Extending time-domain ptychography to generalized phase-only transfer functions

We extend the time-domain ptychographic iterative engine to generalized spectral phase-only transfer functions. The modified algorithm, i$^2$PIE, is described and its robustness is demonstrated by different numeric simulations. The concept is experimentally verified by reconstruction of a complex supercontinuum pulse from an all normal dispersion fiber.Comment: 5 pages, 4 figures, submitted to Optic

Low noise all-fiber amplification of a coherent supercontinuum at 2 \mu m and its limits imposed by polarization noise

We report the amplification of an all-normal dispersion supercontinuum pulse in a Thulium / Holmium co-doped all-fiber chirped pulse amplification system. With a -20 dB bandwidth of more than 300 nm in the range 1800-2100 nm the system delivers high quality 66 fs pulses with more than 70 kW peak power directly from the output fiber. The coherent seeding of the entire emission bandwidth of the doped fiber and the stability of the supercontinuum generation dynamics in the silicate glass all-normal dispersion photonic crystal fiber result in excellent noise characteristics of the amplified ultrashort pulses

Noise Fingerprints of Fiber Supercontinuum Sources

We present a novel technique for measuring unique ”noise fingerprints” of fiber supercontinuum (SC) sources, revealing a strong dependence of SC relative intensity noise not only on the dispersion of the fiber, but also on its cross-sectional geometry

Temporal fine structure of all-normal dispersion fiber supercontinuum

Experimental characterization of spectro-temporal structure of octave-spanning, coherent fiber supercontinuum pulses is performed and full-field information is retrieved using time-domain ptychography. Fast femtosecond oscillations are observed and traced back to imperfections of the pump pulses

Time domain ptychography

Thesis (PhD)--Stellenbosch University, 2015.ENGLISH ABSTRACT: In this work we investigate a new method to measure the electric field of ultrafast laser pulses by extending a known measurement technique, ptychography, in the spatial domain to the time domain which we call time domain ptychography. The technique requires the measurement of intensity spectra at different time delays of an unknown temporal object and a known probe pulse. We show for the first time by measurement and calculation that this technique can be applied with excellent results to recover both the amplitude and phase of a temporal object. This technique has several advantages, such as fast convergence, the resolution is limited by the usable measured spectral bandwidth and the recovered phase has no sign ambiguity. We then extend the technique to pulse characterization where the probe is derived form the temporal object by filtering meaning the probe pulse is also unknown, but the spectrum of the probe pulse must be the same as the spectrum of the temporal object before filtering. We modify the reconstruction algorithm, now called ptychographic iterative reconstruction algorithm for time domain pulses (PIRANA), in order to also reconstruct the probe and we show for the first time that temporal objects, a.k.a laser pulses, can be reconstructed with this new modality.AFRIKAANSE OPSOMMING: In hierdie werk het ons ’n nuwe metode ondersoek om die elektriese veld van ’n ultravinnige laser puls te meet deur ’n bekende meettegniek wat gebruik word in die ruimtelike gebied, tigografie, aan te pas vir gebruik in die tyd gebied genaamd tyd gebied tigografie. Die tegniek vereis die meting van ’n reeks intensiteit spektra by verskillende tyd intervalle van ’n onbekende ‘tyd voorwerp’ en ’n bekende monster puls. Ons wys vir die eerste keer deur meting en numeriese berekening dat hierdie tegniek toegepas kan word met uitstekende resultate, om die amplitude en fase van ’n ‘tyd voorwerp’ te meet. Hierdie tegniek het verskeie voordele, die iteratiewe proses is vinnig, die resolusie van die tegniek word bepaal deur die spektrale bandwydte gemeet en die fase van die ‘tyd voorwerp’ word met die korrekte teken gerekonstrueer. Ons het hierdie tegniek uitgebrei na puls karakterisering waar die monster pulse afgelei word, deur ’n bekende filter te gebruik, van die onbekende ‘tyd voorwerp’ nl. die inset puls. Ons het die iteratiewe algoritme wat die ‘tyd voorwerp’ rekonstrueer aangepas om ook die monster puls te vind en ons wys dat ons hierdie metode suksesvol kan gebruik om laser pulse te karakterisee

Investigation of a wool measurement device for determining the mean diameter of a sample consisting of multiple wool fibres

Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: In the wool trade the mean diameter of wool is a primary indicator of wool quality. It is currently standard practice for a wool grower to send samples to a laboratory for classification before and after shearing. The devices used to make measurements on samples are often big and bulky and sensitive to the environment, thus they are not ideally suited for on site testing. A brief discussion of the industry is given with background information on existing devices as well as information about organic fibres in general. We test an experimental device which has the potential to be robust and compact based on the Fourier optical principle. Two initial designs are considered and the transmission design is further developed into a working system. The working system is evaluated in a sample measurement experiment. In our sample measurement experimentwe determine the mean diameter of a set of samples which has been analysed by an external testing body such that the measurements could be compared.AFRIKAANSE OPSOMMING: In diewol bedryfword die gemiddelde diameter vanwol as ’n primêre kwaliteitindeks gebruik. Dit is tans gebruiklik om wol monsters na ’n laboratorium te stuur vir klassifikasie voor en na die skape geskeer word. Die toestel wat gebruik word om die wol monsters te klassifiseer is geneig om groot, lomp en sensitief vir die omgewing te wees en is sodoende nie ideaal vir veld gebruik nie. ’n Kort uitleg van die industrie word gegee tesame met agtergrond inligting van bestaande toestelle asook agtergrond oor organiese vesels in die algemeen. Ons toets ’n eksperimentele toestel wat potensieel kompak en aanpasbaar kan wees en gebaseer is op die Fourier optiese prinsiep. Twee aanvanklike ontwerpe word oorweeg en eindelik word die transmissie ontwerp verder ontwikkel tot ’n werkende sisteem. Die sisteem word geëvalueer in ’n monster meting eksperiment. In die monster meting eksperiment bepaal ons die gemiddelde diameter van ’n stel monsters waarvan die gemiddelde diameter deur ’n eksterne liggaam bepaal is om sodoende die metings te kan vergelyk

Polarization-dependent relative intensity noise of fiber supercontinuum sources

Detailed experimental polarization-dependent relative intensity noise (RIN) measurements of all-normal dispersion (ANDi) and conventional supercontinuum (SC) sources are presented. We show that the polarization-maintaining ANDi fiber suppresses polarization noise, is robust against pump polarization fluctua- tions, and allows ultra-low noise SC generation with RIN identi- cal to the pump laser (< 0.05%)

Towards effective schools for all

SIGLEAvailable from British Library Document Supply Centre-DSC:q97/00192 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Low noise all-fiber amplification of a coherent supercontinuum at 2 µm and its limits imposed by polarization noise

We report a low noise, broadband, ultrafast Thulium/Holmium co‐doped all‐fiber chirped pulse amplifier, seeded by an Erbium‐fiber system spectrally broadened via coherent supercontinuum generation in an all‐normal dispersion photonic crystal fiber. The amplifier supports a − 20 dB bandwidth of more than 300 nm and delivers high quality 66 fs pulses with more than 70 kW peak power directly from the output fiber. The total relative intensity noise (RIN) integrated from 10 Hz to 20 MHz is 0.07%, which to our knowledge is the lowest reported RIN for wideband ultrafast amplifiers operating at 2 μm to date. This is achieved by eliminating noise‐sensitive anomalous dispersion nonlinear dynamics from the spectral broadening stage. In addition, we identify the origin of the remaining excess RIN as polarization modulational instability (PMI), and propose a route towards complete elimination of this excess noise. Hence, our work paves the way for a next generation of ultra‐low noise frequency combs and ultrashort pulse sources in the 2 μm spectral region that rival or even outperform the excellent noise characteristics of Erbium‐fiber technology

White light wavefront control with a spatial light modulator

Please cite as follows:Spangenberg, D-M., et al. 2014. White light wavefront control with a spatial light modulator.Optics Express, 22(11): 13870-13879, doi:10.1364/OE.22.013870.The original publication is available at http://www.opticsinfobase.org/oe/home.cfmPublication of this article was funded by the Stellenbosch University Open Access Fund.Spatial light modulators are ubiquitous tools for wavefront control and laser beam shaping but have traditionally been used with monochromatic sources due to the inherent wavelength dependence of the calibration process and subsequent phase manipulation. In this work we show that such devices can also be used to shape broadband sources without any wavelength dependence on the output beam’s phase. We outline the principle mathematically and then demonstrate it experimentally using a supercontinuum source to shape rotating white-light Bessel beams carrying orbital angular momentum.printPublishers' Versio