System and method for improving calibration transfer between multiple Raman analyzer devices

Abstract

The present invention relates to systems and methods for improving calibration transfer between multiple Raman analyzer devices. A method for coordinating the responses of multiple Raman analyzers includes the following steps: calibrating the intensity axis response of a spectrometer to a reference light source; and measuring the laser wavelength of the laser using a spectrometer. The method also includes the following steps: using a spectrometer to measure the fluorescence spectra induced by the laser at the laser wavelength of multiple standard reference material samples; measuring the temperature of each standard reference material sample while measuring the fluorescence spectra; and correcting the fluorescence spectrum of each standard reference material sample based on the corresponding temperature. The method further includes the following steps: deploying each standard reference material sample in one of a plurality of field calibrator devices; and using one of the field calibrator devices and the corrected fluorescence spectrum of the corresponding standard reference material sample to calibrate the intensity axis of one of the Raman analyzers.

Description

Technical Field

[0001] The present disclosure relates generally to spectroscopy, and more particularly to apparatus and methods for using spectroscopic reference materials to ensure reliable, repeatable, and accurate results. Background Art

[0002] Induced radiation effects such as Raman scattering and fluorescence have become extremely valuable tools associated with the non-destructive determination of molecular composition. Any Raman system contains three main components: an excitation source, a sampling device, and a detector. Modern Raman instruments use lasers as excitation sources, spectrometers as detectors, and microscopes or fiber optic probes as sampling devices.

[0003] Each Raman instrument has a unique spectral responsivity, so that the spectral shape and absolute intensity of a single sample are different on each instrument, and even different at different times on the same instrument. Therefore, the procedure of correcting the relative intensity of Raman spectra using, for example, spectral reference materials has become increasingly important. In this procedure, the luminescence of an intensity standard with known relative irradiance is used to establish an instrument response function. This function is then used to correct the sample spectrum to the true relative Raman intensity.

[0004] The National Institute of Standards and Technology (NIST) has developed a series of standard reference materials (SRMs) for calibrating Raman intensity. In particular, NIST offers a class of fluorescent glasses that can be used with Raman systems as intensity calibration light sources. These SRM glasses have some advantages over more traditional calibration light sources such as halogen bulbs (which belong to the general class of blackbody radiators) in that they do not age or drift over time, do not require a power source (thus making them more suitable for field work), and allow for more direct correction of sample system optics.

[0005] However, NIST's SRMs are sensitive to temperature and excitation wavelength. Moreover, the spectral profile of each SRM is slightly different. Thus, each SRM glass must be characterized with respect to temperature and wavelength to obtain a calibration curve that allows each to be effectively "normalized." Although in theory, all actual SRM emission spectra, when measured under the same conditions used to generate those curves (i.e., by NIST), are certified to fall within the uncertainty bands published in the NIST documentation, these bands vary across the emission spectrum, allowing for band shape variability of approximately several percent. In order to ensure reliable, repeatable, and accurate results, it would be advantageous to have a system and method to determine whether the correct calibration curve file is being used for each SRM, thereby achieving better than a few percent band shape variability. Summary of the invention

[0006] The present invention improves calibration transfer between multiple Raman analyzer installations, thereby improving analyzer-to-analyzer consistency without relying on published calibration spectra and information provided by standard reference materials (SRMs). Use of the present invention provides an improved degree of analyzer-to-analyzer variability, even when different devices are used in different environments, based on the actual emission spectra of SRMs generated in the field across multiple installations running the same Raman analysis. The goal is to achieve consistent results when analyzing the same reference sample in the field, with higher accuracy than what the published SRM spectra alone can provide.

[0007] The present invention takes into account a variety of factors that affect system-to-system results, including: 1. sample-to-sample variability within the uncertainty band of the standard spectrum published by the SRM; 2. sample temperature when it is different from the temperature that characterizes the SRM; 3. illumination geometry, particularly focal depth and numerical aperture; and 4. laser excitation wavelength, whose sensitivity is a function of the type of SRM used.

