Open Source Spectrometer Lit Review
As follows is the chronological order of articles related to Open Source Spectrometer design. Current as of Q1 2014.
Spectrometer Design
Design and implementation of a high-resolution, high-efficiency optical spectrometer
Abstract: We present the design, implementation and testing of a high-efficiency, high-resolution transmission grating spectrometer for measurements of near-ultraviolet to visible-range spectra of light from an electron beam ion trap, where geometry is constrained. The system consists of two 5 in. diameter f/4.6 achromatic lenses, a 6 in. diameter transmission grating ion-beam etched in fused silica, and a thinned, backilluminated CCD detector. The simple design minimizes the number of optical components, each with optimal throughput and high efficiency. Using a 30 μm wide entrance slit, a resolving power (λ/Δλ) of 15 400 at λ≈3850 Å has been demonstrated. The features and limitations of the instrument have been explored and an in situ calibration technique for use on the Livermore EBIT-II and SuperEBIT electron beam ion traps has been developed. © 2002 American Institute of Physics.
Chirped holographic grating used as the dispersive element in an optical spectrometer
Abstract: We have developed a new design of optical spectrometer based on the use of a chirped holographic grating inscribed on a flat substrate. This type of grating has a surface modulation with a spatially varying period. The ability of the chirped grating to focus a beam is exploited to reduce significantly the physical dimensions of the instrument. Wavelength selection is achieved by a pure translation of the chirped grating. The properties of the chirped grating spectrometer have been characterized with different lasers and arc lamps and compared with those of two commercial spectrometers. A performance parameter has been defined, enabling the various instruments to be compared. © 2005 Optical Society of America
Cavity ring‐down optical spectrometer for absorption measurements using pulsed laser sources
Abstract: We have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources. The technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined within a closed optical cavity. The decay of the light intensity within the cavity is a simple exponential with loss components due to mirror loss, broadband scatter (Rayleigh, Mie), and molecular absorption. Narrowband absorption spectra are recorded by scanning the output of a pulsed laser (which is injected into the optical cavity) through an absorption resonance. We have demonstrated the sensitivity of this technique by measuring several bands in the very weak forbidden b1Σg-X3Σg transition in gaseous molecular oxygen. Absorption signals of less than 1 part in 106 can be detected.
Digital optical spectrometer-on-chip
Abstract: A concept of digital optical spectrometer-on-chip is proposed and results of their fabrication and characterization are reported. The devices are based on computer-designed digital planar holograms which involves millions of lines specifically located and oriented in order to direct output light into designed focal points according to the wavelength. Spectrometers were fabricated on silicon dioxide and hafnium dioxide planar waveguides using electron beam lithography and dry etching. Optical performances of devices with up to 1000 channels for a central wavelength of 660 nm are reported.
Compact, Self-Contained Optical Spectrometer
Abstract: We describe the construction and performance of a self-contained, battery-operated, hand-held optical spectrometer. This unit contains an onboard optical excitation source, miniaturized monochromator, CCD detector, Peltier cooler, LCD display module, and microprocessor control. We demonstrate capabilities for qualitative fluorescence determinations and semiquantitative fluorescence and absorption measurements. Resolution is λ/δλ ≍ 1200 at 434 nm.
Abstract: A new charge-coupled device (CCD) spectrometer has been studied and constructed by using a two-dimensional CCD detector and an integrated grating consisting of 10 subgratings. Effective spectral images of 268 mm along the dispersion direction have been densely folded 10 times to cover the full 200–1000 nm working wavelength range without any mechanical moving elements. The results show that the system has a spectral resolution and acquisition time of better than 0.07 nm and less than 100 ms, respectively, in the entire spectral range after system calibration.
Abstract: We present a steady-state radially resolved diffuse reflectance spectrometer capable of measuring the absorption and transport scattering spectra of tissue-simulating phantoms over an adjustable 170-nm wavelength interval in the visible and near infrared. Measurements in a variety of phantoms are demonstrated over the relevant range of tissue optical properties, and the accuracy of the instrument is found to be approximately 10% in both scattering and absorption. Monte Carlo simulations designed to test the accuracy of the instrument are presented that support the experimental findings.
