Progress towards 3-D subsurface structuring of polymers using femtosecond lasers is presented. Highly localised refractive index changes can be generated deep in transparent optical polymers without pre doping for photosensitisation or post processing by annealing. Understanding the writing conditions surpasses the limitations of materials, dimensions and chemistry, to facilitate unique structures entirely formed by laser-polymeric interactions to overcome materials, dimensional, refractive index and wavelength constraints.. Numerical aperture, fluence, temporal pulselength, wavelength and incident polarisation are important parameters to be considered, in achieving the desired inscription. Non-linear aspects of multiphoton absorption, plasma generation, filamentation and effects of incident polarisation on the writing conditions will be presented.
We report on the fabrication of optical Bragg type phase gratings in polymethyl methacrylate substrates irradiated by a
femtosecond Ti: Sapphire laser. In order to investigate the distribution of the refractive index change produced by the
femtosecond laser irradiation, we performed a two-dimensional visualization and spatially resolved optical analysis of
the induced refractive index profile by using a digital holographic technique and an adaptive-iterative algorithm for
wavefront reconstruction. The technique gives a direct and quantitative two-dimensional profile of the index of
refraction in irradiated samples, providing information how the fabrication process depends on the laser irradiation.
Previously, in high repetition rate femto second laser processing novel laser matter interacting effects were reported,
such as heat accumulation and particle shielding. In this study, high repetition rate laser processing was investigated to
discuss and understand the impact of laser repetition rate and accompanied accumulative laser material interacting
effects. Therefore, a high repetition rate femto second fibre laser setup joint together with galvo scanner technology was
applied in laser micro machining of metals (copper, stainless steel, aluminium). High repetition rate laser processing of
aluminium and stainless steel lead to considerably lowered ablation thresholds accompanied with higher ablation rates.
Laser ablation behaviour of copper was almost independent of the repetition rate with neither considerable lower ablation
thresholds nor higher ablation rates. For explanation, heat accumulation caused by higher repetition rates were assumed
as mainly ablation behaviour influencing effect, but thermal material properties have to be considered.
Furthermore laser machining examples demonstrate the possibilities and limits of high repetition rate laser processing in
3d micro structuring. Thus, by using innovative scanning systems and machining strategies very short processing times
were achieved, which lead to high machining throughputs and attract interest of the innovative laser technology in Rapid
Micro Tooling. For discussion, high repetition rate processing results are evaluated by means of comparative machining
examples obtained with 1 kHz femto second laser system.
Techniques to directly write localised refractive index structures in polymer optical fibres (POF) are presented, using UV
(400nm) ultrafast laser with pulse lengths of 100 fs to create in-fibre gratings for sensing. No doping is necessary for
photosensitisation so commercially available POF is used. An in-fibre grating consisting of a 1.8 μm wide refractive
index structure with a periodicity of 189 nm was demonstrated in single mode polymer fibre with optimised laser
We present a polymer optical fibre sensor to sense skin moisture and droplet formation when sweating occurs. The
sensor used evanescent field attenuation, by exploiting a moisture sensitive cladding with moisture indicator
(fluorescein) contained within a porous cladding (HEMA). The sensor was designed to be comfortable to wear and
unobtrusive, hygienic, with sterilised interchangeable sensing elements. It had maximum sensitivity between 98% and
100% humidity, and response time of 24 seconds.
An optical fibre biosensor that uses an oxygen sensitive coating; Ruthenium complex [Dichlorotris(1,10-phenantroline)-ruthenium(II) hydrate], incorporated into an adhesive inorganic-organic hybrid polymer coating (ORMOCER) is described. The Ruthenium/ ORMOCER layer is used with optical fibres to form an extrinsic or intrinsic sensor. It can be applied to a microscope slide or lens to be interrogated by optical fibres, or form a cladding layer for an evanescent field optical fibre sensor. The Ruthenium complex is caused to fluoresce by a high brightness blue LED at 470 nm and the excitation light at 600nm is detected by a photomultiplier tube used as a photon counter, to measure fluorescence lifetime. The fluorescence is quenched by oxygen depletion within the layer, which can be linked to glucose by incorporation of suitable enzymes. The detection threshold is 0.7mg(O2)/litre, and the sensitivity is 70 ns/mg per litre.
