Mid-IR laser for wavefront correction in gravitational wave detectors

The next-generation gravitational wave detectors aim to enhance our understanding of extreme phenomena in the Universe. The high-frequency sensitivity of these detectors will be maximized by injecting squeezed vacuum states into the detector. However, the performance advantages offered by squeezed state injection can be easily degraded by losses in the system. A significant source of loss is the mode mismatch between optical cavities within the interferometer. To overcome this issue, new actuators are required that can produce a highly spherical wavefront change, with minimal higher order aberrations, whist adding low phase noise to the incident beam

Femtosecond laser direct-written waveguides in bismuth germanate for spatial resolved radiation detection

We demonstrate direct laser written low loss waveguides in bismuth germanate for sensing applications in high energy physics. We discuss the suitability of waveguide arrays in this material for spatial resolved radiation detection.2 page(s

Femtosecond direct written waveguides in Bismuth Germanate

Bismuth germanate (Bi4Ge3O12) BGO is an interesting material for a wide range of optical sensing applications. The high electro-optic coefficient makes BGO suitable for high voltage and field sensing applications with high accuracy [1]. Further, single crystals are used as scintillator in combination with photo multiplier tubes or avalanche photodiodes. Arrays of these scintillator devices are used for positron emission tomography (PET), a common medical imaging system. However, the size of crystals arrays limits the resolution and makes the system expensive. To fully enhance the potential of this material in integrated optical circuits the fabrication of buried waveguides by ion implantation has been discussed [2]. The highly flexible technique of optical waveguide writing by tightly focused femtosecond laser pulses is a promising alternative; however, the inscription of positive index changes in crystals is difficult due to the crystal lattice.1 page(s

Direct inscription of photonic band-gap waveguides into bulk optical glass

Utilizing a recently developed novel two-step fabrication process we present the first experimental demonstration of photonic band-gap waveguiding structures inscribed into bulk optical glass via the femtosecond laser direct-write technique. The waveguides are fabricated by placing an array of circular high-index contrast rods around an unmodified core. We observe the formation of discrete band-gaps that can be precisely tuned by controlling the diameter of the individual rods.4 page(s

Fibre grating inscription and applications

The diverse range of opportunities and activity in fibre sensing and fibre lasers has triggered an equally diverse range of research into new grating fabrication methods using femtosecond lasers. Femtosecond laser written fibre gratings can now exhibit similar spectral properties yet superior thermal stability compared to those produced using conventional methods. Foremost of the advantages offered by femtosecond laser fibre grating inscription is the reduced need for photosensitivity. Key examples include demonstrations of high temperature sensors based on sapphire fibres and high power fibre lasers with intra-core optical resonators. Research and development of femtosecond grating inscription methods, properties and devices is reviewed.29 page(s

Actively Q-Switched integrated waveguide lasers

Actively Q-Switched lasers typically require bulky optical components. By incorporating a novel liquid crystal cell into a waveguide laser cavity, an all integrated and monolithic short-pulsed laser can be realized.2 page(s

Structural changes in BK7 glass upon exposure to femtosecond laser pulses

A general picture of refractive index change mechanisms in glass modified by a femtosecond laser has proven elusive. In this paper, Raman microscopy was used in conjunction with refractive near-field profilometry to analyse the structure of borosilicate glass (Schott BK7) modified by a femtosecond laser and determine the mechanism of the observed refractive index change. For a pulse repetition rate of 1 kHz, it was determined that the refractive index change was due to an elevated population of non-bridging oxygen atoms, resulting in more ionic bonds forming within the glass network and increasing the molar refractivity of the glass. For a pulse repetition rate of 5.1 MHz, the dominant mechanism of refractive index change was densification and rarefaction of the glass network. Different refractive index change mechanisms were attributed to different thermal conditions imparted to the glass under different pulse repetition rates. Implications for device fabrication are also discussed. These findings constitute an important step toward a complete overview of femtosecond-laser-induced refractive index change in glass. Waveguides were fabricated in BK7 glass using femtosecond laser pulses and subsequently investigated using Raman microscopy. It was determined that for waveguides written at a 1 kHz pulse repetition rate, refractive index change correlated with the formation of B-O- groups, whereas for waveguides written at a 5.1 MHz repetition rate, refractive index change correlated with changes in density of the glass. The mechanism behind these structural changes and the implications on device fabrication are discussed.4 page(s

Compact integrated actively Q-switched waveguide laser

A miniaturized deformed helix ferroelectric liquid crystal transducer cell was used in combination with a femtosecond laser inscribed active waveguide to realize a compact actively Q-switched laser source. The liquid crystal cell was controlled by a low-voltage frequency generator and laser pulse durations below 40 ns were demonstrated at repetition rates ranging from 0.1 kHz to 20 kHz and a maximum slope efficiency of up to 22%. This novel, integrated and low-cost laser source is a promising tool for a broad range of applications such as trace gas sensing, LIDAR, and nonlinear optics. To the best of our knowledge, this is the first demonstration of an actively Q-switched glass waveguide laser that has a user-variable repetition rate and can be fully integrated.10 page(s

Studies on the laser removal of consolidants and protective coatings from samples of Australian Aboriginal bark paintings

8 page(s