A method for determining an optical pathlength through a cuvette of a spectrophotometric apparatus includes obtaining a first single beam spectrum of a liquid zero-material at least in a first energy region in which the liquid zero-material absorbs at least a portion of incident optical radiation; obtaining a second single beam spectrum of a second liquid at least in the first energy region, the second liquid having a composition excluding the liquid zero-material and having no absorption of incident optical radiation in the first energy region; determining a dual beam spectrum of the liquid zero-material relative to the second liquid at least in the first energy region from the first and second single beam spectra; and calculating an optical pathlength through the cuvette based on processing spectral information obtained from the first energy region of the determined dual beam spectrum.

A method for determining an optical pathlength through a cuvette of a spectrophotometric apparatus includes obtaining a first single beam spectrum of a liquid zero-material at least in a first energy region in which the liquid zero-material absorbs at least a portion of incident optical radiation; obtaining a second single beam spectrum of a second liquid at least in the first energy region, the second liquid having a composition excluding the liquid zero-material and having no absorption of incident optical radiation in the first energy region; determining a dual beam spectrum of the liquid zero-material relative to the second liquid at least in the first energy region from the first and second single beam spectra; and calculating an optical pathlength through the cuvette based on processing spectral information obtained from the first energy region of the determined dual beam spectrum.

Methods and apparatus are presented for measuring a photoluminescence (PL) response, preferably a spatially resolved image of a PL response, from an object exposed to solar irradiation. In certain embodiments signals from the object are measured in two or more different spectral bands selected such that one of the measured signals has a higher PL component relative to ambient reflectance compared to another measured signal, enabling the PL component to be enhanced by a suitable differencing procedure. In other embodiments a signal from an object is measured in a spectral band selected such that at least 20% of the measured signal comprises PL generated from the object by the solar irradiation. The methods and apparatus have particular application to outdoor inspection of photovoltaic modules without having to modulate the operating point of the modules.

System for performing chemical spectroscopy on samples from the scale of nanometers to millimeters or more with a multifunctional platform combining analytical and imaging techniques including dual beam photo-thermal spectroscopy with confocal microscopy, Raman spectroscopy, fluorescence detection, various vacuum analytical techniques and/or mass spectrometry. In embodiments described herein, the light beams of a dual-beam system are used for heating and sensing.

System for performing chemical spectroscopy on samples from the scale of nanometers to millimeters or more with a multifunctional platform combining analytical and imaging techniques including dual beam photo-thermal spectroscopy with confocal microscopy, Raman spectroscopy, fluorescence detection, various vacuum analytical techniques and/or mass spectrometry. In embodiments described herein, the light beams of a dual-beam system are used for heating and sensing.

Modulation-encoded light, using different spectral bin coded light components, can illuminate a stationary or moving (relative) target object or scene. Response signal processing can use information about the respective different time-varying modulation functions, to decode to recover information about a respective response parameter affected by the target object or scene. Electrical or optical modulation encoding can be used. LED-based spectroscopic analysis of a composition of a target (e.g., SpO2, glucose, etc.) can be performed; such can optionally include decoding of encoded optical modulation functions. Baffles or apertures or optics can be used, such as to constrain light provided by particular LEDs. Coded light illumination can be used with a focal plane array light imager receiving response light for inspecting a moving semiconductor or other target. Encoding can use orthogonal functions, such as an RGB illumination sequence, or a sequence of combinations of spectrally contiguous or non-contiguous colors.

A method for calibrating sensitivity of a photometer includes measuring, by a double-beam spectrophotometer, an absorbance spectrum of a control solution, which has been diluted and includes a control substance. The method further includes linearly regressing the absorbance spectrum of the control solution over a predetermined range of wavelengths and determining whether a first slope of the linearly regressed absorbance spectrum of the control solution falls within a range of slopes of lines obtained from linearly regressing absorbance spectra of a plurality of reference solutions over the predetermined range of wavelengths. A concentration of chromophore in each reference solution is known and the absorbance spectra of the plurality of reference solutions have been obtained by the double-beam spectrophotometer.

A method for calibrating sensitivity of a photometer includes measuring, by a double-beam spectrophotometer, an absorbance spectrum of a control solution, which has been diluted and includes a control substance. The method further includes linearly regressing the absorbance spectrum of the control solution over a predetermined range of wavelengths and determining whether a first slope of the linearly regressed absorbance spectrum of the control solution falls within a range of slopes of lines obtained from linearly regressing absorbance spectra of a plurality of reference solutions over the predetermined range of wavelengths. A concentration of chromophore in each reference solution is known and the absorbance spectra of the plurality of reference solutions have been obtained by the double-beam spectrophotometer.

In one aspect, a method of detecting a trace gas is disclosed. The method includes containing the trace gas in an optical cavity. The method further includes injecting a first laser light from a first laser into the optical cavity causing the trace gas to transition from an energy state lower that a first excited energy state to the first excited energy state, and injecting a second laser light from a second laser into the optical cavity causing the trace gas to transition from the first excited energy state to a second excited energy state. The method includes measuring, by a detector, a first cavity ringdown intensity as a function of time after turning off the second laser with the first laser on, and a second cavity ringdown intensity as a function of time after turning off the second laser with the first laser off.

Disclosed herein is an all-digital phase and timing correction procedure for coherent averaging in dual-comb and multiheterodyne spectroscopy—applicable to any dual-comb spectroscopy setup. It can account for large frequency/phase instabilities of the used sources, yielding a significant reduction of the noise pedestal and an increase in signal-to-noise ratio (SNR) of the radio frequency (RF) beat notes. This technique is computationally efficient and can be conveniently implemented either as a post-processing algorithm or in a real-time data acquisition and processing platform without the necessity of adding any additional optical elements to the dual-comb spectroscopy system. By implementing this technique, the performance of any comb- or comb-like-source-based DCS system with a sufficient degree of mutual coherence between the optical modes can be improved in terms of SNR and number of spectroscopically-usable RF beat notes. The described technique is compatible with a DC-centered RF spectrum, where the negative frequencies are folded to the positive domain to double the number of beat notes within the detector bandwidth. The technique enables coherent averaging over extended time-scales even for free-running combs, thus increasing the sensitivity of absorption and dispersion DCS measurements.