We experimentally demonstrate a femtosecond mode-locked, all-fiberized laser that operates in the 2 μm region and that incorporates a saturable absorber based on a bulk-structured bismuth telluride (Bi(2)Te(3)) topological insulator (TI). Our fiberized saturable absorber was prepared by depositing a mechanically exfoliated, ~30 μm-thick Bi(2)Te(3) TI layer on a side-polished optical fiber platform. The bulk crystalline structure of the prepared Bi(2)Te(3) layer was confirmed by Raman and X-ray photoelectron spectroscopy measurements. The modulation depth of the prepared saturable absorber was measured to be ~20.6%. Using the saturable absorber, it is shown that stable, ultrafast pulses with a temporal width of ~795 fs could readily be generated at a wavelength of 1935 nm from a thulium/holmium co-doped fiber ring cavity. This experimental demonstration confirms that bulk structured, TI-based saturable absorbers can readily be used as an ultra-fast mode-locker for 2 μm lasers.

A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi 2 Te 3 topological insulator

We demonstrate the use of an all-fiberized, mode-locked 1.94 μm laser with a saturable absorption device based on a tungsten disulfide (WS2)-deposited side-polished fiber. The WS2 particles were prepared via liquid phase exfoliation (LPE) without centrifugation. A series of measurements including Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the prepared particles had thick nanostructures of more than 5 layers. The prepared saturable absorption device used the evanescent field interaction mechanism between the oscillating beam and WS2 particles and its modulation depth was measured to be ~10.9% at a wavelength of 1925 nm. Incorporating the WS2-based saturable absorption device into a thulium-holmium co-doped fiber ring cavity, stable mode-locked pulses with a temporal width of ~1.3 ps at a repetition rate of 34.8 MHz were readily obtained at a wavelength of 1941 nm. The results of this experiment confirm that WS2 can be used as an effective broadband saturable absorption material that is suitable to passively generate pulses at 2 μm wavelengths.

Mode-locked, 1.94-μm, all-fiberized laser using WS₂ based evanescent field interaction.

An in-depth experimental investigation was conducted into the use of a graphene oxide-based saturable absorber implemented on a side-polished fiber platform for femtosecond pulse generation in the 2 μm region. First, it was experimentally shown that an all-fiberized thulium-holmium (Tm-Ho)-codoped fiber ring laser with reduced cavity length can produce stable femtosecond pulses by incorporating a graphene oxide-deposited side-polished fiber. Second, the measurement accuracy issue in obtaining a precise pulse-width value by use of an autocorrelator together with a silica fiber-based 2 μm-band amplifier was investigated. It showed that the higher-order soliton compression effect caused by the combination of anomalous dispersion and Kerr nonlinearity can provide incorrect pulse-width information. Third, an experimental investigation into the precise role of the graphene oxide-deposited side-polished fiber was carried out to determine whether its polarization-dependent loss (PDL) can be a substantial contributor to mode-locking through nonlinear polarization rotation. By comparing its performance with that of a gold-deposited side-polished fiber, the PDL contribution to mode-locking was found to be insignificant, and the dominant mode-locking mechanism was shown to be saturable absorption due to mutual interaction between the evanescent field of the oscillated beam and the deposited graphene oxide particles.

Mode-locked pulse generation from an all-fiberized, Tm-Ho-codoped fiber laser incorporating a graphene oxide-deposited side-polished fiber

By coupling black phosphorus (BP) nanoplatelets (NPs) with a fiber-taper evanescent light field, a saturable absorber (SA) based on the BP NPs has been successfully fabricated and used in a thulium/holmium-doped fiber laser as the mode locker. The SA had a modulation depth of ∼9.8% measured at 1.93 μm. A stable mode-locking operation at 1898 nm was achieved with a pulse width of 1.58 ps and a fundamental mode-lock repetition rate of 19.2 MHz. By increasing the pump intensity, phenomena of multi-pulsing operations, including harmonic mode-locked states and soliton bunches, were obtained in the experiment, showing that the BP NPs possess an ultrafast optical response time. This work suggests that the BP NPs-based SA is potentially useful for ultrashort, pulsed laser operations in the eye-safe region of 2 μm.

Thulium/holmium-doped fiber laser passively mode locked by black phosphorus nanoplatelets-based saturable absorber.

