Ultrasonic transcutaneous energy transfer for powering implanted devices

This paper investigates ultrasonic transcutaneous energy transfer (UTET) as a method for energizing implanted devices at power level up to a few 100 mW. We propose a continuous wave 673 kHz single frequency operation to power devices implanted up to 40 mm deep subcutaneously. The proposed UTET demonstrated an overall peak power transfer efficiency of 27% at 70 mW output power (rectified DC power at the load).The transducers consisted of PZT plane discs of 15 mm diameter and 1.3 mm thick acoustic matching layer made of graphite. The power rectifier on the implant side attained 88.5% power transfer efficiency.The proposed approach is analyzed in detail, with design considerations provided to address issues such as recommended operating frequency range, acoustic link matching, receiver’s rectifying electronics, and tissue bio-safety concerns. Global optimization and design considerations for maximum power transfer are presented and verified by means of finite element simulations and experimental results.     

Passively Q-switched diode-pumped Cr:YAG/Nd:GdVO4 monolithic microchip laser

The realization of high repetition rate passively Q-switched monolithic microlaser is a challenge since a decade. To achieve this goal, we report here on the first passively Q-switched diode-pumped microchip laser based on the association of a Nd:GdVO₄ crystal and a Cr⁴⁺:YAG saturable absorber. The monolithic design consists of 1 mm long 1% doped Nd:GdVO₄ optically contacted on a 0.4 mm long Cr⁴⁺:YAG leading to a plano-plano cavity. A repetition rate as high as 85 kHz is achieved. The average output power is approximately 400 mW for 2.2 W of absorbed pump power and the pulse length is 1.1 ns.     

High repetition rate Q-switched microchip Nd:YVO4 laser with pulse duration as short as 1.1 ns

We have demonstrated a compact and an efficient passively Q-switched microchip Nd:YVO₄ laser by using a composite semiconductor absorber as well as an output coupler. The composite semiconductor absorber was composed of an LT (low-temperature grown) In_0.25Ga_0.75As absorber and a pure GaAs absorber. To our knowledge, it was the first demonstration of the special absorber for Q-switching operation of microchip lasers. Laser pulses with durations of 1.1 ns were generated with a 350 μm thick laser crystal and the repetition rate of the pulses was as high as 4.6 MHz. The average output power was 120 mW at the pump power of 700 mW. Pulse duration can be varied from 1.1 to 15.7 ns by changing the cavity length from 0.45 to 5 mm. Pulses with duration of 1.67 and 2.41 ns were also obtained with a 0.7 mm thick laser crystal and a 1 mm thick laser crystal, respectively.     

Diode-pumped passively Q-switched Nd:GdVO4 laser at 1342 nm with V:YAG saturable absorber

We have demonstrated an efficient diode-pumped passively Q-switched Nd:GdVO₄ laser working at 1342 nm by using an uncoated V³⁺:YAG crystal as the saturable absorber, in which both a-cut and c-cut Nd:GdVO₄ crystals are employed. At the maximum absorbed pump power of 9.45 W, the maximum average output power can reach 519 mW and 441 mW corresponding to the output coupler with different transmission of 3% and 10% by using an a-cut Nd:GdVO₄ crystal at 1342 nm, while the shortest pulse duration could be as low as 21.7 ns and 22.3 ns with the repetition rate of 48.41 kHz and 53.25 kHz by using a c-cut Nd:GdVO₄ crystal, corresponding to the output coupler with different transmission of 3% and 10% at 1342 nm, and the single Q-switched pulse energy are 6.67 uJ and 7.06 uJ, the pulse peak power are 307 W and 316 W, respectively. The experimental results show that c-cut Nd:GdVO₄ laser can generate shorter pulse with higher peak power in comparison with a-cut one.     

High conversion efficiency solar laser pumping by a light-guide/2D-CPC cavity

A simple and efficient light-guide/2D-CPC solar pumping approach is proposed. A fused silica light-guide assembly is used to transmit 6 kW concentrated solar power from the focal spot of a large parabolic mirror to the entrance aperture of a 2D-CPC pump cavity, where a long and thin Nd:YAG rod is efficiently pumped. Numerical calculations are made for different light-guides, 2D-CPC cavities and laser rods. The laser output power is investigated through finite element analysis. With 4 mm diameter rod, the maximum calculated laser power of 75.8 W is obtained, corresponding to the conversion efficiency of more than 11 W/m². The tracking error dependent laser power losses are lower than 4%. A small scale prototype was constructed and tested, reaching 8.1 W/m² conversion efficiency.     

