M. Odstrcil, P. Baksh, C. Gawith, R. Vrcelj, J. G. Frey, and W. S. Brocklesby
Abstract
Ptychographic Coherent diffractive imaging (PCDI) is a significant advance in imaging allowing the measurement of the full electric field at a sample without use of any imaging optics. So far it has been confined solely to imaging of linear optical responses. In this paper we show that because of the coherence-preserving nature of nonlinear optical interactions, PCDI can be generalised to nonlinear optical imaging. We demonstrate second harmonic generation PCDI, directly revealing phase information about the nonlinear coefficients, and showing the general applicability of PCDI to nonlinear interactions.
Second Harmonic Generation Using a Monolithic, Linearly Polarized Thulium Doped Fiber Laser
M. Ganija, , A. Hemming, et al.
Abstract
We investigate the potential for power scaling of 975 nm cw radiation from frequency doubling a monolithic, polarized thulium fiber laser in a periodically poled non-linear material.
Dual-color deep-tissue three-photon microscopy with a multiband infrared laser
K. Guesmi, L. Abdeladim, S. Tozer, P. Mahou, T. Kumamoto, K. Jurkus, P. Rigaud, K. Loulier, N. Dray, P. Georges, M. Hanna, J. Livet, W. Supatto, E. Beaurepaire & F. Druon
Abstract
Multiphoton microscopy combined with genetically encoded fluorescent indicators is a central tool in biology. Three-photon (3P) microscopy with excitation in the short-wavelength infrared (SWIR) water transparency bands at 1.3 and 1.7 µm opens up new opportunities for deep-tissue imaging. However, novel strategies are needed to enable in-depth multicolor fluorescence imaging and fully develop such an imaging approach. Here, we report on a novel multiband SWIR source that simultaneously emits ultrashort pulses at 1.3 and 1.7 µm that has characteristics optimized for 3P microscopy: sub-70 fs duration, 1.25 MHz repetition rate, and µJ-range pulse energy. In turn, we achieve simultaneous 3P excitation of green fluorescent protein (GFP) and red fluorescent proteins (mRFP, mCherry, tdTomato) along with third-harmonic generation. We demonstrate in-depth dual-color 3P imaging in a fixed mouse brain, chick embryo spinal cord, and live adult zebrafish brain, with an improved signal-to-background ratio compared to multicolor two-photon imaging. This development opens the way towards multiparametric imaging deep within scattering tissues.
Zn-indiffused diced ridge waveguides in MgO:PPLN generating 1 watt 780 nm SHG at 70% efficiency
SAM A. BERRY, LEWIS G. CARPENTER, ALAN C. GRAY, PETER G. R. SMITH, AND CORIN B. E. GAWITH
Abstract
We present a metallic zinc indiffused diced ridge waveguide in magnesium doped periodically poled lithium niobate (MgO:PPLN) capable of generating over 1 W of 780 nm with 70% efficiency. Our 40 mm long waveguide has near circular fundamental mode output with diameter 10.4 μm and insertion loss of -1.17 dB. Using a commercial 2 W EDFA-based system, the SHG output power did not exhibit roll-off at maximum available pump power.
Investigation of PPLN Waveguide Uniformity via Second Harmonic Generation Spectra
Alan C. Gray ; Sam A. Berry ; Lewis G. Carpenter ; James C. Gates ; Peter G. R. Smith ; Corin B. E. Gawith
Abstract
Experimental data collection methods and a corresponding numerical model are presented to investigate the quality of waveguide fabrication in nonlinear optics. The method utilises white light interferometry and standard image recognition techniques to calculate a waveguide propagation constant function. This enables comparison of a numerical second harmonic spectrum in quasi-phasematched materials, such as periodically poled lithium niobate, with the waveguide’s experimental phasematching spectrum. Using the presented method, a 3rd order polynomial fit to waveguide ridge width is demonstrated to be in good agreement with experimental phasematching spectra. The presented technique provides a nondestructive route to discriminate between issues in fabrication steps in nonlinear waveguide design.
Two-photon quantum interference and entanglement at 2.1 um
Shashi Prabhakar, Taylor Shields, Adetunmise C. Dada, Mehdi Ebrahim, Gregor G. Taylor, Dmitry Morozov, Kleanthis Erotokritou, Shigehito Miki, Masahiro Yabuno, Hirotaka Terai, Corin Gawith, Michael Kues, Lucia Caspani, Robert H. Hadfield, Matteo Clerici
Abstract
Quantum-enhanced optical systems operating within the 2- to 2.5-um spectral region have the potential to revolutionize emerging applications in communications, sensing, and metrology. However, to date, sources of entangled photons have been realized mainly in the near-infrared 700- to 1550-nm spectral window. Here, using custom-designed lithium niobate crystals for spontaneous parametric down-conversion and tailored superconducting nanowire single-photon detectors, we demonstrate two-photon interference and polarization-entangled photon pairs at 2090 nm. These results open the 2- to 2.5-um mid-infrared window for the development of optical quantum technologies such as quantum key distribution in next-generation mid-infrared fiber communication systems and future Earth-to-satellite communications.
