Patent Application
20240255421
The invention relates to a method of measuring a spectral response of a sample and a spectroscopic measuring apparatus being configured for measuring a spectral response of a sample. In particular, the invention relates to a method of measuring the spectral response by irradiating the sample with broadband mid-infrared probe light and sensing changes of the probe light spectral content and/or temporal structure, resulting from an interaction of the probe light with the sample. In addition, the invention relates, in particular, to a spectroscopic measuring apparatus including a broadband mid-infrared light source for irradiating the sample with probe light and a detector device for detecting changes of the probe light resulting from an interaction of the probe light with the sample in spectral and/or time domains. Applications of the invention are available in spectroscopy, in particular high dynamic range field-resolved infrared spectroscopy, of a sample, e.g. a biological sample or another sample having an IR response, in particular for analysing a (molecular) composition of a sample and/or changes thereof.
For illustrating background art relating to the invention, reference is made to the following prior art documents:
It is generally known that broadband infrared spectroscopy can distinguish changes in molecular composition of a complex sample by detecting the variation of absorptions in the spectral range from 400 cm−1 to 3300 cm−1 or 3 μm to 25 μm (so-called molecular fingerprint absorptions), making it an ideal metrology for biomedical sensing [1].
It has recently been shown that field-resolved spectroscopy (FRS) based on femtosecond mid-infrared (MIR) laser pulses can achieve higher dynamic range, sensitivity and specificity for molecular detection when compared to current state-of-the-art Fourier transform infrared (FTIR) spectroscopy [2]. In FRS, a few-optical-cycle, broadband MIR pulse excites the sample, and the full electric field including the molecular response in the wake of the pulse is directly captured in a time-domain electro-optic sampling (EOS) measurement. Despite its success and the prospect to reach multi-octave spectral coverage in future, FRS still faces in particular the following limitations:
There is a need to overcome the limitations to better employ the potential of the FRS or other high-dynamic-range/high-sensitivity techniques.
The objective of the invention is to provide an improved apparatus and method for measuring a spectral response of a sample, e. g., for measuring the molecular composition and/or changes in the molecular composition of the sample, which avoids disadvantages of conventional techniques. In particular, the objective of the invention is to provide a method and a measuring apparatus for measuring a spectral response of a sample with an increased sensitivity, improved signal-to-noise-ratio (SNR), enhanced selectivity, improved uniformity of the spectral density across a targeted wavelength range and/or improved capability of covering an extended spectral range, e.g., in the mid-infrared spectral range (MIR).
These objectives are solved by the subject matter of the independent claims. Preferred embodiments and applications of the invention are defined in the dependent claims.
According to a first general aspect of the invention, a spectroscopic measuring apparatus is provided. The spectroscopic measuring apparatus is configured for measuring a spectral response of a sample, e.g., a biological sample or another sample with an IR response. To this end, the spectroscopic measuring apparatus comprises a femtosecond (fs) laser source device (e.g., including a Ho-YAG laser, an Yb:YAG thin-disk laser, a Ti:Sa laser, an Er:fiber laser or a Cr:ZnS laser) being arranged for an irradiation of the sample with a sequence of probe light pulses having a primary spectrum. Preferably, the primary spectrum—i.e., the spectral composition of the probe light pulses—is a continuous or quasi-continuous spectrum in the mid-infrared range. For example, the primary spectrum may cover the wavelength range from 5 μm to 15 μm. Further, the spectroscopic measuring apparatus comprises a detector device (e.g., an FTIR-spectrometer; preferably field-resolved detection with EOS) being arranged for a spectrally and/or temporally resolved detection of response light pulses having an altered spectrum and/or temporal structure and resulting from an interaction of the probe light pulses with the sample. Each of the response light pulses results from one of the probe light pulses interacting with the sample. In other words, the detector device may be arranged to measure the spectral composition and/or temporal profile of the modified probe light pulses (i. e., the response light pulses), whose spectra and/or temporal structures may differ from that of the initial probe light pulses due to light-matter interactions (e.g., excitation of vibrational and/or rotational molecular states of the sample) and may be used, for example, for analysing the molecular composition of the sample.
