All Mephisto family products utilize a Non-Planar Ring Oscillator (NPRO). This is a miniature monolithic laser cavity with the intracavity path completely inside the Nd:YAG crystal. The beam is reflected four times per round trip, three times via total internal reflection (TIR) and once at a quasi-normal incidence on the output mirror, coated directly on the YAG crystal. The combination of a non-planar structure, an externally applied magnetic field, the TIRs and polarization-sensitive output coupling enable unidirectional operation that is the foundation for single frequency operation. The small size of the resonator enables a wide separation of the longitudinal modes and simple thermal stabilization for optimum frequency stability. The application of mechanical force via a PZT enables fast frequency tuning at 100 kHz bandwidth over a 200 MHz frequency range.

The NPRO structure is the ultimate contamination-free solid-state laser because the entire resonator is enclosed in the bulk of the crystal. Over 15 years of expertise enabled to scale up the output power of these lasers to a 2 watt level, maintaining the extremely narrow linewidth of 1 kHz.

The NPRO head and its supporting electronics are at the heart of all Mephisto series products – Prometheus, Mephisto MOPA, MTS and Mephisto Q. All products except for the Mephisto MOPA are cooled by convection in air (heads) and by forced convection (controller). This ensures the lowest possible noise on the optical table. Mephisto MOPA requires liquid cooling via a user-supplied chiller.

All Mephisto systems use an analog controller unit. The all-analog linear design insures the lowest possible electrical noise which translates into an extremely low optical noise in the pump diodes and all the control electronics. An additional “noise-eater” circuit located in the laser head minimizes the residual pump diode and YAG relaxation oscillation noise up to 1 MHz.