Surface plasmons have been launched from free space optical beams (at an excitation wavelength of 700 nm) and
focused in the plane using concentric curved gratings (or plasmonic lenses) etched into 30 nm-thick gold films. The
performance of these devices was studied with numerical simulation and verified by near-field scanning optical
microscopy experiments. These plasmonic lenses have been demonstrated to focus the launched surface plasmons
effectively to a high intensity focal spot.
Temporal spectral astronomy or time resolved astronomy is the study of astrophysical phenomena that show
spectral variability on very short timescales. These timescales are often too short to be resolved by current
astronomical equipment. The lack of detailed observations in this area keeps important theoretical descriptions
of astronomical events unclear or incomplete. To resolve this, instruments with very high spectral resolution
and fast read-out speeds are needed. Photonic devices such as fibre Bragg gratings (FBGs) offer potential
advantages. The use of Bragg gratings in optical fibres allows for very high spectral resolution and the stability
and precision needed for the observation of the fast variation of one particular spectral line, with the potential to
observe multiple spectral lines at once. Here, we present the concept for a fibre Bragg grating based instrument
specifically for temporal spectral astronomy and we discuss the different profiles of FBGs for such applications.
In the “real world”, Photonics is somewhat invisible to those who rely upon it worldwide. We would like students to connect their everyday experiences of communications with the underlying ideas in Photonics. To do this, we have developed the Photonics Simulator to illustrate to high school students how text or information is coded into binary optical signals which are relayed through photonic communications networks from sender to receiver. Using our simulator, students construct a virtual network, and then test it by sending messages. The messages are coded using ASCII binary code as digital signals in data packets with address headers, which need to be switched, combined, amplified, or delayed to get to their designated address. The students must manage their power budget, correctly target each message address, and avoid collisions of data packets to send their messages uncorrupted and error-free. We tested an early version of the simulator with five Year 9 and 10 classes. The students provided many constructive comments and their feedback was used to improve the graphical interface of the simulator. We subsequently tested the simulator with 80 Year 9 students in short workshops. Overall we had a very positive response - it was more fun than a normal class, and interactivity helped students retain information. Students enjoy the visual aspects– they see how messages are delivered, and learn the function of each network component by experiment. Tests of the simulator at the Macquarie Siemens Science Experience were also encouraging, with one student even sneaking back to class to complete his challenges!
We have developed an alternative FRD empirical model for the parallel laser beam technique which can accommodate
contributions from both scattering and modal diffusion. It is consistent with scattering inducing a Lorentzian contribution
and modal diffusion inducing a Gaussian contribution. The convolution of these two functions produces a Voigt function
which is shown to better simulate the observed behavior of the FRD distribution and provides a greatly improved fit over
the standard Gaussian fitting approach. The Voigt model can also be used to quantify the amount of energy displaced by
FRD, therefore allowing astronomical instrument scientists to identify, quantify and potentially minimize the various
sources of FRD, and optimise the fiber and instrument performance.
We present a parametric study of self-assembled photonic crystal growth as a function of radius of curvature. To do this,
we used a combination of microscope slides, glass capillaries and optical fibres as substrates to grow the self-assembled
films on. Microscope and SEM images, as well as broadband transmission spectra were used to characterise the crystal,
and the effect the changing surface curvature had on the crystal quality. Limitations for fabricating the crystals on highly
curved surfaces will be presented.
We have performed measurements using a purpose-built Near-field Scanning Optical Microscope and shown that
waveguides written with a fs laser in the kHz regime have an asymmetry associated with the unidirectional nature of the
writing beam. Further, the asymmetry becomes more pronounced with increasing pulse energy. At very high pulse
energies (5-10 J) the presence of multiple guided regions was also observed, indicating that the refractive index profile
of the waveguide possesses several maxima, a result which is consistent with current studies on the filamentation process
that high-powered laser pulses experience in a dielectric medium. In this paper we will present these observations, their
subsequent analysis and implications for photonic device fabrication using this method.