Diode-end-pumped linear-polarized single-frequency Tm:YAG laser at room temperature

By using two solid uncoated etalons, we present a diode-pumped linear-polarized single-frequency Tm:YAG laser operating at 2 μm. Placing one 0.1 mm F-P etalon at nearly Brewster angle in the cavity, the linear-polarization laser is achieved. The other 1 mm F-P etalon was turned in the range of very small angle, single-longitudinal-mode (SLM) could be obtained. The maximum output power of linear-polarized single-frequency laser of 60 mW is achieved at the wavelength of 2013 nm. The degree of the polarization is over 30 dB. Long-term frequency stability was also investigated, with the results of wavelength fluctuation about 2.55 × 10⁻¹³ m within 3 min and frequency change about 18.86 MHz, corresponding to a frequency stability of 1.27 × 10⁻⁷.     

Continuous-wave broadly tunable Cr:ZnSe laser pumped by a thulium fiber laser

We describe a compact, broadly tunable, continuous-wave (cw) Cr²⁺:ZnSe laser pumped by a thulium fiber laser at 1800 nm. In the experiments, a polycrystalline ZnSe sample with a chromium concentration of 9.5 × 10¹⁸ cm⁻³ was used. Free-running laser output was around 2500 nm. Output couplers with transmissions of 3%, 6%, and 15% were used to characterize the power performance of the laser. Best power performance was obtained with a 15% transmitting output coupler. In this case, as high as 640 mW of output power was obtained with 2.5 W of pump power at a wavelength of 2480 nm. The stimulated emission cross-section values determined from laser threshold data and emission measurements were in good agreement. Finally, broad, continuous tuning of the laser was demonstrated between 2240 and 2900 nm by using an intracavity Brewster cut MgF₂ prism and a single set of optics.     

Numerical analysis of amplification characteristics of ErxY2 − xSiO5

The gain characteristics of Er_xY_2 − xSiO₅ waveguide amplifiers have been investigated by solving rate equations and propagation equations. The gain at 1.53 μm as a function of waveguide length, Er³⁺ concentration and pump power is studied pumping at three different wavelengths of 654 nm, 980 nm and 1480 nm, respectively. The optimum Er³⁺ concentrations of 1 × 10²¹ cm^− 3-2 × 10²¹ cm^− 3 with the high gain are obtained for all three pump wavelengths. Pumping at 654 nm wavelength is shown to be the most efficient one due to weak cooperative upconversion. A maximum 16 dB gain at 1 mm waveguide length under a 30 mW pump with Er³⁺ concentration of 1 × 10²¹ cm^− 3 is demonstrated pumping at 654 nm wavelength.     

Low-pump-threshold tunable optical parametric oscillator using periodically poled MgO:LiNbO3

We fabricated and characterized periodically poled MgO:LiNbO₃ device with five gratings in 0.5 μm increments from 29 μm to 31 μm for optical parametric oscillator (OPO). The OPO operation threshold is 30 μJ using this device with a 50 mm effective length. At 560 mW input pump power, we have achieved 300 mW of the total output power, and the conversion efficiency is 54%. Multi-periods and temperatures tuning of the OPO yields a signal wavelength range from 1.45 to 1.72 μm and an idler wavelength range from 2.8 to 4.05 μm in the mid infrared.     

Semiconductor optical amplifier based swept wavelength source at 1060 nm using a scanning Fabry-Perot filter and an YDFA-based booster amplifier

We demonstrate a tuneable laser operating in the 1-1.1 μm wavelength region with a tuning range of 43 nm (FWHM), an output power of 19 mW and coherence length of 14 mm. The source is based on a master laser consisting of a cavity tuned ring configuration with a fibre Fabry-Perot filter used as a tuning element and a semiconductor amplifier as gain medium. The output of the master laser is subsequently power boosted using an Ytterbium doped fibre amplifier (YDFA). In addition to providing a power boost, we demonstrate that by tailoring the gain spectrum of the YDFA it is possible to increase the FWHM scanning range by 7 nm compared to that of the master laser.     