In addition, according to the invention, the claimed spectroscopic measuring apparatus further includes a pulse modification device comprising at least one quantum cascade laser (QCL). This type of laser is basically known in the prior art and refers to a (inter-subband) semiconductor laser emitting around a centre wavelength ranging in the mid-infrared (e.g., from 3 μm to above 24 μm) with, e. g., up to several Watts of output power. Advantageously, the emission properties of QCLs can be designed by creating specific quantum well structures with semiconductor-multilayer sequences, providing a plethora of powerful and customizable on-chip lasers [6, 7].
According to the invention, the pulse modification device is configured to modify the probe light pulses and/or the response light pulses by amplifying one or more spectral components of the probe light pulses and/or the response light pulses with the at least one quantum cascade laser. In other words, the pulse modification device may be configured to modify the probe light pulses before reaching, in particular interacting with, the sample, and/or to modify the response light pulses before entering the detector device. As described in detail below, the use of the QCL technology within the claimed spectroscopic measuring apparatus advantageously allows for boosting the power of the probe light pulses from the usual tens-of-milli-Watt regime (see, e.g., [2]) to a multi-Watt level, increasing the molecular response and leading to a higher detected signal/noise and hence higher sensitivity. A further advantage of the claimed pulse modification device is that it may allow for shaping the primary spectrum (e.g., by selectively enhancing specific spectral regions, for example with typical absorption bands), such that each probe light pulse optimally excites the sample. Alternatively, or in addition, the pulse modification device may also be used for time-gated amplification of the probe light pulses and/or the response light pulses, in particular to selectively enhance the molecular response in the wake (tail) of the main (excitation) pulse, thus strongly reducing the demands on the dynamic range of the detector.
The inventors have found, that a QCL, compared with other available amplification techniques, provides in particular the following further advantages, which can be employed in the spectroscopic measurement. The energy conversion in QCLs is very efficient since it allows the re-use of each electron to generate multiple photons. The direct conversion of electric energy into photons and their small size give QCLs also advantages in reaching lower amplification noise compared to, e. g., optical parametric amplifiers (OPAs). In addition, the energy conversion efficiency in the MIR OPA is limited by its low quantum efficiency, defined by the photon energy ratio between MIR output and NIR pump laser. It thus requires high power pump lasers in order to achieve similar output as QCLs. Besides, the OPA requires multiple optical elements and usually takes up much more space than a QCL that implements amplification on a chip.
In the present context, the term “probe light pulse” may generally refer to a light pulse in the optical path between the fs laser source device and the sample, though it may eventually be a “modified probe light pulse” when interacting with the sample. Similarly, the term “response light pulse” may generally refer to a light pulse in the optical path between the sample and the detector device, though it may eventually be a “modified response light pulse” when entering the detector device.
For creating the sequence of probe laser pulses, the fs laser source device preferably is a pulsed fs laser source device which may be configured to generate periodic pulse trains, preferably with a repetition rate in a range from e. g. 100 kHz to 10 MHz or more, e. g., to several hundreds of MHz. Furthermore, it is clear to those skilled in the art that, though the invention is primarily described in the context of sequences of probe/response light pulses, its teaching can also be applied in the context of employing a few or a single probe light pulse(s).
The basic advantage of the invention results from employing one or more quantum cascade lasers for selectively amplifying spectral components of the probe light before reaching the sample and/or for selectively amplifying spectral components of the response light, resulting from the interaction of the probe light with the sample, before reaching the detector. By this, for example, the power of the probe light can be boosted from the usual tens-of-milli-Watt regime (see e.g. [2]) to a multi-Watt level, increasing the molecular response and leading to a higher detected signal/noise and hence higher sensitivity. Additionally, or alternatively, the quantum cascade laser(s) can also be used for modifying the response light, e.g. by selectively enhancing only the molecular response after the main pulse, which results in signal levels of the molecular response similar to the excitation pulse, thus strongly reducing the demands on the dynamic range of the detector.
