Gamma-shaped long-cavity normal-dispersion mode-locked Er-fiber laser for sub-nanosecond high-energy pulsed generation

We propose the design of a novel ?-shaped fiber laser resonator and apply it to build a long-cavity normaldispersion mode-locked Er-fiber laser which features enhanced functionalities for management and optimization of pulsed lasing regimes. We report the generation of sub-nanosecond pulses with the energy of ~0.5 µJ at a kilohertz-scale repetition rate in an all-fiber system based on the new laser design. A combination of special design solutions in the laser, such as polarization instability compensation in the ultra-long arm of the resonator, intra-cavity spectral selection of radiation with a broadband fiber Bragg grating, and polarization selection by means of a tilted refractive index grating, ensures low amplified spontaneous emission (ASE) noise and high stability of the laser system output parameters.

Direct cavity assessment and mode optimisation technique for DFB fibre laser

A technique for direct real-time assessment of a distributed feedback fibre laser cavity conditions during operation is demonstrated and used to provide a cavity mode conditioning feedback mechanism to optimise output performance. Negligible wavelength drift is demonstrated over a 52 mW pump power range.

Gamma-shaped long-cavity normal-dispersion mode-locked Er-fiber laser for sub-nanosecond high-energy pulsed generation

We propose the design of a novel ?-shaped fiber laser resonator and apply it to build a long-cavity normaldispersion mode-locked Er-fiber laser which features enhanced functionalities for management and optimization of pulsed lasing regimes. We report the generation of sub-nanosecond pulses with the energy of ~0.5 µJ at a kilohertz-scale repetition rate in an all-fiber system based on the new laser design. A combination of special design solutions in the laser, such as polarization instability compensation in the ultra-long arm of the resonator, intra-cavity spectral selection of radiation with a broadband fiber Bragg grating, and polarization selection by means of a tilted refractive index grating, ensures low amplified spontaneous emission (ASE) noise and high stability of the laser system output parameters.

Optical fiber cavity ring down measurement of refractive index with a microchannel drilled by femtosecond laser

A microchannel was inscribed in the fiber of a ring cavity which was constructed using two 0.1%:99.9% couplers and a 10-m fiber loop. Cavity ring down spectroscopy was used to measure the refractive index (RI) of gels infused into the microchannel. The ring down time discloses a nonlinear increase with respect to RI of the gel and sensitivity up to 300 µs/RI unit and an index resolution of 1.4 × 10 was obtained. © 2009 IEEE.

Broadly tunable InGaAsP-InP strained multiquantum-well external cavity diode laser

In this letter, we demonstrate a broadly tunable InGaAsInP strained multiquantum-well external cavity diode laser, which operates in the spectral range of 14941667 nm. A maximum continuous-wave output power in excess of 81 mW and sidemode suppression ratio higher than 50 dB were achieved in the central part of the tuning range. Different pump current and temperature regimes are investigated. © 2006 IEEE.

202nm continuous tuning from high-power external-cavity InAs/GaAs quantum-dot laser

Record broadly tunable high-power external cavity InAs/GaAs quantum-dot diode laser is demonstrated. A maximum output power of 455mW and a side-mode suppression ratio >45dB in the central part of the tuning range are achieved. ©2010 IEEE.

Broadly tunable CW green-to-red laser source based on frequency doubling of a quantum-dot external cavity diode laser in a PPKTP waveguide

Here we present a compact tunable all-room-temperature frequency-doubling scheme, using a periodically poled potassium titanyl phosphate (PPKTP) waveguide and a QD-ECDL. A broad wavelength tunability of the second harmonic generated light (SHG) in the spectral region between 567.7 and 629.1 nm was achieved, with maximum conversion efficiencies in range of 0.34%-7.9%. The maximum output power for the SHG light was 4.11 mW at 591.5 nm, achieved for 52 mW of launched pump power at 1183 nm, resulting in a conversion efficiency of 7.9%.

Broad wavelength tunability from external cavity quantum-dot mode-locked laser

Broadband wavelength tunability over 136 nm (between 1182.5 nm and 1319 nm) of picosecond pulses in passive mode-locked regime is demonstrated in a multi-section quantum-dot laser in external cavity configuration at room temperature. The maximum peak power of 870 mW with 15 ps pulse duration was achieved at 1226 nm wavelength. © 2012 American Institute of Physics.

Surface roughness after excimer laser ablation using a PMMA model:profilometry and effects on vision

PURPOSE: To show that the limited quality of surfaces produced by one model of excimer laser systems can degrade visual performance with a polymethylmethacrylate (PMMA) model. METHODS: A range of lenses of different powers was ablated in PMMA sheets using five DOS-based Nidek EC-5000 laser systems (Nidek Technologies, Gamagori, Japan) from different clinics. Surface quality was objectively assessed using profilometry. Contrast sensitivity and visual acuity were measured through the lenses when their powers were neutralized with suitable spectacle trial lenses. RESULTS: Average surface roughness was found to increase with lens power, roughness values being higher for negative lenses than for positive lenses. Losses in visual contrast sensitivity and acuity measured in two subjects were found to follow a similar pattern. Findings are similar to those previously published with other excimer laser systems. CONCLUSIONS: Levels of surface roughness produced by some laser systems may be sufficient to degrade visual performance under some circumstances.