[0008] The present invention does not actually adjust or correct the SRM curves published by NIST, but instead replaces those curves with improved accuracy based on independent measurements of each reference glass under identical conditions. Although the effective "adjustment" imparted by this method with respect to the standard NIST curve can be obtained by subtraction, the present invention actually derives an independent characterization of the reference material, which may inherently include other considerations, such as illumination geometry.

[0009] As for analytical corrections such as temperature and / or laser wavelength dependence, the present invention contemplates the distribution and use of a Raman Calibration Tool (RCT) and associated software to aid in intensity calibration across multiple analyzer devices. Use of this module provides analytical adjustments based on the temperature of the sample measured in the field versus the temperature at which it was characterized in the laboratory. The same temperature correction transformation equations as published in the NIST document can be used, but over a wider temperature range than that certified by NIST, where the effectiveness of the improved temperature characterization has been experimentally confirmed over a wider temperature range.

[0010] In summary, the present invention improves the accuracy of Raman analyzer calibration through temperature correction, focus control and multi-source cross-validation. Placing the calibration material (i.e., SRM) in a sealed volume and switching the light into and out of the module reduces (if not eliminates) environmental contamination and degradation over time. As a further alternative, the SRM material can form part of a waveguide or mixing rod to reduce position sensitivity and increase calibration signal levels.

[0011] A method for improving calibration transfer between multiple Raman analyzer devices, including the step of providing multiple standard reference material (SRM) samples. Under factory-controlled conditions, a Raman reference spectrum is generated for each SRM sample using the same measurement instrument and measurement parameters. At least one SRM sample is provided to each of the multiple Raman analyzer devices together with the measurement parameters and Raman reference spectrum generated for each SRM sample. Each SRM reference sample is analyzed at a corresponding one of the Raman analyzer devices to generate a Raman calibration spectrum for the SRM sample, and the intensity axis of the Raman spectrometer at the calibration device is calibrated using the Raman calibration spectrum and the Raman reference spectrum.

[0012] In a preferred embodiment, the SRM samples are existing fluorescent glasses, each provided with a published calibration spectrum.

[0013] The measurement parameters may include the temperature of the SRM sample when generating the Raman reference spectrum, in which case the method may include the following steps: measuring the temperature of the SRM sample when generating the calibration spectrum; and correcting the device calibration based on the difference between the sample temperature during calibration and the sample temperature when generating the Raman reference spectrum.

[0014] The measured parameters may include an illumination geometry of a laser used to generate a Raman reference spectrum. For example, the illumination geometry of the laser may include a focal depth of the laser in the SRM sample. The method may include the following steps: measuring the illumination geometry of the SRM sample when generating a calibration spectrum; and correcting the device calibration according to the difference between the geometry used to illuminate the sample during calibration and the geometry used to illuminate the sample when generating the Raman reference spectrum.

[0015] The measurement parameters may include the wavelength of the laser used to generate the Raman reference spectrum, whereby the method may include the following steps: measuring the wavelength of the laser used to irradiate the SRM sample when generating the calibration spectrum; and correcting the device calibration based on the difference between the wavelength of the laser used to irradiate the sample during calibration and the wavelength of the laser used to irradiate the sample when generating the Raman reference spectrum.

[0016] The Raman reference spectrum may be stored in a memory or otherwise stored to the Raman analyzer being calibrated. The analyzer may then compare the Raman reference spectrum to a calibration spectrum generated by the Raman analyzer during illumination of the SRM sample to adjust the intensity axis of the Raman analyzer based on the difference between the reference spectrum and the calibration spectrum.

