prof.dr.ir. H.L. Offerhaus (Herman)

RESEARCH INTEREST

Nonlinear spectroscopy: CARS spectroscopy, heterodyne detection of CARS, CARS with shaped light fields.   Spatial and spectral control: phase behaviour, holographic feedback, coherent control, functional gratings, phased arrays, antenna structures.   Near field optics: directed plasmon generation, micro-fluidics for single molecule applications.   Lasers: solid-state laser, fibre lasers, fibre Raman lasers, high power lasers, diode lasers, Q-switching, Modelocking, beam analysis, pulse characterization (FROG, GRENOUILLE, SPIDER).   Non-linear optics: OPG/OPA/OPO, OPA of chirped pulses, PPLN, periodic poling and patterning, Atom optics, Frequency conversion/division/transformation.  Holography: Holographic recording techniques and materials, porous glass, interferometric recording, phase-only shaping.

CURRENT/RECENT PROJECTS

 

HYPERSPECTRAL DATA ANALYSIS: Combination of hyperspectral imaging with heterodyne detection (see below) allows for the retrieval of complex spectra during imaging. This complex data should rpovide ample information for selective detection. We are investigating advanced extraction algorithms like end-member detection to retrieve components with high specificity and selectivity.

INTERFEROMETRIC STROBOSCOPIC IMAGING OF PRESSURE WAVES IN A MICROCHANNEL: Resonant excitation of microchannels generates strong pressure waves. To visualize the excitation of the waves we have built an interferometric imaging setup. The light source is a broadband diode that can be operated to flash stroboscopically in synch with the piezo excitation of the pressure to generate 4 exposures per cycle that are measured independently. By scanning the delay in the reference arm of the interferometer we obtain 4 (OCT-like) interferograms per pixel. From these interferograms we can extract the optical pathlength per pixel at different points in the pressure cycle. From that we can infer the local pressure inside the channel at the peak of the pressure cycle and the relative phase at each position.

Oever, J.J.F. van 't, Frentrop, R., Wijnperlé, D., Offerhaus, H.L., Ende, D. van den, Herek, J.L. & Mugele, F. Imaging Local Acoustic Pressure in Microchannels. Applied optics, 54(21), 6482-6490 (2015) [Link]

FAST INTERFEROMETRIC HEIGHT MEASUREMENTS: Using a spatially incoherent incoherent spectrally broad diode we illuminate a line on a surface. We combine the reflected light with a reference arm and image the line on the input slit of an imaging spectrograph to obtain a interferogram per pixel along the line (similar to spectral OCT). Since the emission from the diode is spatially incoherent, the inteferferograms are also incoherent to each other and each interferogram can be viewed independently. From the interferograms a height profile along the line can be extracted. Using a flashing diode, multiple images can be taken so that a surface can be scanned or a contunous line can be obtained.

SALT DETECTION ON CHIP: The waterabsorption in the NIR (900-1100nm) show overtones of the OH-bands. These band are influenced (width and position) by dissolved ions (slats) in the water. Careful comparison between the absorption of clean water and the absorption of water with salts yields differential absorption spectra. These spectra (see graph) show characteristic profiles for the diferent salts. We want to measure such differential absorption spectra to detect, analyse and qunatify salt presence. A viable detection systems requires that the measurement take place on chip in an integrated way. Optofluidic chips have been designed and realized in collaboration with LioniX.

G.W. Steen, E.C. Fuchs, A.D. Wexler, and H.L. Offerhaus, "Identification and quantification of 16 inorganic ions in water by Gaussian curve fitting of near-infrared difference absorbance spectra," Appl. Opt. 54, 5937-5942 (2015) [Link]

HYPERSPECTRAL CARS/SRS: By scanning the Lyot filter of the OPO rapidly we can collect images at different wavelength and collect a "hyperspectral datacube" that contains a spectrum per pixel. The broader spectral information is essential for the detection of different polymorphs in parmacy applications.A fast projection algorithm shows the spectral information as color (as if our vision would extend into the IR). The projection allows for rapid indentification of areas of interest. These areas can then be selected and analysed for further identification. This two-step approach allows for fast inspection and avoids slow analsysi and losing the information (as can happen in a PCA).

Erik T. Garbacik, Jennifer L. Herek, Cees Otto and Herman L. Offerhaus, "Rapid identification of heterogeneous mixture components with hyperspectral coherent anti- Stokes Raman scattering imaging" Journal of Raman Spectroscopy may 3, 2012 doi:10.1002/jrs.4064 [Link]

BUGZAPPER: By recording sound with multiple microphones at different locations, the relative phase of the sound on the different microphones can be determined and the distance from the microphones can be established. Using the phase (timing-difference information) the location of the source can be estimated. We have designed, built and explored such a system to track mosquitos and to try to hit them with a laserbeam as they are flying.

