Optical Parametric Oscillation and Amplification

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. 

F ure 2.21 Different types of three-wave interaction in a nonlinear media (at the photon level) (a) sum-frequency generation and (b) the optical parametric generation. 

The interaction can be described as an inelastic scattering of a pump photon, hcop by the nonlinear medium, in which the pump photon is absorbed and two new photons, 

Fignre 2.21 shows an illustration, at the photon level, of the parametric processes compared to the sum-frequency generation process. 

In the parametric oscillation, energy conservation requires that 

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Enhancement of x2 will lead to improvement (in terms of efficiency per interaction volume) in the following applications up-conversion in the visible or near U.V. of powerful I.R. laser radiation, frequency modulation of a laser carrier beam, optical parametric oscillation and amplification for solid state infrared tunable coherent devices. 

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. 

Some of the relevant applications of nonlinear optics are currently used in laser technology and fiber communications, such as optical frequency conversion, optical parametric oscillation and amplification, the linear electrooptic effect (Pockels... 

We will restrict our description to those processes and systems that have been developed more over recent years those based on the optical parametric oscillation or amplification processes. The practical devices involve two of the most relevant solid state lasers nowadays the Nd YAG laser and the Ti-sapphire laser. 

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. 

Measurements of optieal amplification were carried out in a pump and probe experimental setup. The pump radiation was provided by an optical parametric oscillator (OPO) sintonized at 975nm with high energy pulses between 50 and 115 mJ/cm. The probe beam was obtained by a lOOOW lamp, giving a signal power density of 195 pW/cm at 650 nm. 

Summary Optical parametric oscillators are coherent devices similar to lasers. There are, however, important differences. While lasers can be pumped by incoherent sources, OPOs require coherent pump sources. Often diode laser-pumped solid state lasers are used. While in lasers coherent amplification can last until the inversion in the active medium has fallen below threshold, in OPO s the time dependence of the coherent output is directly coupled to that of the pump laser. Since the pump photon is split into signal and idler photon with u> = u>i, the energy of the output equals that of the input i.e. there is no energy, i.e. heat deposited in the active crystal. The spectral tuning range is by far wider than for tunable lasers. Most OPOs operate in the near infrared but can be tuned from the visible region to the far infrared. 

Figure 6 Block diagram of the two-color optical parametric amplifier (OPA) and IR-Raman apparatus. CPA = Chirped pulse amplification system Fs OSC = femtosecond Ti sapphire oscillator Stretch = pulse stretcher Regen = regenerative pulse amplifier SHGYAG = intracavity frequency-doubled Q-switched Nd YAG laser YAG = diode-pumped, single longitudinal mode, Q-switched Nd YAG laser KTA = potassium titanyl arsenate crystals BBO = /J-barium borate crystal PMT = photomultiplier tube HNF = holographic notch filter IF = narrow-band interference filter CCD = charge-coupled device optical array detector. (From Ref. 96.)...

Applications of second order nonlinear optical materials include the generation of higher (up to sixth) optical harmonics, the mixing of monochromatic waves to generate sum or difference frequencies (frequency conversion), the use of two monochromatic waves to amplify a third wave (parametric amplification) and the addition of feedback to such an amplifier to create an oscillation (parametric oscillation). 

Bortz, M. L., Arbore, M. A., and Fejer, M. M., Quasi-phase-matched optical parametric amplification and oscillation in periodically poled LiNbOj waveguides, Opt. Lett., 20, 49-51 (1995). 

Polymeric materials are playing an increasingly important role in electronic and photonic applications ". This includes application in active devices utilizing optical effects attributable to the nonlinear polarization of the medium, A number of applications such as frequency mixing, second harmonic generation, optical bistability, optical parametric amplification and oscillation, electrooptic and all optical switching and modulation etc. have been proposed. 

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