According to a preferred embodiment of the invention, the at least one quantum cascade laser may comprise an array of multiple (i. e., at least two, e.g., five or up to ten or even more) quantum cascade lasers with different centre wavelengths. In this context, the term “centre wavelength” may be considered as the respective wavelength corresponding to the centre of mass of the spectrum in frequency domain of the QCL. Preferably, the centre wavelengths of the QCLs of the array are evenly distributed in the mid-infrared regime. Since the spectral bandwidth of a single QCL is usually limited to around 5% of the centre wavelength the inventive use of multiple quantum cascade lasers advantageously allows to possibly cover the full spectrum of an ultra-broadband (e.g., a super-octave) mid-infrared pulse.
As a result, the pulse modification device may be used for a section-wise spectral amplification, which advantageously allows for a controlled tailoring of the pulse spectrum (e.g. flattening the spectrum, enhancing the spectral wings, and/or to increase the power spectral density at frequencies of expected molecular resonances).
According to another preferred embodiment of the invention, the multiple quantum cascade lasers of the array may be arranged in a parallel configuration. Like in the context of parallel electrical circuits, the term “parallel” refers to a configuration, where the QCLs are arranged in different optical branches extending between two common nodes in the optical path. Advantageously, this enables simultaneously amplifying different spectral regimes, thus providing a fast and low-loss solution for modifying mid-infrared light pulses.
In addition, or alternatively, the pulse modification device may comprise a splitter device configured to spatially separate a laser beam input into several sub-beams with different spectral intervals. Furthermore, the pulse modification device may comprise a relaying device configured to direct each of the sub-beams to one of the multiple quantum cascade lasers respectively. In other words, the relaying device—which may also be referred to as a guiding or deflecting device in this context—may be configured to guide each of the sub-beams generated by the splitter device to a respective QCL. Preferably, the assignment of the sub-beams to the respective QCLs is based on the spectral interval of the sub-beams, i.e., the middle of each spectral interval may correspond to a centre wavelength of a QLC. Furthermore, the pulse modification device may comprise a combiner device configured to collimate an amplified output of each of the multiple quantum cascade lasers into a single laser beam output. By this, advantageously, a simultaneous amplification of different spectral regimes is enabled, wherein the usually compact chip design of QCLs facilitates a very space-saving implementation of the pulse modification device.
According to an alternative or additional aspect of the invention, the multiple quantum cascade lasers may be arranged in a sequential configuration (or: serial configuration). Like in the context of serial electrical circuits, also here the term “sequential” may refer to a configuration, where the multiple QCLs are connected “in a line” within a single optical path. Alternatively, or in addition, the pulse modification device may also comprise a relaying device configured to direct a laser beam input in a consecutive order to each of the multiple quantum cascade lasers. Advantageously, this allows for a successive amplification or modification of different spectral regimes.
The parallel and sequential configurations can be combined. Thus, according to another aspect of the invention, the pulse modification device may comprise a first QCL-subset and a second QCL-subset, wherein the first QCL-subset of the multiple quantum cascade lasers is arranged in a parallel configuration and the second QCL-subset of the multiple quantum cascade lasers is arranged in a sequential configuration. In other words, some QCLs of the pulse modification device may be arranged in parallel, e.g., for amplifying the respective spectral regimes simultaneously, while some QCLs of the pulse modification device may be arranged sequentially, e.g., for amplifying the respective spectral regimes consecutively. Each of the first and second subset may include different QCLs, or the first and second subset may share at least one QCL. Thereby, the pulse modification device may also comprise the respective devices (splitter device, relaying device, combiner device) mentioned before in the context of the exclusively parallel or sequential configurations.
According to another aspect of the invention, at least one quantum cascade laser has an output power of at least 1 Watt and/or a centre wavelength in the range between 3 μm and 24 μm. If the pulse modification device comprises an array of multiple QCLs, preferably, all QCLs have an output power of at least 1 Watt and/or a centre wavelength in the range between 3 μm and 24 μm, respectively. Advantageously, this allows for boosting the power of the light pulses from the usual tens-of-milli-Watt regime (see e.g. [2]) to a multi-Watt level. The increased power may result in a correspondingly stronger molecular response, leading to a higher detected signal/noise and hence higher sensitivity in the measurement.
