Periodic Reporting for period 1 - CEMoS-OFC (Computationally-enhanced molecular sensing using optical frequency combs)
Reporting period: 2021-12-01 to 2023-11-30
Since its inception, laser absorption spectroscopy has become an indispensable analytical technique for environmental monitoring, security, and medical diagnostics applications, particularly in the gas phase.
Recently, optical frequency combs (OFCs) have attracted considerable attention as a promising source for multi-species air quality monitoring. This is dictated by the European Union’s effort to reduce air pollution, which necessitates continuous monitoring of pollutant concentrations. The new National Emissions Ceilings (NEC) Directive (2016/2284/EU) has set commitments for member states on several important air pollutants such as nitrogen oxides (NOx), sulfur dioxide (SO2), ammonia (NH3), non-methane volatile organic compounds (NMVOCs), and persistent organic pollutants (POPs). Although the first four can be detected using existing electrochemical sensors or marketed tunable laser spectrometers, selective detection of volatile organic compounds often remains elusive for broadband optical instruments, which in turn often suffer from low signal-to-noise ratios.
This niche can be perfectly filled by OFC spectroscopy. Not only does it allow for probing broad features of NMVOCs with high brightness, but also it is well suited for simultaneous multi-species detection.
Using digital signal processing platforms, quasi-real-time coherent averaging of spectroscopic signals has been obtained in an unstabilized dual-comb spectrometer (without any moving parts) for sensing molecular species. This lifts the requirement of user supervision or manual processing of acquired spectroscopic data.
Next, nonlinear interactions in laser oscillators have been studied. They often lead to poor noise performance and corrupt spectroscopic signal. It has been found that incorporation of optical filters into the cavity, while reducing some amounts of intensity and phase noise, leads to the creation of dispersive structures and spectral sidebands. A reasonable filter bandwidth was found to improve lower the timing jitter and intensity noise of a typical 1550 nm oscillator. A numerical model to simulate the effects of intracavity spectral filtering has also been developed.
Another interesting aspect explored during the project are chip-scale OFC sources emitting natively in the mid-infrared region with battery-operation capabilities. Diode laser frequency combs are generally easier to fabricate than more sophisticated cascade-type lasers. The fact that it is possible to employ these devices for unstabilized dual-comb systems in the spectroscopically-relevant 3 micron region makes them attractive for future portable air quality monitoring systems.
Recently, optical frequency combs (OFCs) have attracted considerable attention as a promising source for multi-species air quality monitoring. This is dictated by the European Union’s effort to reduce air pollution, which necessitates continuous monitoring of pollutant concentrations. The new National Emissions Ceilings (NEC) Directive (2016/2284/EU) has set commitments for member states on several important air pollutants such as nitrogen oxides (NOx), sulfur dioxide (SO2), ammonia (NH3), non-methane volatile organic compounds (NMVOCs), and persistent organic pollutants (POPs). Although the first four can be detected using existing electrochemical sensors or marketed tunable laser spectrometers, selective detection of volatile organic compounds often remains elusive for broadband optical instruments, which in turn often suffer from low signal-to-noise ratios.
This niche can be perfectly filled by OFC spectroscopy. Not only does it allow for probing broad features of NMVOCs with high brightness, but also it is well suited for simultaneous multi-species detection.
Using digital signal processing platforms, quasi-real-time coherent averaging of spectroscopic signals has been obtained in an unstabilized dual-comb spectrometer (without any moving parts) for sensing molecular species. This lifts the requirement of user supervision or manual processing of acquired spectroscopic data.
Next, nonlinear interactions in laser oscillators have been studied. They often lead to poor noise performance and corrupt spectroscopic signal. It has been found that incorporation of optical filters into the cavity, while reducing some amounts of intensity and phase noise, leads to the creation of dispersive structures and spectral sidebands. A reasonable filter bandwidth was found to improve lower the timing jitter and intensity noise of a typical 1550 nm oscillator. A numerical model to simulate the effects of intracavity spectral filtering has also been developed.
Another interesting aspect explored during the project are chip-scale OFC sources emitting natively in the mid-infrared region with battery-operation capabilities. Diode laser frequency combs are generally easier to fabricate than more sophisticated cascade-type lasers. The fact that it is possible to employ these devices for unstabilized dual-comb systems in the spectroscopically-relevant 3 micron region makes them attractive for future portable air quality monitoring systems.
The project has resulted in 7 published peer-reviewed publications and one preprint. They are thematically divided into 3 sub-groups.
The first group includes studies on laser oscillators in a single- and dual-comb operation mode. It focuses on the laser source for gas-sensing applications.
In the dual-comb mode, the influence of the dispersion regime (normal vs anomalous) has been investigated for a solid-state laser with polarization multiplexing – two combs are generated from the same laser cavity. Studies performed on the same laser system have revealed a slight decrease in the timing jitter when one of the combs operated in the normal dispersion regime. This indicates future directions for improving the passive stability of dual-comb oscillators. This topical group also covers the effects of incorporating an optical filter into the laser cavity and optical soliton dynamics.
The second group includes quasi-real time correction of spectroscopic signals implemented for a pair of free-running oscillators. While currently the duty cycle is lower than 1%, the update rate of 1.5 seconds already provides sufficient temporal resolution for supervision-free acquisition of broadband spectral data. These results have been published in Optics Express and Applied Physics Letters in collaboration with Japanese researchers from prof. Minoshima’s group.
The third group comprises studies on chip-scale battery-operated frequency combs operating in the 3 micrometer regime for future portable spectrometers.