DETECTION OF LOW LEVEL FLUORESCENCE: The detection of small amount of fluorescence in a clinical or forensic setting can be imroved by eliminating signals from other light sources and detector/camera noise. Using modulation of the exciation source makes it possible to do lock-in detection of the fluorescence signal so that other light sources are suppressed. High modulation frequencies allow for rapid imaging. Using multiple modulated sources, absorption diferences or narrow fluorescence features taht would normally be insignificant can be revealed. A new type of camera (a TOF camera) allows for very high modulation frequencies (up 10 20MHz) which might even allow for full-field of view lifetime evaluation. We develop different modulation schemes and try to adept the systems for medical and forensic imaging

DETECTION OF PARTICLES IN WATER: To detect small and rare (pathogenic) particles in water we need to concentrate the particles and identify them. We are using standing acoustic waves to concentrate the particles in a small region and detect them using stimulated Raman

BROADBAND SHAPED CARS SPECTROSCOPY and MICROSCOPY: By shaping the pump (and probe) pulses we try to enhance the specificity of the CARS excitation. By substracting the signal for a phase profile from the signal for the phase conjugate phase profile we reject the fully non-resonant component. This allows for imaging on the (spectrally) integrated signal. The applied phase profiles are based on the phase profiles of the molecular response themselves. We use genetic algorithms to optimize the phase profiles.

Sytse Postma, Alexander C. W. van Rhijn, Jeroen P. Korterik, Jennifer L. Herek, Herman L. Offerhaus, “Application of spectral phase shaping to high resolution CARS spectroscopy“ Optics Express Vol. 16, Issue 11, pp. 7985-7996 (2008) [PDF]

HETERODYNE CARS SPECTROSCOPY and MICROSCOPY: The use of an OPO allows for a cascaded phase preserving chain where the OPO-signal matches the CARS wavelength and phase. The OPO-signal can therefore serve as the Local Oscillator for a heterodyne detection scheme where the phase and amplitude of the CARS are retrieved. Detection of the complex amplitude has three advantages: 1) It allows for the extraction of the resonant part of the signal (rejection of the non-resonant background). 2) It allows for decomposition of a signal from multiple substances because the amplitude is linear in the constituent concentrations. 3) Interferometric amplification of the signal allows for shot noise limited detection. M. Jurna, J. P. Korterik, C. Otto, J. L. Herek, and H. L. Offerhaus, "Background free CARS imaging by phase sensitive heterodyne CARS," Opt. Express 16, 15863-15869 (2008) [PDF]M. Jurna, J.P. Korterik, C. Otto, and H.L. Offerhaus, “Shot noise limited heterodyne detection of CARS signals” Optics Express Vol. 15, No. 23 p15207-15213 (2007) [PDF]

CARS SPECTROSCOPY and MICROSCOPY: We use a green (532nm) pumped OPO to do Coherent Anit-stokes Raman Spectroscopy (CARS). We develop this technique together with other groups (Cees Otto of the BPE group) and work with industry (Coherent Inc and APE-Berlin GmbH, FrieslandFoods, PamGene) to get this spectroscopy applied to food and health.

M. Jurna, J. P. Korterik, H. L. Offerhaus and C. Otto “Noncritical phase-matched lithium triborate optical parametric oscillator for high resolution coherent anti-Stokes Raman scattering spectroscopy and microscopy” Appl. Phys. Lett. 89, 251116 (2006) [Link}

COHERENT CONTROL: By applying a phase modulation to the spectrum of a short pulse you can shape the temporal profile of the pulse. Such a shaped pulse can be tailored to fit the absorption dynamics of a molecule in a specific way so that only certain states are excited or only a selected group of molecules will be affected. We aim to use this type of shaping to coherently control the excitation of single molecules. First to study the influence of the enviroment on their excitation spectrum and secondly to achieve control over the entering and exit of socalled dark states to create long lived coherent states. The phase modulation is achieved by placing a computer controller LCD screen in the Fourier plane of a compressor (as shown inthe picture). By adjusting the pixels on the LCD you control the time structure of the pulses.

S. Postma, P. van der Walle, H.L. Offerhaus and N.F. van Hulst, “Compact high-resolution spectral phase shaper” Rev. Sci Instrum, 76(12) 123105, (2005), Virtual Journal of Ultrafast Science, (2006) [Link]

PLASMON GENERATION: Plasmons can be generated by phase shaping light that impinges on a surface. The simples form is to tilt the impinging light but a grating can produce more complex spatial strucrures that generate directed ligthfields. The generated fields can be studied using a phase sensitive Photon Scanning Tunneling Microscope (PSTM aka SNOM/NSOM). 

