Second harmonic generation efficiencies

Greenhalgh, C., Prent, N., Green, C., Cisek, R., Major, A., Stewart, B., and Barzda, V. 2007. Influence of semicrystalline order on the second-harmonic generation efficiency in the anisotropic bands of myocytes. Appl. Opt. 46 1852-59. 

A-priori, given that FLC phases possess polar order, and the DOBAMBC structure should possess a substantial molecular second order hyperpolarizability P, it seems reasonable that %(2) of a material such as DOBAMBC in the FLC phase might be large. Measured values of the second harmonic generation efficiencies of DOBAMBC and of several other FLC materials, however, indicate that in fact the dcff of FLCs is very small relative to LiNb03. 

Finally, forward ISRS excitation can be followed by measurement of time-dependent absorption or Raman spectra, second harmonic generation efficiency, or any other optical property that may be affected by vibrational distortion. Preliminary time-resolved absorption spectroscopy of nonequilibrium, vibrationally distorted species is discussed further in the next section [46]. 

In a recent study, Ashwell et al. have observed that centrosymmetric squaraine dyes incorporated into LB monolayers showed second harmonic generation efficiencies, which compare favourably with the highest values hitherto reported for LB monolayers of noncentrosymmetric dyes [126]. Based on comparison of the absorption spectra and SHG characteristics of the LB films of squaraine 45 (Structure 15) as well as the effect of deposition pressure on these properties, it has been suggested that formation of noncentrosymmetric aggregates is responsible for these effects. Nonlinear optical studies have also shown that symmetric squaraines have quite large molecular second hyperpolarizabilities [127-131]. 

Table I lists typical pulse repetition rates, fundamental peak power densities and frequency doubling efficiencies obtainable with various visible laser sources. For the cw and quasi-cw dye laser sources, peak power densities are estimated assuming that 1.0 watt of visible radiation is focused to a 50 ym spot within the frequency doubling crystal. Because the beam energy is bunched into short duration pulse packets with the quasi-cw source, the obtainable focused peak power density and the resultant second harmonic generation efficiency are much larger with this source than with a cw dye laser source. 

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. 

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). 

Optical frequency up-conversion, or second harmonic generation (SHG), in nanostructured surfaces can be also considered as a kind of field enhance-menf [61]. In general, SHG efficiency is proportional to the square of nonlinear polarization ha (x [P (2second order susceptibility. For a nanostructured surface, the incident field is transformed to the local field given by Eq. 19, yielding ... 

Second harmonic generation (SHG) was first observed in single crystal quartz by Franken and coworkers (1) in 1961. These early workers frequency doubled the output of a ruby laser (694.3 nm) into the ultraviolet (347.15 nm) with a conversion efficiency of only about 10 % in their best experiments, but the ground had been broken. 

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