We present a diode-pumped Yb<sup>3+</sup>: YAl<sub>3</sub>(BO<sub>3</sub>)<sub>3</sub> (Yb:YAB) laser system and measured the polarized outputs of the CW and femtosecond mode-locked lasers with semiconductor saturable-absorber mirrors (SESAM) at the fundamental wavelength. For the CW output, polarization ratios were 88.1% and 87.2% . For the mode-locked system, polarization ratio reached 38.5%.
We report the use of sub-picosecond near-IR and ps UV pulsed lasers for precision ablation of freshly extracted human teeth. The sub-picosecond laser wavelength was ~800nm, with pulsewidth 150 fs and pulse repetition rate of 1kHz; the UV laser produced 10 ps pulses at 266 nm with pulse rate of ~1.2x10<sup>5</sup> pulses/s; both lasers produced ~1 W of output energy, and the laser fluence was kept at the same level of 10-25 J/cm<sup>2</sup>. Laser radiation from both laser were effectively absorbed in the teeth enamel, but the mechanisms of absorption were radically different: the near-IR laser energy was absorbed in a plasma layer formed through the optical breakdown mechanism initiated by multiphoton absorption, while the UV-radiation was absorbed due to molecular photodissociation of the enamel and conventional thermal deposition. The rise in the intrapulpal temperature was monitored by embedded thermocouples, and was shown to remain low with subpicosecond laser pulses, but risen up to 30°C, well above the 5°C pain level with the UV-laser. This study demonstrates the potential for ultra-short-pulsed lasers to precision and painless ablation of dental enamel, and indicated the optimal combination of laser parameters in terms of pulse energy, duration, intensity, and repetition rate, required for the laser ablation rates comparable to that of mechanical drill.
Fabrication processes such as laser micromachining and laser based photolithography are well established within the automotive, electronics and aeronautic industries, however, except in a handful of cases, laser based micro-processing is infrequently used in the fabrication of photonic devices. In this paper novel laser assisted methods for rapid prototyping of photonic devices such as periodically poled lithium niobate and 2-D photonic crystal structures are reviewed.
All-solid-state laser devices operating in the 1.5 - 1.6 μm wavelength range have many practical applications. The most notable of these is their use in optical telecommunications, but the current research drive is to increase the output power from high beam quality, solid-state devices for eye-safe applications such as laser range finding and target acquisition, remote sensing of trace elements in air, light detecting and ranging, medicine, metrology and atmospheric phenomena such as measurements of wind shear.
Yb<sup>3+</sup> ions are co-doped into the host material to improve the pumping efficiency by taking advantage of commercial InGaAs diode lasers emitting at 980 nm. The absorbed pump is then non-radiative transferred to the Er<sup>3+</sup> ions, and rapidly decaying to the <sup>4</sup>I<sub>13/2</sub> upper-laser level. Laser operation in Er,Yb co-doped systems has been dominated by glass hosts (in particular, phosphate) with attempts in crystalline materials yielding disappointing results despite their superior mechanical and thermal properties.
In this paper we will present efficient diode-pumped laser operation of the crystalline host material Er,Yb:YCOB at 1.55 μm. By studying the energy transfer mechanisms of this material, we have identified the optimum dopant concentrations and 250 mW of continuous wave (cw) output in TEM00 transverse mode has been obtained with a 2mm crystal in an hemispherical cavity. Also, >150 mW cw has been obtained in a flat-flat cavity arrangement. The output coupling in each case was 1%. The slope efficiency of the laser was 21.9%.
An in vitro study was performed using an 808nm-diode laser in conjunction with indocyanine green-doped albumin protein solders to repair bovine aorta specimens. Investigations were conducted to determine optimal solder and laser parameters for tissue repair in terms of tensile strength, temperature rise and damage and the microscopic nature of the bonds formed. Liquid and solid protein solders prepared from 25% and 60% bovine serum albumin (BSA), respectively, were compared.