H. L. Offerhaus, B. van den Bergen, M. Escalante, F. B. Segerink, J. P. Korterik, and N. F. van Hulst, "Creating Focused Plasmons by Noncollinear Phasematching on Functional Gratings", Nano Lett. 5(11) pp 2144-– 2148 (2005) [Link]J. Jose, F. B. Segerink, J. P. Korterik, and H. L. Offerhaus, "Near-field observation of spatial phase shifts associated with Goos-Hänschen and Surface Plasmon Resonance effects," Opt. Express 16, 1958-1964 (2008) [PDF]

BRIGHTDIODES: In this project we are trying to lock all the seperate emitters on a high power diode array using a holographic external cavity. If we can lock the diode, we can extract all the power in the array while maintaining a single mode output profile. We have explored narrowband holographic locking in photorefractive crystal and polymers and wavelength-division-multiplexed locking on a grating.

H.L. Offerhaus, “Werkwijze en inrichting voor het genereren van een coherente laserstraal alsmede werkwijze voor het vervaardigen van een daarbij toe te passen hologram”, EP1017779, April 5 2001P. D. van Voorst, H. L. Offerhaus, K.-J. Boller, “Single frequency operation of a broad area laser diode by injection locking of a complex spatial mode via a double phase conjugate mirror”, Opt. Lett. 31(8) pp. 1061-1063 (2006) [Link] P. D. van Voorst, M. R. de Wit, H. L. Offerhaus, S. Tay, J. Thomas, N. Peyghambarian, and K. -. Boller, "Holographic injection locking of a broad area laser diode via a photorefractive thin-film device," Opt. Express 15, 17587-17591 (2007) [PDF]

HOLOGRAPHY: A phaseplate before a lens causes the Fourier transform of the plate to be projected in the focus of the lens. The spatial frequencies in the hologram will show up as spots in the focus. Using these principles we have designed and fabricated holographic beamsplitters that allow parallel hole drilling. The hologram shown below produces at the MESA+ institute and creates an array of 4x4 equal spots.  This work is done in collaboration with the Otto van Donselaar of the NCLR.

PREVIOUS WORK IN REVERSED CHRONOLOGICAL ORDER (SORT OF)

LASERWAKEFIELD ACCELERATION: Plasma waves can yield enormous potential differences as they travel through a plasma. These waves are going to be exploited for the acceleration of electrons to energies comparable to the energies reached at the CERN acclerator ring. By carefully combining a number of high energy laser pulses the plasma wave can be generated that is strong enough for this type of acceleration. The electrons are then injected at the appropriate time and "surf" the plasma wave.

This work is performed by Fred van Goor in the group of prof. Boller.

GRENOUILLE: To characterise the extremely short pulses needed in the Wakefield experiments one needs to characterise both the amplitude and the phase of the pulse. Measurements of this type can be done in a so called FROG setup (see below) but there is a much simplified system possible for short pulses. This Grenouille setup has less scan range but requires less components and measures a lot faster. The picture on the right shows the GRENOUILLE trace of two chirped pulses seperated by several pulse lengths. Time runs horizontal and spectrum runs vertical. Summing all the columns therefore gives you the integrated spectrum (with the expected modulation due to two consequetive) pulses and summing all the rows gives you the autocorrelation trace of a conventional autocorrelator.

This work is pursues by Fred van Goor in the group of prof. Boller.

POSTDOC AT AMOLF INSTITUTE, AMSTERDAM

AMOLF: My work at the AMOLF institute revolved around the interaction between strong fields and atoms or molecules. I worked on three major projects: Alignment of molecules in intense fields, X-ray generation in water droplets, Harmonic generation in capillaries, imaging of slow photo-electrons and some PPLN stuff

SHORT WAVELENGTH GENERATION: Creating X-rays from solid targets has the advantage of the high density of the solid but creates debris and destroys the materials surface. In this project we tried to use water droplets as the solid target. Droplet is vacuum however is not an easy thing a they immendiatley turn to ice. This work was done togther with Emma Springate. With Arjan Houtepen we also tried to generate phasematched third hamronic in a gas filled capillary. Unfortunately the relatively long pulse duration seemed to induce too much ionization to allow for effective phasematching.

