649results about "Interferometric spectrometry" patented technology

The invention discloses a high-precision three-degree-of-freedom attitude adjustment platform for a spectrometer, which is based on a simplified design of a Stewart platform and comprises a movable platform, a static platform and a three-degree-of-freedom driving mechanism connected between the movable platform and the static platform. The driving mechanism is composed of three sets of servo electric cylinders, telescopic rods and servo motors and is driven by a ball screw, and posture adjustment of the platform is achieved. According to the platform, a laser interferometer is adopted as a high-precision sensor, a closed-loop feedback control system is combined, and submicron displacement measurement and attitude control are achieved. The platform can achieve translation in the Z-axis direction and rotation around the X axis and the Y axis, the rotation angle can reach + / -15 degrees, and the precision can reach 0.02 mm. According to the invention, the device ensures high precision and stability in a complex working environment, has the characteristics of stable movement, quick response, easy maintenance and the like, and is suitable for the fields of optical experiments, spectral analysis and attitude adjustment and error compensation of precise instruments.

The invention relates to the field of spectral imaging, in particular to a double-step Fabry-Perot interference snapshot imaging spectrometer, which comprises a telescopic system, a micro lens array, a Fabry-Perot array interference system and an area array detector, and is characterized in that the telescopic system is used for collecting a target light field and carrying out view field limitation and collimation on the target light field; the Fabry-Perot array interference system is used for modulating a target light field into an interference light field array, the Fabry-Perot array interference system comprises two step lenses which are orthogonal in the step direction, the highest steps of the two step lenses are tightly attached, and an air gap with the thickness changing in a checkerboard-shaped two-dimensional increasing mode is formed between the two step lenses; the microlens array is used for imaging the interference light field array onto the area array detector through each imaging channel; and the area array detector is used for receiving the transmission image field of the microlens array to obtain an interference image array. The invention has the advantages of small volume, light weight, compact structure, static state, stability, reliability and the like.

A platform for characterizing biomolecules, biological tissue sections, viruses, or other particles of interest in a non-invasive, high-throughput, cost-effective, and label-free manner. The platform includes a merged set of imaging modalities including and capable of interferometric microscopy and wide-field or confocal microscopy (such as, for example, a wide-field super-resolution surface enhanced Raman spectroscopy, SERS), although some aspects may be employed with data sets only received from wide-field or confocal microscopy. Related devices, systems, methods, techniques, and variations to the same are also provided.

Aspects relate to a compact and low-cost gas analyzer that can be used for different types of gas analysis, such as air quality analysis. The gas analyzer can include a light source, a gas cell configured to receive a sample (e.g., a gas under test), a spectral sensor including a spectrometer and a detector, and an artificial intelligence (AI) engine. Light can enter the gas cell and interact with the sample to produce output light that may be measured by the spectral sensor. The resulting spectrum produced by the spectral sensor may be analyzed by the AI engine to produce a result. The gas analyzer further includes a self-calibration component configured to enable calibration of the sample spectrum to compensate for spectral drift of the spectral sensor.

A measurement system may direct an illumination beam including at least one of a first frequency comb or a second frequency comb to a sample, and generate a sequence of images of the sample based on the first frequency comb and the second frequency comb. The system may include one or more coding optical elements to encode data associated with one or more transfer matrix elements into the sequence of images of the sample. The system may further generate a transfer matrix dataset including measurements of at least one of the one or more transfer matrix elements associated with the sample based on at least one of spectral, spatial, or temporal analysis of the sequence of images, and generate one or more measurements of the sample based on the transfer matrix dataset.

The invention belongs to the field of optical coherence layer imaging, and particularly discloses a spectrum calibration method for a linear field spectral domain OCT (optical coherence tomography) system, which comprises the following steps: acquiring interference signal instantaneous phases corresponding to two optical path differences by adjusting a lifting platform at a sample mirror in the linear field spectral domain OCT system, and subtracting the interference signal instantaneous phases to obtain an instantaneous phase difference; based on the calibration light source, discrete spectral lines are generated on a detector through a sample arm in the shielding line view field spectral domain OCT system, and spectral intensity distribution corresponding to the calibration light source is obtained; calculating the sub-pixel position of the peak value of each spectral line and the instantaneous phase difference corresponding to the sub-pixel position based on the instantaneous phase difference and the spectral intensity distribution corresponding to the calibration light source; and based on the wave number and the instantaneous phase difference corresponding to each spectral line, determining a linear relationship between the instantaneous phase difference and the wave number through linear fitting, and calibrating the corresponding wave number based on the linear relationship. According to the method and the device, the linear field OCT spectrum calibration result with higher precision can be realized.

