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Monitoring of heart rate has the potential to provide excellent data for the remote monitoring of animals, and heart rate has been associated with stress, pyrexia, pain and illness in animals. However monitoring of heart rate in domesticated animals is difficult as it entails the restraint of the animal (which may in turn affect heart rate), and the application of complex monitoring equipment that is either invasive or not practical to implement under commercial farm conditions. Therefore accurate non-invasive automated remote monitoring of heart rate has not been possible in domesticated animals. Biomagnetism associated with muscle and nerve action provides a promising emerging field in medical sensing, but it is currently confined to magnetically-shielded clinical environments. In this study, we use biomagnetic sensing on commercial dairy cattle under farm conditions as a model system to show proof-of-principle for non-contact magnetocardiography (MCG) outside a controlled laboratory environment. By arranging magnetometers in a differential set-up and using purpose-built low-noise electronics, we are able to suppress common mode noise and successfully record the heart rate, the heart beat intervals and the heart beat amplitude. Comparing the MCG signal with simultaneous data recorded using a conventional electrocardiogram (ECG) allowed alignment of the two signals, and was able to match features of the ECG including the P-wave, the QRS complex and the T-wave. This study has shown the potential for MCG to be developed as a non-contact method for the assessment of heart rate and other cardiac attributes in adult dairy cattle. Whilst this study using an animal model showed the capabilities of un-shielded MCG, these techniques also suggest potentially exciting opportunities in human cardiac medicine outside hospital environments.

We present an unshielded, double-resonance magnetometer in which we have implemented a feed-forward measurement scheme in order to suppress periodic magnetic noise arising from, and correlated with, the mains electricity alternating current line. The technique described here uses a single sensor to track ambient periodic noise and feed forward to suppress it in a subsequent measurement. This feed forward technique has shown significant noise suppression of electrical mains-noise features of up to 22 dB under the fundamental peak at 50 Hz, 3 dB at the first harmonic (100 Hz), and 21 dB at the second harmonic (150 Hz). This technique is software based, requires no additional hardware, and is easy to implement in an existing magnetometer.

Laser-cooled atoms and coherent population trapping (CPT) are promising tools for realizing a compact microwave frequency reference with excellent stability. To realize a high performance device, it is necessary to understand and minimize all sources of technical noise. Here, we investigate the role of laser frequency noise in cold-atom CPT with an apparatus based on the grating magneto-optical trap (GMOT). We compare the performance of our setup with an external cavity diode laser (ECDL) and a distributed feedback diode laser (DFB). With the DFB, laser frequency noise is one of the dominant noise sources in our system. With the ECDL, it is significantly reduced. We also report frequency stability measurements of our apparatus with a short-term Allan deviation $\sigma_{y}(\tau) \approx 3 \times 10^{-11} / \sqrt{\tau}$ up to $\tau =10\mathrm{s}$.

The combination of coherent population trapping (CPT) and laser cooled atoms is a promising platform for realizing the next generation of compact atomic frequency references. Towards this goal, we have developed an apparatus based on the grating magneto-optical trap (GMOT) and the high-contrast lin ⊥ lin CPT scheme in order to explore the performance that can be achieved. One important trade-off for cold-atom systems arises from the need to simultaneously maximize the number of cold atoms available for interrogation and the repetition rate of the system. This compromise can be mitigated by recapturing cold atoms from cycle to cycle. Here, we report a quantitative characterization of the cold atom number in the recapture regime for our system, which will enable us to optimize this trade-off. We also report recent measurements of the short-term frequency stability with a short-term Allan deviation of 3 × 10-11/τ up to an averaging time of τ = 10 s.

We describe an optically pumped Cs magnetometer containing a 1.5 mm thick microfabricated vapor cell with nitrogen buffer gas operating in a free-induction-decay (FID) configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarize the atomic sample however, synchronous modulation of the light field actively drives the precession and maximizes the induced spin coherence. Both amplitude and frequency modulation have been implemented with noise floors of 3 pT / √ Hz and 16 pT / √ Hz respectively within the Nyquist limited bandwidth of 500 Hz .

