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Ghost imaging with correlated photon pairs has been applied to remote sensing without the spatially detected photons interacting with the object: here we demonstrate for the first time ghost imaging using correlated atom pairs.

We have developed and characterised a stable, narrow linewidth external-cavity laser (ECL) tunable over 100 nm around 1080 nm, using a single-angled-facet gain chip. We propose the ECL as a low-cost, high-performance alternative to fibre and diode lasers in this wavelength range and demonstrate its capability through the spectroscopy of metastable helium. Within the coarse tuning range, the wavelength can be continuously tuned over 30 pm (7.8 GHz) without mode-hopping and modulated with bandwidths up to 3 kHz (piezo) and 37(3) kHz (current). The spectral linewidth of the free-running ECL was measured to be 22(2) kHz (Gaussian) and 4.2(3) kHz (Lorentzian) over 22.5 ms, while a long-term frequency stability better than 40(20) kHz over 11 hours was observed when locked to an atomic reference.

A chirp-minimized, nanosecond-pulsed system has been developed to generate tunable coherent ultraviolet light at ∼212.5 nm by fourth-harmonic conversion of output from an amplified, injection-seeded optical parametric oscillator (OPO). Our CHAPS (coherent heterodyne-assisted pulsed spectroscopy) method is used to characterize the frequency stability and optical bandwidth of the system’s output radiation by recording sub-Doppler two-photon excitation spectra of krypton. In our new scanned-reference variant of CHAPS, the central frequency for each amplified OPO pulse is logged by the optical-heterodyne chirp-analysis software, with the frequency of the seed laser slowly tuned and monitored by a high-resolution wavemeter, unlike our previous implementation of CHAPS where the seed-laser frequency was fixed. For the amplified, up-converted pulses at ∼212.5 nm, our CHAPS measurements indicate an optical bandwidth of ∼100 MHz, consistent with the Fourier-transform limit of their duration (∼4.5 ns).

International audience; Powerful ultrafast laser pulses have a unique capability to ablate material from the surface without heat propagation into the bulk due to the nonlinear nature of the laser-surface interaction. This quality offers a new application of ultrafast lasers for restoration of objects of art and heritage artefacts. We discuss the laser-based cleaning methods used in art restoration, analyse the potential advantages and challenges of using ultrafast laser pulses, and present new encouraging results on using ultrafast lasers in the field of heritage conservation.

Ghost imaging is a counter-intuitive phenomenon-first realized in quantum optics-that enables the image of a two-dimensional object (mask) to be reconstructed using the spatio-temporal properties of a beam of particles with which it never interacts. Typically, two beams of correlated photons are used: one passes through the mask to a single-pixel (bucket) detector while the spatial profile of the other is measured by a high-resolution (multi-pixel) detector. The second beam never interacts with the mask. Neither detector can reconstruct the mask independently, but temporal cross-correlation between the two beams can be used to recover a 'ghost' image. Here we report the realization of ghost imaging using massive particles instead of photons. In our experiment, the two beams are formed by correlated pairs of ultracold, metastable helium atoms, which originate from s-wave scattering of two colliding Bose-Einstein condensates. We use higher-order Kapitza-Dirac scattering to generate a large number of correlated atom pairs, enabling the creation of a clear ghost image with submillimetre resolution. Future extensions of our technique could lead to the realization of ghost interference, and enable tests of Einstein-Podolsky-Rosen entanglement and Bell's inequalities with atoms.

Passive phase-conjugation enables precise fiber-optical transfer of radio-frequency reference signals over long distances, yielding high long-term stability for radio-astronomy and remote-sensing applications without active path-length stabilization.