E. Springate, H.L. Offerhaus, V. Kumarappan and M. Vrakking “X -ray generation from laser-irradiation of a water jet”, Conference on plasma physics Barcelona (2001)

ALIGNMENT: When Iodine molecules are subjected to a strong force he induced dipole moment creates a force that aligns the molecules along the direction of the polarization. If the aligning pulse is sufficiently short and intense then the kick that the aligns the molecules creates rotational wavpackets that persist and show revivals long after the pulse has passed. Most of the work on those experiments was done by Florentina Rosca-Pruna.

F. Rosca-Pruna, E. Springate, H.L. Offerhaus, M. Krishnamurthy, C. Nicole and M.J.J. Vrakking, “Spatial alignment of diatomic molecules in intense laser fields (I): experimental results”, J. Phys B 34 (23), pp. 4919-4938 (2001).[PDF] E. Springate, F. Rosca-Pruna, H.L. Offerhaus, M. Krishnamurthy, C. Nicole and M.J.J. Vrakking, “Spatial alignment of iodine, molecules in intense laser fields (I)”: numerical modelling, J. Phys B 34 (23), pp. 4939-4956 (2001).

SLOW PHOTOELECTRONS: When electrons are very nearly ionized they can be dragged out of the atom in an applied external field. That field however has to compete with the electric field of the ionic core and the combination means that only a specific window opens up for the electrons to escape. Since only a few trajectories can escape the core influence the interference between these pathways can be seen and the electrons emerge in a "diffraction" pattern. Since this pattern is very small a magnifying lens was added to the electron detection systems. The simulated trajectories through the lens and the interference pictures are shown on the right. The major part of these measurements was done by Celine Nicole.

H.L. Offerhaus, C. Nicole, F. Lepine, C. Bordas, F. Rosca-Pruna, M.J.J. Vrakking, “A magnifying lens for velocity map imaging of electrons and ions”, Rev. Sci Instrum. 72(8) pp. 3245-3248 (2001) C. Nicole, H.L. Offerhaus, M.J.J. Vrakking, F. Lepine, C. Bordas, “Photoionization microscopy”, Phys Rev. Lett., 88(13), 133001 (2002). [PDF] L. Dinu L, A.T.J.B. Eppink, F. Rosca-Pruna, H.L. Offerhaus, W.J. van der Zande, M.J.J. Vrakking, “Application of a time-resolved event counting technique in velocity map imaging”, Rev. Sci. Instrum. 73(12), 4206-4213 (2002)

VACUUM FLUCTUATIONS: I tried to find a special situation where a PPLN crystal was phasematched at the dividing point of the pump wavelength, such that the pump photon is split in 1/3 for the idler and 2/3 for the signal AND was phasematched to convert the idler into the signal. In that case both SHG and THG are phasematched (SHG/THG of the idler). In the situation where you pump the crystal but there is no feedback (OPG) the pump photons are converted to signal and idler and the inital phase between them determines whether the energy then flow to the signal or the idler. This original phase difference is determined by the vacuum fluctuations so that the distribution of the energy among idler and signal at the end of the crystal tell you something about the vacuum fluctuations at the start fo the crystal. More recently these experiments have been revived in a noncollinear geometry in HeXLN where the extra degree of freedom in the pattern allows for the double phasematching. This has produced some stunnigly colorful pictures but nothing useful so far.

H.L. Offerhaus, H.K. Nienhuys, G.W. Ross and H.J. Bakker, “Multifunctional PPLN to probe the phase of vacuum fluctuations”, Jaarlijkse conferentie van de Sectie Atoomfysica en Quantumelectronica van de Nederlandse Natuurkundige Vereniging (NNV), November (2000)

RESEARCH FELLOW AT THE OPTOELECTRONICS RESEARCH CENTRE, IN THE GROUP OF DAVE RICHARDSON

General refs  H.L. Offerhaus, “Fibre, for a balanced laser diet”, in Nederlandse Natuurkundige Vereniging (NNV) Najaarsvergadering van de sectie Atoomfysica en Quantumelectronica, Lunteren, The Netherlands, paper M5 (1998) H.L. Offerhaus, “Optical Technology in Telecommunications”, English Language Section School of Modern Languages, University of Southampton , August 3 (1998) H.L. Offerhaus, “Internet and the optical backbone”, English Language Section School of Modern Languages, University of Southampton , September 2 (1999) United Kingdom Patent Application No 9814526.1, “Optical fibre and Optical Fibre Device”, Univ. of Southampton (3 July 1998), now also PCT/GB99/02136 D. Richardson, H. Offerhaus, J. Nilsson and A. Grudinin, “New fibers portend a bright future for high-power lasers”, Laser Focus World, June 1999, pp. 92-94 D.J. Richardson, H.L. Offerhaus, N.G.R. Broderick, “Large mode area fiber lasers and their applications”, ASSL 2000 Davos, Switzerland 13-16 February 2000 (Invited)