[0017] The method and system may include packaging the SRM sample in a sealed field calibrator device for distribution to multiple Raman analyzer devices. The field calibrator device may include a port for inserting a temperature probe to measure the temperature of the SRM sample when generating a calibration spectrum. The field calibrator device may also include a port for inserting a Raman probe to establish a predetermined depth of focus in the SRM sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The embodiments and other features, advantages and disclosures contained herein and the manner in which they are obtained will become apparent and the present disclosure will be better understood by referring to the following description of various embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0019] Figure 1 shows a simplified schematic diagram of a reference light source and a spectrometer configured to perform an intensity axis response calibration of the spectrometer using the reference light source;

[0020] Figure 2 shows a simplified schematic diagram of a laser and spectrometer configured to measure the laser wavelength of the laser using a calibrated spectrometer;

[0021] Figure 3 Shown include Figure 1 and Figure 2 A schematic diagram of a spectroscopy system comprising a spectrometer and a laser configured to measure the fluorescence spectrum of each of a plurality of standard reference material samples;

[0022] Figure 4 shows a graph depicting an exemplary fluorescence spectrum measured by a spectrometer and an exemplary temperature-corrected fluorescence spectrum;

[0023] Figure 5 showing a plurality of Raman analyzers configured to be calibrated using a standard reference material sample and a corrected fluorescence spectrum of a corresponding one of the standard reference material samples;

[0024] Figure 6 A flow chart showing a method for coordinated response of the plurality of Raman analyzers according to the present disclosure is shown;

[0025] Figure 7a A field calibrator module containing NIST fluorescent glass standard reference materials (SRMs) is shown to provide a factory-characterized spectral output for intensity standardization of Raman instruments and analyzers; and

[0026] Figure 7b Depicts the temperature probe insertion Figure 7a A field calibrator module is provided to measure the temperature of the SRM during the calibration procedure. DETAILED DESCRIPTION

[0027] Various embodiments of the present disclosure will now be presented and / or discussed in conjunction with the accompanying drawings that illustrate the embodiments.It should be understood that the scope of the present disclosure is not intended to be limiting.

[0028] The present disclosure describes a system and method for ensuring the accuracy of a Raman analyzer, including coordinating the response of multiple Raman analyzer deployments, particularly for similar process analysis. The present disclosure can be applied to any of a variety of different types of spectrometers and / or analyzers, each of which can generally include or utilize an emission source that produces a spectrum, an optical system that collimates and disperses the spectrum, and a detection device that measures the intensity of the emission lines. The embodiments provided herein are not intended to limit the present invention in any way.

[0029] Reference now Figure 1 , which shows a simplified schematic diagram 10 of a reference light source 12 and a spectrometer 14. A signal processor 16 is also shown, which may be integrated with the spectrometer 14 or not integrated with the spectrometer 14. The reference light source 12 can be any dedicated, stable and calibrated light source. The spectrometer 14 may include various components for recording and measuring spectra. The signal processor 16 may include software that provides various options for spectral processing. The reference light source 12, the spectrometer 14, and the signal processor 16 can be used to calibrate the intensity axis response of the spectrometer 14 to the reference light source 12. In order to calibrate the spectrometer 14, the calibration data can be interpolated and applied to the measured spectrum to remove the system response.

[0030] An exemplary spectrum 20 produced by the reference light source 12, spectrometer 14, and signal processor 16, and a predetermined spectral distribution profile 22 corresponding to the reference light source 12 (such as provided by NIST) are shown on graph 18. The spectrometer 14 may be calibrated to calibrate the intensity axis response based on a comparison of the exemplary spectrum 20 to the predetermined spectral distribution profile 22, or a calibration curve (not shown) may be generated based on the comparison for use with the spectrometer 14. The primary goal of the intensity calibration is to calibrate the y-axis, thereby allowing the spectrometer 14 to detect and analyze a sample or light source independent of the spectral response of the system.

