Alan Paterson

Output Characteristics of Q-switched Solid-State Lasers Using Intracavity MEMS Micromirrors

The output behavior of a Nd:YAG solid-state laser actively Q-switched by a MEMS scanning micromirror is presented. Using a gold-coated micromirror, maximum average output powers of 50 mW and pulse durations as short as 120 ns were obtained with a dual beam output. This output pattern originates from a pulse emission when the micromirror is at an angle from the cavity axis. The temporal and spatial behavior of this laser was experimentally characterized and then modeled using a numerical simulation of the laser rate equations. Finally, prospects for power scaling this MEMS-based Q-switch technique are demonstrated using a dielectric-coated micromirror, which led to average output powers of up to 650 mW and pulse energies above 40 μJ.

Range Extension of a Bimorph Varifocal Micromirror Through Actuation by a Peltier Element

A bimorph varifocal micromirror actuated thermoelectrically by a Peltier element is reported. The single-crystal silicon micromirror is 1.2 mm in diameter with a centered 1-mm-diameter gold coating for broadband reflection. The actuation principle is capable of varying the micromirror temperature above and below the ambient temperature, which contributed to a 57% improvement in the addressable curvature range in comparison to previously reported electrothermal and optothermal actuation techniques for the device. Altering the device temperature from 10 °C to 100 °C provided a mirror surface radius of curvature variation from 19.2 to 30.9 mm, respectively. The experimental characterization of the micromirror was used as a basis for accurate finite-element modeling of the device and its actuation. Negligible optical aberrations are observed over the operating range, enabling effectively aberration-free imaging. Demonstration in an optical imaging system illustrated sharp imaging of objects over a focal plane variation of 212 mm.

Q-switched tunable solid-state laser using a MOEMS mirror

Simultaneous wavelength tuning and Q-switching of a Yb:KGW laser using a single, electrothermally actuated MOEMS mirror is reported for the first time. A 15.4 nm tuning range is achieved at 2.06 kHz pulse repetition frequency.

Wavelength tuning of a solid-state laser with a tilting MEMS micromirror

Wavelength tuning of a Yb:KGW solid-state laser is presented using an electrothermally-actuated micromirror and a diffraction grating or dispersing prism. 27 nm and 7.5 nm tuning ranges are achieved using extracavity and intracavity configurations respectively.

Comparison of modeled and experimental behavior of a thermoelectrically actuated varifocal micromirror

The finite element analysis (FEA) simulation results of a bimorph silicon-gold varifocal micromirror (VFM) are reported. For a 1.2 mm diameter silicon VFM, the simulation shows that a variation of the surface radius of curvature (ROC) from 18.8 mm to 31.3 mm can be achieved between device temperatures of 10 °C and 100 °C. The ROC versus temperature relationship is highly sensitive to the values of Youngs modulus and residual stress of the gold layer used in this model. The simulation results are compared with our experimentally measured ROCs obtained at different temperatures, yielding accurate modeling of the VFM behavior.

Intracavity control of solid-state lasers using MEMS micromirrors

Active control of key laser output beam parameters, such as optical power and transverse intensity profile, of a continuous-wave (CW) Nd:YAG laser is reported. This was achieved by accurately controlling the surface profile of an intracavity MEMS micromirror through active control of its substrate temperature. An output power variation (>20%) and a significant modification of the transverse mode profile could be observed for a temperature variation of ~35 °C.

Interferometric time division FBG interrogator and multiplexer with static, dynamic, and absolute wavelength measurement capabilities

We report on the design and preliminary testing of an interferometric interrogator capable of large-scale time-division multiplexing of FBG sensors. The scheme employs a passive algorithm for phase demodulation, allowing changes in FBG sensor reflected wavelengths to be calculated instantaneously upon arrival, and incorporates a technique for identification of initial absolute sensor wavelengths in order to overcome the measurement ambiguity associated with interferometric schemes. The proposed system will allow for high-speed interrogation of large-scale FBG sensor arrays with interferometric resolution and the capability for dynamic, static, and absolute FBG wavelength measurement.