, N 0 and HCN has been achieved with total inversion 2 in a three-level scheme while the lasing in HBr and DF has been demonstrated with partial inversion in a two-level scheme. Typical energy level diagrams for a three-level system in DF/C02 and for a twolevel system in DF/HBr are illustrated in Figures 1 and 2, respectively. In the latter approach, a larger upper level population density is required because the lower laser level is the ground state; this high upper level density causes intramolecular V-V exchange in the acceptor to become a dominant process. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980963