The MEthane Remote sensing Lidar missioN (MERLIN) aims at demonstrating the spaceborne active measurement of atmospheric methane, a potent greenhouse gas, based on an Integrated Path Differential Absorption (IPDA) nadir-viewing LIght Detecting and Ranging (Lidar) instrument. MERLIN is a joint French and German space mission, with a launch currently scheduled for the timeframe 2021/22. The German Space Agency (DLR) is responsible for the payload, while the platform (MYRIADE Evolutions product line) is developed by the French Space Agency (CNES). The main scientific objective of MERLIN is the delivery of weighted atmospheric columns of methane dry-air mole fractions for all latitudes throughout the year with systematic errors small enough (<3.7 ppb) to significantly improve our knowledge of methane sources from global to regional scales, with emphasis on poorly accessible regions in the tropics and at high latitudes. This paper presents the MERLIN objectives, describes the methodology and the main characteristics of the payload and of the platform, and proposes a first assessment of the error budget and its translation into expected uncertainty reduction of methane surface emissions.

https://hal-insu.archives-ouvertes.fr/insu-01664230/document

MERLIN: A French-German Space Lidar Mission Dedicated to Atmospheric Methane

We report airborne measurements of CO2 column abundance conducted during two 2009 campaigns using a 2.05 μm laser absorption spectrometer. The two flight campaigns took place in the California Mojave desert and in Oklahoma. The integrated path differential absorption (IPDA) method is used for the CO2 column mixing ratio retrievals. This instrument and the data analysis methodology provide insight into the capabilities of the IPDA method for both airborne measurements and future global-scale CO2 measurements from low Earth orbit pertinent to the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons mission. The use of a favorable absorption line in the CO22 μm band allows the on-line frequency to be displaced two (surface pressure) half-widths from line center, providing high sensitivity to the lower tropospheric CO2. The measurement repeatability and measurement precision are in good agreement with predicted estimates. We also report comparisons with airborne in situ measurements conducted during the Oklahoma campaign.

Atmospheric CO_2 measurements with a 2 μm airborne laser absorption spectrometer employing coherent detection

This paper discusses the design and current development status of the coherent lidar transceiver being developed by Coherent Technologies Inc for the NASA program, SPARCLE (SPAce Readiness Coherent Lidar Experiment). SPARCLE is intended as a precursor mission to a fully operational satellite system, measuring global wind profiles from the Space Shuttle, with a planned launch date in March 2001.

Design and development of the SPARCLE coherent lidar transceiver

We describe the development of a coherent laser r designed to measure planetary boundary layer COz from an airborne platform to a concentration precision of 1 ppmv, using the technique of Laser Absorption Spectrometry. Coherent Technologies Inc. (CTI) has a 3 year program with NASA-PL to develop and field a coherent transceiver for measurements of atmospheric carbon dioxide using the technique of Laser Absorption Spectrometry (LAS). This measurement technique is based on integrated path differential absorption at two wavelengths, on-line and off- line, using light collected from the ground surface return. The instrument operates at 205 lnm, at which wavelength the column content measurement of CO2 is strongly biased towards concentrations found in the Planetary Boundary Layer (PBL). This feature improves the ability of the instrument to idene large-scale sources and sinks of the carbon cycle, which are most readily identified in the PBL. The LAS instrument will operate from the NASA DC8 Scientific Aircraft, with the capability of measuring CO2 concentrations below the aircraft to a precision goal of lppmv. The transmitted beam is aligned slightly off-nadir to produce a Doppler frequency shift in the ground- scattered light, enabling heterodyne signal detection. A key benefit of coherent detection LAS, compared with Qrect detection, is the reduction in power-aperture product for the instrument, making this approach particularly suited to operation from a space-based platform, where reduction in both power and mass are critical design factors. The purpose of the airborne sensor development and testing is to prepare the technology and science understanding for operation in a space-based mission ( 1,2). preliminary testing of the hardware prior to the flight campaign planned for the end of 2004. 'Ihe LAS transceiver has 3 on-board CW lasers. Figure 1 shows the wavelength selection for these lasers. In this paper, we describe the general design features of the COz LAS instrument and results obtained during

Mark W. Phillips

Papers

Atmospheric CO_2 measurements with a 2 μm airborne laser absorption spectrometer employing coherent detection

Design and development of the SPARCLE coherent lidar transceiver

Development of a Coherent Laser Transceiver for the