LARGE MODE AREA (LMA) FIBRE: Most of my work at the ORC revolves around the development and use of Large Mode Area (LMA) fibres. The inrease in modesize in these fibres lowers the gain efficiency and thereby limits the buildup of ASE. This means an increase in the energy that can be stored in the fibre. The increase in modesize also decreases the effective nonlinearity of the fibre which leads to a higher energy for solitons. The fibres have an index profile that is specifically designed to increase the modesize while maintaining single mode operation. This is done firstly by lowering the Numerical Aperture (NA) of the fibre and secondly by tailoring the doping profile inside the fibre. The low NA ensures that only a low number of modes can propagate in the fibre and the doping profile ensures a preferential excitation of the lowest mode. The low NA increases the sensitivity of the fibre to bend losses. these losses are suppressed by the addition of an extra ring of raised index in the profile. To demonstrate the two main features of these fibres we have built Q-switched (energy storage) and modelocked (high soliton energy) lasers in several different configurations.

Actively Q-switched Large Mode Area (LMA) fibreH.L. Offerhaus, N.G. Broderick, D.J. Richardson, R. Sammut, J. Caplen and L. Dong, “High energy single-transverse-mode Q-switched fiber laser based on a multimode large-mode area erbium-doped fiber” Opt. Lett. vol 23(21), pp. 1683-1685 (1998). [PDF] H.L. Offerhaus, N.G. Broderick, D.J. Richardson, R. Sammut, J. Caplen and L. Dong, “0.5mJ pulses from a single transverse-mode Q-switched erbium fibre laser”, In Conference on Lasers and Electro Optics-Europe, Glasgow UK, paper CTuB3 (1998) Modelocked LMA fibreN.G. Broderick, H.L. Offerhaus, D.J. Richardson, R. Sammut, J. Caplen and L. Dong, “ Passive Mode-locked operation of Large Mode Area fibre lasers”, In Conference on Lasers and Electro Optics-Europe, Glasgow UK, paper CTuF2 (1998) N.G.R. Broderick, H.L. Offerhaus, D.J. Richardson, RA Sammut, J. Caplen, L. Dong, “Large mode area fibres for high power applications”, Optical Fibre Technology vol. 5, pp. 185-196 (1999) N.G. Broderick, H.L. Offerhaus, D.J. Richardson, J. Caplen, L. Dong and R. Sammut, “Large Mode Area Fibres for High Power Lasers” In Australian Conference on Optical Fibre Technology, Melbourne Australia, paper A001 (1998) N.G. Broderick, H.L. Offerhaus, D.J. Richardson, R. Sammut, “Power Scaling in passively mode locked large mode area fibre lasers”, IEEE Photonics Technology Letters Vol.10(12), pp. 1718-1720 (1998)

HeXLN: is pronounced "hexlin" and stands for Hexagonally poled PPLN. The picture on the left shows the hexagonal honeycomb structure that we have patterned onto a LiNbO3 crystal and subsequently poled into it. This 2D pattern allows quasi phasematching in different directions. It also allows for simultaneous phase matching of different processes in different directions. The picture in the middle shows the angle tuning characteristics for second harmonic generation in this new crystal. The pictures on the right show the output for different input angles. The multicolour output is due to the concurrent generation of second, third and fourth harmonic. This work is performed in collaboration with Graeme Ross and Dave Hanna.     

N.G.R. Broderick, G.W. Ross, H.L. Offerhaus, D.J. Richardson and D.C. Hanna, ”Hexagonally Poled Lithium Niobate: A two dimensional Nonlinear photonic crystal” Physical Review Letters Vol.84(19) pp.4345-4348 (2000). [PDF] N.G.R.Broderick, G.W.Ross, D.J.Richardson, D.C.Hanna, "HeXLN: A 2-dimensional nonlinear photonic crystal" Nonlinear Guided Waves & Their Applications `99 Dijon 1-3 September 1999 (Postdeadline), PD1 G.W. Ross, N.G.R. Broderick, H.L. Offerhaus, P.G.R. Smith, D.J. Richardson, D.C. Hanna “Hexagonally-poled lithium niobate (HEXLN) “ CLEO 2000 San Francisco, 7-12 May 2000, CWH3 (Invited) 

A SEmiconductor SAturable Mirror (SESAM) consists of a numbers of quantum well layers that is generally combined with a dielectric coating. The characteristics of the quantum wells (such as central wavelength and recovery time) can be tailored during the growth process. An increase in the number of defects lowers the recovery time although it also increases the non-saturable losses. The dielectric coating and the number of quantum wells determine the saturation fluence and the reflectivity modulation. In general modelocking and passive Q-switching with these devices is self starting and environmentally stable which makes them an ideal partner for a fibre laser system. The work on the SESAM passively Q-switched LMA fibre was done in together with Rüdiger Paschotta of the ETH in Zurich. The figures on the right depict the laser cavity and the timestructure of the output pulses.

