Fused Silica Optical Fibers Research Articles

Enhanced backscatter and unsaturated blue wavelength shifts in F-doped fused silica optical fibers exposed to extreme neutron radiation damage

Amorphous fused silica (a-SiO2) optical fibers, with and without inscribed Bragg gratings, were interrogated using infrared (∼1550 nm) optical backscatter reflectometry during ∼25 days of intense neutron irradiation to a fast (energy > 0.1 MeV) neutron fluence of ∼1021 n/cm2, or ∼1.5 atomic displacements per atom. The reflected light amplitudes in Ge-doped core telecommunications fiber dropped below detection limits (>15 dB attenuation) within 3 days of irradiation (∼1020 fast n/cm2). Amplitudes from a pure silica core, F-doped silica cladding fiber reached equilibrium levels ∼1.5–2 dB higher than pre-irradiation values, whereas Bragg gratings inscribed in the same fiber using a femtosecond laser (point-by-point method) suffered > 45 dB attenuation. Blue wavelength shifts were initially consistent with previous radiation-induced compaction models but increased linearly with increasing neutron fluence (no evidence of saturation) beyond 1020 n/cm2 and exceeded 0.6%, which corresponds to >1,000 °C drift if used to measure temperature changes.

Remedies to Thermal Radiation in Fused Silica Optical Fibers

During fire incidents, optical fibers located with-in a fire-resistant cable are usually exposed to temperatures of 800ºC to 1000ºC. Hot fibers generate narrowband thermal (incandescent) radiation and collect broadband thermal radiation originating from the heated surroundings. The power of the second component, initially negligible, increases with time due to the rising number of fiber cracks and other defects acting as couplers for external radiation. Thermal radiation may interfere with fiber attenuation measurements performed during a fire test, but is rather unlikely to prevent data transmission with typical GbE and 10 GbE transceivers during a fire. This problem may be remedied by combining the following methods: using single mode fibers instead of multimode fibers, using bandpass filters to block thermal radiation, and selecting proper transmitter power, wavelength and photodetector.

A Panda fiber temperature sensor up to 900°C

The use of Panda-type polarization-maintaining (PM) fiber for the localized sensing of high temperatures was analyzed with simulations and experiments up to 900°C. Accuracy and repeatability of the results started to decline above 800°C. Fused silica optical fiber melts at 1700°C, which sets an ultimate limit for measurable temperatures. In practice, optical fiber birefringence restricts the maximum temperature to 1060°C where PM fiber loses its ability to maintain polarization. Three sensor fibers (4, 5 and 10 cm long) were spliced at 45° angles to input/output fibers and calibrated in an oven from room temperature to 850–900°C temperature range. Two superluminescent light-emitting diodes (SLEDs) were coupled together as a broadband light source. Birefringence-induced change of the polarization in the sensor fiber was measured with a polarization splitter and an optical spectrum analyzer (OSA) as a function of the wavelength. Temperature-dependent birefringence generates a sinusoidal reflection spectrum from the input polarization mode to the orthogonal output polarization mode. Temperature changes could be concluded from variations in these spectra. Finally, a small fusion device, NORTH, at DTU, Denmark was successfully used as a testbed to make sure that the sensors can handle transportation and the instrumentation required for vacuum operation and still produce sensible data from a harsh environment.

High Temperature Effects in Fused Silica Optical Fibers

High Temperature Effects in Fused Silica Optical Fibers

Optimization of light scattering enhancement by gold nanoparticles in fused silica optical fiber.

A conventional distributed fiber optic sensing system offers close to linear sensitivity along the fiber length. However gold nanoparticles (NP) have been shown to be able to enhance the contrast ratio to improve the quality of signal detection. The challenge in improving the contrast of reflected signals is to optimise the nanoparticle doping concentration over the densed sensing length to make best use of the distributed fiber sensing hardware. In this paper, light enhancement by spherical gold NPs in the optical fibers was analyzed by considering the size-induced NP refractive index changes. This was achieved by building a new model to relate backscattered light from a gold NP suspension between the optical fiber end tips and backscattered light from gold NPs in the core of the optical fiber. The paper provides a model to determine the optimized sizes and concentrations of NPs for sensing at different desired penetration depths in the optical fiber.