We demonstrate a system for intensity stabilisation of optical pulse sequences used in laser-driven quantum control of trapped ions. Intensity instability is minimised by active stabilisation of the power (over a dynamic range of $$> 10^{4}$$ ) and position of the focused beam at the ion. The fractional Allan deviations in power were found to be $$

Double-resonance optically pumped magnetometers are an attractive instrument for unshielded magnetic field measurements due to their wide dynamic range and high sensitivity. Use of linearly polarised pump light creates alignment in the atomic sample, which evolves in the local static magnetic field, and is driven by a resonant applied field perturbation, modulating the polarisation of transmitted light. We show for the first time that the amplitude and phase of observed first- and second-harmonic components in the transmitted polarisation signal contain sufficient information to measure static magnetic field magnitude and orientation. We describe a laboratory system for experimental measurements of these effects and verify a theoretical derivation of the observed signal. We demonstrate vector field tracking under varying static field orientations and show that the static field magnitude and orientation may be observed simultaneously, with experimentally realised resolution of 1.7 pT and 0.63 mrad in the most sensitive field orientation., Comment: 8 pages, 7 figures

Optically pumped atomic magnetometers (OPMs) offer highly sensitive magnetic measurements using compact hardware, offering new possibilities for practical precision sensors. Double-resonance OPM operation is well suited to unshielded magnetometry, due to high sensor dynamic range. However, sensor response is highly anisotropic with variation in the orientation of the magnetic field. We present data quantifying these effects and discuss implications for the design of practical sensors., IEEE Sensors 2017 paper preprint

Double resonance optically pumped magnetometry can be used to measure static magnetic fields with high sensitivity by detecting a resonant atomic spin response to a small oscillating field perturbation. Determination of the resonant frequency yields a scalar measurement of static field ($B_0$) magnitude. We present calculations and experimental data showing that the on-resonance polarimeter signal of light transmitted through an atomic vapour in arbitrarily oriented $B_0$ may be modelled by considering the evolution of alignment terms in atomic polarisation. We observe that the amplitude and phase of the magnetometer signal are highly dependent upon $B_0$ orientation, and present precise measurements of the distribution of these parameters over the full 4{\pi} solid angle.

An integrated system of hardware and software allowing precise definition of arbitrarily oriented magnetic fields up to |B| = 1 {\mu}T within a five-layer mumetal shield is described. The system is calibrated with reference to magnetic resonance observed between Zeeman states of the 6S$_{1/2}$ F = 4 $^{133}$Cs ground state. Magnetic field definition over the full 4{\pi} solid angle is demonstrated, with one-sigma tolerances in magnitude, orientation and gradient of {\delta}|B| = 0.94 nT, {\delta}{\theta} = 5.9 mrad and {\delta}$\nabla$ B = 13.0 pT/mm, respectively. This field control is used to empirically map Mx magnetometer signal amplitude as a function of the static field (B0) orientation., Comment: 14 pages, 10 figures

We have laser cooled 3$\times10^6$ $^{87}$Rb atoms to 3$\mu$K in a micro-fabricated grating magneto-optical trap (GMOT), enabling future mass-deployment in highly accurate compact quantum sensors. We magnetically trap the atoms, and use Larmor spin precession for magnetic sensing in the vicinity of the atomic sample. Finally, we demonstrate an array of magneto-optical traps with a single laser beam, which will be utilised for future cold atom gradiometry., Comment: 8 pages, 6 figures

Laser cooled atomic samples have resulted in profound advances in precision metrology [1], however the technology is typically complex and bulky. In recent publications we described a micro-fabricated optical element, that greatly facilitates miniaturisation of ultra-cold atom technology [2], [3], [4], [5]. Portable devices should be feasible with accuracy vastly exceeding that of equivalent room-temperature technology, with a minimal footprint. These laser cooled samples are ideal for atomic clocks. Here we will discuss the implementation of our micro-fabricated diffractive optics towards building a robust, compact cold atom clock.