Fluorescence and persistent spectral hole burning of Eu in Ge-Ga-S-KBr glasses

Fluorescence and efficient persistent spectral hole burning of Eu³⁺ at 77 K were observed in chalcohalide glasses. The depth of the hole was approximately 30% after a burning process of 1 min with 50 mW power, and it was completely erased with Ar⁺ laser irradiation. The hole survived room temperature heat treatment and showed good thermal stability. The hole-burning mechanism was most probably the photo-reduction of Eu³⁺→Eu²⁺. Fluorescence from Eu³⁺ decreased with increasing temperature and disappeared at the temperature above ∼130 K.     

Intra-cavity second harmonic generation with Nd:YVO4/BIBO laser at 542 nm

We report, for the first time, an efficient intra-cavity second-harmonic generation (SHG) at 1084 nm in a nonlinear optical crystal, BiB₃O₆(BIBO) at the direction of (θ, ?) = (170.1°, 90°), performed with a LD end-pumped cw Nd:YVO₄ laser. With 590 mW diode pump power, a continuous-wave (cw) SHG output power of 19 mW at 542 nm yellow-green color has been obtained using a 1.5 mm-thick BIBO crystal. The optical conversion efficiency was 3.22%. It was found that the output wavelength could be 532 nm, 537 nm or 542 nm according to regulating the angle of BIBO.     

Low threshold, actively Q-switched Nd:YVO4 self-Raman laser and frequency doubled 588 nm yellow laser

We reported an actively Q-switched, intracavity Nd³⁺:YVO₄ self-Raman laser at 1176 nm with low threshold and high efficiency. From the extracavity frequency doubling by use of LBO nonlinear crystal, over 3.5 mW, 588 nm yellow laser is achieved. The maximum Raman laser output at is 182 mW with 1.8 W incident pump power. The threshold is only 370 mW at a pulse repetition frequency of 5 kHz. The optical conversion efficiency from incident to the Raman laser is 10%, and 1.9% from Raman laser to the yellow.     

Sm-doped polymer optical waveguide amplifiers

Trivalent samarium ion (Sm³⁺) doped SU8 polymer materials were synthesized and characterized. Intense red emission at 645 nm was observed under UV laser light excitation. Spectroscopic investigations show that the doped materials are suitable for realizing planar optical waveguide amplifiers. About 100 μm wide multimode Sm³⁺-doped SU8 channel waveguides were fabricated using a simple UV exposure process. At 250 mW, 351 nm UV pump power, a signal enhancement of ∼7.4 dB at 645 nm was obtained for a 15 mm long channel waveguide.     

White organic electroluminescent device with photovoltaic performances

Organic device with structure of indium tin oxide (ITO)/1,3,5-tris-(3-methylphenylphenylamino)triphenylamine (m-MTDATA)/2-tert-butyl-9,10-di-beta-naphthylanthracene (TBADN)/2,9-dimethyl-4,7-diphenyl-1,10-phenan-throline (BCP)/LiF/Al, was fabricated, which show high efficient white electroluminescence (EL) or photovoltaic (PV) properties when it was driven by direct current (DC) bias or illuminated by ultraviolet (UV) light. Under a DC bias, the device shows efficient white EL emission. A maximum luminous efficiency of 1.1 lm/W was obtained at 8 V, which corresponds the Commission International de L’Eclairage coordinates (CIE) of (x = 0.298, y = 0.365). When the bias was increased to 12 V, the device shows bright white emission with the maximum brightness of 4300 cd/m², corresponding CIE coordinates of (x = 0.262, y = 0.280). When the diode was irradiated by a 365 nm UV-light (4 mW/cm²), the open-circuit voltage (V_oc) of 1.2 V, short-circuit (I_sc) of 0.065 mA/cm², fill factor (FF) of 0.24 and power conversion efficiency of 0.47% have been determined, respectively. The generation mechanisms of white light and PV of the bi-functional diode were discussed as well.     

Diode pumped Nd:GSAG and Nd:YGG laser at 942 and 935 nm

Two new Nd³⁺ doped crystals show laser activity between the ⁴F_3/2 and ⁴I_9/2 levels. Diode pumped emission of Nd:GSAG at 942 nm wavelength with 950 mW output power and 14% optical to optical efficiency as well as laser emission of Nd:YGG at 935 nm with 700 mW output power and 11% efficiency have been obtained. These wavelengths are useful for water vapour absorption measurements.     

