we investigate experimentally the phenomenon of intra-envelope four-wave mixing in optical fibers. This phenomenon arises when two lasers, having nearly identical central frequencies, interact by four wave mixing process with each other. As a result, new spectral components are created within the existing spectra. We successfully isolate these components using a third laser through a multi-heterodyne detection process.
We present design and first performance results of an airborne differential absorption lidar laser transmitter that can measure CO2 and water isotopes at different wavelengths around 2 µm with the same setup. This laser will be integrated into an airborne lidar, intended to demonstrate future spaceborne instrument characteristics with high-energy (several tens of millijoules nanosecond-pulses) and high optical frequency-stability (less than a few hundreds of kilohertz long-term drift).
The transmitter consists of a widely tunable OPO with successive OPA that are pumped by a Nd:YAG MOPA and generates the on- and offline wavelength of the addressed species with narrow bandwidth.
We experimentally demonstrate a novel approach to generate a multi-frequency comb light source with a high mutual coherence in an all-fiber system. Starting from EOM combs, we exploit spatial light multiplexing in a 3-core all-normal nonlinear silica fiber at 1550 nm. Each pulse propagates in its own core to experience a nonlinear broadening but within the same fiber. We obtained 3 almost similar output flat-top spectra spanning over 14 nm with 3 nJ per pulse at 250 MHz and a flat phase noise spectrum down to -125 dBc/Hz. The signal-to-noise ratio of interferograms is about 40 dB.
We present our activities on the development of narrow linewidth tunable optical parametric sources and their integration in lidar systems. In particular, we present different implementations of the nested cavity optical parametric oscillator (NesCOPO) that enables tunable single-frequency emission from the SWIR to the LWIR, when pumped by a fixed or a tunable wavelength laser beam. We show how to amplify the output energy and while preserving the spectral linewidth to perform standoff detection of greenhouse gases and toxic chemicals with direct detection lidars.
The Lidar Emitter and Multi-species greenhouse gases Observation iNstrument (LEMON) is a novel Differential Absorption Lidar (DIAL) sensor concept for greenhouse gases and water vapor measurements from space.1,2 It is based on a versatile transmitter allowing for addressing various absorption lines of different molecules. This highly flexible emitter design requires a universal frequency referencing scheme. Here we present a concept employing a 1 GHz frequency comb, which allows the absolute referencing over a spectral range from 0.95 μm to 1.15 μm. By using an intermediate frequency doubling stage, this allows for DIAL measurements on CO2, H2O/HDO, and CH4 in the 2 μm range. Absolute referencing is obtained by using a GPS disciplined oscillator as the common time base for frequency measurements. The concept of the LEMON Frequency Reference UnIT (FRUIT) is designed to match the requirements of the vibration loads associated with airborne operation to allow implementation on the airborne demonstrator for LEMON. In addition, the requirements for a future space development are considered in the design. For example, radiation critical items have been identified and radiation tested within the project and a compact wavemeter design has been implemented.
We report on the current design and preliminary developments of the airborne Lidar Emitter and Multi-species greenhouse gases Observation iNstrument (LEMON), which is aiming at probing H2O and its isotope HDO at 1982 nm, CO2 at 2051 nm, and potentially CH4 at 2290 nm, with the Differential Absorption Lidar method (DIAL). The infrared emitter is based on the combination of two Nested Cavity OPOs (NesCOPOs) with a single optical parametric amplifier (OPA) line for high-energy pulse generation. This configuration is enabled by the use of high-aperture periodically poled KTP crystals (PPKTP), which provide efficient amplification in the spectral range of interest around 2 μm with slight temperature adjustments. The parametric stages are pumped with a Nd:YAG laser providing 200 mJ nanosecond double pulses at 75 Hz. According to parametric conversion simulations supported by current laboratory experiments, output energies in the 40 - 50 mJ range are expected in the extracted signal beam whilst maintaining a good beam quality (M² < 2). The ruler for all the optical frequencies involved in the system is planned to be provided by a GPS referenced frequency comb with large mode spacing (1 GHz) against which the emitter output pulses can be heterodyned. The frequency precision measurement is expected to be better than 200 kHz for the optical frequencies of interest. The presentation will give an overview of the key elements of design and of preliminary experimental characterizations of sub-systems building blocks.
The sensitivity achieved by large ring-laser gyroscopes will make it possible to detect faint relativistic effects related to the rotation of the Earth’s mass. This task requires a strict control of the ring cavity geometry (shape and orientation), which can be performed by a novel network of portable heterodyne interferometers, capable of measuring the absolute distance betweeen two retro-reflectors with a nominal accuracy better than 1nm. First steps have been taken towards the realization of this device and a starting prototype of distance gauge is under development and test.
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