Walter Lubeigt

Continuous-wave diamond Raman laser

Continuous-wave operation of a diamond Raman laser is demonstrated. Low-birefringence synthetic single-crystal diamond is used and is intracavity pumped by a Nd:YVO(4) laser. A cw output power of 200 mW is achieved at the Raman wavelength (1240 nm), and 1.6 W of on-time output power is obtained in quasi-cw mode. Losses in the diamond (approximately 1% per pass) and thermal effects in the Nd:YVO(4) limit the efficiency.

1.6 W continuous-wave Raman laser using low-loss synthetic diamond.

Low-birefringence (Δn<2x10(-6)), low-loss (absorption coefficient <0.006 cm(-1) at 1064 nm), single-crystal, synthetic diamond has been exploited in a CW Raman laser. The diamond Raman laser was intracavity pumped within a Nd:YVO4 laser. At the Raman laser wavelength of 1240 nm, CW output powers of 1.6 W and a slope efficiency with respect to the absorbed diode-laser pump power (at 808 nm) of ~18% were measured. In quasi-CW operation, maximum on-time output powers of 2.8 W (slope efficiency ~24%) were observed, resulting in an absorbed diode-laser pump power to the Raman laser output power conversion efficiency of 13%.

Enhancement of laser performance using an intracavity deformable membrane mirror

An intracavity deformable membrane mirror has been successfully used to optimise the brightness of solid-state lasers--a side-pumped Nd(3+):YAlO laser where the oscillation of a low-order transverse mode was obtained, and a grazing incidence Nd(3+):GdVO(4) laser where a brightness increase by an order of magnitude with negligible drop in power was achieved. Several search algorithms were also implemented in the system and compared with respect to intracavity optimisation.

An intra-cavity Raman laser using synthetic single-crystal diamond.

Low birefringence synthetic single-crystal diamond was used as a Raman laser medium inside a Q-switched Nd:YVO(4) laser. A maximum average output power of 375 mW was achieved at a wavelength of 1240 nm and a repetition rate of 6.3 kHz. This equates to a conversion efficiency of 4% from the diode laser to the first Stokes component at 1240 nm. Optical losses within the diamond (approximately 1% per single pass) limited the performance and are currently the main barrier to the demonstration of an efficient CW diamond Raman laser.

Continuous-wave Raman laser pumped within a semiconductor disk laser cavity

A KGd(WO₄)₂ Raman laser was pumped within the cavity of a cw diode-pumped InGaAs semiconductor disk laser (SDL). The Raman laser threshold was reached for 5.6 W of absorbed diode pump power, and output power up to 0.8 W at 1143 nm, with optical conversion efficiency of 7.5% with respect to the absorbed diode pump power, was demonstrated. Tuning the SDL resulted in tuning of the Raman laser output between 1133 and 1157 nm.

Design, Simulation, and Characterization of a Bimorph Varifocal Micromirror and Its Application in an Optical Imaging System

A 1.2-mm-diameter gold-silicon bimorph varifocal micromirror (VFM) has been designed and investigated for imaging applications. Several prototypes have been fabricated in a 10-μm-thick single-crystal silicon-on-insulator material. Controlled variation of the radius of curvature using electrothermal and optothermal actuation has been demonstrated. A finite-element-based simulation of the device behavior has been undertaken. Experimental characterization has shown that the device focusing power varied from an initial 87 dioptre to 69 dioptre by applying dc electrical power of 33 mW and produced a focusing power value of 59 dioptre when optothermally actuated with a normally incident laser beam of 488-nm wavelength and 43 mW. When electrothermally driven, the mechanical rise and fall times of the device were measured as 130 and 120 ms, respectively. Experimental and theoretical analyses using Zernike coefficients show that, throughout the actuation range, the aberration of the VFM is mainly a small defocus term, with negligible higher order aberrations. A compact active imaging system incorporating the VFM has been also demonstrated. This system was capable of focusing several objects located along the optical axis with a maximum tracking range of 134 mm.

Search-based active optic systems for aberration correction in time-independent applications

We describe a protocol for the use of a control feedback loop incorporating an iterative optimization routine for a range of time-independent adaptive optics applications. These applications are characterized by the quasi steady state of the aberrative effects (>0.1 s) and contrast, for instance, to astronomical applications where the aberrations constantly vary at frequencies above 10 Hz. For optimal performance in such time-independent applications, the control systems typically require specialized tailoring. A typical example of two different types of time-independent adaptive optics applications--an adaptive optic microscope and an adaptive optic laser platform--are detailed and compared. It is shown that implementing a number of minor, but crucial, application-specific modifications to the control system results in an improved efficiency of an already extremely successful technique for aberration compensation. We present a description of the crucial parameters to consider in a search-based adaptive optics system.

Control of solid-state lasers using an intra-cavity MEMS micromirror

Low-cost scanning MEMS micro-mirrors were incorporated within the cavities of Nd:based laser systems to control the output beam characteristics. Successful Q-switching was obtained from these solid-state intra-cavity MEMS lasers resulting in pulse durations of 220ns and peak powers of 13.2W at a wavelength of 1064nm.

Reduction of the time-to-full-brightness in solid-state lasers using intra-cavity adaptive optics.

Several adaptive-optics techniques, based on the active modification of the optical properties of the laser cavity, were used to significantly reduce the time-to-full-brightness of solid-state lasers. Resonator re-configuration was achieved using a mechanical translation stage and both multi- and single-element deformable bimorph mirrors. Using these techniques the effects of thermally induced distortion in Nd:YLF and Nd:YAG lasers can be minimized and the warm-up time reduced by a factor of 3-6.

Ultrashort-pulse laser with an intracavity phase shaping element.

A novel ultrashort-pulse laser cavity configuration that incorporates an intracavity deformable mirror as a phase control element is reported. A user-defined spectral phase relation of 0.7 radians relative shift could be produced at around 1035 nm. Phase shaping as well as pulse duration optimization was achieved via a computer-controlled feedback loop.