The use of laser technology for cleaning heritage artefacts is gaining increasing interest both in Australia and overseas. Laser cleaning is a dry and contact-free process, which selectively removes contaminating dirt or coatings (including hazardous contaminants such as radioactivity and biological material), minimises mechanical and chemical disruption of historic surfaces and generates minimal waste. However, the disadvantage of current lasers for conservation is that their relatively long pulse duration allows heat and shock waves to travel into the substrate, potentially causing damage to historic surfaces. Different laser types are also needed to treat different materials, which limits the range of materials any one laser unit can treat. The femtosecond pulses used by ultrafast lasers however, are too short to allow heat or shock waves to travel into the substrate. They ablate very thin surface layers through a process known as non-thermal or non-equilibrium laser ablation. This allows highl...

A method for optimizing the design and construction of a Zeeman slower coil is presented. Unlike traditional designs, the measured magnetic field profile very accurately matches the desired field profile, enabling significant advantages for loading a magneto-optic trap.

We discuss the quantum reflection of metastable 2 3 S helium atoms in (square) hollow optical fibres of fused silica, used as atomic waveguides. Under realistic experimental conditions, retardation effects in the atom-surface potential play a dominant role; they can increase the reflection probability by an order of magnitude and lead to a significant yield of quantum reflected atoms, amounting to several percent of the incident atomic flux.

We present a novel design for a single-mode, hollow optical fibre, which is suitable for use as a waveguide for atomic de Broglie waves. The design, development and characterisation of such a fibre are discussed, as well as an optimised method for coupling light into the fibre.

The realisation of an atomic waveguide will be an important component for the development of future atom optic devices such as large angle atom interferometers. Hollow optical fibres that employ repulsive (blue detuned) evanescent light fields to guide the atoms are one approach to this technology. We report here on multimode guiding of metastable helium ( 2 3 S 1 ) atoms through hollow optical fibres that support multimode light fields. In order to produce efficient single-mode atom guiding, hollow fibres supporting single light mode propagation will be required to generate uniform evanescent light fields inside fibre wall. We have recently developed such a fibre and report on the suitability of its light transmission characteristics for atom waveguiding.

The transverse velocity distribution of a sodium atomic beam, laser cooled in one dimension, has been measured with sub-recoil resolution. A velocity-selective detection system was employed to separate the longitudinal and transverse velocity components to provide a direct measure of the transverse velocity distribution. The effects of varying the cooling laser intensity and detuning on the derived transverse temperature are presented, and show a remarkable insensitivity to the laser intensity. Atomic velocities within a factor of two of the recoil velocity are

In this paper we present a novel frequency dissemination technique which uses an all-optical interferometer to sense length fluctuations with high precision, and then utilises this information to simultaneously stabilise a transmitted optical and signal and a microwave signal.

We present a novel optical fiber-based radio-frequency distribution system that incorporates low-cost commercially available components. It has a fractional frequency stability of 7×10−17 (averaged over 104 s) for distribution of an 80-MHz signal.

Speckle patterns produced by multiple independent light sources are a manifestation of the coherence of the light field. Second-order correlations exhibited in phenomena such as photon bunching, termed the Hanbury Brown-Twiss effect, are a measure of quantum coherence. Here we observe for the first time atomic speckle produced by atoms transmitted through an optical waveguide, and link this to second-order correlations of the atomic arrival times. We show that multimode matter-wave guiding, which is directly analogous to multimode light guiding in optical fibres, produces a speckled transverse intensity pattern and atom bunching, whereas single-mode guiding of atoms that are output-coupled from a Bose-Einstein condensate yields a smooth intensity profile and a second-order correlation value of unity. Both first- and second-order coherence are important for applications requiring a fully coherent atomic source, such as squeezed-atom interferometry.

Ultracold atoms whose de Broglie wavelength is of the same order as an extended confining potential can experience waveguiding along the potential. When the transverse kinetic energy of the atoms is sufficiently low, they can be guided in the lowest order mode of the confining potential by analogy with light guided by a single mode optical fiber. We have obtained the first images of the transverse mode structure of guided matter waves in a confining potential with up to 65% of atoms in the lowest order mode. The coherence of the guided atomic de Broglie waves is demonstrated by the diffraction pattern produced when incident upon a two dimensional periodic structure. Such coherent waveguides will be important atom optic components in devices with applications such as atom holography and atom interferometry.