A new basic structure suitable for a fully integrated all-fiber-optic stimulated emission dye source

In the present work, our research is focused on an innovative compact all-fiber-optic structure suitable for the development of fully integrated dye lasers. The structure is based on a standard fiber-optic glass ferrule with two parallel openings along its length with diameters of 125 μm. A Fabry-Perot cavity is formed in one of the openings using two fused silica optical fibers with flat end facets. An angle-polished optical fiber with a reflective metal coating is placed in the second opening through which the active medium is pumped transversely. The active medium used is the Rhodamine 6G dye dissolved in glycerine, which is pumped by the 337.1-nm wavelength laser pulses of a nitrogen TEA laser. The ferrule-based design allows for a simplified set-up procedure and the integration of the pumping system to the basic structure of the laser, thus making it very compact. The design of the light source presented allows its future use in applications, such as lab-on-a-fiber, lab-on-a-chip and total analysis micro systems.

Progress Toward Sapphire Optical Fiber Sensors for High-Temperature Applications

High-temperature measurements are of significant importance in various harsh-environment engineering fields, such as fossil fuel production, and the metallurgical and aviation industries. In recent years, there is a steady trend to shift from conventional electronic sensors to optical fiber sensors for high-temperature applications. In particular, optical fiber sensors are small in size, immune to electromagnetic interference, readily applicable for remote sensing, have high elasticity, and incorporate capabilities for multiplexing and distributed sensing. However, commonly used fused silica optical fiber sensors exhibit severe limitations at ultrahigh temperatures due to significantly degraded optical and mechanical properties at temperatures 1000 °C. The excellent optical transparency, thermal and chemical stability, mechanical robustness, and high melting temperature (~2040 °C) of single-crystal sapphire fibers (SFs) make them a strong candidate for sensing applications in high-temperature environments. Translation of the sensing schemes from mature silica fiber sensors to SF sensors has undergone tremendous growth and advancements in the past two decades. However, hurdles to the development of a near-term deployable SF sensing system have proven persistent due to the highly multimodal nature of SFs. This article reviews sensing techniques that have been implemented with SFs recently. The aim is to provide a comprehensive summary of past research on SF sensing systems. Perspectives on further research into the challenging yet promising arena are also discussed.

Endovascular Ultraviolet Laser-Facilitated Reversal of Vasospasm Induced by Subarachnoid Hemorrhage in Canines.

Because treatments for cerebral arterial spasm-a delayed consequence of subarachnoid hemorrhage (SAH)-are clinically inconsistent, we describe here a new method for reversal of arterial spasm, possibly extensible to nitric oxide (NO)-sensitive microvasculature. We subjected dogs to the intracisternal double-hemorrhage model of SAH (autologous blood injection on days 1 and 3) and began endovascular treatment of the spasmed basilar artery (BA) on Day 4. A conical-tip fused silica optical fiber was introduced via a microcatheter (inserted femorally) into the proximal vicinity of the spasmed BA. After local saline flushing of blood, an ultraviolet (UV) pulsed laser beam (355 nm Nd:YAG) was focused into the optical fiber and converted into a concentric ring beam, which facilitated endovascular irradiation for 30s at intensities of 12-20W/cm2. BA diameters were measured angiographically using a semiautomated routine over the entire BA length as well as the proximal, medial, and distal segments. On Day 4 the BAs had constricted by 21±11%. After UV laser irradiation on Day 4, the constricted BAs dilated to 93±15% of their normal diameters within minutes, and the dilation (91±12%) persisted on Day 5. Most BA segments recovered to their respective baselines after UV irradiation, even when the UV beam was located considerably proximal to the BA origin. At days 4 and 5, the percent BA dilation normalized to Day 4 pre-treatment decreased linearly (by scatter plot, p<0.02) over a range of about 60 mm from the UV irradiation site. We conjecture that the vasodilator nitric oxide, produced at high local concentration from its vascular storage forms (chiefly nitrites) by UV laser-induced photoscission, stimulates a wave of arterial dilation, possibly by longitudinal propagation of transnitrosation reactions in the arterial wall, which reverses cerebral vasospasm semi-locally and thus avoids the deleterious effects of systemic treatment.

