Xiongjun Zhang

One-pulse driven plasma Pockels cell with DKDP crystal for repetition-rate application

Pockels cell (PPC), which can use a thin crystal to perform the uniform electro-optical effect, is ideal component as average-power optical switch with large aperture. In this paper, the key problems in PPC are analyzed for repetition-rate application, and thermo-optical effects are simulated by means of numerical modeling when average power is loaded on the electro-optical crystal. By reformative design and employing a capacity to share the gas discharge voltage, the DKDP PPC driven by one pulse is realized. As gas breakdown delay time is stable, and discharge plasma is uniformly filled the full aperture, it meets the demand of plasma electrode for the repetition-rate PPC with DKDP crystal. The switch efficiency of PPC at the whole aperture is better than 99%.

A reflecting Pockels cell with aperture scalable for high average power multipass amplifier systems.

In high average power multi-pass amplifier systems, Pockels cell, used for isolating and controlling number of passes, encounters both limitation of aperture and thermo-effects. We propose and demonstrate for the first time, as far as we know, a reflecting Pockels cell (RPC) which is longitudinally excited based on KD*P utilizing matched a discharge chamber and a copper plate as electrodes. In the RPC, electro-optic crystal can be longitudinally conduction-cooled. This device, with a 40 mm x 40 mm clear aperture, can be scaled to larger, and driven by one low voltage pulse. Excellent switching efficiency, high static extinction ratio, and negligible thermo-effects have been achieved.

Investigating on stress-induced birefringence in vacuum windows of plasma-electrode Pockels cell

An analytical model has been developed to predict the stress-induced birefringence for both circular and square windows. Our main result is that circular windows lead to minimum birefringence because of their symmetric geometry.

Single-pulse driven, large-aperture 2×1 array plasma-electrodes optical switch for SG-II upgrading facility

We demonstrate the design and performance of an optical switch that has been constructed for the SG-II upgrading facility. The device is a longitudinal, potassium di-hydrogen phosphate (KDP), 360 mm×360 mm aperture, and 2×1 array electro-optical switch driven by a 20 kV output switching-voltage pulse generator through two plasma electrodes produced at the rise edge of the switching-voltage pulse. The results show that the temporal responses and the spatial performance of the optical switch fulfill the operation requirements of the SG-II upgrading facility.

Progress of rep-rate plasma Pockels cell technology in RCLF

Plasma Pockels cell (PPC), which can use a thin crystal to perform the uniform electro-optical effect, is ideal component as average-power optical switch with large aperture. In this paper, by reformative design and employing a capacity to share the gas discharge voltage, the DKDP PPC driven by one pulse is realized. As gas breakdown delay time is stable, and discharge plasma is uniformly filled the full aperture, it meets the demand of plasma electrode for the repetition-rate PPC with DKDP crystal. A rep-rate plasma Pockels cell (PPC) with Φ30mm aperture has been fabricated. It is optimized with the limited space of repetition rate diode pumped laser. The specification of the PPC is: static transition of 97.2%, switching efficiency of 99.8%, the switch rising time of 8.6ns. In the LD pumped Yb:YAG plate laser system, the PPC can steadily work on 10Hz repetition rate performed as Q-switch. The key problems in PPC are analyzed for repetition-rate application, and thermo-optical effects are simulated by means of numerical modeling when average power laser is loaded on the electro-optical crystal. Furthermore, the principium design of rep-rate PPC with longitudinally conductive cooled structure is described in this paper. It will efficiently abate the thermo-optical effects under repetition rate application.

Single-pulse driven plasma Pockels cell with 350mm×350mm aperture

Large-aperture plasma Pockels cell is one of important components for inertial confinement fusion laser facility. We demonstrate a single-pulse driven PPC with 350mm×350mm aperture. It is different to the PPC of NIF and LMJ for its simple operation to perform Pockels effect. With optimized operation parameters, the PPC meets the optical switching requirement of SGII update laser facility. Only driven by one high voltage pulser, the simplified PPC system would be provided with less associated diagnostics, less the maintenance, and higher reliability.

The effect of ultraviolet light on one-pulse process Pockels cell gas discharge

Pockels cell driven by one-pulse process (OPP) is a new technique different from the regular plasma electrode Pockels cell (PEPC). In the OPP regime, only the positive and negative switching pulses will be supplied on opposite sides of the crystal. The OPP Pockels cell developed in our laboratory can work well at high working pressure. In this working pressure range, the gas is steady broken at the start of the switching pulse flattop. When the working gas is evacuated to low pressure, the discharge is unsteady. In an invariable electric field, the gas discharge is determined by the initial free electrons. At low pressure, the low density of initial electrons leads to the instability of gas discharge. The ultraviolet light conduces to increasing the density of the initial free electrons, and reducing the randomness of the initial free electrons. In this experiment, the ultraviolet light is used to irradiate the cathode of the Pockels cell. The experimental results show that, at low pressure, the breakdown of the working gas is steady, and the breakdown delay is shorter with ultraviolet irradiation.