In order to advantageously enhance specific regions of a light pulse in the time domain, according to another aspect of the invention, the pulse modification device may be configured to shape a temporal profile of the probe light pulses and/or the response light pulses by time-gated amplifying one or more spectral components of the probe light pulses and/or the response light pulses. In this context, the term “time-gated” refers to a temporal enhancement of the probe and/or response light pulse based on a controlled on/off-switching of the QCL(s) for a predetermined time interval. For this, e.g., a time gate provided by a radio frequency (RF) setup may be used. In an exemplary embodiment, RF pulses may be generated by illuminating a fast photodiode with a fraction of a driving pulse of the fs laser source device used to generate the (mid-infrared) probe light pulses. The power of the—optionally delayed—RF pulse may then be increased by an amplifier so that the QCL(s) can operate above threshold, driven by the RF pulse, wherein the on-switching of the QCL(s) will be synchronized with the probe light pulse.
This time-gated setup advantageously enables for example to amplify a temporal section of the response light pulse (preferably the part following the main excitation), in which the sample response is encoded. In the context of the “temporal section amplification”, it should be noted that the response light pulse in a typical FRS measurement usually contains a main pulse, which mainly corresponds to the probe light pulse, and the molecular response in the wake (tail) of the main pulse. Therefore, the onset of the RF pulse is advantageously timed such that amplification starts after the main pulse. By fast switching on and off the RF pulse, the molecular response at the pulse tail may be selectively amplified. Since the time-gated amplification acts on each pulse waveform individually, this implementation is also suited both for multi-shot acquisition, and for a detection scheme that measures the full EOS trace with a single laser shot.
Alternatively, the time-gated setup also advantageously enables a delay-dependent amplification, wherein the time-gated QCL(s) amplification acts on the full pulse waveform, either before or after sample interaction. Thereby, the on/off switching of amplification may be synchronized with the delay in a multi-pulse scanning experiment, like conventional EOS detection. In this context, the spectroscopic measuring apparatus may comprise a delay device (e.g., a mechanical delay stage) configured to delay the driving pulse temporally driving the time gate relative to the probe light pulse.
According to another embodiment of the invention, the spectroscopic measuring apparatus may further comprise a control device. The control device may be configured to control the pulse modification device to generate a predefined, i.e., a previously determined, spectral and/or temporal profile of the at least one of the probe light pulses and the response light pulses. In other words, the control device may be configured to cause the pulse modification device to modify the spectral and/or temporal shape of the probe light pulse and/or the response light pulse in a defined way. Advantageously, this facilitates for example to shape the probe light pulse spectrally and/or temporally such that it optimally excites the sample, e.g. by increasing the power spectral density at frequencies of expected molecular resonances.
According to another advantageous aspect of the invention the fs laser source device may be adapted for generating the probe light pulses with at least one of the following features: The probe light pulses may comprise ultra-broadband mid-infrared pulses. The probe light pulses may have a pulse duration below 100 fs, in particular below 50 fs. The probe light pulses may have an average power above 10 mW, in particular above 100 mW. The primary spectrum of the probe light pulse may cover at least one frequency octave, in particular at least two frequency octaves. The primary spectrum of the probe light pulse may cover a wavelength range from 5 μm to 15 μm, in particular from 3 μm to 30 μm. The primary spectrum of the probe light pulse may be a continuous or quasi-continuous spectrum.
