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In this work, we report on the implementation of a closed-loop liquid-loaded resonant mass sensor as a test vehicle for the realization of highly sensitive miniaturized biomarker assays. Using thin-film piezoelectric-on-silicon (TPoS) contour-mode disc resonators that are specifically designed and optimized for liquid-phase operation, a liquid-loaded low power (~1.6 mW) oscillator at ~17 MHz is demonstrated with a single transistor. By proper placement of the electrodes and the supporting tethers, a high liquid-loaded quality factor (~380) and a low insertion loss (~19 dB) are concurrently achieved which enable the accurate frequency tracking of the potential mass microbalance. The frequency shifts due to the liquid-loading and the preliminary characterized frequency stability of the oscillator imply a minimum mass detection resolution in the picograms range. [2020-0177]

A novel resonant micro-accelerometer is implemented with an operational frequency of ~27 MHz in which an acceleration-induced change of capacitance is transformed to a frequency shift in a piezoelectric resonator utilizing the piezoelectric stiffening mechanism. In this device the mass-spring system is not embedded within the resonator, enabling a large degree of freedom in choosing the resonance frequency of the resonator. The piezoelectric resonator and the capacitive mass spring (CMS) structure are both fabricated on a silicon-on-insulator (SOI) wafer covered by a thin film of sputtered aluminum nitride. The feasibility and the efficiency of this novel sensing mechanism has been proven by demonstrating a ~600 Hz shift in the resonance frequency as the sample accelerometer was rotated 1800 yielding a 300Hz.g-1 sensitivity.

In this work a frequency-modulated (FM) resonant accelerometer operating based on the piezoelectric stiffening effect is introduced for the first time. In this device, the acceleration-sensitive variation of a capacitive mass-spring (CMS) system is up converted to a carrier frequency which is set by the resonance frequency of a thin-film piezoelectric-on-silicon (TPoS) resonator due to the piezoelectric stiffening effect. The mechanical decoupling of the acceleration-sensitive component from the resonant component allows for an additional degree of freedom in the design and a larger dynamic range, while enabling high frequency operation of the accelerometer. Proof-of-concept Z-axis accelerometers at ∼27 MHz are presented with an acceleration sensitivity of ∼300 Hz/g, The acceleration/axis sensitivity is mainly dependent on the design of the CMS and ultimately limited by the effective electromechanical coupling of the TPoS resonator.

Experimental data for 15-stage 5.6- $\mu \text{m}$ quantum cascade lasers based on Al0.78In0.22As/In0.69Ga0.31As active region composition are presented. Pulsed slope efficiency, threshold current density, and wall-plug efficiency for a $2.1~\text {mm} \times 10.4~\mu \text{m}$ device with a high reflection-coated back facet were measured to be 1.45 W/A, 3.1 kA/cm2, and 18%, respectively. Corresponding continuous wave values for the same parameters were measured to be 1.42 W/A, 3.7 kA/cm2, and 12%. Demonstrated continuous wave optical power level exceeding 0.5 W per millimeter of cavity length makes quantum cascade lasers with reduced number of stages suitable for high power infrared applications.

In this article, the microfluidic channels that deliver liquid to a microscale thin-film piezoelectric-on-silicon (TPoS) gravimetric resonant sensor are incorporated into the backside of the silicon-on-insulator (SOI) wafer on which the resonator is fabricated. Specifically, a microwell is embedded at the bottom of the disk -shaped TPoS resonator, while a very thin layer of parylene covering the backside of the resonator and the microwell forms an isolation layer between the liquid and the top device-layer features. In this way, the liquid is in contact with the backside of the resonator, while the device-defining trenches and the electrical connections to the resonator stay clear, thus mitigating the acoustic energy loss and undesirable feedthroughs. The impact of the parylene layer thickness on a few symmetric ( ${S}$ ) and antisymmetric ( ${A}$ ) Lamb wave modes of the resonator is experimentally studied, and the performance of such modes in the liquid is characterized by filling the microwells through a PDMS-based microfluidic channel. The parylene layer, while marginally affecting the resonator in the air, is found to substantially enhance its performance in the liquid media. Strong resonance peaks with high quality factors ( ${Q}$ ) are observed for the ${S}$ modes, among which ${Q}$ values above 400 are recorded for a specific mode named ${S}$ ( 4 , 2 ) (among the highest ever reported). This article can potentially facilitate the realization of highly stable and sensitive resonant mass sensors (i.e., microbalance) for real-time applications. Additionally, the effect of the acoustic energy radiation in the form of evanescent shear and longitudinal waves in liquid on the ${Q}$ and resonance frequency of the disk resonators is experimentally validated.