Thermally induced emission from hydroxyl groups in fused silica optical fibers

Abstract Hydroxyl is one of the most common impurities in fused silica optical fibers. For an optical fiber based sensor operating at lower temperatures, hydroxyl presence in the fiber core causes absorption in the near infrared region. When the sensor is exposed to a high temperature environment, emission from hydroxyl can be strong enough to affect accuracy of the sensor. To better understand the hydroxyl emission phenomenon in silica optical fibers at high temperatures, the emission intensity of step index, pure silica core, multimode fibers was measured at temperatures from 600 °C to 1200 °C, and was used to evaluate the activation energy of the thermally induced emission. The removal of hydroxyls by annealing the silica fiber in a nitrogen environment was also conducted at selected temperatures to determine the time dependence of the process. The measurements and calculations show that the hydroxyl emission intensity increases exponentially with temperature, and that the hydroxyl removal process also follows an Arrhenius relationship. The results give insight into appropriate optical fiber sensor designs to minimize signal degradation caused by hydroxyl emission intensity change.

Fused silica optical fibers with graded index nanostructured core

The ability to shape the index profile of optical fibers holds the key to fully flexible engineering of their optical properties and future applications. We present a new approach for the development of a graded index fused silica fiber based on core nanostructurization. A graded index core is obtained by means of distribution of two types of subwavelength glass rods. The proposed method allows to obtain arbitrary graded distribution not limited to the circular or any other symmetry, such as in the standard graded index fibers. We have developed a proof of concept fiber with parabolic refractive index core and showed a perfect match between its predicted, designed and measured properties. The fiber has a core composed of 2107 rods of 190 nm of diameter made of either pure fused silica or Ge-doped fused silica with 8.5% mol concentration. The proposed method breaks the limits of standard fabrication approaches used in fused silica fiber technology.