The utility model discloses an ultrafast space-time light field measuring system, which performs dispersion separation on an interference light field generated after superposition of a laser pulse to be measured and a reference pulse, and performs wavelength screening on the interference light field after dispersion separation by using a wavelength screening element to obtain a laser light field with a target wavelength. Acquiring light field complex amplitude information corresponding to the laser light field of the target wavelength; and reconstructing according to the light field complex amplitude information to obtain a light field corresponding to the laser pulse to be measured. According to the system disclosed by the utility model, the delay between the signal light and the reference light in the measured laser pulse does not need to be regulated and controlled, and the ultrafast space-time light field can be reconstructed only by enabling the same-frequency components to interfere in the same spatial position to obtain the interference pattern of each frequency. The system provided by the utility model has the characteristics of convenience in implementation, interference resistance, low background noise, low data volume, high measurement efficiency and high measurement result accuracy.

Provided are a laser interferometer capable of reducing the frequency of a signal calculated and processed in a demodulation circuit and reducing the cost of the demodulation circuit, and a spectroscopic device provided with the laser interferometer. A laser interferometer is provided with: an optical modulator that adds a modulation signal to laser light using a resonator element; a light receiving element that detects a change in the intensity of the laser light including the sampled signal and the modulated signal, and outputs a laser reception signal; a signal oscillation unit that generates a reference signal of a first frequency with the vibration element as a source vibration; and a demodulation circuit that demodulates the sampled signal from the laser reception signal on the basis of the reference signal, the demodulation circuit comprising: a DC offset removal unit that removes the offset; a first phase regulator that regulates the phase of the reference signal; a first multiplier that multiplies the laser reception signal by a reference signal; a first filter; a second multiplier multiplying the first multiplication signal by a reference signal; a second filter; and a phase calculator that calculates a phase.

The invention provides Fourier transform spectrum equipment based on phase regulation and control and a spectrum detection method, and relates to the technical field of spectrum measurement. The Fourier transform spectrum equipment comprises a light source module used for providing detection light; the spectroscope is used for splitting the detection light into first scanning light and first reference light; the scanning module is used for introducing phase delay linearly related to the light frequency into the first scanning light to obtain second scanning light, and providing the second scanning light for the sample through the spectroscope; the reference module is used for reflecting the first reference light to obtain second reference light and providing the second reference light for the sample through the spectroscope; the photoelectric detector is used for receiving the second scanning light acted on the sample and the second reference light acted on the sample to obtain a first interference pattern; and the processing module is used for processing the first interference spectrum to obtain a spectrum detection result of the sample.

The invention discloses a spectral interference system resolution improving method and system, and the method comprises the steps: building an ISE-Net end-to-end deep neural network model, enabling the convolution kernel size of an efficient channel attention module of the ISE-Net end-to-end deep neural network model to be adaptively determined according to the number of input channels, and constructing a mapping relation between narrowband and broadband interference signals; and generating an ideal narrowband signal and a double-bandwidth target signal according to a spectral interference physical formula, defining a loss function by minimizing deviation between model output and the target signal, updating parameters and dynamically adjusting a learning rate by using an AdamW optimizer until model loss is converged, and completing data generation and training. An input narrowband signal horizontal axis is converted to a corresponding frequency domain axis, and is subjected to time shifting and intensity scaling preprocessing to adapt to the model. A signal processing flow suitable for a single / multi-layer structure is constructed, a bandwidth expansion signal is obtained through decomposition, expansion and reconstruction, and the resolution of a spectrum interference system is improved. The method has the advantages of high calculation efficiency, high generalization and flexible deployment.