The tensile strengths of the repairs were greatly improved with an increase in BSA concentration from 25% to 60% and a reduction in ICG dye concentration from 2.5 mg/ml to 0.25 mg/ml. Increasing the later irradiance and thus surface temperature resulted in an increased severity of histological injury. Thermal denaturation of the tissue substrate increased laterally and in depth with higher temperatures. Optimal repairs in terms of bond strength and thermal damage were achieved by denaturing a solid protein solder composed of 60% BSA and .025mg/ml ICG with an irradiance of 6.4 W/cm<sup>2</sup>. Using this combination of solder and laser parameters, surface temperatures were observed to reach 85±5°C with an average temperature difference across the solder strips of 15°C across a thickness of 150 μm. Histological examination of the repairs formed using these parameters showed negligible evidence of collateral thermal damage to the underlying tissue. Scanning electron microscopy suggested albumin intertwining within the itssue collagen matrix and subsequent fusion with the collagen as the mechanism for laser tissue soldering.
Variations in laser irradiance, exposure time, solder composition, chromophore type and concentration have led to inconsistencies in published results of laser-solder repair of tissue. To determine optimal parameters for laser tissue soldering, an in vitro study was performed using an 808-nm diode laser in conjunction with an indocyanine green (ICG)- doped albumin protein solder to weld bovine aorta specimens. Liquid and solid protein solders prepared from 25% and 60% bovine serum albumin (BSA), respectively, were compared. The effects of laser irradiance and exposure time on tensile strength of the weld and temperature rise as well as the effect of hydration on bond stability were investigated. Optimum irradiance and exposure times were identified for each solder type. Increasing the BSA concentration from 25% to 60% greatly increased the tensile strength of the weld. A reduction in dye concentration from 2.5 mg/ml to 0.25 mg/ml was also found to result in an increase in tensile strength. The strongest welds were produced with an irradiance of 6.4 W/cm<SUP>2</SUP> for 50 s using a solid protein solder composed of 60% BSA and 0.25 mg/ml ICG. Steady-state solder surface temperatures were observed to reach 85 plus or minus 5 degrees Celsius with a temperature gradient across the solid protein solder strips of between 15 and 20 degrees Celsius. Finally, tensile strength was observed to decrease significantly (20 to 25%) after the first hour of hydration in phosphate-buffered saline. No appreciable change was observed in the strength of the tissue bonds with further hydration.
Laser-assisted repair of nerves is often unsatisfactory and has a high failure rate. Two disadvantages of laser assisted procedures are low initial strength of the resulting anastomosis and thermal damage of tissue by laser heating. Temporary or permanent stay sutures are used and fluid solders have been proposed to increase the strength of the repair. These techniques, however, have their own disadvantages including foreign body reaction and difficulty of application. To address these problems solid protein solder strips have been developed for use in conjunction with a diode laser for nerve anastomosis. The protein helps to supplement the bond, especially in the acute healing phase up to five days post- operative. Indocyanine green dye is added to the protein solder to absorb a laser wavelength (approximately 800 nm) that is poorly absorbed by water and other bodily tissues. This reduces the collateral thermal damage typically associated with other laser techniques. An investigation of the feasibility of the laser-solder repair technique in terms of required laser irradiance, tensile strength of the repair, and solder and tissue temperature is reported here. The tensile strength of repaired nerves rose steadily with laser irradiance reaching a maximum of 105 plus or minus 10 N.cm<SUP>-2</SUP> at 12.7 W.cm<SUP>-2</SUP>. When higher laser irradiances were used the tensile strength of the resulting bonds dropped. Histopathological analysis of the laser- soldered nerves, conducted immediately after surgery, showed the solder to have adhered well to the perineurial membrane, with minimal damage to the inner axons of the nerve. The maximum temperature reached at the solder surface and at the solder/nerve interface, measured using a non-contact fiber optic radiometer and thermocouple respectively, also rose steadily with laser irradiance. At 12.7 W.cm<SUP>-2</SUP>, the temperatures reached at the surface and at the interface were 85 plus or minus 4 and 68 plus or minus 4 degrees Celsius respectively. This study demonstrates the feasibility of the laser-solder repair technique for nerve anastomosis resulting in improved tensile strength. The welding temperature required to achieve optimal tensile strength has been identified.