DFT studies of refractive index of boron-doped diamond

The density functional theory is one of the optimal solutions in calculation of optical properties of materials on the quantum scale. In this paper, we have investigated refractive index of a boron-doped diamond structure with the usage of Atomistic Toolkit software from Synopsys. During this study, various methods and pseudopotentials were checked to obtain an optimal performance-accuracy method for calculation of such materials. Leading method used in calculation was used meta-GGA with Fritz-Haber Institute pseudopotential. Full Text: PDF ReferencesW. Kohn and L. J. Sham, "Self-Consistent Equations Including Exchange and Correlation Effects", Phys. Rev., vol. 140, no. 4A, pp. A1133–A1138 (1965). CrossRef J. P. Perdew, K. Burke, and M. Ernzerhof, "Generalized Gradient Approximation Made Simple", Phys. Rev. Lett., vol. 77, no. 18, pp. 3865–3868 (1996). CrossRef Y. Yan, J. Gong, and Z. Zong, "Superconductivity of p-type diamond (001) and (111) thin films: Ab initio calculations", Thin Solid Films, vol. 518, no. 17, pp. 4989–4996 (2010). CrossRef M. P. Desjarlais, "Density functional calculations of the reflectivity of shocked xenon with ionization based gap corrections", Contributions to Plasma Physics, vol. 45, no. 3–4, pp. 300–304 (2005). CrossRef L. G. Ferreira, M. Marques, and L. K. Teles, "Approximation to density functional theory for the calculation of band gaps of semiconductors", Physical Review B, vol. 78, no. 12, (2008). CrossRef J. M. Soler et al., "The SIESTA method for ab initio order- N materials simulation", Journal of Physics: Condensed Matter, vol. 14, no. 11, pp. 2745–2779 (2002). CrossRef L. Kleinman and D. M. Bylander, "Efficacious Form for Model Pseudopotentials", Phys. Rev. Lett., vol. 48, no. 20, pp. 1425–1428 (1982). CrossRef Synopsys QuantumWise, Atomistix Toolkit version 2017.12.F. Tran and P. Blaha, "Accurate Band Gaps of Semiconductors and Insulators with a Semilocal Exchange-Correlation Potential", Phys. Rev. Lett., vol. 102, no. 22, p. 226401 (2009). CrossRef D. R. Lide, Ed., CRC Handbook of Chemistry and Physics, 83rd Edition, Boca Raton, Fla.: CRC Press, 2002.N. Troullier and J. L. Martins, "Efficient pseudopotentials for plane-wave calculations", Phys. Rev. B, vol. 43, no. 3, pp. 1993–2006 (1991). CrossRef W. A. Harrison, Solid state theory. McGraw-Hill, 1970.M. Sobaszek et al., "Optical and electrical properties of ultrathin transparent nanocrystalline boron-doped diamond electrodes", Optical Materials, vol. 42, pp. 24–34 (2015). CrossRef M. Ficek et al., "Optical and electrical properties of boron doped diamond thin conductive films deposited on fused silica glass substrates", Applied Surface Science, vol. 387, pp. 846–856 (2016). CrossRef R. Maezono, A. Ma, M. D. Towler, and R. J. Needs, "Equation of State and Raman Frequency of Diamond from Quantum Monte Carlo Simulations", Phys. Rev. Lett., vol. 98, no. 2, p. 025701 (2007). CrossRef R. Bogdanowicz et al., "Opto-Electrochemical Sensing Device Based on Long-Period Grating Coated with Boron-Doped Diamond Thin Film", J. Opt. Soc. Korea, JOSK, vol. 19, no. 6, pp. 705–710, (2015). CrossRef M. Ficek et al., "Linear antenna microwave chemical vapour deposition of diamond films on long-period fiber gratings for bio-sensing applications", Opt. Mater. Express, OME, vol. 7, no. 11, pp. 3952–3962 (2017). CrossRef M. Ficek, R. Bogdanowicz, and J. Ryl, "Nanocrystalline CVD Diamond Coatings on Fused Silica Optical Fibres: Optical Properties Study", Acta Physica Polonica A, vol. 127, no. 3, pp. 868–873 (2015). CrossRef P. J. Stephens, F. J. Devlin, C. F. Chabalowski, and M. J. Frisch, "Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields", J. Phys. Chem., vol. 98, no. 45, pp. 11623–11627 (1994). CrossRef P. Rivero, W. Shelton, and V. Meunier, "Surface properties of hydrogenated diamond in the presence of adsorbates: A hybrid functional DFT study", Carbon, vol. 110, pp. 469–479 (2016). CrossRef

Linear antenna microwave chemical vapour deposition of diamond films on long-period fiber gratings for bio-sensing applications

The growth processes of nanocrystalline diamond (NCD) thin films on fused silica optical fibers with UV-induced long-period gratings (LPGs) were investigated with regard to biosensing applications. The films were deposited using a linear antenna microwave plasma enhanced chemical vapor deposition system, which allows for the growth of diamond at temperatures below 350&#x00B0;C. The films exhibited a high refractive index n = 2.32, as estimated at &#x03BB; = 550 nm. The biosensing applications of NCD-coated LPG were considered in relation to bovine serum albumin (BSA) as an external medium. In response to BSA binding and the subsequent formation of a thin bio-layer on the NCD surface, the LPG resonances slightly split and shifted towards lower wavelengths.

Molecular absorption measurements with an optical fibre coupled array of ultra-violet light-emitting diodes

A photometric detector based on eight different light-emitting diodes covering the ultraviolet range from 255 nm to 350 nm is described. These are coupled with fused silica optical fibres to a conventional cuvette with 1 cm optical path length or to a low volume flow through cell for detection in high-performance liquid chromatography. Photodiodes are employed for the measurement of the transmitted intensity as well as of a reference signal and the photocurrents are processed with a log-ratio amplifier to obtain a voltage proportional to absorbance values. The wavelength desired for the measurement at hand is selected by electronically switching on the requisite light-emitting diode. The detector was found to have a low noise level of 80 μAU. In batch-wise measurements as well as in detection for high-performance liquid chromatography dynamic ranges of 2–3 orders of magnitude were possible. Reproducibilities in peak areas for the latter application were better than 1%.

