A 2 kW, 8 GHz-Linewidth Yb-Doped Polarization-Maintained Fiber Laser with Quasi-Flat-Top Pseudo Random Binary Sequence Phase Modulation for SBS Suppression.

We demonstrated a narrow-linewidth high-power Yb-doped polarization-maintaining (PM) fiber laser with near-diffraction-limited beam. The laser system consisted of a phase-modulated single-frequency seed source and four-stage amplifiers in the master oscillator power amplifier configuration. A quasi-flat-top pseudo random binary sequence (PRBS) phase-modulated single-frequency laser with a linewidth of 8 GHz was injected into the amplifiers for suppressing stimulated Brillouin scattering. The quasi-flat-top PRBS signal was readily generated from the conventional PRBS signal. The maximum output power was 2.01 kW with polarization extinction ratio (PER) of ~15 dB. The beam quality (M2) was less than 1.3 over the power scaling range.

Reflective Fourier ptychographic microscopy using a parabolic mirror.

Fourier ptychography uses a phase retrieval algorithm to reconstruct a high-resolution image with a wide field-of-view. Reflective-type Fourier ptychographic microscopy (FPM) is expected to be very useful for surface inspection, but the reported methods have several limitations. We propose a darkfield illuminator for reflective FPM consisting of a parabolic mirror and a flat LED panel. This increases the signal-to-noise ratio of the acquired images because the normal beam of each LED is directed toward the object. Furthermore, the LEDs do not have to be far from the object because they are collimated by the parabolic surface before illumination. Based on this, a reflective FPM with a synthesized numerical aperture (NA) of 1.06 was achieved, which is the highest value by reflective FPM as far as we know. To validate this experimentally, we measured a USAF reflective resolution target and reconstructed a high-resolution image. This resolved up to the period of 488 nm, which corresponds to the synthesized NA. Additionally, an integrated circuit was measured to demonstrate the effectiveness of surface inspection of the proposed system.

Coherent beam combination using self-phase locked stimulated Brillouin scattering phase conjugate mirrors with a rotating wedge for high power laser generation.

The self-phase locking of a stimulated Brillouin scattering-phase conjugate mirror (SBS-PCM) allows a simple and scalable coherent beam combination of existing lasers. We propose a simple optical system composed of a rotating wedge and a concave mirror to overcome the power limit of the SBS-PCM. Its phase locking ability and the usefulness on the beam-combination laser are demonstrated experimentally. A four-beam combination is demonstrated using this SBS-PCM scheme. The relative phases between the beams were measured to be less than λ/24.7.