[0031] refer to Figure 2 , which shows a simplified schematic diagram 30 including a laser 32 as well as a spectrometer 14 and a signal processor 16. The laser 32 is an exemplary device that emits light through an optical amplification process based on simulated emission of electromagnetic radiation. Figure 2 30 , the laser 32 , the calibrated spectrometer 14 , and the signal processor 16 may be configured to measure a laser wavelength 34 of the laser 32 using the calibrated spectrometer 14 .

[0032] The exemplary spectroscopy system 40 is Figure 3 1 and generally includes a laser 32, a sample 42, a temperature measurement device 44, a diffraction grating 46, a detector 48, and a signal processor 16. The calibrated spectrometer 14 may be represented by a detector holder for the sample 42, the temperature measurement device 44, the diffraction grating 46, the detector 48, and the signal processor 16. As described above, the intensity axis response of the calibrated spectrometer 14 has been calibrated for the reference light source 12, and the laser wavelength 34 of the laser 32 has been measured using the spectrometer 14.

[0033] Sample 42 may be one of a plurality of standard reference material samples 42a, 42b, and 42c that have sample-to-sample variation for analysis using spectroscopy system 40. According to an exemplary embodiment, standard reference material samples 42a, 42b, and 42c may include NIST traceable luminescent materials, such as fluorescent SRM glass pieces. In some cases, each of standard reference material samples 42a, 42b, and 42c may be provided with a unique standard temperature and wavelength corrected spectrum.

[0034] The spectroscopy system 40 can be used to measure a unique standard reference material fluorescence spectrum 50 of each of a plurality of standard reference material samples 42a, 42b, and 42c using a calibrated spectrometer 14, as shown by curve 52, wherein the standard reference material fluorescence spectrum is induced by a laser 32 at a laser wavelength 34. The laser 32 and the calibrated spectrometer 14 can be coupled to the plurality of standard reference material samples 42a, 42b, and 42c via controlled excitation / collection numerical apertures and focus positions, representing a device that will be used to perform in-situ calibration of a plurality of Raman analyzers using the plurality of standard reference material samples 42a, 42b, 42c, as described below.

[0035] Spectroscopy system 40 may also include a temperature measurement device 44 positioned and configured to measure the temperature of one of standard reference material samples 42a, 42b, and 42c when one of the standard reference material samples 42a, 42b, and 42c is analyzed using spectroscopy system 40. In particular, the temperature of each standard reference material sample 42a, 42b, and 42c may be measured while spectroscopy system 40 is measuring the fluorescence spectrum 50 of the corresponding standard reference material sample 42a, 42b, and 42c. The fluorescence spectrum 50 of each of standard reference material samples 42a, 42b, and 42c may then be corrected based on the corresponding temperature. For example, and with reference to Figure 4 60 , the fluorescence spectrum 62 of each of the standard reference material samples 42a , 42b , and 42c may be adjusted to a corrected fluorescence spectrum 64 based on a standard temperature (such as by using a previously characterized temperature dependence of the fluorescence spectrum 62 ).

[0036] Next, each of the standard reference material samples 42a, 42b, and 42c may be deployed in one of a plurality of field calibrator devices 70a, 70b, and 70c, such as Figure 5 , so as to calibrate multiple Raman analyzers 72a, 72b, and 72c. According to one embodiment, each of the field calibrator devices 70a, 70b, and 70c may include one of the standard reference material samples 42a, 42b, and 42c, a temperature measurement device, and an optomechanical interface, wherein the optomechanical interface ensures a common focal depth of the collection probes of the corresponding Raman analyzers 72a, 72b, and 72c in the corresponding standard reference material samples 42a, 42b, and 42c.

[0037] Each Raman analyzer 72a, 72b, and 72c may include or use: a corresponding laser 74a, 74b, and 74c operating at a laser wavelength; one of the field calibrator devices 70a, 70b, and 70c supporting one of the standard reference material samples 42a, 42b, and 42c; a spectrometer 76a, 76b, and 76c; and a signal processor 78a, 78b, and 78c, including a memory 80a, 80b, and 80c. The memory 80a, 80b, and 80c may store the corrected fluorescence spectra 86a, 86b, and 86c.

