Multipass Optical Cavities Research Articles

Ambient Hydrocarbon Detection with an Ultra-Low-Loss Cavity Raman Analyzer.

The detection of ambient outdoor trace hydrocarbons was investigated with a multipass Raman analyzer. It relies on a multimode blue laser diode receiving optical feedback from a retroreflecting multipass optical cavity, effectively creating an external cavity diode laser within which spontaneous Raman scattering enhancement occurs. When implemented with ultra-low-loss mirrors, a more than 20-fold increase in signal-to-background ratio was obtained, enabling proximity detection of trace motor vehicle exhaust gases such as H2, CO, NO, CH4, C2H2, C2H4, and C2H6. In a 10-min-long measurement at double atmospheric pressure, the limits of detection obtained were near or below 100 ppb for most analytes.

Toward the measurement of the hyperfine structure of muonic hydrogen in the FAMU experiment: Multi-pass cavity optimization for experiments with pulsed sources.

We consider a simplified model of the optical multi-pass cavity that is being currently developed by the FAMU collaboration for the measurement of the hyperfine splitting in the ground state of muonic hydrogen and of the Zemach radius of the proton. The model is focused on the time distribution of the events of laser-stimulated hyperfine transitions in the muonuc atom and may be helpful in the preliminary design of the FAMU experimental set-up and, more generally, in the optimization of multi-pass optical cavities for experiments with pulsed lasers.

Potassium tune-out-wavelength measurement using atom interferometry and a multipass optical cavity

The longest tune-out wavelength for potassium atoms, ${\ensuremath{\lambda}}_{\mathrm{zero}}=768.9701(4)$ nm, was measured using an atom interferometer with a large irradiance gradient supported in a multipass optical cavity. Systematic errors in ${\ensuremath{\lambda}}_{\mathrm{zero}}$ measurements that arise from laser light, Doppler shifts, and the Earth's rotation are described. The ratio of oscillator strengths for the potassium $D2$ and $D1$ lines inferred from this ${\ensuremath{\lambda}}_{\mathrm{zero}}$ measurement is $\ensuremath{\rho}={f}_{D2}/{f}_{D1}=2.0066(11)$, and the ratio of line strengths is $R={S}_{D2}/{S}_{D1}=1.9977(11)$.

Modeling Herriott cells using the linear canonical transform.

We demonstrate a new way to analyze stable, multipass optical cavities (Herriott cells), using the linear canonical transform formalism, showing that re-entrant designs reproduce an arbitrary input field at the output, resulting in useful symmetries. We use this analysis to predict the stability of cavities used in interferometric delay lines for temporal pulse addition.

Demonstration of improvement in the signal-to-noise ratio of Thomson scattering signal obtained by using a multi-pass optical cavity on the Tokyo Spherical Tokamak-2.

The multi-pass Thomson scattering (TS) scheme enables obtaining many photons by accumulating multiple TS signals. The signal-to-noise ratio (SNR) depends on the accumulation number. In this study, we performed multi-pass TS measurements for ohmically heated plasmas, and the relationship between SNR and the accumulation number was investigated. As a result, improvement of SNR in this experiment indicated similar tendency to that calculated for the background noise dominant situation.

Numerical prediction of optical lattice-induced gas heating within multipass optical cavities

Direct simulation Monte Carlo was used to investigate the potential of non-resonant optical lattice gas heating in the context of two proposed multipass optical cavity designs. One-dimensional lattices were formed by two 5 ns, 100 mJ, 532 nm simulated laser pulses in the presence of molecular nitrogen. Simulations suggest that these cavity designs are able to facilitate a several fold increases in deposited energy as a result of optical lattice gas heating, with the more efficient of these designs leading to a 14-fold increased temperature change (ΔT ≈ 350 K) for the first ten passes over the single-pass case (ΔT ≈ 25 K).

Laser mode selection in reflective multipass optical cavity

The performance of a simple resonator that couples a reflective multipass interferometer cavity and a Fabry-Perot etalon to obtain high efficiency tunable single-longitudinal mode (SLM) oscillation in a TEA CO2 laser is reported. A numerical model of the resonator was explained to predict the mode behavior of the laser as well as to optimize the resonator to achieve SLM operation, and the predicted mode characters are experimentally verified.

Multipass optical cavity for inverse Compton interactions

The recycling of laser beams in the focal region of non-resonant multipass optical cavities has been investigated as a means of providing a high intensity of photons for weak interaction experiments. Ray-tracing simulations and measurements with an Ar-ion laser have been carried out to examine the intensity profiles of the laser field in different 2-mirror geometries. In particular, the use of such cavities in the generation of X-rays by inverse Compton scattering is considered. X-ray yields are calculated for electron beams of 0.05, 0.1, 0.2 and 0.5 mm diameter yielding enhancement factors of 10–200 compared to a free space laser interaction.

Multipass/multipulse Thomson scattering on CDX-U (abstract)

A multipass/multipulse Thomson scattering system has been implemented on CDX-U in collaboration with the Ioffe Institute, St. Petersburg. The system consists of a low energy (1.5– 2.5 J), passively Q-switched ruby laser, and a multipass optical cavity enclosing the plasma. Multiple reflections of the beam within the cavity increase by about an order of magnitude the number of scattered photons, allowing temperature density to be measured with good accuracy even at very low plasma density. By feeding the returned beam back into the laser, the system can deliver several pulses over a 1 ms period. However, the experiments on CDX-U show that a mechanical shock wave reaching the multipass system affects the feedback and laser output per pulse drops significantly. Therefore we operate the system by fine tuning the laser cavity, so that output is practically independent of feedback from multipass cavity. Also, by optimizing the transmission of the passive Q-switch and the pumping power, we obtain that laser output is concentrated in single large pulse of 2–2.5 J energy. We achieve circulating energy in the plasma in excess of 12 J per pulse, while minimizing at the same time stray light. As shown by results from CDX-U, this enables in some cases better than 10% accuracy, despite relatively low plasma density conditions.

Compact high efficiency free-electron lasers using multipass optical cavities

Abstract Compact and very effecient free-electron lasers may be realized by using novel, multipass optical cavities. These cavities may also be used externally to form very compact photon storage devices. We describe the essential characteristics of such cavities and establish critical design requirements for high efficiency FEL operation.

Laser Raman sensor for measurement of trace-hydrogen gas

A new optical hydrogen sensor based on spontaneous Raman scattering of laser light has been designed and constructed for rugged field use. It provides good sensitivity (better than 100 parts in 10(6)), rapid response (several seconds), and the inherent Raman characteristics of linearity and background gas independence of the signal. Efficient light collection and discrimination by using fast optics and a bandpass interference filter compensate for the inefficiency of the Raman-scattering process. A multipass optical cavity with a Herriott-type configuration provides intense illumination from an air-cooled cw gas laser. The observed performance is in good agreement with the theoretical signal and noise level predictions.

Measurement of the magnetic birefringence of neon gas

We constructed a sensitive ellipsometer to study extremely small ellipticities that are acquired by laser light when it traverses a multipass optical cavity in a 9-m-long superconducting magnet. This setup was used to measure the Cotton–Mouton constant (CCM) of neon at 514.5 nm. We find for 760 Torr (1 atm) and 25°C that CCM(Ne) = (5.5 ± 0.3) × 10−20 G−2 cm−1.