According to a second general aspect of the invention, a method of measuring a spectral response of a sample (e.g., a biological sample) is provided. To this end, the method comprises the step of irradiating the sample with a sequence of probe light pulses generated by a fs laser source device (e.g., including an Yb-YAG laser), wherein the probe light pulses have a primary spectrum. Preferably, the primary spectrum is a continuous or quasi-continuous spectrum in the mid-infrared regime, e.g., covering the wavelength range from 5 μm to 15 μm. Further, the method comprises the step of spectrally resolved detecting a response light pulse by a detector device (e.g., a detector device configured for electro-optic sampling), wherein the response light pulse has an altered spectrum resulting from an interaction of the probe light pulses with the sample. In addition, the method includes the step of modifying the probe light pulses and/or the response light pulses with a pulse modification device. Thereby, the pulse modification device comprises at least one quantum cascade laser, wherein one or more spectral components of the probe light pulses and/or the response light pulses are amplified with the at least one quantum cascade laser. By this, advantageously, the power of the probe light may be boosted from the usual tens-of-milli-Watt regime (see, e.g., [2]) to a multi-Watt level, increasing the molecular response and leading to a higher detected signal/noise and hence higher sensitivity.
Preferably, the method of the second general aspect of the invention or embodiments thereof is executed by the spectroscopic measuring apparatus of the first general aspect of the invention or embodiments thereof.
According to a preferred embodiment of the invention, the probe light pulses are modified before reaching the sample. Alternatively, or in addition the response light pulses are modified before reaching and/or entering the detector device. Advantageously, this allows for a controlled shaping of the probe light pulses, as well as the response light pulses in dependence of the particular requirements in the different parts of the measurement.
According to another aspect of the invention the at least one quantum cascade laser may comprise an array of multiple quantum cascade lasers with different centre wavelengths. For example, the array of multiple QCLs may comprise 2 to 10 or more QCLs. Preferably, the centre wavelengths of the respective QCLs (i.e., the wavelength of each QCL's bandwidth that might be considered its “middle”) are evenly distributed in the mid-infrared regime. Advantageously, the pulse modification device enables such a section-wise spectral amplification, which allows for a controlled tailoring of the pulse spectrum (e.g., flattening the spectrum, enhancing the spectral wings, and/or increasing the power spectral density at frequencies of expected molecular resonances).
According to another aspect of the invention the multiple quantum cascade lasers may be arranged in a parallel configuration. Advantageously, this enables simultaneous amplification of different spectral regimes, thus providing a fast and low-loss solution for modifying a mid-infrared light pulse. Alternatively, or in addition, the step of modifying may include the following steps: splitting the probe light pulses and/or the response light pulses by a splitter device into several sub-beams with different spectral intervals; directing each of the sub-beams to one of the several quantum cascade lasers respectively by a relaying device; and collimating an amplified output of each of the multiple quantum cascade lasers into a single laser beam output by a combiner device.
According to another aspect of the invention the multiple quantum cascade lasers may be arranged in a sequential configuration. Alternatively, or in addition, the step of modifying may include the step of directing the probe light pulses and/or the response light pulses in a consecutive order to each of the several quantum cascade lasers by a relaying device. Advantageously, this allows for a successive amplification or modification of different spectral regimes.
According to another aspect of the invention the pulse modification device may comprise a first QCL-subset and a second QCL-subset, wherein the first QCL-subset of the multiple QCLs is arranged in a parallel configuration and the second QCL-subset of the multiple QCLs is arranged in a sequential configuration. In other words, some QCLs of the pulse modification device may be arranged in parallel, e.g. for amplifying the respective spectral regimes simultaneously, while other QCLs of the pulse modification device may be arranged sequential, e.g. for amplifying the respective spectral regimes consecutively. Thereby, the pulse modification device may also comprise the respective devices (splitter device, relaying device, combiner device) mentioned before in the context of the only parallel or sequential configurations.
According to another aspect of the invention the at least one quantum cascade laser may have an output power of at least 1 Watt and/or a centre wavelength in the range between 3 μm and 24 μm. If the pulse modification device comprises an array of multiple QCLs, preferably, all QCLs have an output power of at least 1 Watt and/or a centre wavelength in the range between 3 μm and 24 μm respectively.
According to another aspect of the invention the method may further comprise the step of determining at least one spectral region of interest (e.g., a frequency of an expected molecular resonance of the sample). Preferably, the spectral region of interest may cover a spectral range, in which a characteristic vibrational and/or rotational transition in the sample may be excited. Further, the step of modifying may include increasing a power spectral density in the spectral region of interest. Advantageously, this allows selectively probing molecular fingerprints of expected constituents of the sample.