Analysis of femtosecond laser surface patterning on bulk single-crystalline diamond

Preliminary work is reported on 2-D and 3-D microstructures written directly with a Yb:YAG 1026 nm femtosecond (fs) laser on bulk chemical vapour deposition (CVD) single-crystalline diamond. Smooth graphitic lines and other structures were written on the surface of a CVD diamond sample with a thickness of 0.7mm under low laser fluences. This capability opens up the opportunity for making electronic devices and micro-electromechanical structures on diamond substrates. The fabrication process was optimised through testing a range of laser energies at a 100 kHz repetition rate with sub-500fs pulses. These graphitic lines and structures have been characterised using optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Using these analysis techniques, the formation of sp2 and sp3 bonds is explored and the ratio between sp2 and sp3 bonds after fs laser patterning is quantified. We present the early findings from this study and characterise the relationship between the graphitic line formation and the different fs laser exposure conditions. © 2012 Taylor & Francis.

Femtosecond laser microstructuring through optical fibre end faces:inscription of surface gratings and sub-surface splitters

We present the results of femtosecond laser microstructuring of optical fibres by direct access of the fibre end face, both at the surface and several hundred microns into the fibre, to realise one-and two-dimensional grating structures and optical fibre splitters, respectively. We show the versatility of this simple but effective inscription method, where we demonstrate classic multiple slit diffraction patterns and show the potential for coarse wavelength division multiplexing for sensor signals. A key advantage for the fibre splitter is that the inscription method avoids the use of oil immersion that compensate for the fibre curvature in the standard side writing method. © 2012 SPIE.

Poly(methyl methacrylate) model study of optical surface quality after excimer laser photorefractive keratectomy

Purpose: To evaluate lenses produced by excimer laser ablation of poly(methyl methacrylate) (PMMA) plates. Setting: University research laboratory. Methods: Two Nidek EC-5000 scanning-slit excimer laser systems were used to ablate plane-parallel plates of PMMA. The ablated lenses were examined by focimetry, interferometry, and mechanical surface profiling. Results: The spherical optical powers of the lenses matched the expected values, but the cylindrical powers were generally lower than intended. Interferometry revealed marked irregularity in the surface of negative corrections, which often had a positive “island” at their center. Positive corrections were generally smoother. These findings were supported by the results of mechanical profiling. Contrast sensitivity measurements carried out when observing through ablated lenses whose power had been neutralized with a suitable spectacle lens of opposite sign confirmed that the surface irregularities of the ablated lenses markedly reduced contrast sensitivity over a range of spatial frequencies. Conclusion: Improvements in beam delivery systems seem desirable.

Optical loading sensor based on single polarization fiber laser incorporating an intra-cavity 45°-TFG

We have experimentally demonstrated an active loading sensor system based on a fiber ring laser with single-polarization output using an intra-cavity 45°-tilted fiber grating (45°-TFG). When the laser cavity fiber subjected to loading, the laser output is encoded with the load and can be measured and monitored by a power metre. A loading sensitivity as high as 0.033/ (kg·m-1) has been achieved using this laser. The experiment results clearly show that single polarization fiber laser may be developed to a low-cost high-sensitivity loading sensor system. © 2014 SPIE.

Optical loading sensor based on ring-cavity fiber laser incorporating a 45°-tilted fiber polarizing grating

We have experimentally demonstrated an active loading sensor system based on a fiber ring laser with singlepolarization output using an intra-cavity 45°-tilted fiber grating. When the laser cavity fiber is subjected to loading, the laser output is encoded with the loading information that can be measured and monitored by a standard power meter. The achieved loading sensitivity is 0.033/kg • m-1 and 0.042/kg • m-1 for two different interaction lengths. The experimental results clearly show that such a single-polarization fiber laser may be commercially developed into a low-cost, high-sensitivity loading sensor system.

On two-wavelength Raman fibre laser based on spectral broadening

Raman fibre lasers and converters using the stimulated Raman scattering (SRS) in optical fibre waveguide are attractive for many applications ranging from telecommunications to bio-medical applications [1]. Multiple-wavelength Raman laser sources emitting at two and more wavelengths have been proposed to increase amplification spectrum of Raman fibre amplifiers and to improve noise characteristics [2,3]. Typically, a single fibre waveguide is used in such devices while multi-wavelength generation is achieved by employing corresponding number of fibre Bragg grating (FBG) pairs forming laser resonator. This approach, being rather practical, however, might not provide a good level of cross coherence between radiation generated at different wavelengths due to difference in FBGs and random phase fluctuations between the two wavelengths. In this work we examine a scheme of two-wavelength Raman fibre laser with high-Q cavity based on spectral intracavity broadening [3]. We demonstrate feasibility of such configuration and perform numerical analysis clarifying laser operation using an amplitude propagation equation model that accounts for all key physical effects in nonlinear fibre: dispersion, Kerr nonlinearity, Raman gain, depletion of the Raman pump wave and fibre losses. The key idea behind this scheme is to take advantage of the spectral broadening that occurs in optical fibre at high powers. The effect of spectral broadening leads to effective decrease of the FBGs reflectivity and enables generation of two waves in one-stage Raman laser. The output spectrum in the considered high-Q cavity scheme corresponds to two peaks with 0.2 - 1 nm distance between them. © 2011 IEEE.