In addition to peer-reviewed publications, dissemination activities have included 9 presentations at international conferences (Germany, USA, Japan, Canada, Poland), of which have been 3 invited talks, and 3 presentations at local conferences given in Polish. Additionally, the MSCA fellow has delivered 2 presentations at local laser workshops and given 3 invited seminars at universities (Austria, USA, Poland).
To communicate science to broader audiences, the MSCA fellow has given an inaugural lecture for the academic year 2023/2024 at the host institution, which focused on laser frequency comb sources for terrestrial and space applications. A presentation for students of a local district school complex on the search for organic matter associated with life in space has also been provided. Under this category fall two grant writing workshops, where the MSCA fellow has given two presentations on his journey toward an ERC grant that strongly relied on the MSCA Fellowship. The fellow has also given 3 popular science interviews (2 on Youtube and 1 for a radio channel) for the local community.
The first group includes studies on laser oscillators in a single- and dual-comb operation mode. It focuses on the laser source for gas-sensing applications.
In the dual-comb mode, the influence of the dispersion regime (normal vs anomalous) has been investigated for a solid-state laser with polarization multiplexing – two combs are generated from the same laser cavity. Studies performed on the same laser system have revealed a slight decrease in the timing jitter when one of the combs operated in the normal dispersion regime. This indicates future directions for improving the passive stability of dual-comb oscillators. This topical group also covers the effects of incorporating an optical filter into the laser cavity and optical soliton dynamics.
The second group includes quasi-real time correction of spectroscopic signals implemented for a pair of free-running oscillators. While currently the duty cycle is lower than 1%, the update rate of 1.5 seconds already provides sufficient temporal resolution for supervision-free acquisition of broadband spectral data. These results have been published in Optics Express and Applied Physics Letters in collaboration with Japanese researchers from prof. Minoshima’s group.
The third group comprises studies on chip-scale battery-operated frequency combs operating in the 3 micrometer regime for future portable spectrometers.
In addition to peer-reviewed publications, dissemination activities have included 9 presentations at international conferences (Germany, USA, Japan, Canada, Poland), of which have been 3 invited talks, and 3 presentations at local conferences given in Polish. Additionally, the MSCA fellow has delivered 2 presentations at local laser workshops and given 3 invited seminars at universities (Austria, USA, Poland).
To communicate science to broader audiences, the MSCA fellow has given an inaugural lecture for the academic year 2023/2024 at the host institution, which focused on laser frequency comb sources for terrestrial and space applications. A presentation for students of a local district school complex on the search for organic matter associated with life in space has also been provided. Under this category fall two grant writing workshops, where the MSCA fellow has given two presentations on his journey toward an ERC grant that strongly relied on the MSCA Fellowship. The fellow has also given 3 popular science interviews (2 on Youtube and 1 for a radio channel) for the local community.
The project has resulted in a number of advances. First a quasi-real-time computational phase correction system has been implemented, which exploits two unsynchronized laser oscillators to perform gas-phase spectroscopy in the near-infrared region. This is in stark contrast to prior attempts in the field that have relied on user-guided script-based post-correction on acquired data.
Second, frequency transfer of one of the oscillators to longer wavelengths (1800 nm-2100 nm) via soliton self-frequency shift has been shown. The center wavelength can be freely tuned by merely adjusting the amplifier pump power preceding the nonlinear fiber. This is highly beneficial for sensing overtone transitions of hydrocarbons or carbon dioxide (above 2000 nm), as it adds a lot of agility to the system. However, the major achievement is the demonstration of dual-comb interaction between lasers at different wavelengths, i.e. without any spectral overlap. This is enabled by two-photon absorption in a semiconductor laser diode, which unexpectedly can produce a detectable signal even at low levels of optical power (microwatts). While the suitability of this approach for molecular spectroscopy is yet to be evaluated, studies on soliton molecules (multi-pulse aggregates in laser oscillators) using this technique have been performed. This research has been published in the high-profile journal Nature Communications and has proven the fellow’s ability to conduct ground-breaking research at the host institution.
Novel laser platforms for gas sensing have also been investigated, resulting in the first battery-operated dual-comb source for sensing in the mid-infrared region (at 3 micrometers). All these achievements pave the way for practical out-of-laboratory sensing systems to address the need for air pollution monitoring according to EU directives.
Second, frequency transfer of one of the oscillators to longer wavelengths (1800 nm-2100 nm) via soliton self-frequency shift has been shown. The center wavelength can be freely tuned by merely adjusting the amplifier pump power preceding the nonlinear fiber. This is highly beneficial for sensing overtone transitions of hydrocarbons or carbon dioxide (above 2000 nm), as it adds a lot of agility to the system. However, the major achievement is the demonstration of dual-comb interaction between lasers at different wavelengths, i.e. without any spectral overlap. This is enabled by two-photon absorption in a semiconductor laser diode, which unexpectedly can produce a detectable signal even at low levels of optical power (microwatts). While the suitability of this approach for molecular spectroscopy is yet to be evaluated, studies on soliton molecules (multi-pulse aggregates in laser oscillators) using this technique have been performed. This research has been published in the high-profile journal Nature Communications and has proven the fellow’s ability to conduct ground-breaking research at the host institution.
Novel laser platforms for gas sensing have also been investigated, resulting in the first battery-operated dual-comb source for sensing in the mid-infrared region (at 3 micrometers). All these achievements pave the way for practical out-of-laboratory sensing systems to address the need for air pollution monitoring according to EU directives.