According to another aspect of the invention the step of modifying may include time-gated amplification of one or more spectral components of the response light pulses for shaping the temporal profile of the response light pulses. As discussed in detail before, this technique advantageously enables to temporally enhance specific regions of the probe light pulses and/or the response light pulses in the time domain by a controlled on/off-switching of the QCL(s). To this end, a time gate provided by a radio frequency (RF) setup may be used, wherein RF pulses (generated by illuminating a fast photodiode with a fraction of a driving pulse of the fs laser source device) are used to trigger the temporal operation of the QCL(s). By this, advantageously a section of each of the temporally extended response light pulse, preferably the molecular response after the main (excitation) pulse, can be selectively enhanced, resulting in signal levels of the molecular response similar to the excitation pulse, thus strongly reducing the demands on the dynamic range of the detector.
According to another aspect of the invention the method may comprise the step of defining a target spectral profile and/or a target temporal profile of the probe light pulses and/or the response light pulses. For example, the target spectral profile may be a spectral profile of a light pulse, where specific spectral regions (e.g., absorption bands, expected molecular resonances, etc.) are enhanced. Further, a target temporal profile may be, for example, a temporal profile of a light pulse, where a specific region of a light pulse in the time domain (e.g. the tail of a pulse) is enhanced. Thereby, the term “target” should be understood such that the respective profile is a profile intended to achieve. In addition, the method may comprise the step of controlling the pulse modification device by a control device based on the defined target spectral and/or temporal profile. In other words, the pulse modification device may be controlled such that it modifies the spectral and/or temporal shape of the probe and/or the response light pulse in order to correspond with the target spectral and/or temporal profile as best as possible. Advantageously, this allows for a controlled shaping of the spectral and/or temporal profile of the light pulses depending on the particular measurement requirements.
According to another aspect of the inventive apparatus or method, the sample may be a biological sample (e.g., a sample from a human or animal organism, a medical sample). In particular, the sample may be, for example, at least one biological cell or part thereof, a cell group or cell culture, or tissue of an organism, a liquid, like, e.g., blood or other body liquids, optionally diluted, an aerosol, like e.g. breath including traces of liquid droplets, a gas and a vapour, e.g., emanating from a biological organism. Preferably, the sample may be a biological sample for diagnostic purposes. In this context, it should, however, be emphasized that the invention is not restricted to the investigation of biological samples, but rather can be implemented with other samples, like, e.g., substance samples from technical processes or environmental samples, that have a light-matter interaction with the probe light pulses.
Further, all features disclosed in this document in connection with the spectroscopic measurement apparatus are also intended to be disclosed and claimable in connection with the method, and vice versa.
Further advantages and details of the invention are described in the following with reference to the attached drawings, which schematically show in:
Features of preferred embodiments of the invention are described in the following with particular reference to the provision of at least one QCL in a spectroscopic measuring setup. Details of QCLs, in particular the configuration and operation thereof, are not described as far as they are known per se from available QCL techniques.
Details of a spectroscopic measuring setup, which are known per se from prior art, like details of FRS, are not described. In the drawings, identical or functionally equivalent elements are labelled with the same reference signs.
Furthermore, the spectroscopic measuring apparatus 100 comprises a detector device 20 being arranged for a spectrally resolved detection of a response light pulse 2′ having an altered spectrum resulting from an interaction of the probe light pulse 2 with the sample 1. For this purpose, the detector device 20 may be a (standard) FTIR-spectrometer. However, preferably more sophisticated detector setups are used. As exemplarily shown in
For example, as illustrated in
For electro-optically sampling the waveform of the response light pulse 2′ in the detector device 20, the response light pulse 2′ and a driving pulse—which will be referred to in the following as a sampling pulse—may be spatially recombined and directed into an electro-optic crystal 21 of the detector device 20. The electro-optic crystal 21 can be an optically non-linear crystal, e.g., GaSe, having a χ2 non-linearity. Thereby, the polarization state of the sampling pulse passing the electro-optic crystal 21 is changed by the electric field of the response light pulses 2′. The sampling pulse with the modified polarization state may pass a half- or quarterwave plate 22 and a Wollaston prism 23 separating sub-pulses and with two orthogonally polarized polarization components of the sampling pulse. These two sub-pulses and carrying the different polarization components are sensed with detector elements 24 and 24′, comprising, e.g., photodiodes. Preferably, the detector elements 24 and 24′ are balanced, i.e. calibrated such that a difference between the detector signals of the detector elements 24 and 24′ is proportional to the electric field of the response light pulse 2′. By iterative measurements, wherein the delay between the two pulses is varied via a delay drive unit (not shown) such that the (short) sampling pulse coincides with different parts of the (longer) response light pulse 2′, the full temporal shape of the response light pulse 2′ can be recovered. Fourier transforming the temporal shape, i.e. Fourier transforming the detector signal difference, lastly yields the spectral response of the sample 1.
