A train of laser pulses with a constant pulse-to-pulse carrier-envelope phase (CEP) shift generates a series of equal-spacing frequencies in the frequency domain, which is called the frequency comb [Rev. Mod. Phys. 75, 325 (2003)]. To explore the interaction between the matter and frequency comb laser, I have developed the time propagation method of the time-dependent Schrödinger equation to handle a pulse train with a long separation of pulses and have extended the many-mode Floquet theorem (MMFT) to exactly treat a series of frequencies. The comb structure and coherence can be extended to the xuv–vuv regimes via high-order harmonic generation (HHG). Using the time propagation method, the nested comb structure is observed within each harmonic, even in the presence of appreciate ionization, which originated from quantum interference among induced dipole pulses [1]. Using MMFT, it is possible to coherently control HHG enhancement by tuning the CEP shift, due to simultaneous multiphoton resonances from all the comb frequencies [2]. Both approaches are complementary and enable us to explore and control the frequency comb structure and coherence. The frequency comb technology can be extended to the study of coherent control of chemical and physical processes in the future.