Microwave assisted chemical vapour deposited bulk diamond products have been used in a range of high power laser systems, due to low absorption across a range of wavelengths and exceptional thermal properties. However the application of polycrystalline products has frequently been limited to applications at longer wavelengths or thermal uses outside of the optical path due to the birefringence and scatter that are intrinsic properties of the polycrystalline materials. However, there are some solid state structures, including thin disc gain modules and amplifiers, that will gain significantly in terms of potential output powers if diamond could be used as a heat spreader in the optical path as well as a heat spreader on the rear surface of the disk. Therefore single crystal grades of diamond have been developed that overcome the limitations of the polycrystalline material, with low absorption, low scatter and low birefringence grades for demanding optical applications. We will present new data, characterising the performance of these materials across infra-red and visible wavelengths with absorption coefficient measured by laser calorimetry at a range of wavelengths from 1064 nm to 452 nm.
We demonstrate power scaling of an Nd:YAG picosecond master oscillator power amplifier system to over 200 W. The ‘z-slab’ amplifier design is a power scalable, edge-pumped zigzag slab amplifier architecture, and it is demonstrated here in two alternative multi-stage implementations at 1064 nm using a picosecond seed laser. In a simple design, an average power of 225 W was generated with up to 450 μJ pulse energy at 11 ps pulse duration. In a compact multi-pass design, 150 W was generated with M2 < 1.75.
Understanding the nonlinear optical processes in semiconductor nanostructures leads to possible applications in areas
including laser amplifiers, optical switches, and solar cells. Here we present a study of the frequency degenerate two-photon
absorption (2PA) spectrum of a series of PbS and PbSe quantum dots (QDs). The influence of the quantum
confinement is analyzed using a four-band model which considers the mixing of valence and conduction bands. In
contrast to our observations of CdSe QDs, the present results point to an increase of the 2PA cross-section (normalized
by the QD volume) as the quantum dot size is made smaller. This is explained by the symmetry between the valence and
conduction bands which allows the density of states to remain high even for small QDs. A study of the ultrafast carrier
dynamics of the PbS quantum dots is also presented. Through nondegenerate femtosecond pump-probe experiments we
show evidence of multi-exciton generation with quantum yield (number of excitons generated per absorbed photon) up
to 170% for excitation with hω> 3 Eg (where Eg is the bandgap energy).
We have been developing tools for nonlinear spectroscopy aimed toward the ultimate goal of building a nonlinear
spectrophotometer analogous to the ubiquitous linear spectrophotometer where a sample is placed in the instrument, a
button is pushed, and the absorption spectrum is obtained sometime later. This paper describes our progress toward this
goal, describing many difficulties and complications as well as opportunities. We also show spectroscopic data and
analysis of a variety of materials that we have taken with preliminary nonlinear spectroscopic instrumentation we have
already developed. One of the more interesting observations obtained along this research path is the realization that
linear dispersion theory can also be applied to nonlinear systems when formulated properly such that Kramers-Kronig
relations can be used to connect the dispersion of nonlinear refraction to the spectrum of nonlinear absorption. In some
circumstances this can be more easily applied to nonlinear systems than to linear systems since the nonlinear absorption
spectrum can be limited in wavelength. In addition, we have developed tools that can simultaneously give the spectrum
of nonlinear absorption as well as the dispersion of the nonlinear refraction over an octave spectral range from 400nnm
to 800 nm, the so called White-Light-Continuum Z-scan. Much of the research on nonlinear optical materials has been a
collaborative effort requiring the skills and expertise of organic chemists and materials manufacturers. The goals of this
part of the research are to determine predictive structure-property relation capabilities. The database needed for this
research makes the nonlinear spectrophotometer a necessity.
We present the design, fabrication and characterization of the optical properties of one-dimensional metal-organic
photonic bandgaps (MO-PBGs) composed of a tetraphenyldiaminobiphenyl-based polymer and ultrathin electrically
continuous Cu layers. The fabricated MO-PBGs achieve a peak transmission of around 44% at 620 nm combined with
very large spectral, around 120 nm FWHM, and angular, more than 120° field-of-view, bandwidths. Using 140 fs pulses
at various wavelengths we have found up to 10 × enhancements in the nonlinear optical (NLO) properties of the MO-PBGs
when compared with the NLO response of ultrathin electrically continuous Cu layers.
We have tested a series of Ytterbium doped large core fibers operating near 10Kpps and producing pulses of approximately 1ns. We have achieved 0.85mJ/pulse resulting in peak powers in excess of 2MW with 0.4ns pulses and near diffraction limited beams. In another fiber, we have achieved over 1.5mJ/pulse with pulses of 900ps corresponding to 1.65MW of peak power and M2 of 2.5. In the latter case, wall-plug efficiencies, excluding cooling of the pump diode lasers, in excess of 15% were also achieved. This fiber amplifier has operated for 2 months without any degradation or observed optical damage.
N-on-1 LIDT measurements were performed on ytterbium doped preforms used to make high peak power fiber amplifiers. Damage measurements were complicated by large index of refraction changes across the preforms. These difficulties were overcome by monitoring the beam profile before and after the samples and by only taking data where the transmitted beam was not significantly distorted. Single and 1000 shot data suggest slight laser conditioning of the preforms and rule out laser fatigue in the doped cores and surrounding fused silica. At 1064 nm, inside the emission spectra, there seemed to be little influence of the Yb dopant concentration on the measured LIDT.