R. Paschotta, R. Häring, E. Gini, H. Melchior, U. Keller, H.L. Offerhaus and D.J. Richardson, “Passively Q-switched 0.1mJ fibre laser system at 1.53mm”, Opt. Lett. Vol.24(6), pp. 388-390 (1999) H.L. Offerhaus, D.J. Richardson, R. Paschotta, R. Häring, E. Gini, H. Melchior and U. Keller, “0.1mJ pulses from a passively Q-switched fiber source”, CLEO ‘99 CWE8

PPLN: Periodically Poled Lithium Niobate (PPLN) uses periodic domain inversion to allow noncritical phase matching over large wavelength ranges. Moreover, the technique allows the use of the largest component of the second-order dielectric tensor reducing the power requirements on sources for efficient frequency conversion. At the same time the output pulse energy/power achievable from fibre systems has increased rapidly- to the point that they can be used to efficiently pump parametric devices based on PPLN. We have demonstrated >80% SHG conversion efficiency and an optical parametric generator/amplifier which produced near transformed limited 3ps tunable from 1.1 to 5 microns with gains in excess of 70dB. We have also built parametric Oscillators (OPO's) pumped directly with pulsed fibre sources. Progress continues towards CW pumped systems. This work is performed in collaboration with Paul Britton, Graeme Ross, Peter Smith, Johan Nilsson, Jose Alvarez-Chavez and Dave Hanna. 

P.E. Britton, H.L. Offerhaus, D.J. Richardson, P.G.R. Smith, G.W. Ross and D.C. Hanna, "A parametric oscillator directly pumped by a 1.55mum erbium fibre laser", Opt. Lett. Vol. 24(14) pp. 975-977 (1999) D. Taverner, P. Britton, P.G.R. Smith, D.J. Richardson, G.W. Ross and D.C. Hanna: "High Efficient second harmonic and sum frequency generation of nanosecond pulses in a cascaded erbium doped fibre:PPLN source",Opt. Lett., Vol.23(3) pp162-4 (1998). P.E. Britton, D. Taverner, K. Puech, D.J. Richardson, P.G.R. smith, G.W. Ross and D.C. Hanna: "Optical Parametric Oscillation in periodically-poled lithium niobate driven by a diode pumped, QW-switched fiber laser", Opt. Lett. Vol.23(8) pp 582-4, (1998). P.E.Britton, N.G.R.Broderick, D.J.Richardson, P.G.R.Smith, G.W.Ross, D.C.Hanna:"Wavelength-tunable high-power picosecond pulses from a fibre pumped diode-seeded high-gain parametric amplifier", Optics Letters, 23, 20, pp 1588-1590, (1998).

GALLIUM PASSIVE Q-SWITCHING: The nonlinearity of Gallium is reasonably fast (several ns at least, and maybe much faster) which allows for passive Q-switching and optical switching. The optical nonlinearity is extremely broadband (at least 630-1550nm). The initial discovery of nonlinearity in liquefying gallium was made by Nick Zheludev of the University's Physics Department and with whom we have developed a strong collaboration. We are interested in exploring using this material in fibre laser systems and have already demonstrated passive Q-switching of both Erbium-doped and Ytterbium-doped LMA-fibre lasers using a single liquefying gallium mirror.

P. Petropoulos, H.L. Offerhaus, D.J. Richardson, S. Dhanjal and N.I. Zhedulev, "Passive Q-switching of fiber lasers using a broadband liquefying gallium mirror", Appl. Phys. Lett. Vol.74(24) pp.3619-21 (1999)

CHIRPED PULSE AMPLIFICATION (CPA): Chirped pulse amplification is an established technique for bulk high power amplifier systems and is used to avoid nonlinear effects that would ordinairily occur within the amplifier. In CPA the pulse to be amplified is stretched in time (by factors of ten-thousand or more) prior to amplification. The low intensity stretched pulse can then amplified to high energies without reaching the threshold for nonlinear distortion and then recompressed to obtain high peak intensities. We are exploring the use of CPA in fibre form to increase the range of powers achievable from fibre systems. A convenient way to stretch a pulse is to reflect it from a linearly chirped fibre grating. Different wavelengths are reflected from different positions within the grating and therefore return at different times. This chirps the pulse and stretches it in time. By using reflection from a second grating (or the reverse side of the same grating) the pulse can be recompressed. We have already demonstrated peak powers in excess of 0.5 MW with an erbium amplifier system based on LMA components using this approach and further increases are expected. Using a bulk final stage compressor >10 MW powers have been achieved. 