5.6μm quantum cascade lasers based on Al0.78In0.22As/In0.69Ga0.31As active region composition with measured pulsed room temperature wall plug efficiency of 28.3% are reported. Injection efficiency for the upper laser level of 75% was measured by testing devices with variable cavity length. Threshold current density of 1.7kA/cm2 and slope efficiency of 4.9W/A were measured for uncoated 3.15mm x 9µm lasers. Threshold current density and slope efficiency dependence on temperature in the range from 288K to 348K can be described by characteristic temperatures T0~140K and T1~710K, respectively. Pulsed slope efficiency, threshold current density, and wallplug efficiency for a 2.1mm x 10.4µm 15-stage device with the same design and a high reflection-coated back facet were measured to be 1.45W/A, 3.1kA/cm2 , and 18%, respectively. Continuous wave values for the same parameters were measured to be 1.42W/A, 3.7kA/cm2 , and 12%. Continuous wave optical power levels exceeding 0.5W per millimeter of cavity length was demonstrated. When combined with the 40-stage device data, the inverse slope efficiency dependence on cavity length for 15-stage data allowed for separate evaluation of the losses originating from the active region and from the cladding layers of the laser structure. Specifically, the active region losses for the studied design were found to be 0.77cm-1, while cladding region losses – 0.33cm-1. The data demonstrate that active region losses in mid wave infrared quantum cascade lasers largely define total waveguide losses and that their reduction should be one of the main priorities in the quantum cascade laser design.

5.6 μm quantum cascade lasers based on Al 0.78 In 0.22 As/In 0.69 Ga 0.31 As active region composition with measured pulsed room temperature wall plug efficiency of 28.3% are reported. Injection efficiency for the upper laser level of 75% was measured for the new design by testing devices with variable cavity length. Threshold current density of 1.7kA/cm2 and slope efficiency of 4.9W/A were measured for uncoated 3.15mm × 9μm lasers. Threshold current density and slope efficiency dependence on temperature in the range from 288K to 348K for the new structure can be described by characteristic temperatures T0 ~ 140K and T1 ~710K, respectively. Experimental data for inverse slope efficiency dependence on cavity length for 15-stage quantum cascade lasers with the same design are also presented. When combined with the 40-stage device data, the new data allowed for separate evaluation of the losses originating from the active region and from the cladding layers of the laser structure. Specifically, the active region losses for the studied design were found to be 0.77 cm-1, while cladding region losses - 0.33 cm-1. The data demonstrate that active region losses in mid wave infrared quantum cascade lasers largely define total waveguide losses and that their reduction should be one of the main priorities in the quantum cascade laser design.

Bessel beams with tunable spot size are desirable for many applications such as laser material processing, optical trapping, and imaging. In this paper, we report experimental and simulation results of using a segmented deformable mirror to generate zero- and higher-order Bessel beams that have a controllable transverse and longitudinal shape. The tilt angle and piston position of the mirror segments are optimized to recreate the phase structure of a reflective axicon. Zero-order Bessel beams are generated at various beam converging angles, and their core diameter, peak intensity, and depth-of-focus are found to agree with the calculated results. By applying a phase ramp along the azimuthal direction, the first-order Bessel beam is generated with the characteristic annular shape. Because deformable mirrors have low absorption and dispersion and operate at a fast frame rate, they are a promising candidate for spatial beam shaping of high-power ultrafast lasers, which are used in material processing applications.

Experimental and model results for 15-stage broad area quantum cascade lasers (QCLs) are presented. Continuous wave (CW) power scaling from 1.62 to 2.34 W has been experimentally demonstrated for 3.15-mm long, high reflection-coated QCLs for an active region width increased from 10 to 20 μm. A semiempirical model for broad area devices operating in CW mode is presented. The model uses measured pulsed transparency current, injection efficiency, waveguide losses, and differential gain as input parameters. It also takes into account active region self-heating and sublinearity of pulsed power versus current laser characteristic. The model predicts that an 11% improvement in maximum CW power and increased wall-plug efficiency can be achieved from 3.15 mm×25 μm devices with 21 stages of the same design, but half doping in the active region. For a 16-stage design with a reduced stage thickness of 300 A, pulsed rollover current density of 6 kA/cm2, and InGaAs waveguide layers, an optical power increase of 41% is projected. Finally, the model projects that power level can be increased to ∼4.5 W from 3.15 mm×31 μm devices with the baseline configuration with T0 increased from 140 K for the present design to 250 K.

5.6 μm quantum cascade lasers based on the Al0.78In0.22As/In0.69Ga0.31As active region composition with the measured pulsed room temperature wall plug efficiency of 28.3% are reported. Injection efficiency for the upper laser level of 75% was measured for the design by testing devices with variable cavity lengths. A threshold current density of 1.7 kA/cm2 and a slope efficiency of 4.9 W/A were measured for uncoated 3.15 mm × 9 μm lasers. Threshold current density and slope efficiency dependence on temperature in the range from 288 K to 348 K for the structure can be described by characteristic temperatures T0 ∼ 140 K and T1 ∼ 710 K, respectively.