Tham khảo tài liệu 'advances in solid-state lasers: development and applicationsduration and in the end limits part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 432 Advances in Solid-State Lasers Development and Applications where S1 and S2 are respectively the distances G1-P2 and P3-G2. For S 2p G1 is imaged behind G2 and the resulting GDD is positive. For S 2p G1 is imaged before G2 and the resulting GDD is negative. The three cases are illustrated in Fig. 17. The chirp of the pulse can be varied by changing S S1 S2. It is simpler to keep S1 constant and to finely adjust S2 for changing the GDD. The variation of S2 is performed by mounting G2 on a linear translator and moving it along an axis coincident with the straight line that connects G2 to P3. Since the beam diffracted from G2 is collimated in a constant direction the radiation reflected from P4 is focused always on the same output point. Therefore the compressor has no moving parts except the translation of G2 for the fine tuning of the GDD. The modeling of the compressor is done by ray-tracing simulations. The group delay is calculated for different values of the distance S. The GDD is then defined as the derivative of the group delay with respect to the frequency. The higher effects on the phase of the pulse can be analogously calculated by successive derivatives. S Ọ P3 P4 -b-G2 G1 - P3 P2 a GDD 0 Intermediate Plane P4 P1 P3 P4 v V G2 _ S S c b GDD 0 S c c GDD 0 Srb-G1 -S-- -G2 Fig. 17. Operation of the XUV attosecond compressor a GDD equal to zero b positive GDD c negative GDD. As a test case of the optical configuration the design of a compressor in the 12-24 nm region is presented. The grazing angle on the mirrors is chosen to be 3 for high reflectivity. The acceptance angle is 6 mrad which matches the divergence of XUV ultrashort pulses. The size of the illuminated portion of the paraboloidal mirrors results 23 mm X mm. On such Diffraction Gratings for the Selection of Ultrashort Pulses in the Extreme-Ultraviolet 433 a small area manufacturers routinely can produce paraboloidal mirrors with very-high quality finishing both in terms of figuring .