1.2W laser amplification at 1427nm on the 4F3/2 to 4I13/2 spectral line in an Nd3+ doped fused silica optical fiber.

A 9.3dB improvement in optical gain and a 100x improvement in total optical power over prior published experimental results from the 4F3/2 to 4I13/2 transition in an Nd3+ doped fused silica optical fiber is demonstrated. This is enabled via an optical fiber waveguide design that creates high spectral attenuation in the 1050-1120nm-wavelength range, a continuous spectral filter for the primary 4F3/2 to 4I11/2 optical transition. A maximum output power at 1427nm of 1.2W was attained for 43mW coupled seed laser power and 22.2W of coupled pump diode laser power at 880nm a net optical gain of 14.5dB. Reducing the coupled seed laser power to 2.5mW enabled the system to attain 19.3dB of gain for 16.5W of coupled pump power. Four issues limited results; non-optimal seed laser wavelength, amplified spontaneous emission on the 4F3/2 to 4I9/2 optical transition, low absorption of pump light from the cladding and high spectral attenuation in the 1350-1450nm range. Future fibers that mitigate these issues should lead to significant improvements in the efficiency of the laser amplifier, though the shorter wavelength region of the transition from 1310nm to >1350nm is still expected to be limited by excited state absorption.

Non-Destructive Optical Measurement of Oxygen Concentration on PEFC Catalyst Layer

Tiny optical fiber sensor was applied to realize non-destructive measurement of oxygen concentration on PEFC catalyst layer.Insufficient supply of oxygen to the cathode catalyst layer caused by transport resistance is critical issue. Fundamental study in order to achieve efficient oxygen transport is required, however; non-destructive and in-situ measurement of oxygen concentration on the catalyst layer was not achieved. In this study, oxygen concentration on the catalyst layer under operating condition was measured by using a tiny optical fiber and oxygen indicator.Figure 1 shows experimental setup. Platinum tetrakis pentrafluoropheny porphine (PtTFPP) was employed as oxygen indicator[1]. When the PtTFPP is exposed to excitation light (l = 405 nm), phosphorescence emission (l = 650 nm) is produced. Phosphorescence intensity is determined by oxygen partial pressure. Thus, quantitative oxygen concentration can be obtained by measuring phosphorescence intensity and using calibration data. In this study, PtTFPP was painted at the edge of fused silica optical fiber of which diameter was 110 mm. In order to measure the phosphorescence intensity, bifurcated optical fibers were connected to excitation light source and spectrometer, respectively.The cell has an active area of 4 cm2 (2 × 2 cm) with straight channels. The channel width and depth were 1.0 and 1.0 mm, respectively, and the rib-to-channel ratio was 1. The carbon paper GDL without MPL (SIGRACET®24BA, SGL Group, USA) was used for both the anode and the cathode side. In order to measure the oxygen concentration on the catalyst layer with reducing insertion effect, optical fiber was inserted from the intrinsic large pore of GDL without boring a hole, and the edge of the fiber was touched on the catalyst layer surface. Flow rates of hydrogen and air were 50NmL/min and 125 NmL/min, respectively. Cell was operated under 33 °C because phosphorescence intensity becomes low under high temperature. Bubbler temperature was 22 °C (relative humidity was 50%)In the experiment, cell voltage was varied from 0.9 V to 0.2 V, and change of current density and oxygen concentration were measured. Figure 2 shows current-voltage (IV) characteristics. In the higher current density condition, variation of plots suggests emergence of flooding in the cathode. Since the flooding decreased gas diffusivity in the cathode catalyst layer, IV characteristics fluctuate at high current density and low cell voltage condition. As shown in Figure 3, change of oxygen concentration on the catalyst layer was measured successfully. Oxygen concentration decreases monotonically with decreasing cell voltage. Minimum value of the concentration was below 2 % at 0.2 V cell voltage. Figure 2 indicated that total cell performance was declined by flooding. On the other hand, local oxygen concentration of the catalyst layer was able to be measured by using a tiny optical fiber. Figure 3 shows large amount of oxygen was still consumed under high current density and it means that power generation concentrated on local surface of the catalyst layer where surface not covered with the liquid water.As discussed above, oxygen concentration on cathode catalyst layer was measured non-destructively. This technique holds further potential to measure oxygen transport phenomena on the catalyst layer under 60-80 °C cell operation by improving optical oxygen sensor sensitivity. AcknowledgementThis study is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Experimental setup in present study was assisted by Yoshihiko Aoki (Tokyo Institute of Technology). Reference[1] CS Chu., CA Lin, Sensors and Actuators B: Chemica, 2014, 195, 259-265. Figure 1

