Efficient diode-pumped Er:YAP master-oscillator power-amplifier system for laser power improvement at 2920 nm

We report on the first demonstration of laser-diode-pumped master-oscillator power-amplifier (MOPA) system based on Er-doped bulk material working at 2920 nm. The relaxation oscillation at the beginning of the laser pulse from the Er:YAlO3 (YAP) oscillator was suppressed effectively when the pump frequency was increased to 140 Hz, as a result of the establishment of a three-level system. In the amplifier, the small signal gain of the Er:YAP strongly depends on pump duration and repetition frequency, and can reach the upper limit of parasitic oscillation. Further, 25.5 mJ of output pulse energy has been achieved from the amplifier at 150 Hz frequency (2.2 ms pump duration), with over 32% of optical-to-optical efficiency. Further improvement of the amplification ability of the MOPA system was discussed

Electro-optically Q-switched operation of a high-peak-power Tb:LiYF4 green laser

We report on an electro-optically Q-switched Tb:LiYF4 green laser pumped by a frequency-doubled optically pumped semiconductor blue laser. The electro-optically Q-switched characteristics were studied under a wide range of repetition rates from 200 Hz to 50 kHz using a KD2PO4 Q-switch. Up to 198 µJ of pulse energy was obtained with a pulse width of 248 ns at a repetition rate of 200 Hz, corresponding to a peak power of 797 W at 544 nm

Verdet constant dispersion of magnesium fluoride for deep-ultraviolet and vacuum-ultraviolet Faraday rotators

The Verdet constant dispersion in magnesium fluoride (MgF2) crystals was evaluated over a wavelength range of 190–300 nm. The Verdet constant was found to be 38.7 rad/(T·m) at a wavelength of 193 nm. These results were fitted using the diamagnetic dispersion model and the classical Becquerel formula. The fitted results can be used for the designing of suitable Faraday rotators at various wavelengths. These results indicate the possibility of using MgF2 as Faraday rotators not only in deep-ultraviolet regions, but also in vacuum-ultraviolet regions owing to its large bandgap

A passively Q-switched compact Er:Lu2O3 ceramics laser at 2.8 μm with a graphene saturable absorber

We have demonstrated a passively Q-switched Er:Lu2O3 ceramics laser using a monolayer graphene saturable absorber (SA). Stable pulsed operation with watt-level average power was achieved by a compact linear cavity without focusing on the SA. This is the first demonstration of a passively Q-switched mid-IR Er:Lu2O3 laser using a graphene SA. A maximum pulse energy of 9.4 μJ and a peak power of 33 W were achieved with a 247 ns pulse duration. To our knowledge, this is the shortest pulse duration, highest pulse energy, and highest peak power obtained with a graphene SA in the 3 μm wavelength region

High-efficiency, continuous-wave Fe:ZnSe mid-IR laser end pumped by an Er:YAP laser

Fe:ZnSe lasers operating in the mid-IR spectral region have gained widespread attention due to their numerous potential applications. This study presents a high-efficiency, continuous-wave Fe:ZnSe laser end pumped by an Er:YAP laser at 2920 nm. The Er:YAP laser was home-constructed and generated an output power of 3.6 W and an average slope efficiency of 36.6% with a good beam quality (M2 ≤ 2). The Fe:ZnSe laser produced a maximum output power of 1 W at 4.06 µm for 2.1 W of absorbed pump power, corresponding to an average slope efficiency of 48%. Theoretical modeling of the continuous-wave Fe:ZnSe laser is presented to determine the prospects for further power scaling

Effect of erbium concentration on the Verdet constant dispersion of LiY1.0-xErxF4 single crystal

The dispersion of the Verdet constant of LiY1.0-xErxF4 crystals was evaluated from 190 nm to 500 nm for different doping concentrations of Er ions. A 15% doping concentration yielded a high Verdet constant of 54.5 rad/(T·m) at 193 nm. This value can be explained by the contribution of the diamagnetic term associated with LiYF4 and the paramagnetic term of the Er ions. Although the LiYF4 crystal yielded a lower value of −36.6 rad/(T·m) at 193 nm from Er-doped LiYF4, it can be used in the vacuum–ultraviolet region because of its high transmittance at wavelengths longer than 120 nm

Conceptual Design of Electron Density Measurement System for DEMO-Relevant Helical Plasmas

Electron density measurement remains indispensable to control fueling on a DEMO reactor. For steady-state operation of the DEMO reactor, density measurement should be highly reliable and accurate. A dispersion interferometer and a Faraday polarimeter are free from measurement errors caused by mechanical vibrations. Hence combination of the two diagnostics yields a suitable system for density measurement on future steady-state fusion reactors. A wavelength around 1 ?m is one of the desirable candidates in terms of the fringe shift and the Faraday rotation angle, the variety of optical components, and the efficiency of frequency doubling for the dispersion interferometer. This paper presents a conceptual design for the dispersion interferometer and Faraday polarimeter with a 1 ?m light source

Nd3+-activated CaF2 ceramic lasers

Nd,Y:CaF2 and Nd,La:CaF2 ceramics featuring good optical quality have been fabricated by reactive sintering and a hot isostatic pressing method. The transmission spectra, emission spectra, and fluorescence decay curves were measured. Lasing at 1064 and 1065 nm was observed in Nd,Y:CaF2 and Nd,La:CaF2, respectively, upon quasi-continuous-wave pumping by a diode laser emitting at 791 nm. To the best of our knowledge, this is the first demonstration of Nd3+-activated CaF2 ceramic laser

Ultra-high-molecular-weight Polyethylene (UHMWPE) Wing Method for Strong Cranioplasty

We developed a new cranioplasty method that utilizes artificial bone made of ultra-high-molecular-weight polyethylene, with a wedge-shaped edge (UHMWPE Wing). This study shows the methods and data of case series and finite element analyses with the UHMWPE Wing. A circumferential wing was preoperatively designed for a custom-made artificial bone made of UHMWPE to achieve high fixed power and to minimize the usage of cranial implants. Here, we present 4 years of follow-up data and finite element analyses for patients treated with the UHMWPE Wing between February 2015 and February 2019. Eighteen consecutive patients underwent cranioplasty using our UHMWPE Wing design. There were no postoperative adverse events in 17 of the patients for at least 18 months. One case of hydrocephalus experienced screw loosening and graft uplift due to shunt malfunction. Placement of a ventriculo-peritoneal shunt immediately returned the artificial bone to normal position. Finite element analyses revealed that a model using the UHMWPE Wing had the highest withstand load and lowest deformation. This is the first report on the UHMWPE Wing method. This method may enable clinicians to minimize dead space and achieve high strength in cranioplasty

Calibrations of the LHD Thomson scattering system

The Thomson scattering diagnostic systems are widely used for the measurements of absolute local electron temperatures and densities of fusion plasmas. In order to obtain accurate and reliable temperature and density data, careful calibrations of the system are required. We have tried several calibration methods since the second LHD experiment campaign in 1998. We summarize the current status of the calibration methods for the electron temperature and density measurements by the LHD Thomson scattering diagnostic system. Future plans are briefly discussed