Zinc-indiffused MgO:PPLN waveguides for blue/UV generation via VECSEL pumping
Alan C. Gray, Jonathan R. C. Woods, Lewis G. Carpenter, Hermann Kahle, Sam A. Berry, Anne C. Tropper, Mircea Guina, Vasilis Apostolopoulos, Peter G. R. Smith, and Corin B. E. Gawith
Abstract
We present the design and characterization of a zinc-indiffused periodically poled lithium-niobate ridge waveguide for second-harmonic generation of _390 nm light from 780 nm. We use a newly developed, broadband near infrared vertical external-cavity surface-emitting laser (VECSEL) to investigate the potential for lower-footprint nonlinear optical pump sources as an alternative to larger commercial laser systems. We demonstrate a VECSEL with an output power of 500 mW, containing an intracavity birefringent filter for spectral narrowing and wavelength selection. In this first demonstration of using a VECSEL to pump a nonlinear waveguide, we present the ability to generate 1mWof_390 nmlight with further potential for increased efficiency and size reduction.
CW demonstration of SHG spectral narrowing in a PPLN waveguide generating 2.5 W at 780 nm
Lewis G. Carpenter, Sam A. Berry, Alan C. Gray, James C. Gates, Peter G. R. Smith, and Corin B. E. Gawith
Abstract
Periodically poled lithium niobate (PPLN) waveguides are a proven and popular means for efficient wavelength conversion. However, conventional PPLN waveguides typically have small mode field diameters (MFD) (≲6 µm) or significant insertion and/or propagation losses, limiting their ability to operate at multi-watt power levels. In this work we utilise zinc indiffused PPLN ridge waveguides that have a larger MFD, favourable pump/SHG modal overlap, and low insertion losses. Here for the first time, we have demonstrated continuous wave (CW) spectral narrowing from a PPLN waveguide, both with high efficiency and multi-watt second harmonic generation (SHG). 2.5 W of 780 nm has been produced by SHG of an amplified 1560 nm telecom laser with a device efficiency of 58% in a 4.0-cm long ridge waveguide. We have modelled conversion efficiency and applied experimentally measured waveguide parameters to show excellent agreement to the SHG spectra. Spectral narrowing of the full width half maximum (FWHM) of 35.7% has been measured as the nonlinear drive is increased. This work demonstrates that single-pass, multi-watt, CW SHG at 780 nm is feasible from our PPLN waveguide in the large conversion regime.
Gravity sensing: cold atom trap onboard a 6U CubeSat
Diviya Devani, Stephen Maddox, Ryan Renshaw, Nigel Cox, Helen Sweeney, Trevor Cross, Michael Holynski, Raffaele Nolli, Jonathan Winch, Kai Bongs, Karen Holland, David Colebrook, Neil Adams, Kevin Quillien, James Buckle, Anupe Karde, Mark Farries, Tom Legg, Richard Webb, Corin Gawith, Sam A. Berry & Lewis Carpenter
Abstract
“Cold atoms” can be used as ultra-sensitive sensors for measuring accelerations and are capable of mapping changes in the strength of gravity across the surface of the Earth. They could offer significant benefits to existing space based gravity sensing capabilities. Gravity sensors in space are already used for many Earth observation applications including monitoring polar ice mass, ocean currents and sea level. Cold atom sensors could enable higher resolution measurements which would allow monitoring of smaller water sources and discovery of new underground natural resources which are currently undetectable. The adoption of cold atom technology is constrained by low technology readiness level (TRL). Teledyne e2v and its partners are addressing this maturity gap through project Cold Atom Space PAyload (CASPA) which is an Innovate UK and Engineering and Physical Sciences Research Council (EPSRC) funded project, involving the University of Birmingham as science lead, XCAM, Clyde Space, Covesion, Gooch & Housego, and the University of Southampton. Through the CASPA project the consortium have built and vibration tested a 6U (approximate dimensions: 100 × 200 × 300 mm) cube Satellite (CubeSat) that is capable of laser cooling atoms down to 100’s of micro kelvin, as a pre-cursor to gravity sensors for future Earth observation missions.
Continuous-wave sodium D2 resonance radiation generated in single-pass sum-frequency generation with periodically poled lithium niobate
J. Yue, C. She, B. Williams, J. Vance, P. Acott, and T. Kawahara
Abstract
With two cw single-mode Nd:YAG lasers at 1064 and 1319 nm and a periodically poled lithium niobate crystal, 11 mW of 2 kHz/100 ms bandwidth single-mode tunable 589 nm cw radiation has been detected using single-pass sum-frequency generation. The demonstrated conversion efficiency is ~3.2%[W−1cm−1]. This compact solid-state light source has been used in a solid-state-dye laser hybrid sodium fluorescence lidar transmitter to measure temperatures and winds in the upper atmosphere (80-105 km); it is being implemented into the transmitter of a mobile all-solid-state sodium temperature and wind lidar under construction.