[0038] The calibration spectra 84a, 84b and 84c generated by the Raman analyzers 72a, 72b and 72c are Figure 5 42c together with the corrected fluorescence spectra 86a, 86b and 86c of the corresponding standard reference material samples 42a, 42b, 42c. According to the present invention, the Raman analyzers 72a, 72b and 72c are calibrated using the spectra 84a, 84b and 84c and the corrected fluorescence spectra 86a, 86b and 86c of the corresponding standard reference material samples 42a, 42b and 42c. That is, the Raman analyzers 72a, 72b and 72c can be calibrated based on the difference between the spectra 84a, 84b and 84c and the corrected fluorescence spectra 86a, 86b and 86c.

[0039] According to one embodiment, the calibration temperature of the standard reference material samples 42a, 42b and 42c may be measured during calibration of the Raman analyzers 72a, 72b and 72c. The standard temperature spectra of the corresponding field calibrator devices 70a, 70b and 70c may be corrected based on the calibration temperature.

[0040] According to another embodiment, the calibration wavelengths of the Raman analyzers 72a, 72b, and 72c may be measured, and the standard excitation wavelength spectra of the corresponding field calibrators 70a, 70b, and 70c may be corrected based on the calibration wavelengths.

[0041] If each of the standard reference material samples 42a, 42b and 42c is set with a unique standard temperature and wavelength-corrected spectrum, the calibration wavelength of the Raman analyzers 72a, 72b and 72c can be measured, and the unique standard reference material sample fluorescence spectra of the corresponding field calibrator devices 70a, 70b and 70c can be calibrated based on the calibration wavelength and the unique standard temperature and wavelength-corrected spectrum of the corresponding standard reference material samples 42a, 42b and 42c.

[0042] Reference below Figure 6 The above method is described in a flowchart 90 of FIG. The method includes a step of calibrating the intensity axis response of the spectrometer 14 to the reference light source 12 at box 92. In particular, the spectrum 20 generated by the reference light source 12 is compared with a predetermined spectral distribution profile 22 corresponding to the reference light source 12. The difference between the spectrum 20 and the predetermined spectral distribution profile 22 is used to adjust or correct the spectral response of the spectrometer 14. The method also includes a step of measuring the laser wavelength 34 of the laser 32 using the spectrometer 14 at box 94, wherein the laser 32 represents the lasers in the deployed Raman analyzers 72a, 72b and 72c.

[0043] Then, at box 96, the method includes the step of measuring the fluorescence spectrum 50 induced by laser 32 at laser wavelength 34 of each of a plurality of standard reference material samples 42a, 42b, and 42c using spectrometer 14. The method also includes the step of measuring the temperature of each of standard reference material samples 42a, 42b, and 42c during the step of measuring the fluorescence spectrum 50 (box 98), and the step of correcting the fluorescence spectrum 50 of each of standard reference material samples 42a, 42b, and 42c based on the corresponding temperature (box 100).

[0044] Thereafter, at box 102, the method includes deploying each of the standard reference material samples 42a, 42b, and 42c in one of the plurality of field calibrator devices 70a, 70b, and 70c. The method further includes the step of calibrating the intensity axis of one of the Raman analyzers 72a, 72b, and 72c using one of the field calibrator devices 70a, 70b, and 70c and the corrected fluorescence spectra 86a, 86b, and 86c of the corresponding standard reference material samples 42a, 42b, and 42c at box 104.

[0045] As described above, each spectrometer, spectroscopy system, or analyzer has a unique spectral response that is affected by spectral modifications caused by optical elements (e.g., lenses, mirrors, and / or detectors) along the optical path. Thus, a spectrometer used for spectral analysis should be calibrated, such as by using spectral reference materials. That is, the spectrometer can collect a spectrum of light that passes through a spectral reference material with known spectral characteristics to adjust or correct the spectral response. Such calibration is important for obtaining consistent results from device to device. However, there may be sample-to-sample variations in the spectral reference material and other factors that may cause inconsistent results from device to device.