Disposable Polydimethylsiloxane (PDMS)-Coated Fused Silica Optical Fibers for Sampling Pheromones of Moths.

In the past decades, the sex pheromone composition in female moths has been analyzed by different methods, ranging from volatile collections to gland extractions, which all have some disadvantage: volatile collections can generally only be conducted on (small) groups of females to detect the minor pheromone compounds, whereas gland extractions are destructive. Direct-contact SPME overcomes some of these disadvantages, but is expensive, the SPME fiber coating can be damaged due to repeated usage, and samples need to be analyzed relatively quickly after sampling. In this study, we assessed the suitability of cheap and disposable fused silica optical fibers coated with 100 μm polydimethylsiloxane (PDMS) by sampling the pheromone of two noctuid moths, Heliothis virescens and Heliothis subflexa. By rubbing the disposable PDMS fibers over the pheromone glands of females that had called for at least 15 minutes and subsequently extracting the PDMS fibers in hexane, we collected all known pheromone compounds, and we found a strong positive correlation for most pheromone compounds between the disposable PDMS fiber rubs and the corresponding gland extracts of the same females. When comparing this method to volatile collections and the corresponding gland extracts, we generally found comparable percentages between the three techniques, with some differences that likely stem from the chemical properties of the individual pheromone compounds. Hexane extraction of cheap, disposable, PDMS coated fused silica optical fibers allows for sampling large quantities of individual females in a short time, eliminates the need for immediate sample analysis, and enables to use the same sample for multiple chemical analyses.

Femtosecond laser microhole drilling inside a fused silica optical fiber with optical inner surface quality

We have demonstrated femtosecond laser microhole drilling inside a fused silica optical fiber with optical inner surface quality. An optical quality microhole with a diameter of \(3\, \upmu \hbox {m}\) and a length of approximately \(35\, \upmu \hbox {m}\) was produced inside an optical fiber of a cladding diameter of \(125\, \upmu \hbox {m}\). The microhole drilling inside an optical fiber was caused as a result of plasma filamentation of focused femtosecond laser irradiation at a wavelength of 400 nm. The size of the microhole was reproduced with a ray trace of the focused laser beam with consideration of self-focusing. The optical quality of the microhole was verified by measuring the transmittance of 94 % of infrared diode emission.

Properties of silicon nitride thin overlays deposited on optical fibers — Effect of fiber suspension in radio frequency plasma-enhanced chemical vapor deposition reactor

This work discusses the effect of sample suspension in radio frequency plasma-enhanced chemical vapor deposition process on properties of the obtained overlays. Silicon nitride (SiNx) overlays were deposited on flat silicon wafers and cylindrical fused silica optical fibers. The influence of the suspension height and fiber diameter on SiNx deposition rate is investigated. It has been found that thickness of the SiNx overlay significantly increases with suspension height, and the deposition rate depends on fiber dimensions. Moreover, the SiNx overlays were also deposited on long-period gratings (LPGs) induced in optical fiber. Measurements of the LPG spectral response combined with its numerical simulations allowed for a discussion on properties of the deposited overlay. The measurements have proven higher overlay deposition rate on the suspended fiber than on flat Si wafer placed on the electrode. Results of this work are essential for precise tuning of the functional properties of new generations of optical devices such as optical sensors, filters and resonators, which typically are based on optical fibers and require the overlays with well defined properties.