The invention relates to the technical field of optics, in particular to a low-crosstalk channel modulation interference polarization spectrum detection method and system, and the system comprises a half-field telescopic module, a phase modulation module, an interference modulation module and a detection module. The half-view-field telescope module is used for performing lower half-view-field beam collimation on an input target beam, the target beam is propagated to the phase modulation module in parallel according to a set range, a composite polarization splitting prism group in the phase modulation module performs light splitting operation based on the target beam output by the half-view-field telescope module, and two parallel polarized lights are emitted, independent phase modulation of the two paths of light is ensured; and the interference modulation module is used for performing light splitting modulation according to the two paths of polarized light to ensure that the two paths of modulated polarized light beams interfere with each other and are transmitted to the detection module for imaging. According to the system, the detection precision of a narrow-band polarization spectrum or a polarization spectrum with an obvious narrow-band wave crest and a narrow-band absorption peak is improved, the polarization spectrum detection capability is high, and the application range is wide.

An aspect of the disclosure provides an interferometric near infrared spectroscopy, iNIRS, system comprising: a light emitting arrangement comprising: a first light source configured to provide wavelength-swept emission of light through a plurality of different wavelengths in a first wavelength range; a second light source configured to provide wavelength-swept emission of light through a plurality of different wavelengths in a second wavelength range different to the first wavelength range; a common sample delivery channel coupled to each of the first and second light sources to receive light therefrom and to deliver said light towards a subject; and one or more reference channels for receiving reference light from the first light source and / or the second light source; a light detecting arrangement comprising an interferometrie optical detector; wherein the optical detector is coupled to the one or more reference channels for receiving reference light from the first and second light sources; wherein the light detecting arrangement is arranged to be coupled to the subject for the optical detector to receive sample light from the first and second light sources, the sample light comprising light which travelled along the common sample delivery channel; wherein the optical detector is arranged to combine the sample light with the reference light to provide combined light signals comprising one or more components at a beat frequency between sample light and reference light; and wherein the iNIRS system is configured to process the combined light signals for providing imaging and analysis of the subject.

The invention discloses a continuous scanning half-wave sampling system for a multi-dimensional coherent spectrum, which comprises a continuous laser, continuous laser output by the continuous laser and femtosecond laser pulse output by an ultra-short femtosecond laser pulse generation device are combined and then split, and modulation and time delay are respectively carried out; the multi-dimensional coherent femtosecond laser pulse sequence is used for exciting a fluorescence signal generated by a sample and converting the fluorescence signal into a first electric signal, and the obtained continuous laser carrying different modulation frequencies is converted into a second electric signal; and demodulating the second electric signal by taking a total mixing signal obtained by mixing the multiple paths of modulation signals as a reference, and demodulating the first electric signal by using the second electric signal. The invention further discloses a continuous scanning half-wave sampling method for the multi-dimensional coherent spectrum. The half-wave sampling method is utilized to accurately calibrate optical time delay so as to obtain the multi-phase multi-dimensional coherent spectrum. The sampling step length breaks through the limitation of the minimum sampling step length of traditional stepping collection, and the sampling bandwidth is remarkably improved.

The invention relates to an uncertainty propagation evaluation method in spatial heterodyne spectral measurement, and belongs to the technical field of hyper-spectral remote sensing detection. The entrance pupil radiance spectral data # imgabs0 # and the output signal # imgabs1 # of the spatial heterodyne spectral measurement system are calculated; the uncertainty # imgabs2 # of the atmospheric parameters is calculated; the uncertainty # imgabs3 # of the signal electron number and the uncertainty # imgabs4 # of the noise are calculated; according to the uncertainty # imgabs5 # of the atmospheric parameters, the uncertainty # imgabs6 # of the signal electron number and the uncertainty # imgabs7 # of the noise, the uncertainty # imgabs8 # of the output signal of the spatial heterodyne spectral measurement system is calculated; the uncertain component of the uncertainty # imgabs9 # is analyzed; sorting influence contributions generated by the uncertain components; the method solves the problems that the design indexes of the spatial heterodyne spectral measurement system cannot quantitatively describe the measurement precision of the radiation energy, the entrance pupil radiance signal and the output signal, and the uncertainty contribution introduced by the spatial heterodyne spectral measurement link.

