Alexandru Popescu

Remote Water Temperature Measurements Based on Brillouin Scattering with a Frequency Doubled Pulsed Yb:doped Fiber Amplifier

Temperature profiles of the ocean are of interest for weather forecasts, climate studies and oceanography in general. Currently, mostly in situ techniques such as fixed buoys or bathythermographs deliver oceanic temperature profiles. A LIDAR method based on Brillouin scattering is an attractive alternative for remote sensing of such water temperature profiles. It makes it possible to deliver cost-effective on-line data covering an extended region of the ocean. The temperature measurement is based on spontaneous Brillouin scattering in water. In this contribution, we present the first water temperature measurements using a Yb:doped pulsed fiber amplifier. The fiber amplifier is a custom designed device which can be operated in a vibrational environment while emitting narrow bandwidth laser pulses. The device shows promising performance and demonstrates the feasibility of this approach. Furthermore, the current status of the receiver is briefly discussed; it is based on an excited state Faraday anomalous dispersion optical filter.

A fiber amplifier and an ESFADOF: Developments for a transceiver in a Brillouin lidar

For the remote sensing of temperature profiles in the ocean, Brillouin scattering can be exploited as a temperature tracer. Such a lidar system is capable of delivering cost-effective on-line data from an extended region of the ocean compared to conventional in situ techniques. The acquired temperature profiles can give valuable input into climate studies and weather forecasts. In this contribution, we present the current status of our experimental setup, consisting of a light source based on a multistage pulsed Yb-doped fiber amplifier and a receiver unit based on an excited-state Faraday anomalous dispersion optical filter.

Towards a Brillouin-LIDAR for remote sensing of the temperature profile in the ocean

For remote sensing of temperature profiles in the ocean Brillouin scattering can be exploited as a temperature tracer. Such a lidar system is capable of delivering cost-effective on-line data from an extended region of the ocean compared to conventional in situ techniques. The acquired temperature profiles can give valuable input to climate studies and weather forecasts. In this contribution we present the current status of our experimental setup, consisting of a light source based on a multistage pulsed Yb:doped fiber amplifier and a receiver unit based on an excited state Faraday anomalous dispersion optical filter. Both components are advancements of laboratory experiments and possess the potential to be operated from an aircraft

Strong transmittance above the light line in mid-infrared two-dimensional photonic crystals

The mid-infrared region of the electromagnetic spectrum between 3 and 8 μm hosts absorption lines of gases relevant for chemical and biological sensing. 2D photonic crystal structures capable of guiding light in this region of the spectrum have been widely studied, and their implementation into miniaturized sensors has been proposed. However, light guiding in conventional 2D photonic crystals is usually restricted to a frequency range below the light line, which is the dispersion relation of light in the media surrounding the structures. These structures rely on total internal reflection for confinement of the light in z-direction normal to the lattice plane. In this work, 2D mid-infrared photonic crystals consisting of microtube arrays that mitigate these limitations have been developed. Due to their high aspect ratios of ∼1:30, they are perceived as semi-infinite in the z-direction. Light transmission experiments in the 5–8 μm range reveal attenuations as low as 0.27 dB/100 μm, surpassing the limitations for light guiding above the light line in conventional 2D photonic crystals. Fair agreement is obtained between these experiments, 2D band structure and transmission simulations.

Combining Photonic Crystal and Optical Monte Carlo Simulations: Implementation, Validation and Application in a Positron Emission Tomography Detector

This paper presents a novel approach towards incorporating photonic crystals (PhCs) into optical Monte Carlo (MC) simulations. This approach affords modeling the full diffractive nature of PhCs including their reflection and transmission behavior as well as the manipulation of the photon trajectories through light scattering. The main purpose of this tool is to study the impact of PhCs on the light yield and timing performance of scintillator-based detectors for positron emission tomography (PET). To this end, the PhCs are translated into look-up tables and implemented into the optical MC algorithm. Our simulations are validated in optical experiments using PhC samples fabricated with electron beam lithography. The experimental results indicate that the simulations match the measurements within the accuracy of the experiments. The application of the combined simulation technique to a PET detector module predicts an increase of the total light yield by up to 23% for PhC coatings versus the reference without PhCs. Timing calculations reveal an improvement of the coincident resolving time by up to 6%. The results underline the potential of PhCs to improve light yield and timing of PET detector modules.

Implementation of photonic crystal simulations into a Monte Carlo code to investigate light extraction from scintillators

Introduction: Nanostructures are used in various forms to increase light extraction from materials with a high refractive index [1,2]. Recently, photonic crystals (PhC) have been proposed to improve the light yield of scintillators used in high energy physics and medical imaging applications [3]. PhCs consisting of a thin slab with a periodically modulated refractive index serve to reduce total internal reflection at the scintillator extraction face. PhC coatings influence the reflection and transmission coefficients of photons impinging on the interface and the photon trajectory. A careful evaluation of the impact of PhCs on the total light yield and the propagation time distribution of extracted photons requires combined simulations in two regimes: i) interaction of electromagnetic waves with PhCs with dimensions similar to the wavelength which requires a full vectorial Maxwell solver and ii) propagation of photons inside the scintillator which is commonly derived from a Monte Carlo (MC) code using laws of geometric optics. This work examines the characteristics of PhCs using Rigorous Coupled Wave Analysis (GD-Calc, KJ Innovation) and ray-tracing (Radiant Zemax) for optical MC simulations.