We have simulated the optical properties of micro-fabricated Fresnel zone plates (FZPs) as an alternative to spatial light modulators (SLMs) for producing non-trivial light potentials to trap atoms within a lensless Fresnel arrangement. We show that binary (1-bit) FZPs with wavelength (1 \mu m) spatial resolution consistently outperform kinoforms of spatial and phase resolution comparable to commercial SLMs in root mean square error comparisons, with FZP kinoforms demonstrating increasing improvement for complex target intensity distributions. Moreover, as sub-wavelength resolution microfabrication is possible, FZPs provide an exciting possibility for the creation of static cold-atom trapping potentials useful to atomtronics, interferometry, and the study of fundamental physics., Comment: 14 pages, to appear in New Journal of Physics Atomtronics special issue

We demonstrate an optically pumped magnetometer (OPM) operated in a free-induction-decay (FID) configuration that is capable of tracking oscillating magnetic signals in the presence of a 50 uT static field. Excellent waveform reconstruction is demonstrated for low frequency modulations with respect to the Nyquist limited bandwidth. A 100 pT oscillation was successfully reconstructed using signal averaging, and an optimum sensitivity of 3.9 pT/sqrt{Hz} was measured from the spectrum of the residuals relative to the sinusoidal fit. The impact of the pump-probe repetition rate and spin depolarization on the frequency response of the sensor is investigated in detail using miniaturized vapor cell technology, with the (-3 dB) bandwidths residing beyond the Nyquist limit in each case. We also discuss technical limitations associated with the magnetometer when exposed to oscillating fields of sufficiently high amplitude or frequency. This is discussed in the context of potential distortions arising in the reproduced signals, induced by frequency-modulation (FM) and aliasing artefacts.

We report on a novel material developed as the gain medium for a vertical-external-cavity surface-emitting laser (VECSEL) operating around 850 nm. The new material departs from the conventional approach of using GaAs as the quantum-well (QW) material and expands the previously reported concept of using InAlGaAs QWs. The inclusion of indium pins dislocation propagation into the active region of the VECSEL. Crucial for the success of this design is also the development of indium and phosphorous containing quinternary strain-compensating layers. These surround the QWs and provide a more substantial resistance to defect propagation. Results are presented for stable high-power single spatial mode operation of a laser based on this material together with measurements of the unsaturated gain of the device and the characteristic temperature for the threshold power

The experimental parameters required in order to maximize the stability of a single-ion based optical clock are analysed. This stability is a trade-off between on the one hand the steepness of the discriminant signal derived from the laser excitation of the ion and on the other the binomial noise associated with the excitation of a single particle. Optimum conditions are found for both Rabi and Ramsey excitation of the clock transition.

We report on a novel and compact reliable laser source capable of short-wavelength two-photon laser scanning fluorescence microscopy based on soliton self-frequency shift effects in photonic crystal fibre. We demonstrate the function of the system by performing two-photon microscopy of smooth muscle cells and cardiac myocytes from the rat pulmonary vein and Chinese hamster ovary cells loaded with the fluorescent calcium indicator fura-2/AM.

A short section of photonic crystal fibre has been used for ultra-short pulse compression. The unique optical properties of this novel medium in terms of high non-linearity and relatively small group velocity dispersion are shown to provide an ideal platform for the standard fibre pulse compression technique used directly on the nano-Joule output pulses from a commercial laser system. We report an order of magnitude reduction of the pulse width to 25 fs FWHM but predict a substantially improved performance with a dedicated fibre design. Good agreement is obtained with a simple model for the spectral broadening in the fibre.

A 3D lattice based on a high-power CO2 laser is considered in the context of laser cooling and trapping of atomic calcium. We expect to be able to realize a system with }10\,000$>>10 000 lattice sites each with more than 100 atoms, and the facility to laser cool all the atoms into the vibrational ground state using the intercombination line. The configuration allows the production of an array of small Bose?Einstein condensates, enabling an investigation of the build-up of phase coherence as a function of atom number.

We investigate the properties of two separate dipole traps, realised using a cw mode-locked Ti:sapphire laser and a cw mode-locked Nd:YVO4 laser, red-detuned by 25 nm and 284 nm, respectively. Approximately 103 laser-cooled 85Rb atoms were confined in the traps at ≈50 μK, with no observable heating after initial loading. The lifetimes of the traps were consistent with limitations imposed by wavelength-dependent photoassociation losses and collisions with background vapour. Determination of the ac Stark shift of the 780 nm cooling transition using a weak probe beam showed no observable difference between using narrow-bandwidth or mode-locked trapping light. Techniques for trapping and focusing of atoms based on the dipole force of blue and uv light become much more accessible through efficient doubling, tripling and quadrupling of mode-locked sources. This opens up the possibility of manipulating more technologically interesting species.

