Junewen Chen

Self-pumped phase conjugation with femtosecond pulses by use of BaTiO 3

Self-pumped phase conjugation is generally believed to be attributed to degenerate four-wave mixing. Accordingly, the phenomenon requires the existence of three waves at certain interaction regions for the excitation of the fourth one. Although this condition is not satisfied by a train of femtosecond pulses with a repetition rate of 110 MHz, we have observed self-pumped conjugate pulses retroref lected by a BaTiO(3) crystal. The conjugate character of the pulses is demonstrated with the distorter method.

Passive Q-switch and mode-locking modulators for Nd : hosted lasers

Abstract Four kinds of currently available Nd : hosted laser passive Q-switch and mode-locking modulators: plastic dye sheet, LiF : F 2 − color center crystal, Cr +4 : YAG crystal and RG1000 colored glass filter were investigated in detail and summarized for comparison for the first time. The LiF : F 2 − crystal with outstanding annealability, long lifetime, low cost and operability at high repetition rates is highly recommended.

Self-pumped phase conjugation with picosecond and femtosecond pulses using BaTiO3

Abstract Self-pumped phase conjugate pulses due to picosecond and femtosecond pulses in near IR have been demonstrated. We generated the conjugate pulses with a BaTiO3 crystal, the direction of the c axis of which in the setup is different from that of the Cat conjugator. The conjugate character of the conjugate pulses are examined with the distorter method. The reflectivity of the picosecond conjugate waves was about six times higher than that of the femtosecond pulses and the rise time of the former was about 30 times faster that of the latter, when the average power of two trains of pulses are equal. Explanation of the phenomenon is proposed.

Energy extraction of Porro resonator in Pockels cell Q-switch operation

Deviation of a practical Pockels cell Q-switch bias voltage from the ideal bias value significantly affects the extraction of useful output energy. The losses of two practical bias voltages are calculated and the properly rotated angle towards the right-hand side prism of the Porro resonator is determined to simulate the different losses. The losses are due to deviation of the Q-switch bias voltage from the ideal value. It not only degrades the useful output energy, but introduces a useless energy loss in the reverse output direction. For the different losses of these two practical Pockels cell bias voltages, the useful output energy difference is about 30%. The useful output energy and lost energy ratios of the two equivalent loss configurations are 0.54 and 0.89, respectively. These ratios agreed quite well with the theoretical results.

Mode selection of slowly opened Q-switch operation

Abstract The beam divergence angle is measured of the Q-switched laser pulse resulting from a resonator switched with a Pockels cell which is driven with a slowly opened circuit using a transformer. The rise time of the output voltage of this transformer type circuit is controllable. After optimization, the beam divergence of the present laser system is decreased by 30% compared with the conventional system using a Krytron. A model concerning the mode selection in the resonator is proposed.

Compact laser sources for photorefractive research

Phase conjugate phenomenon and mechanism with BaTiO3 photorefractive crystals have been investigated using various cw sources and all the way down with ultrashort pulses of the femtosecond region. Our laser sources support all the various pulsewidths at a wide range of different spectral regions.

Ordinary polarized phase conjugator using the photovoltaic effect

Abstract Self-pumped phase conjugators so far always work with extraordinary (e) polarized light waves. Theoretical analysis however has pointed out that the e-polarized waves and ordinary (o) polarized waves could be coupled together via the circular photovoltaic effect. We report here an experimental realization of this theoretical prediction and present an o-polarized conjugator. The core element of this setup is a 0°-cut undoped BaTiO 3 crystal, which is aligned in a Cat-conjugator architecture with respect to an incident beam of e-polarized waves. Simultaneously we shine a beam of o-polarized waves on the crystal. Upon the appearance of the e-conjugate waves, we also observed the o-conjugate waves. The resolution of this ordinary polarized phase conjugator is comparable to that of the prevailing e-waves conjugators.