Mode-converters for rectangular-core fiber amplifiers to achieve diffraction-limited power scaling.

A rectangular-core (ribbon) fiber that guides and amplifies a single higher-order-mode (HOM) can potentially scale to much higher average powers than what is possible in traditional circular-core large-mode-area fibers. Such an amplifier would require mode-conversion at the input to enable interfacing with seed sources that typically output TEM(00) mode radiation and at the output to generate diffraction-limited radiation for end-user applications. We present the first simulation and experimental results of a mode conversion technique that uses two diffractive-optic-elements in conjugate Fourier planes to convert a diffraction limited TEM(00) mode to the HOM of a ribbon fiber. Mode-conversion-efficiency is approximately 84% and can theoretically approach 100%. We also demonstrate a mode-converter system that converts a single HOM of a ribbon fiber back to a diffraction-limited TEM(00) mode. Conversion efficiency is a record 80.5%.

Brightness enhancement in a high-peak-power cladding-pumped Raman fiber amplifier.

We demonstrate a cladding-pumped Raman fiber amplifier (CPRFA) whose brightness-enhancement factor depends on the cladding-to-core diameter ratio. The pump and the signal are coupled independently into different input arms of a pump-signal combiner, and the output is spliced to the Raman amplifier fiber. The CPRFA generates 20 microJ, 7 ns pulses at 1100 nm at a 2.2 kHz repetition rate with 300 microJ (25.1 kW peak power) of input pump energy. The amplified signal's peak power is 2.77 kW, and the brightness-enhancement factor is 192--the highest peak power and brightness enhancement achieved in a CPRFA at any wavelength, to our knowledge.

High-gain photonic crystal fiber regenerative amplifier.

We have demonstrated a photonic crystal fiber-based regenerative amplifier at 1.078 microm. The input signal pulse energy is 20 pJ in a 12 ns pulse at a 3 kHz repetition rate. At 8.6 W of input pump power, the amplified output pulse energy is 157 microJ, yielding a gain of 69 dB. To our knowledge, this is the highest gain achieved in a fiber-based regenerative amplifier to date at any wavelength.

Zigzag slabs for solid-state laser amplifiers: batch fabrication and parasitic oscillation suppression.

We have developed a 100 W class Nd:YAG master oscillator power amplifier system based in part on an end-pumped zigzag slab power amplifier. This amplifier incorporates parasitic oscillation suppression by using roughened edges and achieves a small-signal gain coefficient (g(0)l) of 8.06. We describe a novel technique for suppression of parasitic oscillations using claddings on slab edges that significantly increases g(0)l to 11.63 and increases the single-pass extracted power in a power amplifier by 50%. Commercial use of these zigzag slab amplifiers has been limited by the time and cost of production. We describe a new batch fabrication technique that improves the quality and significantly reduces the cost of zigzag slabs.