A simple optical sideband injection locking technique is demonstrated to frequency offset-lock a 674 nm slave extended cavity diode laser to a single frequency source. By injecting light from a master laser into either sideband of the frequency modulated extended cavity slave laser, it is shown that the carrier of the slave is frequency locked to the master laser with a relative linewidth much less than 10 Hz. The locking bandwidth is investigated to determine the largest capture range. An observation of the 674 nm 2 S 1/2 – 2 D 5/2 transition in a single ion of 88 Sr + was performed using this laser system, yielding ≈1 kHz linewidth Zeeman structure, limited by the master laser linewidth. National Physical Laboratory

A novel variation of the technique of two-photon frequency modulation (FM) spectroscopy has been developed, which allows signals to be obtained from small (∼10 5 atoms) and dilute (∼10 10 cm −3 ) samples – in this case laser-cooled rubidium atoms. This was possible by detecting and demodulating the fluorescence signal rather than the transmission through the sample. Data are presented demonstrating the dependence of the signal on phase and frequency of the imposed modulation. Initially the atoms were held in a magneto-optic trap but, in order to eliminate line broadening due to the presence of the trapping fields, data were taken with the atoms in free fall. A similar signal, slightly shifted and broadened by the trapping fields, was obtained while the trap was on and used for long-term stabilisation of the probe laser.

Using laser cooled samples of 85Rb and 87Rb in a magneto-optical trap, high resolution spectroscopy of the two-photon transitions 5 S 1 2 −5 D 3 2 , 5 S 1 2 −5 D 5 2 and 5 S 1 2 −7 S 1 2 have been investigated using the output from a mode-locked titanium sapphire laser. The hyperfine constants for the 7S terms of both isotopes have been measured with improved accuracy.

A scheme is demonstrated for optical pumping of a vertical-external-cavity surface-emitting laser. The scheme is based on absorption of the pump light within the wells of the multiple-quantum-well gain structure rather than the conventional approach of absorption of a shorter wavelength in the barrier regions. The operation of a laser around 850 nm pumped by an 808 nm source demonstrates the potential of this technique for allowing operation at a significantly shorter range of wavelengths for these devices in general and specific application of high-brightness pump lasers for devices in this spectral region. A further advantage is the smaller quantum defect which results in reduced heating of the gain medium. These advantages are achieved while maintaining a slope efficiency of up to 18%, which is comparable to results obtained with a traditional pumping scheme with a similar gain medium.

We report the power scaling of a diode-pumped GaAs-based 850-nm vertical external-cavity surface-emitting laser, by use of an intracavity silicon carbide (SiC) heatspreader optically contacted to the semiconductor surface. To our knowledge, this is the first demonstration of bonding of SiC to a III-V semiconductor structure using the technique of liquid capillarity. High output power of >0.5 W in a circularly symmetric, TEM/sub 00/ output beam has been achieved with a spectral shift of only 0.6 nm/W of pump power. No thermal rollover was evident up to the highest pump power available, implying significant further output-power scaling potential using this approach.

Laser excitation of the 4s4p 3P2 – 4s3d 1D2 transition in atomic calcium has been observed and the wavelength determined to 1530.5298(6) nm. The metastable 4s4p 3P2 atoms were magnetically trapped in the quadrupole magnetic field of a magneto-optical trap. This state represents the only “loss” channel for the calcium atoms when laser cooled on the 4s2 1S0 – 4s4p 1P1 transition. A rate equation model shows that an order of magnitude more atoms are trapped in this state compared with those taking part in the main cooling cycle. Excitation of the 3P2 atoms back up to the 4s3d 1D2 state provides a means of accessing these atoms. Efficient repumping is achieved if the 1530-nm laser is used in conjunction with a 672-nm laser driving the 4s3d 1D2 – 4s5p 1P1 transition. In the present experiment, we detected about 4.5×104 trapped 3P2 atoms, a relatively low atom density, and measured a lifetime of approximately 1 s, which is limited by background collisions.