Research of time fiducial laser and probe laser of velocity interferometer system for any reflector for Shenguang-III laser facility

Time fiducial laser is an important timing marker for different diagnostic instruments in high energy density physics experiments. The probe laser in velocity interferometer system for any reflector (VISAR) is also vital for precise shock wave diagnosis in inertial confinement fusion (ICF) research. Here, time fiducial laser and VISAR probe laser are generated from one source in SG-III laser facility. After generated from a 1064 nm DFB laser, the laser is modulated by an amplitude modulator driven by a 10 GS/s arbitrary waveform generator. Using time division multiplexing technology, the ten-pulse time fiducial laser and the 20 ns pulse width VISAR probe laser are split by a 12 multiplexer and then the time fiducial and VISAR pulses will be selected individually by acoustic-optic modulators. Using this technology, the cost for the system can be reduced. The technologies adopted in the system also include pulse polarization stabilization, high stable Nd: YAG amplification, high precision thermally controlled frequency conversion, fiber coupling, and energy transmission. The fiber laser system is connected to the Nd: YAG rod amplifier stage with polarizing (PZ) fibers to maintain the polarization state. The output laser of Nd: YAG amplification stage is coupled with different kinds of energy transfer fibers to propagate enough energy and maintain the pulse shape for the time fiducial and VISAR probe laser. The input and output fibers are all coupled to the rod amplifiers with high precision and being easy to plug and play for users. Since the time fiducial and imaging VISAR laser system is far from the front end room and located in the target area, the system also uses an arbitrary waveform generator (AWG) to generate the shaped ten-pulse time fiducial laser and 20 ns VISAR laser. This AWG and the other three AWGs used for the main laser pulse of SG-III laser facility will be all synchronized by 10 GHz clock inputs, realizing the smaller than 7 ps (RMS) jitter between the main laser pulse, time fiducial laser and VISAR pulse. After amplification and frequency conversion, the time fiducial laser finally generates 12 beam 2 and 4-beam 3 laserbeams, providing important reference marks for different detectors in the ICF experiments and making it convenient for the analysis of multiple diagnostic data. The VISAR laser pulse is also amplified by the Nd: YAG amplifiers and frequency-converted to 532 nm green light by a thermally controlled LBO crystal, with output energy larger than 20 mJ. Finally, the 532 nm VISAR probe laser beam is coupled with a 1-mm core diameter fused silica optical fiber, and then propagates 30 meters to the imaging VISAR system. The VISAR probe laser has been used in many high energy density physics experiments. The shock wave loading and slowdown processes are measured. Function for measuring velocity history of shock wave front movement in different kinds of materials can be also added to the SG-III laser facility.

Improved surface coverage of an optical fibre with nanocrystalline diamond by the application of dip-coating seeding

Growth processes of diamond thin films on the fused silica optical fibres (10cm in length) were investigated at various temperatures. Fused silica pre-treatment by dip-coating in a dispersion consisting of detonation nanodiamond (DND) in dimethyl sulfoxide (DMSO) with polyvinyl alcohol (PVA) was applied. Nanocrystalline diamond (NCD) films were deposited on the fibres using the microwave plasma assisted chemical vapour deposition (MW PA CVD) method. The longitudinal variation of NCD morphology, structure and optical parameters were specifically investigated. The evolution of the film morphology and film thickness along the fibre length was studied using scanning electron microscopy (SEM). The chemical composition of the NCD film was examined with micro-Raman Spectroscopy. The sp3/sp2 band ratio was calculated using the Raman spectra deconvolution method. An approximately 5cm-long homogeneous diamond film has been obtained on the surface of the fibre sample. Thickness, roughness and optical properties of NCD films in the VIS–NIR range were investigated on the reference quartz slides using spectroscopic ellipsometry. The samples exhibited relatively low deviations of refractive index (2.3±0.25) and extinction coefficient (0.05±0.02) along the length of 5cm, as estimated at a wavelength of 550nm. In order to show the effectiveness of deposition process on optical fibres, diamond films were also grown on the fibre with induced long-period grating (LPG). The results of transmission measurements demonstrated that an LPG with diamond overlay exhibits the appropriate dependency on the optical properties of external medium. Thus, the deposition process has a negligible effect on the fibre transmission properties.