Optical parametric oscillation OPO

DTGS = deuterated triglycine sulfate KRS — 5 = mixed thallium bromide-iodide LT = lithium tantalate MCT = mercury cadmium telluride and OPO = optical parametric oscillator. 

CD = circular dichroism CCD = charge coupled device EPR = electron paramagnetic resonance FTIR = fourier transform infra-red FWHM = full width (at) half maximum MCD = magnetic circular dichroism MLCT = metal-to-ligand charge-transfer NMR = nuclear magnetic resonance OPOs = optical parametric oscillators PSII = photosystem 11. 

CRDS Cavity ring-down spectroscopy OPO Optical parametric oscillator... 

If the phase matching condition is satisfied, the OPO (optical parametric oscillator) laser can continuously emit light of various wavelengths within the range indicated by the equation... 

NCI Non-covalent interactions OPO Optical parametric oscillator PES Potential energy surface SC Side-chain... 

Light sources can either be broadband, such as a Globar, a Nemst glower, an incandescent wire or mercury arc lamp or they can be tunable, such as a laser or optical parametric oscillator (OPO). In the fomier case, a monocln-omator is needed to achieve spectral resolution. In the case of a tunable light source, the spectral resolution is detemiined by the linewidth of the source itself In either case, the spectral coverage of the light source imposes limits on the vibrational frequencies that can be measured. Of course, limitations on the dispersing element and detector also affect the overall spectral response of the spectrometer. 

In order to achieve a reasonable signal strength from the nonlinear response of approximately one atomic monolayer at an interface, a laser source with high peak power is generally required. Conuuon sources include Q-switched ( 10 ns pulsewidth) and mode-locked ( 100 ps) Nd YAG lasers, and mode-locked ( 10 fs-1 ps) Ti sapphire lasers. Broadly tunable sources have traditionally been based on dye lasers. More recently, optical parametric oscillator/amplifier (OPO/OPA) systems are coming into widespread use for tunable sources of both visible and infrared radiation. 

The OPA should not be confiised with an optical parametric oscillator (OPO), a resonant-cavity parametric device that is syncln-onously pumped by a femtosecond, mode-locked oscillator. 14 fs pulses, tunable over much of the visible regime, have been obtained by Hache and co-workers [49, with a BBO OPO pumped by a self-mode-locked Ti-sapphire oscillator. 

Optical parametric oscillators (OPOs) represent another tunable soHd-state source, based on nonlinear optical effects. These have been under development for many years and as of this writing (ca 1994) are beginning to become commercially available. These lasers may be tuned by temperature or by rotating a crystal. Models available cover a broad wavelength range in the visible and infrared portions of the spectmm. One commercial device may be tuned from 410 to 2000 nm. 

Materials for Frequency Doubling. Second-order NLO materials can be used to generate new frequencies through second harmonic generation (SHG), sum and difference frequency mixing, and optical parametric oscillation (OPO). The first, SHG, is given in equation 3. 

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. 

It is well known that by inserting an optical amplifier obtained by population inversion in an optical cavity, one can realize sources of coherent radiations, namely lasers. One can operate in the same way with parametric amphfication as shown on Fig. 1. A nonlinear crystal illuminated by an input pump is inserted in an optical cavity. This cavity is represented for convenience as a ring cavity but consists usually of a linear cavity. An important difference with the laser is that there are three different fields, insfead of one, which are presenf in the amplifying medium, all these fields being able to be recycled by the cavity mirrors. One obtain thus different types of "Optical Parametric Oscillators" or OPOs. 

We have shown the different aspects of Optical Parametric Oscillators which explain the present interest for these sources, in fundamental as well as in applied physics. The very rapid development of compact, not power demanding sources including the pump laser and the OPO, should lead to an even wider use of such sources, in particular for industrial or medical applications. 

Optical parametric oscillator (OPO, see 20) is the real equivalent to the radio frequency shifter however OPO can be replaced by a simple addition of a local oscillator (e.g. laser) through a beam splitter. Multiplication takes place at the level of detectors. For sake of S5mimetry, detectors can be placed at both output of the beam splitter, the intermediate frequency is then the output of the differential amplifier. 

For 2PA or ESA spectral measurements, it is necessary to use tunable laser sources where optical parametric oscillators/amplifiers (OPOs/OPAs) are extensively used for nonlinear optical measurements. An alternative approach, which overcomes the need of expensive and misalignment prone OPO/OPA sources, is the use of an intense femtosecond white-light continuum (WLC) for Z-scan measurements [71,72]. Balu et al. have developed the WLC Z-scan technique by generating a strong WLC in krypton gas, allowing for a rapid characterization of the nonlinear absorption and refraction spectra in the range of 400-800 nm [72]. 

A useful source of continuously tunable radiation from the near UV to the near-IR with unexplored potential in fluorescence studies is the optical parametric oscillator (OPO). These devices have been around since the 1960s(73) and have received a lot of coverage recently in laser and optoelectronic journals/74 This resurgence of interest in OPOs has been brought about by recent improvements in nonlinear crystals and the development of all-solid-state pump-laser sources with the required levels of coherence and intensity. 

The optical parametric oscillator (OPO) is based on the parametric interaction of a strong pump wave with a nonlinear medium that has a highly nonlinear susceptibility. 

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