The invention discloses a high-resolution FPI spectrum demodulation method, and relates to the field of optical fiber sensing. Comprising the following steps: acquiring an FPI interference spectrum, and performing pretreatment, including spectrum standardization, wave number conversion and wave number domain interpolation, on the acquired spectrum; performing FFT (Fast Fourier Transform) on the interpolated spectrum to obtain an amplitude spectrum and a phase spectrum; roughly estimating the F-P cavity length through a corrected amplitude spectrum Buneman algorithm; and the F-P cavity length is accurately calculated in combination with the phase spectrum. The FPI sensor demodulated according to the method can realize real-time monitoring of various environmental parameters including vibration, pressure and temperature, and compared with other demodulation methods, the method provided by the invention has the characteristics of high resolution, small calculation amount and large dynamic range, and has stable performance under the condition of low signal-to-noise ratio.

The invention discloses a one-dimensional ultra-wide field-of-view ultra-high spectral resolution dispersion coherent imaging spectrometer, which belongs to the technical field of spectral imaging, and comprises a first microlens array used for obtaining incident light of a one-dimensional ultra-wide field-of-view in a horizontal plane; the plurality of optical fibers are used for transmitting incident light of a one-dimensional ultra-wide field of view; the second micro lens array is used for collimating incident light from each optical fiber into broadband parallel light beams; the grating beam splitter interferometer is used for dispersing the broadband parallel light beams into a plurality of narrow-band parallel light beams with different propagation directions; the cylindrical lens is used for converging the two paths of coherent light of each narrow-band parallel light beam to a target block of the detector, and converging the narrow-band parallel light beams with different propagation directions to different target blocks respectively; and the detector is used for obtaining a continuous broadband ultra-high resolution spectrum according to the two paths of coherent light received by each target block. According to the invention, a one-dimensional ultra-wide field of view is obtained in a horizontal plane, and ultra-high spectral resolution can be obtained.

This invention relates to the field of optical imaging and detection technology, specifically providing a broadband snapshot-type polarization interferometry imaging detection system and method for breast tumors. A broadband light source illuminates a breast tumor tissue sample. The reflected signal light is collected and collimated by a pre-optical system, then sequentially passes through a first and a second ray shaping unit for two shearing and two polarization state transformations, resulting in two beams of linearly polarized light and two beams of circularly polarized light. These beams are imaged by an imaging lens to an area array detector to obtain a polarization interferogram, which is then demodulated to obtain all Stokes parameters of the breast tumor tissue sample. This invention achieves broadband snapshot imaging of breast tumors with all Stokes parameters without using an analyzer, doubling the light throughput compared to traditional polarization imaging instruments using analyzers. Furthermore, this invention has advantages such as compact structure, no moving parts, easy assembly and adjustment, and no need for image registration.

The invention relates to the field of spectral imaging, in particular to a checkerboard Fabry-Perot interference snapshot imaging spectrometer, which comprises a telescopic system, a micro-lens array, a Fabry-Perot array interference system and an area array detector, and is characterized in that the telescopic system is used for collecting a target light field and carrying out view field limitation and collimation on the target light field; the Fabry-Perot array interference system is used for modulating a target light field into an interference light field array and comprises a parallel flat plate and a checkerboard step mirror, the step height is distributed in a checkerboard-shaped two-dimensional decreasing mode, and an air gap with the thickness changing in a two-dimensional increasing mode is formed between the parallel flat plate and the checkerboard step mirror. The thickness of each area of the air gap corresponds to one optical path difference; the microlens array is used for imaging the interference light field array onto the area array detector through each imaging channel; and the area array detector is used for receiving the transmission image field of the microlens array to obtain an interference image array. The invention has the advantages of small volume, light weight, compact structure, static state, stability, reliability and the like.

The invention relates to a method for calibrating a spectrometric measuring device (20) using a spectrometric calibration device (01). The calibration device (01) comprises a control unit, an interferometer with mirrors (02, 03) and a beam splitter (04), a broadband first radiation source (06), a laser (07) as a second radiation source, and a first detector (08). The method includes emitting broadband radiation (12a) and simultaneously emitting radiation (12b) by the laser (07), as well as simultaneously coupling these two radiations (12a, 12b) into the interferometer of the calibration device. A first interferogram is acquired based on the radiation (12b) of the laser (07). A second interferogram is acquired based on the broadband radiation (12a). A first data set with the spectral properties of the spectrometric measuring device (20) is created on the basis of the recorded interferograms.A second dataset, consisting of high-resolution sample spectra and chemically determined constituent values, is provided. Simulated sample spectra are calculated from the two datasets. A chemometric calibration model for the measuring device (20) is created from the simulated sample spectra. The invention also relates to a spectrometric calibration device (01).

