1 Introduction ................................................. 9
1.1 Short pulses and frequency combs ........................ 9
1.2 Short pulses in dispersive materials ................... 13
1.3 Generation of frequency combs .......................... 13
1.4 Measurement of carrier envelope offset frequency ....... 15
1.5 Applications of frequency combs ........................ 17
1.5.1 A frequency reference for high precision
spectroscopy .................................... 17
1.5.2 Direct excitation with frequency comb ........... 23
1.6 High precision spectroscopy of He+ ..................... 24
1.7 Frequency conversion into the ultraviolet region ....... 29
2 XUV frequency comb generation with a femtosecond
enhancement cavity .......................................... 31
2.1 Introduction ........................................... 31
2.2 High harmonic generation (HHG) ......................... 32
2.2.1 Single atom response of HHG: perturbative
regime .......................................... 32
2.2.2 Single atom response of HHG: non-perturbative
regime .......................................... 33
2.2.3 Single atom response of HHG: numerical
simulations ..................................... 40
2.2.4 Other important remarks of high harmonic
generation ...................................... 41
2.3 Femtosecond enhancement cavity ......................... 43
2.3.1 Femtosecond and continuous wave optical
cavities ........................................ 43
2.3.2 A basic model of a femtosecond cavity ........... 46
2.3.3 The effect of intracavity dispersion ............ 57
2.4 Experiments and results ................................ 59
2.4.1 Positively chirped oscillator at 10 MHz
repetition rate ................................. 59
2.4.2 Enhancement cavity .............................. 60
2.4.3 Locking of the cavity ........................... 61
2.4.4 Dispersion management of enhancement cavity ..... 65
2.4.5 High precision intracavity dispersion
measurement ..................................... 68
2.4.6 Designing chirped mirrors for high precision
dispersion compensation ......................... 73
2.4.7 Dispersion compensated broadband enhancement
cavity .......................................... 78
2.4.8 Intracavity high harmonic generation ............ 80
2.5 Conclusion ............................................. 85
3 Non-collinear high harmonic generation (NCHHG) .............. 87
3.1 Introduction ........................................... 87
3.1.1 Current outcoupling methods ..................... 87
3.1.2 New outcoupling methods ......................... 89
3.1.3 Previous demonstrations of non-collinear high
harmonic generation ............................. 94
3.1.4 A simple picture of non-collinear high
harmonic generation ............................. 95
3.2 Experimental ........................................... 97
3.3 Discussion of results .................................. 98
3.3.1 NCHHG beam profiles ............................. 98
3.3.2 Estimation of outcoupling efficiency ........... 100
3.3.3 Systematic investigation of NCHHG .............. 101
3.4 Numerical Simulation .................................. 103
3.4.1 Discussion of results .......................... 107
3.5 Conclusions ........................................... 113
3.6 Future prospects ...................................... 114
4 High repetition rate cryogenic amplifier for femtosecond
laser pulses ............................................... 117
4.1 Introduction .......................................... 117
4.1.1 Mode-locked oscillator with high average
power .......................................... 117
4.1.2 High repetition rate amplifier ................. 121
4.2 Experiments and discussions ........................... 122
4.2.1 Cryogenic Amplifier: setup ..................... 122
4.2.2 Cryogenic Amplifier: Amplification results ..... 123
4.2.3 Cryogenic Amplifier: Spectrum and pulse
duration ....................................... 124
4.2.4 Cryogenic Amplifier: White light generation
in a bulk crystal .............................. 127
4.2.5 Cryogenic Amplifier: Phase noise of the
carrier-envelope offset frequency after
amplification .................................. 127
4.2.6 Cryogenic Amplifier: Amplification of 200fs
pulses ......................................... 129
4.2.7 Peltier cooled amplifier ....................... 129
4.2.8 Beam profiles .................................. 131
4.3 Conclusions ........................................... 132
4.4 Future prospects ...................................... 133
4.4.1 Multi pass amplifier ........................... 133
4.4.2 High power oscillator combined with high
repetition rate amplifier ...................... 134
4.4.3 Heat dissipation in the enhancement cavity ..... 135
4.4.4 Coupling to the cavity ......................... 135
5 Future Prospects ........................................... 137
5.1 Ytterbium-based systems ............................... 137
5.2 Cavity-assisted high harmonic generation at shorter
fundamental wavelengths ............................... 138
5.3 Cavity-assisted high harmonic generation at
extremely high repetition rates ....................... 139
5.4 Other applications of femtosecond enhancement
cavities .............................................. 139
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