Valery Philippov

High-energy in-fiber pulse amplification for coherent lidar applications

An Er:Yb codoped fiber amplifier chain for the generation of pulses for coherent lidar applications at a wavelength near 1.5 microm is reported. The final 1.8-m-long power amplification stage had a 50-microm core diameter and yielded a 23-dB energy gain, resulting in 0.29-mJ, 100-ns pulses at a repetition rate of 4 kHz with no Brillouin scattering and an M2 of 2.1.

A 980-nm Yb-doped fiber MOPA source and its frequency doubling

A continuous-wave (CW) master oscillator-power amplifier (MOPA) fiber source, tunable around 978 nm, was frequency-doubled to 488.7 nm. Both the laser and the amplifier were made with cladding-pumped jacketed air-clad Yb-doped fibers. The MOPA generated up to 2.7 W of power in an output beam with an M/sup 2/ value of 1.8. This was frequency-doubled in a periodically poled potassium titanyl phosphate crystal at room temperature, in a single-pass configuration. The generated blue light had a CW power of 18.1 mW, a nearly Gaussian spatial intensity profile, and an M/sup 2/ value of 1.7.

Neodymium-doped cladding-pumped aluminosilicate fiber laser tunable in the 0.9-/spl mu/m wavelength range

A tunable high-power cladding-pumped neodymium-doped aluminosilicate fiber laser is demonstrated. The maximum power reached was 2.4 W with a slope efficiency of 41% and a threshold pump power of 1.68 W, both with respect to launched pump power, when cladding pumped by two 808-nm diode pump sources at both fiber ends. The dependence of the tuning range on the fiber length is investigated. The tuning range changed from 922 to 942 nm for a 25-m-long fiber to 908-938 nm with a 14-m-long fiber, because of reabsorption effects. The output linewidth was 0.26 nm in a diffraction-limited beam. Operation on the challenging 0.9-/spl mu/m three-level transition in neodymium-doped double-clad fiber laser was facilitated by a W-type core refractive index profile. This filtered out the unwanted and competing strong transition at 1.06 /spl mu/m while guidance of 0.9 /spl mu/m remained intact.

Modal power decomposition of beam intensity profiles into linearly polarized modes of multimode optical fibers.

We calculate the modal power distribution of a randomly and linearly polarized (LP) multimode beam inside a cylindrical fiber core from knowledge of spatial-intensity profiles of a beam emitted from the fiber. We provide an exact analysis with rigorous proofs that forms the basis for our calculations. The beam from the fiber end is collimated by a spherical lens with a specific focal length. The original LP-mode basis is transformed by the spherical lens and forms another orthogonal basis that describes the free-space beam. By using this basis, we calculate the modal power distribution from the mutual-intensity profile. This is acquired by adopting a well-known mutual-intensity-profile-retrieving technique based on measurements of the intensity patterns several times after two orthogonal cylindrical lenses with varying separation. The feasibility of our decomposition algorithm is demonstrated with simulations.

Kilowatt-class single-frequency fiber sources

We discuss the dramatic development of high-power fiber laser technology in recent years and the prospects of kilowattclass single-frequency fiber sources. We describe experimental results from an ytterbium-doped fiber-based multihundred-watt single-frequency, single-mode, plane-polarized master-oscillator power amplifier (MOPA) operating at 1060 nm and a similar source with 0.5 kW of output power, albeit with a degraded beam quality (M2 = 1.6) and not linearly polarized. Experiments and simulations aimed at predicting the Brillouin limit of single-frequency system with a thermally broadened Brillouin gain are presented. These suggest that single-frequency MOPAs with over 1 kW of output power are possible. In addition, the power scalability of a simple single-strand fiber laser to 10 kW is discussed.

All-fiber 1.15-mJ pulsed eye-safe optical source

We report a MOPA (master oscillator - power amplifier) pulsed optical fiber source emitting high-brightness radiation (M2 = 1.65) in the “eye-safe” 1.55 μm region. A high pulse energy of 1.15 mJ was reached at low repetition rates while the maximum average output power was 2.2 W at a wavelength of 1562 nm.

Passively Q-switched Er-Yb double-clad fiber laser with Cr2+:ZnSe and Co2+:MgAl2O4 as a saturable absorber

Here we report, for the first time to our knowledge, a cladding-pumped passively Q-switched Er-Yb codoped fiber laser with Cr2+:ZnSe and Co2+:MgAl2O4 as saturable absorbers. The maximum average output power for both crystals was 1.4 W, with typical pulse energy was 20 μJ corresponding to 60 W peak power. The pulse duration could be varied between 370 - 700 ns and repetition rate between 20 and 85 kHz by adjusting the pump power.

A 4.3W 977nm ytterbium-doped jacketed-air-clad fiber amplifier

A cladding pumped jacketed-air-clad ytterbium-doped fiber amplifier operating at 977 nm produced 4.3 W of single-mode output power with 300 mW of input power from a diode seed laser. The small-signal gain was 19 dB.

Recent advances in high power fiber lasers

We will review recent progress on cladding-pumped fiber devices with output powers up to the kilowatt level and broad wavelength tunability in the 1 - 2 µm wavelength regime where silica fibers work well.

Passively Q-switched thulium-doped silica fiber laser

A thulium-doped fiber laser generated pulses with 12 /spl mu/J energy and 16 ns duration at 1822 nm, when passively Q-switched by a Cr/sup 2+/:ZnSe crystal saturable absorber. The repetition rate varied between 2-20 kHz.