[0046] To aid in analyzer-to-analyzer calibration, the apparatus aspects of the invention include a Raman Calibration Tool (RCT) configured for distribution and use in the field. When used in conjunction with an accompanying calibration protocol (including those described herein), the RCT allows different instruments to be standardized so that they produce accurate spectra in terms of intensity when measuring a given sample. Thus, "standardization" refers to the process of normalizing the relevant performance of individual analyzers using radiometric means so that spectral models, as well as chemical models, can be transferred to multiple analyzers.

[0047] Figure 7a is a graph of RCTs containing NIST fluorescent glass standard reference materials, providing factory-characterized spectral output for intensity standardization of Raman instruments and analyzers. Each Raman excitation wavelength associated with the standardization process requires a wavelength-specific SRM. For example, SRM-532 is used for 534.5nm (nanometers) to 694.0nm; SRM-785: 790.7nm to 1074.5nm; and SRM-1000: 1012.6nm to 1304.6nm.

[0048] The upper portion of the RCT unit has a port for inserting a Raman probe, and the lower portion of the RCT unit (not shown) has a window that indicates the status of the internal color changing desiccant. The standard RCT interfaces with a 1 / 2" (inch) probe tip, but the module can be designed to alternative sizes. A desiccant humidity indicator is provided to avoid degradation of the fluorescent glass provided within the housing.

[0049] The upper and lower parts of the RCT can be rotated relative to each other in order to select one of four different modes for the unit. Mode selection is accomplished by pulling the two parts of the unit slightly apart and rotating the two parts relative to each other until the mode selection arrow points to one of the following modes:

[0050] STORE: This mode moves the dust cover into place to protect the probe or RCT calibration accessories;

[0051] LOAD: This mode is used to load the unit onto the probe until it bottoms out at a fixed, predetermined distance from the reference material;

[0052] CAL (Calibration): CALIBRATE mode is used to actually present the fluorescent glass to the probe; and

[0053] BG (Background Setting): The BACKGROUND setting enables the RCT to capture the background signal of the probe to account for probe-to-probe background variations when normalizing the instrument.

[0054] Figure 7b The RCT is shown with a temperature measurement probe 710 inserted into the apparatus 700 to determine the temperature of the NIST glass during the calibration process.

[0055] Each RCT is provided with a source spectrum file (SSF) that describes the relative spectral output of the device measured when the probe tip is in contact with the NIST SRM. The software used to operate the Kaiser analyzer is configured to directly read the SSF of the device during the instrument standardization process. The SSF is relative rather than absolute, so that only the normalized shape of the measured spectrum is corrected using the RCT, rather than the absolute amplitude. Nevertheless, the intensity normalization process still corrects for instrument-to-instrument response variations, including removing fixed-style "noise" caused by pixel-to-pixel variations in response to a single CCD detector; spectral variations in signal intensity due to optical components, and spectral variations in the quantum efficiency of the CCD camera used in the spectrometer.

[0056] The recommended calibration / qualification sequence is summarized below:

[0057] 1 Wavelength calibration (Neon standard)

[0058] 2Intensity calibration / standardization (intensity standards)

[0059] 3. Probe background normalization (probe BG)

[0060] 4 Laser wavelength calibration (Raman shift standard)

[0061] 5 Calibration Qualification (Raman Shift Standard)

[0062] The systems and methods described herein can be used to normalize fluorescent glass spectral reference materials to coordinate the response of multiple process Raman analyzer deployments for similar process analysis. When multiple samples of fluorescent glass spectral reference materials are deployed, improved calibration transfer or accuracy can be obtained by measuring and correcting for sample-to-sample variability. The systems and methods described herein are used to account for this sample-to-sample variation.

