A Seeded Optical Parametric Generator/Amplifier

The seeded optical parametric generator (OPG) is a broadly tunable, narrow linewidth source.  The OPG principal is shown in Figure 1 below.  On a single pass through the crystal, the conversion efficiency of a pump laser to the signal and idler can be high for nsec pulses.  However, as shown in figure 2, the bandwidth is large.  Our approach to narrowing up the bandwidth is to inject a narrow linewidth seed that is tuned within the signal bandwidth.  Currently we us a diode laser, but we have used other schemes such as the filtered output of a first stage OPG. 
OPG Stage
 

Figure 1.  An OPG:  simply focus a pump laser through a crystal.  If the crystal nonlinearity is high enough, and for high peak-power pump pulses, the efficiency can be high (~20%). 

 

Figure 2.  The signal output of an OPG both seeded and unseeded.  Note that the seeded axis is the left axis and the unseeded is the right axis.  The seeded peak intensity is approximately 30 times the unseeded peak intensity. 

The tunability of the device is determined by the phasematching properties of the OPG crystal.  In the case of periodically poled crystals such as PPLN, any frequency within the transparency range of lithium niobate is accessible. We have demonstrated tunabilty from 1.4 to 4.7 microns, see Figure 3.

 

Figure 3.  Tuning range for the OPG system.