Mid-infrared gas filled photonic crystal fiber laser based on population inversion.

We demonstrate for the first time an optically pumped gas laser based on population inversion using a hollow core photonic crystal fiber (HC-PCF). The HC-PCF filled with 12C2H2 gas is pumped with ~5 ns pulses at 1.52 µm and lases at 3.12 µm and 3.16 µm in the mid-infrared spectral region. The maximum measured laser pulse energy of ~6 nJ was obtained at a gas pressure of 7 torr with a fiber with 20 dB/m loss near the lasing wavelengths. While the measured slope efficiencies of this prototype did not exceed a few percent due mainly to linear losses of the fiber at the laser wavelengths, 25% slope efficiency and pulse energies of a few mJ are the predicted limits of this laser. Simulations of the laser's behavior agree qualitatively with experimental observations.

Large-core acetylene-filled photonic microcells made by tapering a hollow-core photonic crystal fiber.

We report on kagomé-lattice photonic microcells with low losses, large outer diameters, and large cores. The large (40-70microm) cores are accommodated by tapering the fibers and splicing the reduced ends to a single-mode fiber. We demonstrate the repeatability of this process and obtain splice losses of 0.6dB by optimizing the taper transition length. Narrow electromagnetically induced transparencies and saturable absorption are demonstrated in an acetylene-filled photonic microcell.

Double photonic bandgap hollow-core photonic crystal fiber.

We report on the design, fabrication and characterization of hollow-core photonic crystal fiber with two robust bandgaps that bridge the benchmark laser wavelengths of 1064 nm and 1550 nm. The higher-order bandgap arises due to the extremely thin struts of the silica cladding and their fine-tuning relative to the apex size. The optimum strut thickness was found to be approximately one hundredth of the cladding pitch.

10 kHz accuracy of an optical frequency reference based on (12)C2H2-filled large-core kagome photonic crystal fibers.

Saturated absorption spectroscopy reveals the narrowest features so far in molecular gas-filled hollow-core photonic crystal fiber. The 48-68 mum core diameter of the kagome-structured fiber used here allows for 8 MHz full-width half-maximum sub-Doppler features, and its wavelength-insensitive transmission is suitable for high-accuracy frequency measurements. A fiber laser is locked to the (12)C2H2 nu(1); + nu(3) P(13) transition inside kagome fiber, and compared with frequency combs based on both a carbon nanotube fiber laser and a Cr:forsterite laser, each of which are referenced to a GPS-disciplined Rb oscillator. The absolute frequency of the measured line center agrees with those measured in power build-up cavities to within 9.3 kHz (1 sigma error), and the fractional frequency instability is less than 1.2 x 10(-11) at 1 s averaging time.

A phase-stabilized carbon nanotube fiber laser frequency comb.

A frequency comb generated by a 167 MHz repetition frequency erbium-doped fiber ring laser using a carbon nanotube saturable absorber is phase-stabilized for the first time. Measurements of the in-loop phase noise show an integrated phase error on the carrier envelope offset frequency of 0.35 radians. The carbon nanotube fiber laser comb is compared with a CW laser near 1533 nm stabilized to the nu(1) + nu(3) overtone transition in an acetylene-filled kagome photonic crystal fiber reference, while the CW laser is simultaneously compared to another frequency comb based on a Cr:Forsterite laser. These measurements demonstrate that the stability of a GPS-disciplined Rb clock is transferred to the comb, resulting in an upper limit on the locked comb's frequency instability of 1.2 x 10(-11) in 1 s, and a relative instability of <3 x 10(-12) in 1 s. The carbon nanotube laser frequency comb offers much promise as a robust and inexpensive all-fiber frequency comb with potential for scaling to higher repetition frequencies.

Visualizing the photonic band gap in hollow core photonic crystal fibers.

The light radiated from the guided mode of a hollow core photonic crystal fiber into free space is measured as a function of angle and wavelength. This enables the direct experimental visualization of the photonic band gap and the identification of localized modes of the core region.

Improved hollow-core photonic crystal fiber design for delivery of nanosecond pulses in laser micromachining applications.

We report the delivery of high-energy nanosecond pulses (approximately 65 ns pulse width) from a high-repetition-rate (up to 100 kHz) Q-switched Nd:YAG laser through the fundamental mode of a hollow-core photonic crystal fiber (HC-PCF) at 1064 nm. The guided mode in the HC-PCF has a low overlap with the glass, allowing delivery of pulses with energies above those attainable with other fibers. Energies greater than 0.5 mJ were delivered in a single spatial mode through the hollow-core fiber, providing the pulse energy and high beam quality required for micromachining of metals. Practical micromachining of a metal sheet by fiber delivery has been demonstrated.