A GaAlAs semiconductor diode laser operating at a wavelength of 796 nm has been sued in conjunction with Indocyanine Green (ICG) dye to ablate carious dentin and enamel from extracted human teeth. The laser-dye ablation technique offers selective ablation as it is controlled by the placement of the ICG dye. In contrast with other laser techniques, the risk of collateral thermal damage is substantially reduced. The diode laser is suitable for ordinary fiber delivery and is cheaper and more compact than the higher power CO<SUB>2</SUB>; Er:YAG, Nd:YAG and Argon lasers currently being used by researchers. This paper reports the ablation of dental caries in fifty extracted teeth with various laser diode powers and dye concentrations. The mass of material ablated, temperature rise in the pulp and surface temperature were measured. The ablation was found to be efficient with negligible thermal damage to surrounding tissue. At the same time average surface temperatures reached during ablation may be sufficient to sterilize the treated surface. Hardness measurements and scanning electron microscopy of the laser treated cavity surfaces show the new surfaces to be suitable for placement of a dental filling.
We report here LD pumped Q-Switched LNYAB Self-frequency-doubling Laser. Under 570mW of O.8O2.tm pumping power, the series pulses of O.53j.im green laser with 4.2ns of pulse width and 750W of peak power have been measured . The laser reliably operates when Q—switching rate ranges from CW to 100kHz. The highest peak power was obtained at repetition rate of 10kHz. To our knowledge, it is the first LD pumped acoustooptic Q-switched LNYAB green laser in the world and should be a desirable and reliable pulsed green laser source in the future.
KEY WORDS: Self-frequency-doubling Laser, LD Pumped, LNYAB, Q-Switched
A 100 micrometer core optical fiber-coupled 75 mW diode laser operating at a wavelength of 800 nm has been used in conjunction with a protein solder to stripe weld severed rat tibial nerves, reducing the long operating time required for microsurgical nerve repair. Welding is produced by selective laser denaturation of the protein based solder which contains the dye indocyanine green. Operating time for laser soldering was 10 plus or minus 5 min. (n equals 24) compared to 23 plus or minus 9 min (n equals 13) for microsuturing. The laser solder technique resulted in patent welds with a tensile strength of 15 plus or minus 5 g, while microsutured nerves had a tensile strength of 40 plus or minus 10 g. Histopathology of the laser soldered nerves, conducted immediately after surgery, displayed solder adhesion to the outer membrane with minimal damage to the inner axons of the nerves. An in vivo study, with a total of fifty-seven adult male wistar rats, compared laser solder repaired tibial nerves to conventional microsuture repair. Twenty-four laser soldered nerves and thirteen sutured nerves were characterized at three months and showed successful regeneration with average compound muscle action potentials (CMAP) of 2.4 plus or minus 0.7 mV and 2.7 plus or minus 0.8 mV respectively. Histopathology of the in vivo study, confirmed the comparable regeneration of axons in laser and suture operated nerves. A faster, less damaging and long lasting laser based anastomotic technique is presented.
A 100 micrometers core optical fiber-coupled 75 mW diode laser operating at a wavelength of 800 nm has been used in conjunction with a protein solder to stripe weld severed rat tibial nerves, reducing the long operating time required for microsurgical nerve repair. Welding is produced by selective laser denaturation of the albumin based solder which contains the dye indocyanine green. Operating time for laser soldering was 10 +/- 5 min. (n equals 20) compared to 23 +/- 9 min. (n equals 10) for microsuturing. The laser solder technique resulted in patent welds with a tensile strength of 15 +/- 5 g, while microsutured nerves had a tensile strength of 40 +/- 10 g. Histopathology of the laser soldered nerves, conducted immediately after surgery, displayed solder adhesion to the outer membrane with minimal damage to the inner axons of the nerves. An in vivo study is under way comparing laser solder repaired tibial nerves to conventional microsuture repair. At the time of submission 15 laser soldered nerves and 7 sutured nerves were characterized at 3 months and showed successful regeneration with compound muscle action potentials of 27 +/- 8 mV and 29 +/- 8 mW respectively. A faster, less damaging and long lasting laser based anastomotic technique is presented.