Lawrence Shah

Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate

High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for rapid writing of low-loss optical waveguides in transparent glasses. A novel femtosecond fiber laser system (IMRA America, FCPA muJewel) providing variable repetition rate between 0.1 and 5 MHz was used to study the relationship between heat accumulation and resulting waveguide properties in fused silica and various borosilicate glasses. Increasing repetition rate was seen to increase the waveguide diameter and decrease the waveguide loss, with waveguides written with 1-MHz repetition rate yielding ~0.2-dB/cm propagation loss in Schott AF45 glass. A finite-difference thermal diffusion model accurately tracks the waveguide diameter as cumulative heating expands the modification zone above 200-kHz repetition rate.

Waveguide writing in fused silica with a femtosecond fiber laser at 522 nm and 1 MHz repetition rate

We report on waveguide writing in fused silica with a novel commercial femtosecond fiber laser system (IMRA America, FCPA microJewel). The influence of a range of laser parameters were investigated in these initial experiments, including repetition rate, focal area, pulse energy, scan speed, and wavelength. Notably, it was not possible to produce low-loss waveguides when writing with the fundamental wavelength of 1045 nm. However, it was possible to fabricate telecom-compatible waveguides at the second harmonic wavelength of 522 nm. High quality waveguides with propagation losses below 1 dB/cm at 1550 nm were produced with 115 nJ/pulse at 1 MHz and 522 nm.

High energy femtosecond Yb cubicon fiber amplifier

The generation of cubicon pulses from an Yb fiber chirped pulse amplification system at pulse energies up to 200 microJ is demonstrated. After pulse compression 650 fs pulses with a pulse energy of 100 microJ are obtained, where pulse compression relies on the compensation of third-order dispersion mismatch between the stretcher and compressor via self-phase modulation of the cubicon pulses in the fiber amplifier. Values of self-phase modulation well in excess of pi can be tolerated for cubicon pulses, allowing for the nonlinear compensation of very large levels of dispersion mismatch between pulse stretcher and compressor.

High-power widely tunable thulium fiber lasers

Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides >150 W of average power, >50% slope efficiency, narrow output linewidth, and >100 nm tunability in the wavelength range around 2 μm.

Laser action in Yb3+:YCOB (Yb3+:YCa4O(BO3)3)

Abstract Infrared laser action in Yb 3+ :YCOB (Yb 3+ :YCa 4 O(BO 3 ) 3 ) is reported for the first time. Maximum output powers of ∼300 mW with a slope efficiency of 35.8% have been obtained. The observation of self-frequency doubling in this material is also reported.

Diode-pumped self-frequency doubling in a Nd3+:YCa4O(BO3)3 laser

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd3+:YCa4O(BO3)3. More than 350 mW of fundamental output power at 1060 nm was achieved with a slope efficiency of 51%. With one watt of absorbed pump power, 62 mW of green cw laser emission at 530 nm was observed with proper phase matching. This initial performance, and the good optical properties of the crystalline host, are encouraging for the development of a high power diode-pumped SFD visible light laser source.

Femtosecond laser deep hole drilling of silicate glasses in air

Femtosecond laser pulses are ideal for many precise and delicate laser processing applications. In this work, we demonstrate that femtosecond laser pulses can be used to produce microscopic holes ( 1 mm) in silicate glasses at atmospheric pressures. These experiments indicate that self-focusing is an important factor affecting hole depth at high laser intensity.

Investigation of diode-pumped, self-frequency doubled rgb lasers from Nd:YCOB crystals

Abstract As a new self-frequency doubling crystal, Nd:YCOB demonstrates a great potential for diode-pumped cw visible solid state lasers in a simple hemispherical cavity. We previously reported 62 mW cw green output with less than 1 W diode pump power absorbed in the crystal. Now we present more than 16 mW red cw laser at 666 nm from 5% Nd:YCOB crystal. As far as we know, it is the first time that diode-pumped cw red lasing is achieved by self-frequency doubling. Our effort on blue laser is also addressed.

Micromachining with a 50 W, 50 µJ, sub-picosecond fiber laser system

A 50 W sub-picosecond fiber chirped pulse amplification system generating 50 muJ pulses at a repetition rate of 1 MHz is demonstrated. As required for precision high speed micro-machining, this system has a practical system configuration enabled by the fiber stretcher and 1780 l/mm dielectric diffraction grating compressor and is capable of ablation rates >0.17 mm3/s metal, ceramic, and glass.

Lasing in thulium-doped polarizing photonic crystal fiber

We describe lasing of a thulium-doped polarizing photonic crystal fiber. A 4 m long fiber with 50 μm diameter core, 250 μm diameter cladding, and d/Λ ratio of 0.18 was pumped with a 793 nm diode and produced a polarized output with a polarization extinction ratio (PER) of 15 dB and an M(2) of <1.15. An intracavity polarizer and half-wave plate minimally increased the PER to 16 dB. The output power had 35% slope efficiency relative to the absorbed pump power. The maximum cw output power was limited to 4 W due to the quantum defect heating of the fiber.