[0063] Although specific embodiments of spectrometers including systems and components have been described in considerable detail herein, these embodiments are provided merely as non-limiting examples of the disclosure described herein. Therefore, it should be understood that various changes and modifications may be made, and equivalent substitutions may be made to its elements and steps without departing from the scope of the disclosure. In fact, the disclosure is not intended to be exhaustive or limit the scope of the disclosure.

[0064] In addition, when describing representative embodiments, the present disclosure may have presented the method and / or process as a specific sequence of steps. However, insofar as the method or process does not rely on the specific sequence of steps set forth herein, the method or process should not be limited to the specific sequence of steps described. Other sequences of steps are also possible. Such a sequence can be varied and still remain within the scope of the present disclosure. Therefore, the specific sequence of steps disclosed herein should not be interpreted as a limitation to the present disclosure.

Claims

1. A method of improving calibration transfer between a plurality of Raman analyzer devices, each device having a laser having a wavelength for illuminating a sample and a spectrometer for generating a Raman spectrum of the sample, the method comprising the steps of: Provide multiple standard reference material (SRM) samples; Wherein, the SRM samples are existing fluorescent glasses, each of which is provided with a published Raman calibration spectrum; packaging the SRM sample in a sealed field calibrator device; Generate Raman reference spectra for each SRM sample under factory-controlled conditions using the same measurement instrument and measurement parameters; Wherein, the measurement parameters include the temperature of the SRM sample when generating the Raman reference spectrum; Wherein, the measurement parameters include the wavelength of the laser used to generate the Raman reference spectrum; storing the Raman reference spectrum in a memory; transmitting the Raman reference spectrum to the Raman analyzer being calibrated; assigning at least one SRM sample to each of the plurality of Raman analyzer devices along with measurement parameters and a Raman reference spectrum generated for each SRM sample; analyzing each SRM reference sample at a corresponding one of the Raman analyzer devices to generate a Raman calibration spectrum for the SRM sample; measuring the temperature of the SRM sample when generating the Raman calibration spectrum; measuring the wavelength of the laser used to illuminate the SRM sample when generating the Raman calibration spectrum; comparing the Raman reference spectrum with the Raman calibration spectrum generated by the Raman analyzer during illumination of the SRM sample; calibrating an intensity axis of a Raman spectrometer at the device using the Raman calibration spectrum and the Raman reference spectrum generated by the Raman analyzer; adjusting the intensity axis of the Raman analyzer based on the difference between the Raman reference spectrum stored in the memory and the Raman calibration spectrum generated by the Raman analyzer by: correcting device calibration based on the difference between the temperature of the SRM sample during generation of the Raman calibration spectrum and the temperature of the SRM sample when generating the Raman reference spectrum, and Device calibration is corrected based on the difference between the wavelength of the laser used to illuminate the SRM sample during generation of the Raman calibration spectrum and the wavelength of the laser used to illuminate the SRM sample when generating the Raman reference spectrum.

2. The method according to claim 1, wherein: The measurement parameters include an illumination geometry of the laser light used to generate the Raman reference spectrum.

3. The method according to claim 2, wherein: The illumination geometry of the laser includes the focal depth of the laser in the SRM sample.

4. The method according to claim 2, comprising the steps of: measuring an illumination geometry of the SRM sample when generating the Raman calibration spectrum; as well as Device calibration is corrected based on the difference between the geometry used to illuminate the SRM sample during generation of the Raman calibration spectrum and the geometry used to illuminate the SRM sample when generating the Raman reference spectrum.

5. The method according to claim 1, further comprising the steps of: At least one of the field calibrator devices is assigned to each of the plurality of Raman analyzer devices.

6. The method according to claim 5, wherein: The field calibrator device includes a port for inserting a temperature probe to measure the temperature of the SRM sample when generating the Raman calibration spectrum.

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