Optical parametric amplification (OPA) may be described as a process of amplifying an input signal in the presence of a higher-frequency pump wave. Apart from signal amplification, an idler wave is also generated in the process.
Generation of an idler wave can be considered to be difference frequency generation.
Optical parametric amplification is a phenomenon that is observed in non-linear medium. Parametric amplification can also be obtained by using optical fibers, in order to make use of their third order non-linearity.
OPA is of two types, based on the type of medium - noncollinear OPA, and multipass OPA.
This article will describe the experimental set up, working, and applications of optical parametric amplification.
Experimental Set Up
In order to generate a parametrically amplified signal, the set up requires a non-linear crystal and an intense pump beam. The non-linear medium is pumped by a titanium sapphire laser, which is a high-power femtosecond laser source.
OPA can be achieved by using a single source or a dual source. The intense beam is use to amplify a low intensity seed beam. Appropriate photomultiplier set up is chosen to receive the amplified signal.
When a larger pump signal and a weaker signal are incident on a non-linear medium, the larger pump source amplifies the weak signal.
An intense pump source, having a frequency f1, and a weaker light source, at frequency f2, are incident on non-linear medium - resulting in the generation of one photon with an amplified frequency equal to f1+f2. In some cases, the weak signal need not be external; the non-linear crystal itself can supply it.
Some of the applications of the optical parametric amplification phenomenon are listed below:
- Spectroscopic measurements
- Wavelength conversion
Sources and Further Reading