We demonstrate the first synchronously in-well pumped vertical-external-cavity surface-emitting laser (VECSEL). Depending on the cavity mismatch, laser pulses with a duration from 1 ps to 7 ps at a repetition rate of 76 MHz were generated directly from the laser at 860 nm. The application of extra-cavity pulse compression further shortened the pulse to a duration of 210 fs providing a peak power of 226 W.

We report on a precision measurement of the 2 {sup 3}{ital S}--3 {sup 3}{ital P} transition in {sup 4}He. Doppler-free spectra of the transition were observed by exciting metastable helium atoms, produced by a chopped rf discharge, using 389-nm radiation generated by a frequency-doubled Ti-doped sapphire laser. A frequency measurement of the Doppler-free lines was made by interferrometric comparison of the Ti-doped sapphire frequency with that of an iodine-stabilized He-Ne laser using a 1-m evacuated Fabry-Perot etalon. The measurement uncertainty was 2 parts in 10{sup 9} (3 standard deviations), which gives an improvement of a factor of 60 in the term value of the 3 {sup 3}{ital P} level with respect to earlier measurements. This result makes it possible to determine the one electron Lamb-shift correction to the 3 {sup 3}{ital P} state with an accuracy of 0.8%.

We have demonstrated a method that efficiently transfers the power from a single-frequency laser into a wideband frequency comb. The comb was produced by a 2.7-GHz electro-optic modulator in a resonant optical cavity. A coupled cavity technique was used to transfer 8.5% of the laser power into a comb with a span of 400 modes, or more than 1 THz.

We report high-performance single-frequency operation of a directly diode-pumped GaSb-based vertical-external-cavity surface-emitting laser (VECSEL) at 2.3mum. Tunability of 70nm and a maximum single frequency output of 0.68W is demonstrated.

A novel technique is demonstrated for stabilizing an intra-cavity etalon used for single-mode selection in a laser cavity. By appropriate polarization analysis of the reflection from an etalon designed as a quarterwave plate an electronic signal can be derived, that enables the implementation of an electronic stabilization scheme. This scheme obviates the need for any modulation of the etalon in order to ensure stable single mode operation of a cw tunable laser.

We report an actively stabilised single-frequency vertical external cavity surface emitting laser operating at 678nm with a 200kHz laser linewidth. More than 10mW of output power was achieved in single-frequency operation.

We report the operation of an optical in-well-pumped vertical-external-cavity surface-emitting laser. The laser delivers 1 W at 855 nm and is pumped with a cost-effective fiber-coupled laser diode emitting at 806 nm. The laser modal gain is examined and ways of optimizing the system are investigated and discussed.

Cold atomic clouds and Bose-Einstein condensates have been stored in a 10cm diameter vertically-oriented magnetic ring. An azimuthal magnetic field enables low-loss propagation of atomic clouds over a total distance of 2m, with a heating rate of less than 50nK/s. The vertical geometry was used to split an atomic cloud into two counter-rotating clouds which were recombined after one revolution. The system will be ideal for studying condensate collisions and ultimately Sagnac interferometry., 4 pages, 5 figures

Coherent optical spectroscopy has been performed on the narrow $5s\phantom{\rule{0.3em}{0ex}}^{2}S_{1∕2}--4d\phantom{\rule{0.3em}{0ex}}^{2}D_{5∕2}$ quadrupole transition in a single Doppler-cooled and trapped $^{88}\mathrm{Sr}^{+}$ ion. High-contrast optical Ramsey spectra have been observed with fringe visibilities up to $\ensuremath{\sim}90%$. The visibility decreased as the free precession period was increased, and was limited by the interrogation laser's coherence. The effect of varying the relative phase of the second Ramsey pulse was investigated. By measuring the difference in excitation probability on reversing a $90\ifmmode^\circ\else\textdegree\fi{}$ relative phase shift between the two Ramsey pulses, we have demonstrated Ramsey's anti-symmetric line shape in the optical domain. A significant advantage of this line shape is the zero crossing at line center and the independence of this center frequency on drifts in signal amplitude. This optical Ramsey line shape is suitable for stabilizing a local oscillator to an atomic reference transition in an optical frequency standard. All observed optical Ramsey signals are well described by a model using the optical Bloch equations.

