Frequency conversion

The incident power dependence of frequency tripling efficiency is shown in Fig. 27. Actually due to the free harmonic wave absorption this efficiency will be slighly smaller. The large light intensity is realized by focusing a 40 nj laser pulse with 10 fs duration pulse on a surface of 100(pm).  

Stegeman and Stolen introduced a merit factor defined as follows 

Townsend et al. (1989) bas studied directional couplers made from poly-4BCMU spun film deposited on a patterned with two channels substrate. At 1.064 Mm operation wavelength they observed nonlinear transmission and switching from one channel to another one both due to a fast (ps) electronic and slow thermal nonlinearities. However the fast switching was due to the refractive index modification via the two photon absorption. 

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The 6 Nd YAG lasers pump the DM0, preamplifier and power amplifier (Fig. 19, Friedman et al., 1998). The YAG lasers are built from commercially available flashlamp/laser rod assemblies, acousto-optic Q-switches and frequency doubling crystals (LBO and KTP). Most of the mirror mounts and crystal holders are commercial. Nd YAGs are frequency doubled to 532 nm using a nonlinear crystal. The Nd YAG rod and nonlinear crystal are both in the pump laser cavity to provide efficient frequency conversion. The 532 nm light is coupled out through a dichroic and fed to multimode fibers which transport the light to the DM0 and amplifier dye cells. 

Abstract Optical Parametric Oscillators provide a very efficient source of tunable coherent radiation. The principle of different kinds of OPOs are described. OPOs are used in astronomy for Laser Guide Star systems, and they may be used for other nonlinear optics applications in astrophysics, such as frequency conversion or parametric amplification. 

A third way of generating continuously tunable coherent radiation uses more complicated systems based on the principle of optical parametric oscillation (and amplification). Since the gain in these systems is not originated by stimulated emission, but by means of a nonlinear frequency conversion process, we will treat them in a separate section. 

Therefore, it is clear that different frequency conversion processes, together with the variety of lasers, have led to a great variety of coherent sources with large and differing tuning ranges. The whole spectral range of 185-3400 nm can be covered by different methods. 

Key words Diode-pumped lasers frequency conversion modelocked lasers waveguides periodic structures, quasi-phasematching, femtosecond pulses. 

The natural way to increase the efficiency of such a frequency conversion process is to use a focused fundamental beam (or, alternatively, a waveguide structure). An established theory of SHG using focused cw beams " predicts, for negligible birefringence waUc-off, an optimal focusing condition which is expressed by the ratio L/b 2.83, where b is the confocal parameter (b = k wQ, where Wqi and ky are the focal spot radius and the wave vector of the fundamental wave respectively). However, this theory applies only to the long-pulse or cw case, where GVM is negligible... 

K.A. Tillman, D.T. Reid, D. Artigas, J. Hellstrom, V. Pasiskevicius, and F. Laurell, Low-threshold, high-repetition-frequency femtosecond optical parametric oscillator based on chirped-pulse frequency conversion, Journal of the Optical Society of America B 20 1309 (2003). 

E.U. Rafailov, D.J.L. Birkin, W. Sibbett, P. Battle, T. Fry, and D. Mohatt, Efficient direct frequency conversion of a non-resonant injection-seeded laser diode using a periodically-poled KTP waveguide crystal. Optics Letters 26(24), 1961-1962 (2001). 

The systems can produce AC or DC power directly by simple electrical additions, and provide shaft power simultaneously. Frequency can be changed by frequency conversion. 

Of the many studies of applications of L-B films, we shall mention at last the development of non-linear optical materials. A molecule such as 4-nitro-aniline has a very large hyperpolarizability (section 7.2) and can be used in principle for frequency conversion in solution if a strong electric field is used to provide an orientation of the dipoles. There is no need for such an external field if similar molecules are used in an L-B film, and hyperpolarizability values far in excess of those of commonly used inorganic crystals have been obtained. Figure 8.24 shows two examples of the molecules used in... 

Second order materials will be used in optical switching (modulation), frequency conversion (SHG, wave mixing) and electro-optic applications, especially EO modulators (SLM). The applications all rely on the manifestation of... 

Recent advances in optical technology have created great interest in the construction of second-order nonlinear optical (NLO) devices for frequency conversion and electrooptic modulation. Although inorganic substances such as LiNbO possess strong second-order NLO properties and... 

Three basic questions must be answered to ensure success in the search for an optimized nonlinear crystal for a particular application What are the most important optical properties which determine the crystal s figure of merit for the intended application What is the best methodology for characterizing those optical properties so that materials of interest can be identified efficiently Where in "materials space" can crystals with such properties be found with the highest probability Answers to these questions will be discussed in the context of a program to find improved frequency conversion crystals for high power lasers. 

Higher pressures of CO2 cause correspondingly larger increases in . At 800 torr an increase of 19% to 183 sec-1 is observed. Based on standard relaxation rate theory (29), increased relaxation rates are indicative of a shift in the average cooperative main-chain motions to higher frequencies. Conversely, this means that even small amounts of CO2 increase the cooperative motions of the polymer chains. 

The titanium-sapphire wavelength itself is too short for vibrational excitation in most molecules, and too long for electronic excitation. However, these high peak powers permit efficient frequency conversion. For example, certain crystals can convert two photons with frequency co into a single photon with frequency 2co. In many ways this can be viewed as similar to a second-order chemical reaction, such as the dimerization of NO2 to form N2O4. The rate of that reaction is proportional to the square of the NO2 concentration the rate of this frequency doubling is proportional to the square of the photon concentration (the intensity), so high powers are very useful. It is also possible to combine two photons with different frequencies co and o>i in either sum-... 

It is assumed that the PCU shaft speed is to remain constant during at-power operation. The basis is the desire to avoid the added cost of frequency conversion hardware at the generator to maintain constant... 

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