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This dissertation focuses on the study of novel high-gain free-electron laser (FEL) operation schemes with external seed lasers. The technique of manipulating the phase space of the electron beam, which is widely used in novel seeded FEL schemes, is systematically studied. Several novel FEL schemes are proposed for the generation of intense coherent FEL pulses with short wavelength, sub-femtosecond pulse length or multiple carrier frequency properties, which meet the needs of FEL users. Results of experiments are described for the recently proposed FEL schemes such as echo-enabled harmonic generation and cascaded high-gain harmonic generation. New photon/electron beam diagnostic methods are also developed for these experiments and future high-gain FEL facilities.

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Introduction.- Basic theory of free-electron laser.- Theoretical studies for novel high-gain FEL schemes.- Experimental studies for novel high-gain FEL schemes.- Conclusions and prospects.

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Dr. Feng received his Ph. D. from Shanghai Institute of Applied Physics in 2013. Currently he is an Assistant Researcher at Shanghai Institute of Applied Physics. His research focuses on the theoretical and experimental studies on high-gain free-electron laser principle, operations schemes, key technologies and advanced beam diagnostic methods.

Awards received by Dr. Feng:
2014 Excellent Doctoral Dissertation of Chinese Academy of Sciences
2013 Chinese Institute of Science Dean´s Award
2013 National Scholarship for PhD students

Publications by Dr. Feng:
1. C. Feng et al., New J. Phys. 16, (2014) 043021.
2. C. Feng, et al., Phys. Rev. ST Accel. Beams 17, (2014) 070701.
3. C. Feng, et al., Phys. Rev. ST Accel. Beams 17, (2014) 100702.
4. H. Deng and C. Feng, Phys. Rev. Lett. 111, (2013) 08480.
5. C. Feng , et al., Nucl. Instrum. Methods A 712 (2013) 113.
5. C. Feng, et al., Phys. Rev. ST Accel. Beams 16, (2013) 060705.
6. Z.T. Zhao et al., Nat Photon 6, (2012) 360.
8. C. Feng et al., Phys. Rev. ST Accel. Beams 15, (2012) 080703.
9. C. Feng et al., Chin. Sci. Bull. 57 (2012) 3423.
10. C. Feng et al., Phys. Rev. ST Accel. Beams 14, (2011) 090701.
11. C. Feng et al., Chin. Sci. Bull. 55 (2010) 221.

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