A minimal-chirp nanosecond-pulsed nonlinear-optical system generates tunable coherent ultraviolet light at ∼212.5 nm. Its frequency stability and optical bandwidth are verified by means of novel sub-Doppler coherent heterodyne-assisted two-photon spectroscopy of krypton.

Output pulses from a Ti:sapphire-amplified OPO are shown to be nearly Fourier-transform-limited with little additional chirp. The power is sufficient to generate narrowband vacuum-ultraviolet radiation (using nonlinear-optical methods) for precision spectroscopy.

There is a need in the context of high-resolution laser spectroscopy for pulsed, tunable, single-longitudinal-mode (SLM) coherent light sources with high peak power and narrow optical bandwidth. This holds particularly in the vacuum ultraviolet (VUV) region, where nonlinear-optical (NLO) upconversion is essential to generate required wavelengths. For instance, narrowband 120-nm VUV radiation, generated by pulsed dye amplification of a cw tunable Ti:sapphire laser and NLO upconversion, has been used [1] to measure the 2 1S ← 1 1S two-photon absorption transition of helium (He) as a test of quantum-electrodynamic theory.

International audience; Powerful ultrafast femtosecond laser pulses have the unique ability to ablate material with minimal collateral damage. This ability offers the potential for new applications of ultrafast lasers for removing surface contamination and unwanted surface layers in the conservation of artworks and heritage objects. In this paper we concentrate on the problem of precise and fast scanning of the laser spot over the treated surface for cleaning relatively large surface areas. Preliminary results are presented for the removal of intrusive paint layers, using a 12-ps laser with 1.5 MHz repetition rate, and 0.5 ps laser with 10 kHz repetition rate.

A chirp-controlled nanosecond-pulsed tunable optical parametric oscillator and two-stage Ti:sapphire amplifier generate high-power coherent light at ~840 nm, with frequency stability and narrow optical bandwidth as needed for high-resolution ultraviolet spectroscopy.

Realization of the analogues of optical components for the manipulation of atomic de Broglie waves has recently become possible through the use of laser-based techniques. The strong fields generated by laser light have already been used to reflect atoms using travelling evanescent waves, and to diffract atomic beams through small angles using transmission gratings formed by a standing laser light wave in vacuo. Present experiments aim to combine these techniques to produce a reflection diffraction grating formed by a standing evanescent laser-light field, and to exploit the larger diffraction angles made possible theoretically by such a scheme.

We use nonlinear optical processes to generate narrowband light from an optical parametric oscillator, yielding significantly improved frequency stability compared with dye lasers where the chirp arises principally from population inversion. We measure chirp using optical heterodyne detection and minimise it by phase matching, producing a near Fourier-transform limited bandwidth.

We simulate spectro-temporal processes in a nanosecond injection-seeded optical parametric oscillator. Our simulations accurately predict the experimental behavior for the frequency chirp, optical bandwidth, and spectral purity, including effects that are not readily observed directly.

Narrowband pulsed 822 nm signal radiation from an injection-seeded optical parametric oscillator (OPO) system is used to record fluorescence-detected sub-Doppler two-photon excitation (TPE) spectra of atomic cesium. An optical-heterodyne technique is used to monitor the frequency chirp as well as the fluctuating central frequency of successive OPO output pulses, thereby providing a novel way to record sub-Doppler TPE spectra. The measured TPE linewidth approaches the ultimate limit imposed by the Fourier transform of the pulse’s temporal profile, demonstrating the utility of this system for pulsed laser spectroscopy applications that require the highest possible resolution.

A new pulsed spectroscopic technique combines optical heterodyne detection with frequency binning. Its utility is demonstrated via Doppler-free two-photon excitation in cesium using an injection-seeded pulsed optical parametric oscillator, operated close to the Fourier-transform limit.