In this paper we have demonstrated monolithic "microchip" vertical external-cavity surface-emitting lasers (VECSEL), in which a cavity is formed between the VECSEL semiconductor back mirror and a dielectric mirror coating on the outer surface of the heat spreader, and where pump-induced thermal lensing may provide cavity stability. We have demonstrated stable, high power operation of composite microchip VECSELs in the 850 nm and 980 nm wavelength region. We have achieved >350 mW output power at 850 nm and >2.5 W at 980 nm. These initial results strongly indicate the promise of the microchip VECSELs as a low cost, high power, compact and versatile source of laser light.

In this paper, we demonstrate that highly advantageous thermal management properties of the SiC heatspreader are wholly compatible with direct diode pumping. We investigate the transverse and longitudinal mode behaviour of the high-power vertical external-cavity surface-emitting semiconductor laser with the intra-cavity heatspreader.

Controlled modulation of laser phase in an optical Ramsey experiment yields an antisymmetric lineshape. This discriminant is used to stabilize a local oscillator to the optical clock transition in a single 88Sr+ ion

The possibility of wavelength tuning and insertion of intra-cavity control elements makes vertical external cavity surface emitting lasers (VECSEL) a useful tool for telecommunication and spectroscopic applications. Very small cavity lengths are desirable for achieving continuous single mode tuning and the fiber-based VECSEL is a simple device which avoids the complicated post-growth processing involved in the fabrication of a membrane-type laser. We report here on the successful operation of an optically-pumped fiber-based VECSEL in the 850 nm wavelength region. The device comprises a half cavity periodic gain structure made of 15 Al/sub 0.2/Ga/sub 0.8/As/GaAs quantum wells designed to be at the anti-nodes of the electric field standing wave, with a 30 pairs Al/sub 0.2/Ga/sub 0.8/As/AlAs distributed Bragg reflector (DBR) as the bottom mirror. The structure is similar to one previously described, used in a macroscopic external cavity geometry. The top mirror of our cavity is a dielectric DBR deposited onto the cleaved end of a single mode fiber whose distance from the semiconductor can be controlled via a piezoelectric actuator to allow for wavelength tuning. The aim of this work is to contribute to the understanding of the operation of this optically pumped fiber-based laser. By comparing the laser performance with the f finesseinesse of an empty cavity with otherwise identical geometry, we are able to conclude that the dominant photon loss mechanism is due to fundamental diffraction limits.

We report on the fabrication and diffraction-limited characterization of parabolic focusing micromirrors. Sub - micron beam waists are measured for mirrors with 10 {\mu}m radius aperture and measured fixed focal lengths in the range from 24 {\mu}m to 36 {\mu}m. Optical characterization of the 3D intensity in the nearfield produced when the device is illuminated with collimated light is performed using a modified confocal microscope. Results are compared directly with angular spectrum simulations, yielding strong agreement between experiment and theory, and identifying the competition between diffraction and focusing in the regime probed., Comment: 7 pages, 5 figures. Accepted to Optics Express

The experimental realisation of gaseous Bose-Einstein condensation (BEC) in 1995 sparked considerable interest in this intriguing quantum fluid. Here we report on progress towards the development of an 87Rb BEC experiment in a large (~10cm diameter) toroidal storage ring. A BEC will be formed at a localised region within the toroidal magnetic trap, from whence it can be launched around the torus. The benefits of the system are many-fold, as it should readily enable detailed investigations of persistent currents, Josephson effects, phase fluctuations and high-precision Sagnac or gravitational interferometry., Comment: 5 pages, 3 figures (Figs. 1 and 2 now work)

