Second harmonic efficiency

U., Steinmeyer, G. and Seeber, W. (2004) Second-harmonic efficiency of ZnO nanolayers. Applied Physics Letters, 84,170. 

The reaction with nitroethanol in the presence of di-)i-bntylammmonium chloride in refluxing iropentyl acetate gives 2-unsnbsdtnted 3-nitro-2H-chromene in 50% yield. Some 3-nitro-2H-chromenes display efficient optical second harmonic generadon for nonhnear opdcal apphcations. 

With commercially available YDFL as pumps, powers > 40 W at 1178 nm are feasible. This sets an upper limit to the conversion efficiency needed in the subsequent second harmonic generation. Numerical simulations for the amplifier and resonator Raman laser configuration indicate feasibility of the system with sufficient SBS suppression. ESO has assembled the amplifier configuration, and has demonstrated up to 4 W CW at 1178 nm. ESO s goal is to have compact and turnkey commercial fiber lasers for LGS/AO within 3 years. 

CB04. The spontaneous polarisation was measured by the pulse pyroelectric technique (Ps = 46 nC/cm ). The piezoelectric coefficient evaluated for CB04 was dsi = 1.6 pC/N. The estimation of the efficiency of the second harmonic generation for compound CB04 gives the value three times more than for quartz. 

The first and third order terms in odd powers of the applied electric field are present for all materials. In the second order term, a polarization is induced proportional to the square of the applied electric field, and the. nonlinear second order optical susceptibility must, therefore, vanish in crystals that possess a center of symmetry. In addition to the noncentrosymmetric structure, efficient second harmonic generation requires crystals to possess propagation directions where the crystal birefringence cancels the natural dispersion leading to phase matching. 

There are many organic and inorganic materials available which exhibit significant non-linear optical properties. In the present context, however, we underline that ferrocene derivatives were the first organo-metallic materials observed possessing non-linear optical properties. In fact, in 1987 it was reported that ci s-ferrocenyl-2-(4-nitrophenyl)ethylene has a 62-fold greater efficiency than urea in generating the second harmonic, Scheme 13.71... 

In the case of SHG in waveguide nonlinear crystals, we describe a theoretical model which accounts for the temporal behavior of the interacting pulses and the possible z-dependence of the phasematching condition. The model also describes the observed saturation and subsequent decrease in SHG conversion efficiency in the waveguide samples, as a result of two-photon absorption (TPA) of the second harmonic (SH) wave. The results of this model are later compared with experimental data from SHG experiments using femtosecond pulses in the waveguide nonlinear crystals of periodically-poled potassium titanyl phosphate (ppKTP) and appKTP. This model is presented in section 2.3. 

The energy of the second harmonic (SH) is found by integrating the SH intensity over space and time while assuming Gaussian spatial and hyperbolic secant temporal profiles. The normalized efficiency,, ... 

Bulk potassium niobate (KNbOs) is well suited to our needs, beeause birefringent type-I non-critical phasematehing (NCPM) can be exploited for highly efficient SHG of 850 nm at room temperature . This NCPM avoids any spatial waUc-off between the fundamental and second harmonic beams, as well as maximizing the angular acceptance of the phasematching process. 

When using the waveguide ppKTP crystal experimentally, the dependence of internal SHG efficiency on input power is characterized by a maximum efficiency of 37 %. A further increase in fundamental pulse energy then leads to a saturation and subsequent decrease in the efficiency of the SHG process (figure 18). This behavior was also observed in the waveguide appKTP crystal (figure 18), and has been reported elsewhere" ". As we have suggested previously, two-photon absorption (TPA) of the second-harmonic (SH) wave is the most likely explanation for this behavior. 

H. Wang and A.M. Weiner, Efficiency of short-pulse type-I second-harmonic generation with simultaneous spatial walk-off, temporal walk-off, and pump depletion, IEEE Journal of Quantum Electronics 39(11), 1600-1618 (2003). 

M. Yamada, N. Nada, M. Saitoh, and K. Watanabe, First-order quasi-phase matched LiNbOs wave-guide periodically poled by applying an external-field for efficient blue second-harmonic generation. Applied Physics Letters 62(5), 435-436 (1993). 

The output from a ruby giant-pulse laser (2 Joule, 30 nsec half-width, = 6943A) passes a KH2PO4 crystal where, due to the nonlinear characteristics of this material, the second harmonic at X = 3471 A is generated with an efficiency of 3 %.The two wavelengths are separated by means of a water filled quartz prism. The ultraviolet light pulse serves as pump pulse. 

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