LD end-pumped intracavity frequency doubled Yb:YAG laser

A laser diode end-pumped 10 at.% doped Yb:YAG microchip crystal intracavity frequency doubled all solid-stated green laser is reported in this paper. Using one plano-concave resonator, with the pump power of 1.2 W, 44.2 mW TEM₀₀ continuous wave (CW) laser at 525 nm was obtained, the optical conversion efficiency was about 3.7%. When a Cr:YAG crystal with initial transmission of 95.5% inserted in the resonator, the maximum output power of 6.4 mW, pulse duration width of 49.1 ns, pulse repetition rate of 2.45 kHz, and peak power of 53.1 W at 515 nm were achieved when the pump power was 1.2 W. The wavelength changed from 525 nm to 515 nm and the threshold was only 725 mW.     

Synthesis and characterization of sprayed Zn-doped polycrystalline CuInS2 thin films

Copper indium disulphide (CuInS₂) is an efficient absorber material for photovoltaic applications. In this work Zn (0.02 and 0.03 M) doped CuInS₂ thin films are (Cu/In = 1.25) deposited onto glass substrates in the temperature range 300–400 °C. XRD patterns depict, Zn-doping facilitates the growth of CuInS₂ thin films along (1 1 2) preferred plane and other characteristic planes. Optical studies show, 90% of light transmission occurs in the IR regions; hence Zn-doped CuInS₂ can be used as an IR transmitter. The absorption coefficient in the UV–vis region is found to be in the order of 10⁴–10⁵ cm⁻¹. Optical band gap energies increase with increase of temperatures (0.02 M – (1.93–2.05 eV) and 0.03 M – (1.94–2.04 eV)). Well defined, broad Blue and Green band emissions are exhibited. Resistivity study reveals the deposited films exhibit semiconducting nature. Zn species can be used as a donor and acceptor impurity in CuInS₂ films to fabricate efficient solar cells and photovoltaic devices.     

Optimization of un-tethered, low voltage, 20-100kHz flexural transducers for biomedical ultrasonics applications

This paper describes optimization of un-tethered, low voltage, 20-100 kHz flexural transducers for biomedical ultrasonics applications. The goal of this work was to design a fully wearable, low weight (<100 g), battery operated, piezoelectric ultrasound applicator providing maximum output pressure amplitude at the minimum excitation voltage.Such implementation of ultrasound applicators that can operate at the excitation voltages on the order of only 10-25 V is needed in view of the emerging evidence that spatial-peak temporal-peak ultrasound intensity (I_SPTP) on the order of 100 mW/cm² delivered at frequencies below 100 kHz can have beneficial therapeutic effects. The beneficial therapeutic applications include wound management of chronic ulcers and non-invasive transdermal delivery of insulin and liposome encapsulated drugs.The early prototypes of the 20 and 100 kHz applicators were optimized using the maximum electrical power transfer theorem, which required a punctilious analysis of the complex impedance of the piezoelectric disks mounted in appropriately shaped metal housings.In the implementation tested, the optimized ultrasound transducer applicators were driven by portable, customized electronics, which controlled the excitation voltage amplitude and facilitated operation in continuous wave (CW) or pulsed mode with adjustable (10-90%) duty cycle. The driver unit was powered by remotely located rechargeable lithium (Li) polymer batteries. This was done to further minimize the weight of the applicator unit making it wearable. With DC voltage of approximately 15 V the prototypes were capable of delivering pressure amplitudes of about 55 kPa or 100 mW/cm² (I_SPTP). This level of acoustic output was chosen as it is considered safe and side effects free, even at prolonged exposure.     

Self-Q-switched and mode-locked 946 nm Cr,Nd:YAG laser

A simultaneous self-Q-switched and mode-locked diode-pumped 946 nm laser by using a Cr,Nd:YAG crystal as gain medium as well as saturable absorber is demonstrated for the first time as we know. The maximum average output power of 751 mW with a slope efficiency of 18.38% is obtained at an intra-cavity average peak power intensity of 4.83 × 10⁶ W/cm². Under this circumstance, the repetition rate of Q-switched envelopes is 9.63 kHz and the pulse width is about 460 ns. Almost 100% mode-locked modulation depth is obtained at all time in the experiment process whether the incident pump power is low or high. The repetition rate of mode-locked pulses within a Q-switched envelope is 135.13 MHz and the mode-locked pulse width is within 600 ps. The laser produces high-quality pulses in TEM₀₀-mode in the simultaneous self-Q-switched and mode-locked experiment.