N.G. Broderick, D.J. Richardson, D. Taverner, J.E. caplen, L. Dong and M.Ibsen:'High power chirped pulse amplification system based on large mode area fiber gratings', Opt. Letts., 8, pp566-569, (1999).

FROG: Precise information on the shape and phase of short pulses is a valuable tool in the development of soliton lasers and the construction of all-fibre Chirped Pulse Amplification (CPA) systems. One technique to obtain this information is Frequency Resolved Optical Gating (FROG) where spectrograms of the autocorrelation of the pulse are taken and the pulse is reconstructed with a generalized projections method. We have recently assembled such a system based on Second Harmonic Generation (SHG) autocorrelation. This work was performed in collaboration with Benn Thomsen and Professor John Harvey from the University of Auckland. On the right you can see an example of a measured (top) and retrieved (bottom) spectrogram measured using our FROG system, the pulses were generated using a 10 GHz fibre ring laser developed for our high speed communications work.

B.C. Thomsen, P. Petropoulos, H.L. Offerhaus, D.J. Richardson, J.D. Harvey, “SHG FROG characterization of a 10 GHz harmonically mode-locked erbium fiber ring laser”, CLEO ‘99 CTuJ5

 

CLADDING PUMPING: In cladding pumping the pump travels through the fibre in the cladding rather than the core. If the cladding has a high NA and a large area one can launch and propagate a lot moignal propagates in the core. Cladding pumping allows the use of relatively low-brightness, high-power broadstripe diodes and diode bars and is the key to high average power (multi-tens of Watts) fiber laser operation.  The LMA fibre core design previously proven in erbium doped fibre has now been applied to the case of ytterbium doping. Two fibres have been fabricated one for cladding pumping and one for core pumping. Different sized versions of cladding pumped fibre pulled from the same preform have already produced >1 mJ pulses in a single mode beam and >2.5mJ pulses in a multimode beam. Average powers in excess of 5W have been achieved. This work was performed together with Jose Alvarez-Chavez, Johan Nilsson, Andy Clarkson and Paul Turner.

H.L. Offerhaus, J. A. Alvarez-Chavez, J. Nilsson, P. W. Turner, W. A. Clarkson, and D. J. Richardson “Multi-mJ multi-Watt Q-switched fiber laser”, Postdeadline CLEO'99 Baltimore, 23-28 May 1999, CPD10 J.A. Alvarez-Chavez, H.L. Offerhaus, J. Nilsson, P.W. Turner, W.A. Clarkson, D.J. Richardson, ”High-energy high-power ytterbium-doped Q-switched fiber laser”, Opt. Lett. 25(1) pp37-39 (2000) C.C. Renaud, H.L. Offerhaus, J.A. Alvarez-Chavez, J. Nilsson, P.W. Turner, W.A. Clarkson, A.B. Grudinin, “Designs for efficient high-energy high brightness Q-switched cladding-pumped ytterbium-doped fibre lasers “ CLEO 2000 San Francisco, 7-12 May 2000, CMP1 D.J. Richardson, H.L. Offerhaus, N.G.R. Broderick, “Large mode area fiber lasers and their applications” ASSL 2000 Davos, Switzerland 13-16 February 2000 (Invited) C.C. Renaud, H.L. Offerhaus, J.A. Alvarez-Chavez, J. Nilsson, W.A. Clarkson, P.W. Turner, D.J. Richardson, A.B. Grudinin, ”Characteristics of Q-switched cladding-pumped ytterbium-doped fiber lasers with different high-energy fiber designs”, IEEE Journal of Quantum Electronics 37(2) pp.199-206 (2001)

During my PhD I worked at the Nederlands Centrum for Laser Research (nclr) at the Universiteit Twente in the Netherlands, on the devlopement a of high brightness, high power diode pumped Nd:YAG laser. The laser consisted of an oscillator and a power amplifier with a phase conjugating mirror after two passes through the amplifier. During that work we constructed a self-referencing interferometer to do single shot beam quality measurements and developed an algorithm to translate these measurements into the commenly used M2 parameter. To show the advantages and a possible applications of this system we also developed a micromachining workstation with a resolution of a few micron. That work was done together with Richard Kleijhorst.