A new precision pulsed laser technique - Coherent Heterodyne-Assisted Pulsed Spectroscopy (CHAPS) - employs optical heterodyne detection for high-resolution measurement using a ns-pulsed optical parametric oscillator/amplifier whose ~18MHz bandwidth is very close to the Fourier transform limit.

We report on several complementary methods for improving the stability of a free running diode laser. We were primarily concerned with: (a) the construction of a stable power supply to reduce the main frequency and rf noise, and (b) long term drift of the laser frequency, for which we have developed a lock-in amplifier to be combined with a simple proportional-integrating circuit. While we have kept everything simple and inexpensive to construct, the stability is comparable with that of far more expensive, commercially available systems. Development and testing of our stabilization scheme was done on the distributed Bragg reflector diode lasers for use in a range of atomic collision and atom optics experiments, but it is applicable to all diode lasers, and can be used in a large range of atomic physics experiments.

We use optical heterodyne and nonlinear-optical spectroscopic techniques to measure the near Fourier-transform limited output from a narrowband tunable injection-seeded, pulsed optical parametric oscillator/amplifier system that has a controllable frequency chirp of

Heterodyne technique is used to measure the optical phase characteristics of a ns-pulsed periodically poled KTiOPO/sub 4/ (PPKTP) OPO that is injection-seeded by a cw tunable diode laser (TDL). How frequency chirp in a TDL-seeded PPKTP OPO is affected by various experimental conditions is investigated.

An injection-seeded optical parametric oscillator (OPO), based on periodically poled KTiOPO4 and pumped by a frequency-doubled, nanosecond-pulsed Nd:YAG laser, generates continuously tunable, single-longitudinal-mode, pulsed output at approximately 842 nm for high-resolution spectroscopy. Optical-heterodyne measurements show that the OPO frequency chirp increases linearly with detuning from the free-running (unseeded) OPO frequency and can be maintained as low as 10 MHz. Other factors affecting chirp are identified.

Intense, highly collimated sources of atoms have many potential applications. Bright beams will be important for competitive high flux and high resolution direct-write techniques in lithography, with the added advantage of parallel writing through laser manipulation. Intense sources will also be useful in other atom optic devices e.g. for loading atoms into hollow fiber waveguides. In atomic physics, many collision processes can only be measured with the sensitivity offered by such high flux sources. We report progress on the development of an intense, collimated beam of metastable helium atoms which improves the brightness generated by conventional nozzle discharge sources by several orders of magnitude. The system uses diode lasers to transversely collimate and then to longitudinally slow the atoms, using Zeeman tuning to compensate for the changing Doppler shift. The slowed, collimated beam is then compressed in a 2D magneto-optic trap before a final collimation stage, to achieve the required increase in intensity. Initial experiments using the helium source for some of the applications above are described.

We present a technique for the simultaneous dissemination of high-precision optical-frequency signals to multiple independent remote sites on a branching optical-fiber network. The technique corrects optical-fiber length fluctuations at the output of the link, rather than at the input as is conventional. As the transmitted optical signal remains unaltered until it reaches the remote site, it can be transmitted simultaneously to multiple remote sites on an arbitrarily complex branching network. This technique maintains the same servo-loop bandwidth limit as in conventional techniques and is compatible with active telecommunication links.

We report on the observation of velocity-tuned (doppleron) resonances in the grazing-incidence reflection of thermal sodium atoms from a moving evanescent light grating created by interference between two counterpropagating laser beams. The relative velocity between the atoms and the grating can be varied continuously by adjusting the frequency of one laser. We observe an exchange of photons between copropagating and counterpropagating fields in an evanescent light grating. The results are in general agreement with a dressed-state model for the diffraction of atoms from such a grating.

Near resonant standing waves can be used to manipulate the spatial distribution of atomic beams. We report two distinct effects: channelling of atoms in a perpendicular standing wave and the reflection of atoms from a grazing incidence mirror formed by a moving evanescent standing wave. The first arrangement allows us to focus an atomic beam over a large distance. The latter arrangement has the potential to demonstrate diffraction of fast atoms and could lead to an application as a beamsplitter.

In order to diffract atoms from an evanescent light reflection grating the Rabi frequency must be greater than the Doppler shift associated with the atomic velocity. For thermal atoms this cannot be achieved using dye lasers. Rather than slow the atoms we have produced a moving light grating and observe resonances in the reflectivity of the grating for certain grating velocities. The position of these resonances fulfils the Doppleron condition Δ’=nΔD’, which is consistent with a dressed state model for diffraction from such a grating.

The demonstration of a mirror for atoms using an evanescent light field to reflect an atomic sodium beam was first reported by Balykin etal.1 following a proposal by Cook and Hill2. In another experiment, Gould etal.3 observed the diffraction of a sodium beam at normal incidence to an optical standing wave transmission grating produced by retroreflecting a laser beam in vacuo. The work reported here aimed to combine these techniques, namely to produce a reflection diffraction grating for atoms consisting of a standing evanescent light wave. Theoretical work by Hajnal and Opat4 predicts that such a grating would have different properties to the transmission grating of Gould etal.3

Complicated spectrotemporal processes are associated with the generation of signal and idler output pulses on a nanosecond timescale in an injection-seeded optical parametric oscillator (OPO). The mechanisms of such spectrotemporal dynamics are revealed by numerical simulation, including innovative modeling of instantaneous-frequency profiles and frequency chirp. These simulations are in satisfactory agreement with optical-heterodyne measurements of output from a nanosecond-pulsed OPO system that is based on periodically poled KTiOPO4, pumped at 532 nm by a Nd:YAG laser and injection-seeded at a signal wavelength of ∼842 nm. Frequency chirp in narrowband signal output pulses from such an OPO system has previously been observed to depend on phase mismatch between the pump, signal, and idler waves, and also on the pump-pulse energy. Our simulations accurately predict this behavior and yield realistic estimates of the frequency chirp, optical bandwidth, and spectral purity of the signal output pulse as it evolves, including effects that are not readily observed directly. This approach provides insight into instrumental conditions that facilitate continuously tunable, single-longitudinal-mode operation of such a pulsed OPO system, with optical bandwidth as close as possible to the Fourier-transform limit.

We present a new technique for high-resolution pulsed spectroscopy that employs optical heterodyne detection to determine the instantaneous frequency of individual optical pulses, together with a frequency-binning method to generate high-precision spectra. We further demonstrate that active tuning of the light source is not necessary if the inherent frequency jitter of the source spans the spectral region of interest. This heterodyneassisted approach to coherent pulsed spectroscopy (CHAPS) is applied in real time by using output from a pulsed, injection-seeded optical parametric oscillator–amplifier (OPO–OPA) system, the optical bandwidth of which is characterized via two-photon excitation of the 6S–8S transition in cesium. The resulting sub-Doppler measurements demonstrate the utility of CHAPS as a high-resolution spectroscopic technique and confirm that the pulsed OPO–OPA system operates very close to the Fourier-transform limit. © 2006 Optical Society of America OCIS codes: 020.4180, 040.2840, 120.6200, 190.4970, 230.4320, 300.3700, 300.6320, 300.6410.

Australia is renowned for its abundant sunlight, which enhances the vibrant colors of the continent. In the scientific realm, Australia is also well known for its outstanding contributions to the study and application of light in science and engineering.

Optical-heterodyne measurements are made on ~842-nm signal output of an injection-seeded optical parametric oscillator (OPO) based on periodically poled KTiOPO4 pumped at 532 nm by long (~27-ns) pulses from a Nd:YAG laser. At low pump energies (/= 2.5 times the free-running threshold), the narrowband tunable OPO output is single-longitudinal-mode (SLM) and frequency chirp can be10 MHz, much less than the transform-limited optical bandwidth (~17.5 MHz). We explore the transition from SLM operation to multimode operation as pump energy or phase mismatch are increased, causing unseeded cavity modes to build up later in the pulse.

An injection-seeded optical parametric oscillator (OPO) based on periodically poled KTiOPO4 is pumped at 532 nm by relatively long (~27-ns) pulses from a specially constructed Nd:YAG laser. This pulsed OPO system generates continuously tunable, single-longitudinal-mode output at signal wavelengths near 842 nm, which is suitable for high-resolution spectroscopy. Optical-heterodyne measurements show that chirp in the instantaneous frequency of the pulsed OPO signal output radiation increases linearly as the seed frequency is detuned from the free-running (unseeded) OPO frequency. The frequency chirp can be maintained below 10 MHz, which is substantially less than the Fourier-transform-limited optical bandwidth (17.5 MHz full width at half-maximum for a 25-ns OPO signal pulse) and is insensitive to variation of the fluence of the pump radiation. The effects of detuning the OPO cavity length from resonance with the seed frequency and the onset of partially seeded OPO operation are also investigated.

We evaluate ways to analyze optical-heterodyne measurements of frequency chirp in pulsed, single-longitudinal-mode output from lasers (or other coherent light sources) that operate on nanosecond time scales. The instantaneous frequency is extracted from the beat signal generated between a continuous-wave reference beam and the output of the pulsed source. Three analysis techniques are tested: Fourier-transform, direct curve fitting, and electronic mixing. We use synthetic beat waveforms based on actual experimental parameters to evaluate the three methods and apply these chirp-measurement techniques to an injection-seeded optical parametric oscillator system.

A novel mirror arrangement that enables large interaction lengths between atomic beams and laser fields by use of a small amount of laser power is presented. Its application to focusing and compression of neutral atomic beams is discussed.

We describe techniques for laser spectroscopy in the vacuum-UV (VUV) spectral region that combine high spectral resolution with high absolute accuracy. A nearly transform-limited nanosecond laser source at 120 nm is constructed with difference-frequency mixing. This source is used to perform the first, to our knowledge, Doppler-free VUV measurement. We measure the inherently narrow 11S–21S two-photon transition in atomic helium with a spectral resolution of 7 parts in 108 (180 MHz), the narrowest line width so far observed at such short wavelengths. Careful measurements of optical phase perturbations allow us to determine the absolute frequency of the line center to a fractional uncertainty of 1 part in 108. Improvements now in progress should reduce this uncertainty to 2 parts in 109.

This article outlines experiments which have highlighted the rapid development of the field of atom optics since the mid 1980s. The distinguishing features of the components used in atom optics are compared with their conceptual analogues in light optics. The potential for atom optic devices, both demonstrated and predicted, are described. Experiments and applications of this new technology are reviewed, and the article concludes with a synopsis of work in this field currently being undertaken in Australasia.

SUMMARY High resolution (better than 20 nm) contact micrographs have been produced with exposure times of about a nanosecond. The illuminating source was a short-lived carbon plasma produced by focusing a single short (∼1 ns) 100 J pulse from the Vulcan laser at the Rutherford Appleton Laboratory (RAL) to a 300 μm spot on a graphite target. This plasma emits strongly in the soft X-ray region, particularly at the CVI (3.37 nm) and CV (4.03 nm) lines. The specimens were behind a 100 nm thick Si3N4 window, at atmospheric pressure in an environmental cell. The images of diatoms recorded on X-ray resist showed features down to the limit of resolution of the SEM used to view the developed resist, which was about 20 nm.

A straightforward method of generating tunable coherent VUV radiation is described. Radiation down to 1362 A was produced by Raman shifting the output of a commercially produced, excimer-pumped dye laser system. It is shown that generation of VUV radiation at 1640 A is more efficient using the 8th anti-Stokes line from a UV dye than by using the 10th anti-Stokes line from a visible dye which had twice the output power.