We demonstrate a system for fast and agile digital control of laser phase, amplitude and frequency for applications in coherent atomic systems. The full versatility of a direct digital synthesis radiofrequency source is faithfully transferred to laser radiation via acousto-optic modulation. Optical beatnotes are used to measure phase steps up to 2π, which are accurately implemented with a resolution of ≤ 10 mrad. By linearizing the optical modulation process, amplitude-shaped pulses of durations ranging from 500 ns to 500 ms, in excellent agreement with the programmed functional form, are demonstrated. Pulse durations are limited only by the 30 ns rise time of the modulation process, and a measured extinction ratio of > 5 × 10(11) is achieved. The system presented here was developed specifically for controlling the quantum state of trapped ions with sequences of multiple laser pulses, including composite and bichromatic pulses. The demonstrated techniques are widely applicable to other atomic systems ranging across quantum information processing, frequency metrology, atom interferometry, and single-photon generation.

Resonant ionization spectroscopy has been employed for measuring the 12S1/2−22S1/2 frequency difference in the hydrogen‐like muonium atom to 2 455 529 002(33)(46) MHz. The 1S‐2S two‐photon transition was induced Doppler‐free using two counter‐propagating laser beams. The 2S state was photo‐ionized by a third photon from the same laser field. The measurement agrees with QED theory within two standard deviations. The mass of the positive muon can be extracted from the isotope shifts in this transition to hydrogen and deuterium to 105.658 80(29)(43) MeV/c2.

We demonstrate highly efficient generation of coherent 420nm light via up-conversion of near-infrared lasers in a hot rubidium vapor cell. By optimizing pump polarizations and frequencies we achieve a single-pass conversion efficiency of 260% per Watt, significantly higher than in previous experiments. A full exploration of the coherent light generation and fluorescence as a function of both pump frequencies reveals that coherent blue light is generated close to 85Rb two-photon resonances, as predicted by theory, but at high vapor pressure is suppressed in spectral regions that do not support phase matching or exhibit single-photon Kerr refraction. Favorable scaling of our current 1mW blue beam power with additional pump power is predicted., Comment: 6 pages, 4 figures. Modified to include referees' improvements

We have realised a 4-beam pyramidal magneto-optical trap ideally suited for future microfabrication. Three mirrors split and steer a single incoming beam into a tripod of reflected beams, allowing trapping in the four-beam overlap volume. We discuss the influence of mirror angle on cooling and trapping, finding optimum efficiency in a tetrahedral configuration. We demonstrate the technique using an ex-vacuo mirror system to illustrate the previously inaccessible supra-plane pyramid MOT configuration. Unlike standard pyramidal MOTs both the pyramid apex and its mirror angle are non-critical and our MOT offers improved molasses free from atomic shadows in the laser beams. The MOT scheme naturally extends to a 2-beam refractive version with high optical access. For quantum gas experiments, the mirror system could also be used for a stable 3D tetrahedral optical lattice., 8 pages, 6 figures, 2 movies

We report on a technique for obtaining dispersive saturated absorption features by two pump beams derived from an acousto-optic modulator. One of the beams is frequency shifted by the modulator allowing for a variable frequency offset of the resulting signal. They are used to saturate the atomic transition in the low-density vapour of the lamp. The sensitivity of the technique is sufficient to observe clear signals from isotopes of calcium unresolved by the inhomogeneous broadening and with natural abundances of less than 0.2%. The technique is used for offset locking the frequency of a Ti:Sapphire laser used for laser cooling and trapping of calcium.

We present a compact apparatus for laser cooling and trapping of atomic calcium. The set-up consisting of a Zeeman-slowed thermal beam and a magneto-optical trap (MOT) has potential use for studying optical lattices, optical clocks, sensitive trace analysis, ultra-cold collisions and the feasibility of achieving quantum degeneracy in an alkaline earth element. Construction of the apparatus is described as well as the characterization of the trap in terms of atom number and lifetime. The lifetime results are compared with a rate equation model for the system.

Recent work done at Stanford in the manipulation of atoms and particles is summarized. Techniques to further increase our control of neutral particles such as atomic fountains, funnels, and trampolines have been demonstrated. These techniques are now being combined with a new type of velocity selection in order to study atom/surface interactions and to improve the limit on the charge neutrality of atoms. Trapping techniques have also allowed us to manipulate single molecules of DNA in aqueous solution while observing the molecules in fluorescence.