edited by GALEN W. EWlNG Seton ha I Lnwerr#ty Soum Orange. New Jersey 01079
XCIV. Dye Laser Instrumentation (concluded)
Therefore, i t is important t o evaluate power outputs accordingly. The nitrogen laser has a relativelv low dutv evcle and althoueh oeak Dowers i n the hieh kilowatt reeion"are reported, their awrag? powers nrr in thr trns oimilliwatts. Many relatively simplp designs for n i t n w n lasers haw heen report~d10, 101. and several commercial units are marketed a t the present time (11,12). Whereas the nitrogen laser is restricted in the wavelength of its emission, the addition of a dve laser head will ~ r o v i d tunablelaser e e n e r n thnughout rha near-ulrravivlrt and \,isilrle rrgims of the ipwtrurn. T h r usually r e c u n w l u ihapeof the nirnlgen lnscr output is convenient far focussing on a dye cell with s cylindrical lens. Construction of a resonant cavity completes the dye laser (Fig. 7). Most usage requires narrower linewidths than orovided bv broadband mirrors so a eratine" is usually skhstituted for the total reflector. When coupled with a grating drive, continuous wavelength tuning over the gain curve of the dye is possible. Since only a thin layer of the dye is excited by the nitrogen laser pump, diffraction causes a significant angular dispersion of the emerging dye emission which severely limits the resolution obtainable with the angle-dependent grating. In addition, only a small area of the grating is illuminated hy the beam. A beam expanding telescope may he inserted within the opticalcavity for collimation and improvement of the dye laser resolution (13). Moreover damage to the grating surface from high intensity radiation is prevented by beam expansion. U~
Robert 8. Green West Virginia Universiiy Morgantown, West Virginia 26506
Nitrogen Laser-Pumped Dye Lasers Pulsed nitrogen lasers have been used to stimulate dyes to initiate laser action with broad band outputs from the near-ultraviolet to the near-infrared. Since the nitrogen laser has an output wavelength a t 337.1 nm which falls within the absorption hand of many organic molecules, this allows efficient optical pumping. Technically, the nitrogen laser is not a laser in the true sense but a superradiant discharee. The sienificance of this is that thr inltintwn and.kintcnanre of thr dicrhargr ( ~ . r . , t h pump r mdlntimj does not rrquirr a n optical cat,ity. 'l'hrrcfwr, an analogy may be drawn between the nitrogen superradiant discharge and a conventional flashlamp. Most of the operating parameters of the nitrogen laser are determined by the atomic structure of the nitrogen molecule resulting in all nitrogen lasers possessing certain basic features. The eyelie transitions of the nitrogen molecule which are involved in the achirvrnmrnt oi the superradiant ronditim may be thought of as a four-lewlsystem
