Figure 2 shows the principle results of this study: the longitudinal mode spectrum of the two lasers in Fig. 1 is 3mw shown at identical output powers of 3-mw/facet. These re- sults are consistent with that observed in Refs. 11 and 12. at higher output power levels(> 7-8 m W/facet)though, both lasers give essentially single-mode output, although the un- coated laser spectrum is somewhat"purer. "Lasers with in- creased facet reflectivity exhibit spectrum of even higher pu rity, due principally to the higher intracavity optical power and the smaller variation in the gain spectrum along the length of the cavity. This research was supported by the Defence Advanced 8 Research Project Agency H. Statz and G deMars, Quantum Electronics, edited by C. H. Towns FIG. 2. Lasing spectrum of the two lasers in Fig. I at 3-m Columbia University, New York, 1960 D. Renner and J. E. Carroll, Electron. Lett. 14, 781( 1978) P. Brosson, w.w. Ruble, N. B. Patel, and J. E Ripper, IEEEJ Quantum Given a pump level (designated by the unsaturated gain Gh), the laser length and facet reflectivities, one can self-consis- 'H. Namizaki, IEEE J Quantum Electron QE.11, 427(1975). tently compute from Eqs. (7)-9)the total power ratio S and KAiki, M. Nakamura, TKuroda,].Umeda,.Ito, and MMaeda the power in each mode IEEE J Quantum Electron Figure 1 shows the computed optical power output (all J. Katz, S. Margalit, D. P, wilt, P. C. Chen, and A, Ya modes)from the exit facet as a function of(Gh +KN Let37,987(19 laser with R,=R2=0.3 and(b)an AR coated laser with R, 706// d Y Suematsu, J Appl. Phys. 52, 2653(1 (which is proportional to the pump current)for(a)a common KSeki,T.Kamiya, and HYanai,IEEEJQuantum QE-17 R.G. Plumb and J. P. Curtis, Electron Lett reduced to 1%o. Also shown is the average intracavity optical Ettenberg,DBotez, DB.Gilbert,Jc and H V,Kowger power in both cases. At comparable output power levels, the IEEE J Quantum Electron. QE-17,2211 laser manifests the large number of longitudinal modes, evi- York, 1978), Part A p 17 eterostructy ACademic, New dent from Eq (9) i4L. W. Casperson, J. Appl. Phys. 48, 258(1977) Femtosecond interferometry for nonlinear optics J-M. Halbout and C L. Tang Materials Science Center, Cornell University, Ithaca, New York 14853 A technique of time-resolved interferometry capable of observing nonlinear optical phenomena lown to 70 fs is presented. We report the direct observation of the rotational contributions to the onlinear refractive index of molecular liquids using this technique. The subpicosecond dynamics of such a nonlinearity in CS, are investigated. This technique can be readily extended to solids, in particular laser glasses PACS numbers: 42. 65.-k. 07.60.Fs a wide variety of nonlinear optical effects arises from tronic distribution around a fixed nuclear configuration of the nonlinear polarization P, third order in the electric the molecules gives rise to the"purely electronic"contribu field. There are two intrinsic contributions to this third-or- tion. The second contribution is of"nuclear"origin, arising der nonlinearity. First, the nonlinear distortion of the elec- from the optical field induced motions of the nuclei of the Appl. Phys. Lett. 40(9), 1 May 1982 00036951/82/09076503501 1982 American institute of Physics Downloaded24May2006to131.215.240.9.RedistributionsubjecttoAlplicenseorcopyrightseehttp:/laplaip.org/apl/copyright.jspDownloaded 24 May 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp