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Growing demand of Juul and other electronic cigarettes, despite critical knowledge gaps about their chemical composition, has led to concerns regarding their potential health effects. We introduce a novel analytical approach, runtime cavity ringdown spectroscopy (rtCRDS) for rapid detection of oxidative products in e-cigarette aerosols, to facilitate the study of aerosol from a single puff of e-liquid. We report a systematic investigation of three flavors of commercial Juul pods (Virginia tobacco, mango, and menthol) and known commercial e-liquid ingredients (propylene glycol (PG), vegetable glycerin (VG), nicotine, ethyl maltol, benzoic acid, and nicotine benzoate) vaped using Juul devices. Juul e-liquids and neat chemical additives spiked into a 30:70 PG/VG solution were vaped and their aerosols were collected in 1-L Tedlar gas bags and analyzed using rtCRDS. Acetaldehyde, formaldehyde, and acetone were identified as primary oxidative products in aerosolized PG/VG. Ethanol was detected as a major constituent of the three commercial Juul flavors. Spectral intensities of carbonyl compounds increased with the addition of spikes, benzoic acid, ethyl maltol, and nicotine to PG/VG, suggesting that oxidative product generation increases with common additives. The method of direct, rapid analysis of e-cig aerosols introduced here can be used to complement traditional methods in vaping exposures.

Natural gas leaks are a serious concern not only because of methane emission but also an explosive threat. We report designing of a portable, miniaturized, laser-based methane tracker for rapid detection of natural gas leaks.

To advance our understanding of ocean chemistry, new in situ sensors are needed. By coupling gas extraction techniques to laser-based sensors, we can measure key gases such as methane and carbon dioxide in ocean environments.

Optical entanglement — a key requirement for many quantum communication protocols — is typically formed between two distinct beams, requiring repeated combination of complex resources, which becomes increasingly difficult as the number of entangled information channels increases. Here entanglement between two spatial modes within one beam is demonstrated.

Cavity-enhanced spectroscopy is a sensitive optical absorption technique but one where the practical applications have been limited to studying small wavelength ranges. This Letter shows that wideband operation can be achieved by combining techniques usually reserved for the communications community with that of cavity-enhanced spectroscopy, producing a multiplexed real-time cavity-enhanced spectrometer. We use multiple collinear laser sources operating asynchronously and simultaneously while being detected on a single photodetector. This is synonymous with radio frequency (RF) cellular systems in which signals are detected on a single antenna but decoded uniquely. Here, we demonstrate results with spectra of methyl salicylate and show parts-per-billion per root hertz sensitivity measured in real-time.

We present new results from a variant of cavity enhanced spectroscopy that allows large spectral bandwidths to be analysed in real time, and demonstrate new methods to apply the technique to real-time monitoring of species with broad absorbances.

The application of quantum optics to spatial measurements with continuous-wave laser beams is discussed. In particular, we summarize the work on measuring small displacements and tilt. We present the required theoretical multi-mode model and discuss how it applies to split detectors and spatial homodyne detectors. We show how spatial measurements can be improved using squeezed light. Finally, we present a demonstration of improved spatial homodyne measurements using squeezed light in a higher order spatial mode.

It is commonly known that we are made up of approximately 60% water, but if fact we are 100% MOLECULES! Sci-Fi shows invent simple instruments to diagnose humans in real-time. Is it science fiction or fact?

Recent advances in digital signal processing have made it possible to make real-time hypertemporal spectroscopic measurements over several wavelength bands simultaneously. This talk will outline the progress made in this area of research and present a view of future application for this technology.

A system is described that employs a diode-pumped Nd:YAG continuous-wave laser source servolocked to a three-mirror optical cavity and an analog detection circuit that extracts the ring-down rate from the exponentially decaying ring-down waveform. This scheme improves on traditional cavity ring-down spectroscopy setups by increasing signal acquisition rates to tens of kilohertz and reducing measurement noise sources. For example, an absorption spectrum of a weak CO2 transition at 1064 nm is obtained in less than 10 s at a spectral resolution of 75 kHz employing a cavity with an empty-cavity ring-down decay lifetime of 2.8 μs and a total roundtrip path length of 42 cm. The analog detection system enables laser frequency scan rates greater than 500 MHz/s. The long-term sensitivity of this system is 8.8×10−12 cm−1 Hz−1/2 and the short-term sensitivity is 1.0×10−12 cm−1 Hz−1/2.

We present unified theoretical expressions for laser intensity noise in the presence of injection locking and feedback. We discuss optimum control strategies for different configurations and frequency regions. We illustrate the various effects with experimental results from Nd : YAG non-planar ring oscillator lasers.

We present design and performance details of three photodetector circuits that have been developed in the authors laboratory over the past eight years. These detectors have been optimized to meet the unique demands of experiments such as high power, high sensitivity interferometry, nonlinear optics, and laser noise measurements. The circuits are: a low-noise dc coupled (dc 20 MHz) general purpose detector, a low-noise broadband (15–1100 MHz) detector capable of detecting 10 mW of light, and a high-power large dynamic range detector (30 kHz–60 MHz) capable of detecting up to 100 mW of light. We present bandwidth dynamic range and noise performance details for all three designs. In addition, we present detailed circuit schematics along with design and construction guidelines to enable assembly and use of these designs.

Polarization-selective optical heterodyne detection is shown to enhance the practical sensitivity of cavity ring-down spectroscopy. Initial experiments demonstrate a signal-to-noise ratio above 31 dB. Minor improvements should yield shot-noise-limited operation.

A fully quantum-mechanical model of feedback to the pump source of a four-level laser is developed with a view to predicting the achievable intensity noise reduction. For solid-state lasers, the model shows that quantum noise sources due to laser dynamics have a significant impact on the optimization of the feedback loop, Experimental results obtained with a diode pumped neodymium:yttrium aluminum garnet (Nd:YAG) laser are found to be in good agreement with the theoretical model. The ultimate limit to the noise suppression comes from the quantum noise due to the measurement processes in the feedback loop. A scheme to overcome this limit using a squeezed vacuum is theoretically demonstrated to be a highly efficient method of generating bright intensity squeezed light, particularly in the kHz regime where bright squeezing is otherwise difficult to obtain. [S1050-2947(97)08111-0].

We experimentally investigate the polarisation dependence of the locking bandwidth and transfer of amplitude modulation within an injection locked laser system. We find that the measured locking bandwidth of our injection locked laser varies by a factor of 2 as a function of polarisation. The transfer function for amplitude modulation on the master laser is strongly polarisation dependent and does not reflect a simple reduction in effective master laser power. As an explanation of the effects observed, we introduce a ''polarisation resonance'' condition for injection locking a laser cavity.

We present a new variant of the Cavity Ringdown Spectroscopy (CRDS) that is able to scan across more than 1400 nm of spectral bandwidth around 6000 nm, acquiring and analysing more than 150,000 spectral datapoints in less than four seconds.

We develop an extended Kalman filter to estimate the ring-down time of a multimode Fabry-Perot optical cavity with a pulse train input. First the extended Kalman filter is applied to data generated from a simulator to show that the estimate of the filter converges to the expected value of the ring-down time. It is also shown that the multimode filter improves the estimation performance, compared to a simplified filter designed from a single-mode model. Then the filter is applied to a set of experimentally obtained output intensity data.

We present a new variant of the Cavity Ringdown Spectroscopy (CRDS) that is able to scan across more than 1400 nm of spectral bandwidth, acquiring and analysing more than 150,000 spectral datapoints in less than four seconds.

We present experimental results that illustrate how laser intensity noise near the quantum-noise limit is transferred in an injection-locked cw Nd:(yttrium aluminum garnet) nonplanar ring-oscillator laser. We show that these results are in extremely good agreement with our quantum-mechanical model describing the injection locking process [T. C. Ralph, C. C. Harb, and H.-A. Bachor, Phys. Rev. A]. Three regions in the intensity-noise spectrum are identified and we show that different minimum noise levels exist in these regions. Finally, we show that the injection-locked laser can generate and preserve nonclassical states. \textcopyright{} 1996 The American Physical Society.

Real lasers show intrinsic noise well above the standard quantum noise limit. We review the properties of lasers and of techniques to suppress this noise. Experimental results of electro-optic feedback techniques and of squeezing in a second harmonic generator are presented. Finally we show that the optimum light source could well be a cascade of different cavities, each one performing a specific task in the noise suppression.

This paper presents offline extended Kalman filter (EKF) estimation results for the decay time-constant for an experimental Fabry-Perot optical cavity for cavity ring-down spectroscopy (CRDS). The decay time for an optical cavity is defined as the amount of time it takes for the light intensity inside the cavity to decay to 1/e times its original intensity in the absence of a sustained light source. An estimation of the decay time for a cavity depends upon the absorbing species inside the cavity along with other miscellaneous losses due to the elements used to construct the cavity. Once the miscellaneous losses are computed experimentally, the decay time due to the absorbing species can be directly computed. The decay rate, as a function of wavelength, can be used to identify trace gas elements such as chemicals and their compounds. For estimation purposes, the cavity is modeled as a low pass filter with unity DC gain and the experimentally obtained light intensity at the output of the cavity is used as measurement. During the process of recording the intensity data, the cavity's resonant frequency is held in sync with the input laser frequency via a proportional-integral (PI) controller. Finally, the estimation results for the decay time of the cavity using the low pass filter model presented in this paper, are compared with the estimation results using a quadrature model for the cavity from a previous work. The estimation results are also compared on filter execution times.

This Letter presents offline estimation results for the decay-time constant for an experimental Fabry-Perot optical cavity for cavity ring-down spectroscopy (CRDS). The cavity dynamics are modeled in terms of a low pass filter (LPF) with unity DC gain. This model is used by an extended Kalman filter (EKF) along with the recorded light intensity at the output of the cavity in order to estimate the decay-time constant. The estimation results using the LPF cavity model are compared to those obtained using the quadrature model for the cavity presented in previous work by Kallapur et al. The estimation process derived using the LPF model comprises two states as opposed to three states in the quadrature model. When considering the EKF, this means propagating two states and a (2×2) covariance matrix using the LPF model, as opposed to propagating three states and a (3×3) covariance matrix using the quadrature model. This gives the former model a computational advantage over the latter and leads to faster execution times for the corresponding EKF. It is shown in this Letter that the LPF model for the cavity with two filter states is computationally more efficient, converges faster, and is hence a more suitable method than the three-state quadrature model presented in previous work for real-time estimation of the decay-time constant for the cavity.

One of the main challenges in remote Fourier transform infrared (FT-IR) spectroscopy is the collection of a reliable background spectrum. Although suggested as a method to address the problem in prior literature, super clip apodization (SCA) has had little reported success for wide spectral features. SCA is a technique that involves the manipulation of different parts of the interferogram to calculate an absorbance spectrum from a single interferogram. A new method called complementary super clip apodization (CSCA) is developed here and is successfully used in conjunction with SCA in an iterative optimization algorithm. The umbrella term of super clip mathematics is also defined to encompass spectral calculation using SCA, CSCA or both in combination. The validity of super clip mathematics is demonstrated in an experimental study of gas-phase nitromethane. In an effort to mimic errors present in standoff detection, uniformly distributed noise and/or wavenumber shifting is added to the interferometric sample data to test the robustness of the algorithm. It will be shown that the implementation of SCA and CSCA in combination is more successful for concentration assessment than using SCA or CSCA alone.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

This paper presents results from a pulsed-laser cavity ring-down spectrometer with novel field programable gate array real-time data collection. We show both theoretically and experimentally that the data extraction can be achieved from a single cavity ringdown event, and that the absorbance can be determined without the need to fit the ringdown time explicitly. This methodology could potentially provide data acquisition rate up to 1 MHz, with the accuracy and precision comparable to nonlinear least squares fitting algorithms.

We investigate the intensity noise properties of a continuous-wave diode pumped Nd:YAG ring-laser system and present results for an active feedback loop that suppresses the relaxation oscillation noise. This system reduces the intensity noise to within 6.1 dB of the quantum noise equivalent level (which is at 1.5/spl times/10/sup -8///spl radic/Hz for 1.5 mA) for frequencies between 10 kHz to 300 kHz and to less than 1/spl times/10/sup -7///spl radic/Hz for frequencies between 300 Hz and 10 kHz. The technical properties of the optimized feedback system are presented. The theoretical limits of performance for the system are discussed and it is shown that the performance is within 3.1 dB of these limits. We also present data from an optical beat experiment demonstrating that the intensity control system does not introduce any new features into the frequency noise spectrum. >

A consortium of researchers at University of New South Wales (UNSW@ADFA), and Loyola University New Orleans (LU NO), together with Australian government security agencies (e.g., Australian Federal Police), are working to develop highly sensitive laser-based forensic sensing strategies applicable to characteristic substances that pose chemical, biological and explosives (CBE) threats. We aim to optimise the potential of these strategies as high-throughput screening tools to detect prohibited and potentially hazardous substances such as those associated with explosives, narcotics and bio-agents.

Phase error compensation is an important consideration in Fourier transform spectroscopy, particularly when obtaining background and sample information from one interferogram. A phase angle optimization algorithm is discussed to address this issue.

This paper considers the application of a discrete-time extended Kalman filter (EKF) to a problem of estimating the ring-down time constant of a Fabry-Perot optical cavity for the purpose of cavity ring-down spectroscopy (CRDS). The ring-down time corresponds to the time taken by the light inside an optical cavity to decay to 1/e of its initial intensity. The online estimation of ring-down time (or decay time) for a cavity is a direct indication of the absorbing species contained in it and can be used to detect improvised explosive devices and concealed explosives. Two cases are considered for EKF design depending on whether the resonant frequency of the optical cavity is perfectly locked to the input laser frequency, or not. In the case of a perfect lock, a three-state EKF is designed to estimate the magnitude and phase quadrature components of the cavity and the ring-down time. In the other case where there is not a perfect lock between the two frequencies, leading to non-zero detuning, a four-state EKF is designed to estimate the detuning parameter in addition to the magnitude and phase quadrature components of the cavity and the ring-down time. The detuning parameter gives an indication of the deviation of laser frequency from the resonant frequency of the cavity, which can then be used by a controller to maintain detuning at zero.

In quantum information systems it is of particular interest to consider the best way in which to use the nonclassical resources consumed by that system. Quantum communication protocols are integral to quantum information systems and are among the most promising near-term applications of quantum information science. Here we show that a multiplexed, digital quantum communications system supported by a comb of vacuum squeezing has a greater channel capacity per photon than a source of broadband squeezing with the same analog band width. We report on the time-resolved, simultaneous observation of the first dozen teeth in a 2.4-GHz comb of vacuum squeezing produced by a subthreshold optical parametric oscillator, as required for such a quantum communications channel. We also demonstrate multiplexed communication on that channel.

We experimentally demonstrate the generation of optical squeezing at multiple longitudinal modes and transverse Hermite-Gauss modes of an optical parametric amplifier. We present measurements of approximately 3 dB squeezing at baseband, 1.7 GHz, 3.4 GHz and 5.1 GHz which correspond to the first, second and third resonances of the amplifier. We show that both the magnitude and the bandwidth of the squeezing at the higher longitudinal modes is greater than can be observed at baseband. The squeezing observed is the highest frequency squeezing reported to date.

We combine experimental improvements to present an in principle demonstration of the use of multiple co propagating modes for quantum protocols.

Position and momentum were the first pair of conjugate observables explicitly used to illustrate the intricacy of quantum mechanics. We have extended position and momentum entanglement to bright optical beams. Applications in optical metrology and interferometry require the continuous measurement of laser beams, with the accuracy fundamentally limited by the uncertainty principle. Techniques based on spatial entanglement of the beams could overcome this limit, and high-quality entanglement is required. We report a value of 0.51 for inseparability and 0.62 for the Einstein-Podolsky-Rosen criterion, both normalized to a classical limit of 1. These results are a conclusive optical demonstration of macroscopic position and momentum quantum entanglement and also confirm that the resources for spatial multimode protocols are available.

Cavity ringdown spectra of ammonia at 10 parts in 10(9) by volume (ppbv) and higher concentrations were recorded by use of a 16-mW continuous-wave quantum-casacde distributed-feedback laser at 8.5 mum whose wavelength was continuously temperature tuned over 15 nm. A sensitivity (noise-equivalent absorbance) of 3.4x10(-9) cm(-1) Hz(-1/2) was achieved for ammonia in nitrogen at standard temperature and pressure, which corresponds to a detection limit of 0.25 ppbv.

The latest results on the experimental generation of the position and momentum (x-p) entanglement for bright optical beams are presented. The measurements of the quantum correlations in the TEM10 mode with two optical parametric amplifiers are demonstrated. TEM10 quadrature entanglement is also demonstrated. Two position squeezed beams on a 50:50 beam splitter are used to demonstrate full x-p entanglement.

In this experiment we use periodically poled potassium titanyl phosphate (PPKTP) as the nonlinear crystal in an optical parametric oscillator (OPO) for the generation of squeezed light on the D1 line of rubidium which lies at 795 nm. Although OPOs have long been used as sources of squeezed light, the shorter wavelengths required for atomic interactions have always been a challenge due to a limited choice of nonlinear crystals. PPKTP is a new material that has recently been shown to be highly effective over a very wide range of optical frequencies (Akamatsu, 2006).

We present the key elements required for continuous variable parallel quantum information protocols based on spatial multimode quantum correlations. We describe techniques for encoding, combining and detecting spatial quantum information with high efficiency in the individual transverse modes. Until now, the missing feature for the implementation of such protocols was the generation of squeezing in higher order transverse Hermite-Gauss modes. We experimentally demonstrate squeezing in selective modes by fine-tuning the phase matching condition of the nonlinear ${\ensuremath{\chi}}^{(2)}$ material and the cavity resonance condition of an optical parametric amplifier. Combined, these results open the way to practical multimode optical quantum information systems.