Application
Ethylene optical spectrometer for apple ripening monitoring in controlled atmosphere store-houses
Abstract: In today's store-houses the ripening of fruit is controlled by managing the ethylene concentration in the ambient atmosphere. Precise and continuous ethylene monitoring is very advantageous since low ethylene concentrations are produced by the fruit itself and are indicative of its ripeness, and on other occasions, ethylene is externally added when ripeness or degreening of the product must be promoted. In this work, a multichannel mid-infrared spectrometer for ethylene measurement is built and characterized. The instrument contains additional channels to reject potential cross-interferences like ammonia and ethanol. Additionally, these channels are useful for monitoring a potential malfunction of the cooling system and possible fouling of the fruit, respectively. The complete spectrometer contains a silicon-based macroporous infrared (IR) emitter, a miniaturized long path cell (white cell), a four-channel detector module, low-noise analog amplification and filtering, and a microcontroller-based lock-in amplifier. The new inner architecture of the detector module features a fourfold thermopile array with narrow band optical filters attached by flip-chip technology, and a Fresnel lens array attached on the lid of the package. Laboratory tests show that the system is able to distinguish between ammonia and ethylene, featuring a detection limit of 30 ppm and 160 ppm (95% confidence) for ethylene and ammonia, respectively. Field tests show that the spectrometer is suitable as an ethylene alarm to detect fruit ripening and prevent fruit to decline into senescence. Simulation results show that system selectivity could be improved by setting ammonia channel to another absorption wavelength.
Analysis of the repetitively pulsed dual‐beam thermo‐optical absorption spectrometer
Abstract: An analysis is presented for the repetitively pulsed dual‐beam thermo‐optical absorption spectrometer, which has been used recently to determine the absorption strengths of several organic liquids in the visible spectral region covered by the cw tunable dye laser. The model succeeds in describing the development of the thermal lens on a pulse‐by‐pulse basis. The equations derived are then used to optimize the spectrometer design with respect to the parameters which are under the control of the experimenter. It is further demonstrated how one identifies the region of linear operation of the spectrometer. Finally, it is shown how the relative absorptivities of compounds may be determined.
Frequency-domain multisource optical spectrometer and oximeter
Abstract: We have designed and constructed a near-infrared spectrometer for the non-invasive optical study of biological tissue. This instrument works in the frequency-domain and employs multiple source-detector distances to recover the absorption coefficient ((mu) (alpha )) and the reduced scattering coefficient ((mu) s') of tissue. The light sources are eight light emitting diodes (LEDs) whose intensities are modulated at a frequency of 120 MHz. Four LEDs emit light at a peak wavelength of 715 nm ((lambda) 1), while the other four LEDs emit at a peak wavelength of 850 nm ((lambda) 2). From the frequency-domain raw data of phase, dc intensity, and ac amplitude obtained from each one of the eight light sources, which are located at different distances from the detector fiber, we calculate (mu) (alpha ) and (mu) s' at the two wavelengths (lambda) 1 and (lambda) 2. The concentrations of oxy- and deoxy-hemoglobin, and hence hemoglobin saturation, are then derived from the known extinction coefficients of oxy- and deoxy-hemoglobin at (lambda) 1 and (lambda) 2. The statistical error in the measurement of the optical coefficients due to instrument noise is about 1 - 2%. The accuracy in the determination of the absolute value of the optical coefficients is within 10 - 20%. Preliminary results obtained in vivo on the forearm of a volunteer during an ischemia measurement protocol are presented.
Miniaturized spectrometer employing planar waveguides and grating couplers for chemical analysis
Abstract: Polymeric and metal oxide planar waveguides were used to demonstrate the potential of a miniature spectrometer. Multiwavelength light was transmitted through the substrate and coupled into the waveguide through a diffraction grating located at the substrate/waveguide interface. A second diffraction grating spatially dispersed the light propagated through the waveguide into component wavelengths for rapid analysis with a photodiode array detector. These results suggest that planar waveguides can be used to perform attenuated total internal reflection measurements in the visible and near-IR regions for chemical analysis of weak vibrational overtones and combination modes with effective path lengths of several millimeters.
Abstract: A spectral-domain white-light interferometric technique with channelled spectrum detection is used to measure the wavelength dependence of the spectral bandpass of a fibre-optic spectrometer. In an experimental setup comprising a halogen lamp, a non-dispersive Michelson interferometer and the spectrometer to be measured, spectral interferograms are recorded for different optical path differences (OPDs) between interfering beams. By processing the recorded spectral interferograms using discrete filtering and a fringe amplitude demodulation method, spectral fringe visibilities, first, as a function of the wavelength for given OPDs, and second, as a function of the OPD at given wavelengths, are obtained. It is confirmed, in accordance with theory, that the latter spectral fringe visibility functions are Gaussian functions with maxima and widths dependent on the wavelength. From the widths of the Gaussian spectral fringe visibility functions the wavelength dependence of the spectrometer bandpass is determined over a wide spectral range.
See also