A method for adjusting a Doppler asymmetric spatial heterodyne interferometer belongs to the technical field of interference spectrums, and aims to solve the problem that an existing Doppler asymmetric spatial heterodyne interferometer is large in overall adjustment error, and the method comprises the steps that a front lens, a rear lens and a collimating lens are installed and corrected in parallel, and a centering instrument detects the adjustment state of the lenses; the reflex mirror is installed and adjusted by using the reference reflector; after the calibration is completed, carrying out complete machine assembly and calibration on a reflex mirror assembly, a beam splitter prism, an optical filter, an interference module and a camera on a load mounting plate, finely adjusting the reflex mirror assembly to ensure that the signal light enters a light path in a collimating manner, and then adjusting a collimating lens reflector to ensure that the calibration light enters the light path in a parallel manner; and adjusting the camera position to obtain clear imaging. By adopting the system integrated installation and adjustment method, the front lens, the rear lens and the collimating lens can be installed and adjusted in parallel, the installation and adjustment efficiency is improved, the whole machine installation and adjustment are carried out with the other parts after the installation and adjustment are completed, an optical path is integrally designed to ensure that optical axes of all elements are not deviated, and the influence of installation errors is reduced, so that high-quality interference fringes are obtained.

The present technology pertains to a measurement device capable of suitably measuring the spectrum of a measurement light. A measurement device according to the present technology is provided with: a luminous flux splitting unit for splitting substantially parallel luminous flux into a first luminous flux and a second luminous flux, refracting and emitting the first luminous flux, and emitting the second luminous flux in a direction symmetrical to the emission direction of the first luminous flux on the basis of a first reference plane that includes the traveling direction of the substantially parallel luminous flux, thereby causing the first luminous flux and the second luminous flux to interfere with each other; a light-condensing unit for condensing the first luminous flux and the second luminous flux on a second reference plane that includes the traveling direction of the substantially parallel luminous flux and is orthogonal to the first reference plane; a sensor unit for detecting interference light between the first luminous flux and the second luminous flux; and a calculation unit for calculating the spectrum of the substantially parallel luminous flux on the basis of a detection result by the sensor unit. The present technology can be applied to, for example, a spectroscopic measurement device.

A broadband interferometry system that includes (i) an interferometer that includes a tilted reference mirror that is oriented by a tilt angle in relation to a normal to an optical axis of a reference beam thereby introducing a range of optical path differences along a first axis while guaranteeing a formation of an interference pattern on a sensor, (ii) a movement unit for introducing a relative movement between the sample and the interferometer, along a second axis that is oriented to the first axis thereby virtually scanning the range of optical path differences, (iii) a processing circuit for receiving interference detection signals and reconstructing interferograms for different points of illumination on the sample. The measurement beam forms an elongated spot on the sample, having a longitudinal axis that is oriented to the first axis and the second axis.

The invention provides an optical fiber spectrometer and a spectral signal demodulation method. The optical fiber spectrometer comprises a light source, a first optical fiber coupler, a second optical fiber coupler, an optical fiber delay line, a first photoelectric detector, a second photoelectric detector, a laser and a controller. The first optical fiber coupler, the optical fiber delay line, the second optical fiber coupler and the first photoelectric detector form a first path, and the second optical fiber coupler, the first optical fiber coupler and the second photoelectric detector form a second path; light waves emitted by the light source are transmitted in the first path and the second path and output electrical time domain signals through the first photoelectric detector, and light waves emitted by the laser are transmitted in the first path and the second path and output time domain interference signals through the second photoelectric detector. And the controller is connected with the first photoelectric detector and the second photoelectric detector and is used for determining a spectral signal of the light wave according to the electric time domain signal and the time domain interference signal. According to the invention, the accuracy and reliability of spectral analysis results are improved.

The invention discloses a light field space alignment detection and correction system and method based on an optical interferometer, the inclination angles of a second beam splitter, a third beam splitter, a first plane mirror and a second plane mirror are the same, two light beams to be aligned and detected are emitted to the second beam splitter and are equally divided into two identical light beams by the second beam splitter, and the two identical light beams are emitted to the first plane mirror. One beam is reflected by the first plane mirror and then enters a third beam splitter, the other beam passes through the second plane mirror and a Dove prism which is horizontally arranged and then enters the third beam splitter, the two beams of light entering the third beam splitter are combined to obtain two different beams of light, one beam is in a symmetrical mode, and the intensity of the beam is detected through a photoelectric detector; the other beam is in an antisymmetric mode, and the intensity of the other beam is detected through a photoelectric detector. The device is simple in structure, the detection and correction process is greatly simplified, and targeted correction can be carried out according to the detection result.