The spatial properties of laser beams can be used to encode, transfer and detect quantum information into high order modes with high efficiency. We demonstrate the use of such states, including spatial squeezing and entanglement.

A quantum mechanical model is formulated to describe the coupling between pump intensity noise and laser frequency noise in a solid-state laser. The model allows us to investigate the limiting effects of closed-loop stabilization schemes that utilize this coupling. Two schemes are considered: active control of the quadrature phase noise of the laser and active control of the amplitude noise of the laser. We show that the noise of the laser in the actively stabilized quadrature is ultimately limited by the vacuum noise introduced by the feedback beamsplitter in both schemes. In the case of active control of the quadrature phase noise, the noise is also limited by the intensity noise floor of the detection scheme. We also show that some sources of noise in the passively stabilized quadrature can be suppressed and that it is possible to achieve simultaneous quadrature amplitude and phase stabilization of a solid-state laser. However, the quantum mechanically driven noise in the passively stabilized quadrature cannot be suppressed. While this poses the ultimate limit to the noise in the passively stabilized quadrature, we show that it is experimentally feasible to observe squeezing directly generated by a solid-state laser using this technique. © 2007 The American Physical Society.

We exploit second order (χ(2)) nonlinear optical phase matching for the selection of individual high order transverse modes. The ratio between the generated components can be adjusted continuously via changes in the phase-matching condition.

We report on the generation of more than 5 dB of vacuum squeezed light at the Rubidium D1 line (795 nm) using periodically poled KTiOPO$_{4}$ (PPKTP) in an optical parametric oscillator. We demonstrate squeezing at low sideband frequencies, making this source of non-classical light compatible with bandwidth limited atom optics experiments. When PPKTP is operated as a parametric amplifier, we show a noise reduction of 4 dB stably locked within the 150 kHz-500 kHz frequency range. This matches the bandwidth of Electromagnetically Induced Transparency (EIT) in Rubidium hot vapour cells under the condition of large information delay., 8 pages, 3 figures. Accepted for Journal of Physics B

We demonstrate quantum correlations in the transverse plane of continuous wave light beams by producing -4.0 dB, -2.6 dB and -1.5 dB of squeezing in the TEM00, TEM10 and TEM20 Hermite- Gauss modes with an optical parametric amplifier, respectively. This has potential applications in quantum information networking, enabling parallel quantum information processing. We describe the setup for the generation of squeezing and analyze the effects of various experimental issues such as mode overlap between pump and seed and nonlinear losses., Comment: 7 pages, 4 figures

The traversal of an elliptically polarized optical field through a thermal vapor cell can give rise to a rotation of its polarization axis. This process, known as polarization self-rotation (PSR), has been suggested as a mechanism for producing squeezed light at atomic transition wavelengths. We show results of the characterization of PSR in isotopically enhanced rubidium-87 cells, performed in two independent laboratories. We observed that, contrary to earlier work, the presence of atomic noise in the thermal vapor overwhelms the observation of squeezing. We present a theory that contains atomic noise terms and show that a null result in squeezing is consistent with this theory.

The multimode operation of an optical parametric oscillator (OPO) operating below threshold is calculated. We predict that squeezing can be generated in a comb that is limited only by the phase matching bandwidth of the OPO. Effects of technical noise on the squeezing spectrum are investigated. It is shown that maximal squeezing can be obtained at high frequency even in the presence of seed laser noise and cavity length fluctuations. Furthermore the spectrum obtained by detuning the laser frequency off OPO cavity resonance is calculated.

We demonstrate a scheme based on homodyne detection with a TEM/sub 10/ local oscillator for optimum small displacement measurements beyond the quantum noise limit. It is demonstrated to be directly extendable to optimum tilt measurement.

Multimode operation of an optical parametric oscillator operating below threshold is calculated. We show that maximal squeezing can be obtained at high frequency even in the presence of seed laser noise and cavity length fluctuations.

We report an experimental demonstration of optimal measurements of small displacement and tilt of a Gaussian beam - two conjugate variables - involving a homodyne detection with a TEM10 local oscillator. We verify that the standard split detection is only 64% efficient. We also show a displacement measurement beyond the quantum noise limit, using a squeezed vacuum TEM10 mode within the input beam., 9 pages, 8 figures