The challenges of teaching optics and optoelectronics in a broad based
Engineering school will be discussed. At Liverpool John Moores University, optical devices and optoelectronics is taught from the second year of degree courses right through to MSc level. At second year, students in Broadcast Technology, Applied Electronics have little physics background and are more interested in networks than basic devices and fundamentals of light. Even at MSc level, students' backgrounds are patchy. The challenge is to get across the basic principles in an interesting way, and excite students' interest by focusing on state of the art, current developments and applications. This is backed up with demonstrations and student projects attached to active research groups. Research groups in the school contribute to teaching in their fields. Members of the Coherent and Electro-optics Research Group teach "Optics and Imaging in Medicine". Members of the Optical Fibre Sensors Research Group teach "Optoelectronics" and "Analogue and Optical Devices". Also discussed are the challenges of teaching Physics students optoelectronics, and the decline of the "Optical Science and
Technology" degree course, due to falling student numbers and the
decline of physics and physics based courses in the UK.
Initial attempts to photo-induce refractive mdcx changes in bulk poly methyl methacrylate (PMMA) and in PMMA based plastic optical fibres (POF) using UV light are described. Optimum changes have been achieved at 216 nm, causing path length changes of 10π, corresponding to possible refractive index modulation of between 5 and 14 % over thicknesses up to 100 μm. The effects of refractive index changes on the far field modal distribution of tapered PMMA plastic optical fibres are described.
We present a sensor for the continuous detection of fluorescent emissions from fluids. The sensor utilizes a patented optical fiber detection system to allow separation of the excitation and emission light without the need for optical filters, has a wide working range and has applications in process control, flow tracing and monitoring. The construction, principles and experimental results of the fiber sensor will be given. The authors have also developed a novel test for total toxicity of aquatic systems, the product of which is fluorescent, enabling the proposal of a rapid, continuous and low cost toxicity measurement system. The biochemistry of the test is easily adapted for all types of aquatic environment and expected pollution levels. Results for several heavy metal and organic contaminants, performed under laboratory conditions, are also presented.
A novel technique for the measurement of air flow velocity using an optical fiber sensor is reported. The sensor measures the deformation of a rubber cantilever beam when subjected to the stresses induced by drag forces in the presence of the airflow. Tests performed in a wind tunnel have indicated a sensitivity of 2 (mu) /(m/s). A qualitative model based on fiber mode propagation has been developed which allows the sensor to be characterized in terms of optical losses. A single 1 mm diameter polymer fiber is mounted on the rectangular section rubber cantilever (section 14 mm by 6 mm) and six grooves are etched into the fiber which extend into the core of the fiber. As the beam deviates the surface deforms (stretches or contracts) and the fiber is subjected to strain. As the strain is increased the grooves become wider and the amount of light transmitted through the fiber is reduced due to increased losses. The sensor described has all the advantages of optical fiber sensors including electrical noise immunity and intrinsic safety for use in hazardous environments. However, its simple construction, robustness, versatility for a number of different fluid applications, as well as relatively low cost make it attractive for use in a wide variety of measurement applications e.g. wind velocity measurement where airborne moisture or chemicals are present.
Toxicity testing using fluorogenic compounds offers a number of advantages. These include a small sample volume, low cost, rapidity, and applicability to both a micro-organism monoculture and a biocenosis. The method relies on measuring the rate of enzymatic intracellular conversion of a fluorogenic substrate into a fluorochrome. We show how the rate of conversion depends on the substrate concentration, the biomass concentration and pH. We also show how the method can be used to measure the toxicities of several different toxicants, to study antagonistic and synergistic effects of different metal combinations and to study inhibition mechanisms. We then show that it is also possible to measure the cytoplasmic viscosity by exciting the fluorescein molecules in the cytoplasm with polarized light and measuring the polarization of the emitted fluorescence.
An optical fiber pH sensor based on the surface absorption of methylene blue dye is reported. Previously obtained results for this sensor have indicated a large linear operating range (3-10 pH) coupled with a relatively short response time and immunity to ionic concentration. Further investigations are reported which include testing reproducibility, accuracy, and sensitivity. In addition to this, a two wavelength referencing technique is introduced where the sensor is illuminated by two wavelengths in sequence in a time domain multiplexed manner. The performance of the sensor in terms of temperature stability and immunity to small perturbations to the launch conditions is improved by the application of the multiplexing technique. Particular attention is given to the ability of this sensor to measure pH at very low ionic strength and the geometry of the sensing element has been refined to reduce the response time to below 45 seconds for solutions of ionic strengths of 100 microsecond(s) . These measurements are significant since many applications for pH measurement require operation at such low ionic concentrations, e.g. underground water monitoring. Results are also included for higher ionic concentrations such as those encountered in blood pH measurement and other medical applications.