A variety of technologies have been so far demonstrated for the carrier-envelope phase (CEP) control of mode-locked oscillators. An instrumental part of these technologies is the configuration of interferometers and the application of feedback control. Of the devices, the collinear ƒ-2ƒ interferometer developed in this work is compact and robust against disturbance because the optical paths of the ƒ and 2 ƒ components are collinear within the interferometer. To compensate for the delay time between the ƒ and 2ƒ components, a birefringent time plate made of α-BBO is installed in the interferometer. We achieved an in-loop CEP stability of 27 mrad (rms) using conventional feedback control with an acousto-optic modulator to control the pump power. We believe that the collinear ƒ-2ƒ interferometer offers the best choice as an interferometer for CEP stabilization of the front-end oscillator in the chirped-pulse amplification system

To generate an intense femtosecond pulse with an energy of several mJ or more, the pulse must be sufficiently stretched and compressed using grating-based optics in a chirped pulse amplification system. However, the stability of the carrier–envelope phase (CEP) is readily degraded by movement of the diffraction gratings due to vibration caused by pump lasers and other equipment. By suppressing the vibration and acoustic waves, we reduced the CEP noise to much less than 100 mrad (rms). With feedback control using a wedge pair with a single shot f - 2 f interferometer (1 ms integration time), we were able to stabilize the CEP, achieving a CEP noise of 58 mrad (rms) at a pulse energy of 0.5 mJ and 99 mrad (rms) at a pulse energy of 7 mJ and a repetition rate of 1 kHz. We also analyzed the effects of vibration on the pulse stretcher and compressor using a geometrical optics approach and found that roof mirrors were the most influential.

We have suppressed the effects of vibration and acoustic waves on the CEP and obtained a CEP stability of 99 mrad (rms) with a pulse energy of 7 mJ at 1 kHz.