An aspect of the disclosure provides a non-invasive intracranial pressure sensing apparatus comprising an interferometric near infrared spectroscopy, iNIRS system, the iNIRS system comprising: a light emitting arrangement comprising: a light source configured to emit light; a sample delivery channel coupled to the light source and arranged to be coupled to the subject's scalp to direct light from the light source towards the subject's brain tissue; and a reference channel coupled to the light source for receiving light therefrom; a light detecting arrangement configured to be coupled to the subject's scalp and the light emitting arrangement, the light detecting arrangement comprising an interferometric optical detector configured to receive: (i) reference light from the reference channel, and (ii) sample light from the subject's brain, the sample light comprising light emitted from the light source; wherein the optical detector is arranged to combine the sample light with the reference light to provide combined light signals comprising one or more components at a beat frequency between sample light and reference light; and wherein the sensing apparatus comprises a controller configured to process data indicative of the combined light signals to determine an indication of intracranial blood pressure for the subject based on at least one property of a pulsatile waveform of one or more identified pulses of blood flow through the subject's brain.

A point of use analyte detection and quantification system for aquatic applications is provided. Related methods are also provided.

A light detection device of the present invention includes: a wiring board; a first support part disposed on a mounting surface of the wiring board; a Fabry-Perot interference filter having a first mirror part and a second mirror part between which a distance is variable and having an outer edge portion disposed in a first support region of the first support part; a light detector disposed on the mounting surface to face the first mirror part and the second mirror part on one side of the first support part; and a temperature detector disposed on the mounting surface, wherein the temperature detector is disposed on the mounting surface such that at least a part of the temperature detector overlaps a part of the Fabry-Perot interference filter when seen in a first direction perpendicular to the mounting surface and such that at least a part of the temperature detector overlaps a part of the first support part when seen in a second direction in which the first support part and the light detector are aligned with each other, and wherein a first distance between the temperature detector and the first support part in the second direction is smaller than a first width of the first support region in the second direction.

The invention discloses a heterodyne laser interferometer signal processing link dynamic performance calibration device based on an acousto-optic frequency shifter and a calibration method of the heterodyne laser interferometer signal processing link dynamic performance calibration device, and relates to the technical field of heterodyne laser interferometer dynamic measurement performance calibration. The calibration result is coupled with the abbe error and cosine error caused by mechanical installation and the like and the data cycle error caused by asynchronous measurement, so that the problem that the dynamic measurement performance of the interferometer in the signal processing link is difficult to evaluate is solved. The calibration device comprises a laser assembly, a first measurement light path, a second measurement light path, an AOFS drive and motor controller light path and a phase meter. The laser assembly emits laser into the beam splitter prism assembly, the beam splitter prism assembly divides incident light into two beams of laser, the two beams of laser enter the first measuring light path and the second measuring light path respectively, and finally the two beams of laser are sent to the phase meter to calculate the phase difference. The device is an equivalent calibration device suitable for dynamic measurement performance of a heterodyne laser interferometer under high-speed movement of a target in a signal processing link.

Systems and methods for remote sensing in a plurality of dimensions simultaneously are provided. The plurality of dimensions include imaging, spectral sensing, and ranging at a range resolution that is orders of magnitude finer than the native time resolution of a detector used in the system.

An optical device includes: an incident optical system; an analysis optical system; and a length measurement optical system. The incident optical system includes a laser light source, and an incident light dividing element that divides the laser light. The analysis optical system includes a first light dividing element that divides the first divided light and then mixes the light, a first mirror that adds a first modulation signal to the one first divided light by movement and reflection, a second mirror, and a first light receiving element that receives the first divided light including a sample-derived signal and the first modulation signal. The length measurement optical system includes a second light dividing element that divides the second divided light and then mixes the light, an optical feedback unit that feeds back the one second divided light to the second light dividing element, and a second light receiving element that receives the second divided light including a displacement signal generated by the first mirror.