Taverner, D., Britton, P.J., Smith, P.G.R., Richardson, D.J., Ross, G.W. and Hanna, D.C.
High efficiency second harmonic and sum frequency generation of nanosecond pulses in a cascaded erbium doped fibre:PPLN source
At 13th Quantum Electronics Conference (QE13), United Kingdom.
08 - 11 Sep 1997.
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Recently, femtosecond erbium fibre lasers have been used with periodically poled lithium niobate(PPLN) to demonstrate frequency doubling with up to 25% conversion efficiency, and using the second harmonic, to pump an Optical Parametric Generator (OPG). However, for many applications e.g. pumping of nanosecond Optical Parametric Oscillators (OPOs) pulses with greater energies are required, for which diode-pumped, large mode-area erbium doped fibre amplifiers (LA-EDFA) and lasers are ideally suited. The combination of diode-pumped, LA-EDFA sources with periodically poled lithium niobate creates an extremely attractive technology for the development of a wide range of practical wavelength tuneable sources. In this work both diode-seeded LA-EDFA chains and Q-switched sources were used to demonstrate extremely high second and third harmonic single pass conversion efficiencies in PPLN. Continuously tunable operation over the erbium gain bandwidth was demonstrated with pulses from 2 to 50ns, repetition rates from 1kHz to 150kHz, and pulse energies of up to 50µJ.
Output pulses at a fundamental wavelength of 1536nm were frequency doubled in PPLN, to produce 768nm light with internal conversion efficiencies as high as 83% in a single pass for a peak power of 1.2kW. A second PPLN crystal was used to mix the second harmonic with the remaining fundamental to generate green light at 512nm, with up to 34% internal conversion efficiency. Both PPLN samples were 16mm long and fabricated in 0.5mm thick z-cut lithium niobate by electrical poling. The periods were 18.05µm for SHG and 6.5µm for sum frequency generation.
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