H.P. Godfried, H.L. Offerhaus and E.A.J.M. Bente “Single transverse mode diode side pumped Nd:YAG Q-switched oscillator” OSA Proceedings on Advanced Solid State Lasers,” B.H.T. Chai and S.A. Payne, eds., Vol. 24, pp. 420-422, OSA, Washington (1995) H.L. Offerhaus “All solid-state diode pumped Nd:YAG MOPA with stimulated Brillouin phase conjugate mirror”, Dutch Physical Society (NNV), Najaarsvergadering, sectie Atoomfysica en Quantum electronica , paper M10 (1995) H.L. Offerhaus and H.P. Godfried “Diode pumped 1kHz high power Nd:YAG MOPA with stimulated Brillouin phase conjugate mirror” Opt. Comm.,128, pp. 61-65 (1996) H.L. Offerhaus and H.P. Godfried “All solid-state diode pumped Nd:YAG MOPA with stimulated Brillouin phase conjugate mirror” ,CLEO-Europe, IEEE cat. no. 96TH8161, paper CMA5 (1996) H.P. Godfried, H.L. Offerhaus and W.J. Witteman “Diode pumped 1kHz high power Nd:YAG laser with excellent beam quality” in XI International Symposium on Gas Flow and Chemical Lasers and High Power Laser Conference, H.J. Baker ed. Proc. SPIE 3092, pp. 29-32, SPIE, Bellingham, Washington (1997) H.L. Offerhaus, C.B. Edwards, W.J. Witteman, “Single shot beam quality (M2) measurement using a spatial Fourier transform of the near field”, Opt. Comm. vol. 151, pp. 65-68 (1998) R.A. Kleijhorst, H.L. Offerhaus and P.Bant, “Micro-machining workstation for a diode pumped Nd:YAG high brightness laser system”, Rev. Sci. Instrum. vol. 69(5), pp. 2118-2119 (1998) H.L. Offerhaus and R.A. Kleijhorst, Dutch patent “meekijk truc”, #10.07068 (1997)

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Courses in the current academic year are added at the moment they are finalised in the Osiris system. Therefore it is possible that the list is not yet complete for the whole academic year.

 

• 191211208 - Internship EE
• 193599010 - Internship
• 193599039 - Master Thesis: Physics Aspects
• 193599089 - Master Thesis: General Aspects
• 201300196 - Clinical Specialization Internship
• 201700185 - Internship
• 201800344 - Master's Assignment: Physics Aspects
• 201800345 - Master's Assignment: General Aspects
• 201900251 - MSc Assignment: General Aspects AM-AP
• 201900252 - MSc Assignment: Scientific Aspects AM-AP
• 201900318 - MSc Assignment AP-BME: General Aspects
• 201900319 - MSc Assignment AP-BME: Scientific Asp.
• 202000682 - Electromagnetics
• 202000716 - Bachelor Assignment
• 202001162 - Bachelor Thesis EE
• 202001433 - Bachelor’s Assignment AM-AP
• 202001434 - Internship EMSYS
• 202200128 - M5 Digestive System
• 202200258 - Double Master Thesis: NT-AP

• 191211208 - Internship EE
• 191211219 - Master Thesis Project
• 193400131 - Nano-Optics
• 193520040 - Exp. Laser Physics and Nonlinear Optics
• 193540900 - CS OS
• 193599010 - Internship
• 193599039 - Master Thesis: Physics Aspects
• 193599089 - Master Thesis: General Aspects
• 201300196 - Clinical Specialization Internship
• 201600017 - Final Project Preparation
• 201600187 - Individual Project
• 201700185 - Internship
• 201800344 - Master's Assignment: Physics Aspects
• 201800345 - Master's Assignment: General Aspects
• 201900200 - Final Project EMSYS
• 201900223 - Capita Selecta Electrical Engineering
• 201900251 - MSc Assignment: General Aspects AM-AP
• 201900252 - MSc Assignment: Scientific Aspects AM-AP
• 201900281 - Ethical and Cultural Awareness
• 201900318 - MSc Assignment AP-BME: General Aspects
• 201900319 - MSc Assignment AP-BME: Scientific Asp.
• 202000682 - Electromagnetics
• 202000716 - Bachelor Assignment
• 202001335 - Electromagnetics
• 202001433 - Bachelor’s Assignment AM-AP
• 202001434 - Internship EMSYS
• 202200128 - M5 Digestive System
• 202200258 - Double Master Thesis: NT-AP
• 202200342 - Combined Final Project EE/I-Tech
• 202200401 - Combined Final Project I-Tech/BME

Organisations

• Faculty of Science and Technology (TNW), Optical Sciences (OS)