Bonn 2000 – scientific programme

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Q: Quantenoptik

Q 46: Erzeugung ultrakurzer Pulse II

Q 46.2: Talk

Friday, April 7, 2000, 12:15–12:30, HS XVI

Transverse coherence properties of a VUV Laser pumped by fs-pulses. — •R. Tommasini, S. Insam, and E. Fill — Max-Planck-Institut für Quantenoptik, D-85748 Garching

Spatial coherence properties of a mirrorless VUV laser, viz. a Lyman-band molecular hydrogen laser, are investigated. The laser is pumped at 10 Hz by 200 mJ/150 fs titan-sapphire laser pulses and emits about 1 µJ at λ=160 nm. We use a Young’s double slit interferometer.

Assuming a Gaussian Schell-model source and applying the generalized van Cittert-Zernike theorem we are able to measure both the coherence length arising from free-space propagation and the coherence length at the source plane. The radiation exhibits a monotonic improvement of coherence with gain-column length, while the source size shows a pronounced decrease. As a consequence, a monotonic decrease in the number of transverse modes with length of the gain medium is observed, demonstrating the effects of gain guiding and refractive antiguiding. This analysis constitutes a new approach to the study of the coherence properties of lasers operating in the Amplified Spontaneous Emission regime and is particularly indicated for x-ray lasers.

In the specific case, the transverse coherence properties of the 160-nm hydrogen laser make it suitable for holography of samples about 1 mm in diameter at distances of about 1 metre. The relatively high repetition rate is a favorable feature for such an application.