Temporal coherence control of Nd:YAG pumped Raman shifter

We study the temporal coherence properties of a Nd:YAG pumped Raman shifter (pump wavelength = 355 nm) and report the control of its temporal coherence length z(e) with hydrogen gas pressure P for different input pump energies E-in. Within the range: 3.1 less than or equal to E-in less than or equal to 6.5 mJ, and for: 0.41 less than or equal to P less than or equal to 4.83 MPa, z(c) exhibits an inverse hump-like dependence with P. The shortest z(e) occurs near a (critical) pressure P = P-c approximate to 0.69 MPa, that is independent of E-in. At P = P-e the eight Stokes and anti-Stokes lines exist at their strongest in the Raman output spectrum. For P < P-c, a sharp increase in z(c) is obtained with decreasing P due to the relative dominance of the 355 nm. Rayleigh line in output spectrum. For P > P-c, a slow increase in z(c) is observed with P due to the dominance of the second-order Stokes line and the weakening of the anti-Stokes lines that is caused by the deterioration of the phase-matching condition for four-wave mixing. (C) 2001 Elsevier Science B.V. All rights reserved.