In addition to the above-mentioned components known per se in field of FRS, the claimed spectroscopic measuring apparatus 100 further includes a pulse modification device 30 comprising at least one quantum cascade laser. In the illustrated embodiment, the pulse modification device 30 is configured to modify the probe light pulses 2 before reaching the sample 1 by amplifying one or more spectral components of each of the probe light pulses 2 with the at least one quantum cascade laser. To this end, the modification device 30 is arranged in the beam path between the fs laser source device 10 and the sample 1. Preferably, the modification device 30, thereby, comprises an array, i.e. an arrangement, of multiple (e.g., ten) quantum cascade lasers 31 . . . 3N with different centre wavelengths λ1 . . . λN, as described in more in the context of
In addition to increasing the power of the probe light pulses 2, which may advantageously result in a stronger molecular response, a higher detected signal/noise ratio, and thus a higher sensitivity, the pre-sample amplification also allows for shaping the (primary) spectrum (e.g. by selectively enhancing of specific spectral regions) such that the probe light pulses 2 optimally excite the sample 1.
In this context, the spectroscopic measuring apparatus 100 may also comprise a control device 40 being configured to control the pulse modification device 30 to generate a predefined spectral and/or temporal profile of the probe light pulse 2. For example, the control device 40 may be configured to activate a particular QCL subset of the array of multiple quantum cascade lasers 31 . . . 3N each for a predetermined time.
Advantageously, the embodiments of
Alternatively or in addition to the afore-mentioned modification in the frequency (wavelength) domain, the respective mid-infrared light pulse can be also varied in the time domain. For this, the output power of the QCLs 31 . . . 3N is individually varied over time, e.g. turned on/off for a predetermined period of time respectively.
While
In total, the parallel configuration with the different optical sub-paths advantageously enables to simultaneously amplify different spectral regimes, thus providing a fast and low-loss solution for modifying a mid-infrared light pulse.
The time-gated amplification provided with the embodiments of
The amplification of a section of the MIR waveform is illustrated in
With more details, the time-gated amplification may be implemented with the control device 40 (see e. g.
The amplification dynamics for this preferred embodiment of amplifying a response light pulse is shown in an exemplary manner in
The delay-dependent MIR amplification in a multi-pulse scanning experiment is illustrated in
With more details, the delay-dependent MIR amplification acts on the full MIR waveform either of the probe light pulses before sample interaction or the response light pulses after sample interaction, with the on/off switching of amplification synchronized with the delay in a multi-pulse scanning experiment, like conventional EOS detection. In the case of EOS the measurement is performed by scanning the delay between the MIR waveform of the probe light pulse and the gate pulse and acquiring the EOS signal at each delay, generating the EOS waveform, that represents with constant amplification the MIR waveform, convolved with the instrumental response.
As shown in
By switching on QCL amplification only at delays after the main pulse, it selectively enhances the signal measured for the molecular response in the wake of the pulse. In this multi-pulse application, the QCLs amplify the full MIR waveform (
In the other embodiment (
The features of the invention disclosed in the above description, the drawing and the claims can be of significance both individually as well as in combination or subcombination for the realisation of the invention in its various embodiments.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/HU2021/050030 | 5/27/2021 | WO |
