Idler frequency

Infrared pulses of 200 fs duration with 150 of bandwidth centred at 2000 were used in this study. They were generated in a two-step procedure [46]. First, a p-BaB204 (BBO) OPO was used to convert the 800 mn photons from the Ti sapphire amplifier system into signal and idler beams at 1379 and 1905 mn, respectively. These two pulses were sent tlirough a difference frequency crystal (AgGaS2) to yield pulses... 

The far-infrared emission of the idler frequency was also detected 81) with an InSb detector cooled with liquid He. The power of the pulses was estimated to be about 5 W. Their frequency was not directly measured but only inferred from energy conservation. Later measurements 83> gave a power from 0.25 W at 60 gm to 3 W at 200 jum and a linewidth of 0.1 to 0.5 cm"1 for the signal radiation. 

A conceptually even simpler approach uses just one optical parametric oscillator, pumped by a dye laser or diode laser at 4f and oscillating at the two frequencies f and 3f. The signal frequency f is enforced by injection locking with light from the 3.39 pm reference laser. The pump frequency is adjusted so that the idler frequency agrees with the third harmonic of the reference laser. The seventh harmonic is then generated by simply summing idler and pump frequency. 

Figure 1 The setup used to generate intense ultrastable IR pulses. In a first frequency conversion step in a BBO optical parametrical amplifier, 800 nm pulses from a Ti sapphire amplifier are split into signal and idler pulse, which subsequently are difference frequency mixed in a AgGaS2 crystal.

One of the important applications of second-order NLO materials is obtaining of tunable laser sources. Second harmonic generation or sum frequency generation systems lead to monochromatic sources. The optical parametric oscillators are based on the parametric generation of two waves with frequencies co (signal) and CO (idler). In noncentrosymmetric materials an incident photon with frequency co creates two photons satisfying the energy... 

Let us analyze the parametric frequency conversion of the signal and idler modes initially in Fock states with photon numbers Na and Nb, respectively. By applying Eq. (67), we readily find the evolution of the two-mode Glauber-Sudarshan P-function... 

In quantum optics a downconversion process may be visualized as the decay of a pump photon into a pair of signal and idler photons of lower frequency. Provided the pumping remains not depleted and phase matching takes place, the energy of the spontaneously downconverted light monotonically increases and that of the pump beam monotonically decreases. From this point of view the downconversion process may be regarded as the decay process of an unstable... 

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