Unique gas cell constructions based on a hollow-core photonic crystal fiber are used, for example, inside a fiber ring laser cavity as an intracavity gas cell. In one embodiment, two simple terminal blocks are coupled to opposite ends of the hollow-core photonic crystal fiber. Each block features a main through-bore with an optical window at one end and an optical fiber chuck fitted at the other end, while a transverse bore intersects the main bore and features a gas fitting for connection to a gas source or vacuum pump. In another embodiment, the hollow-core photonic crystal fiber is contained within an enclosure whose exterior walls are fitted with optical windows and gas ports. Inside the enclosure, fiber clamps supports the ends of the hollow-core photonic crystal fiber at positions adjacent to an in alignment with the optical windows.

Systems, devices, and methods including one or more optical cavities; one or more light sources configured to emit a specified wavelength or band of wavelengths of light; and one or more photovoltaic detectors configured to receive the emitted light that has traveled over one or more path lengths, where the one or more photovoltaic detectors are configured to detect at least one of: a first trace gas species and a second trace gas species.

A gas absorption spectroscopy device includes a laser light source, an acousto-optic modulator, a resonator, a signal detector, and a controller that measures a concentration of a target component in a gas provided in the resonator based on an attenuation time constant of a ring-down signal. The acousto-optic modulator is switchable between an ON state in which first order light is output to the resonator and an OFF state in which the first order light is not output to the resonator and the zeroth order light is output to outside. The gas absorption spectroscopy device further includes a timing detector that detects an intensity of the zeroth order light of the acousto-optic modulator. The controller determines the starting point of the ring-down signal based on an output signal of the timing detector.

Devices, systems, and methods for determining gas characteristics to monitor transformer operation include extracting gas from transformer fluid for analysis.

Spectroscopic apparatus and methods incorporating a gas sensor configured to detect low concentration gases, including gases that are hazardous volatiles are provided. Low concentration gases can comprise gases where detection of concentrations on the order of parts-per-million (ppm), and in many embodiments part-per-billion (ppb) is required. The gas may be a species, such as, for example hydrogen sulfide (H.sub.2S) that may be produced in drilling and/or volcanic eruptions. The spectroscopic apparatus and methods are configured to operate in particular atmospheres where gas detection can be challenging, such as in ambient air and/or in space where various contaminants may be present. The spectroscopic apparatus and methods may incorporate a long path length detector, such as, for example, a cavity-enhanced absorption spectrometer. The methods and apparatus further incorporate a wavelength modulation technique to improve the signal-to-noise ratio.

A method of generating laser pulses (1) includes: creating a circulating light field in resonator device (11) having resonator length L and an intra-cavity dispersion and configured for supporting light field resonator modes, and generating a pulse train of laser pulses (1) by a mode-locking mechanism. Laser pulses (1) are generated with a repetition frequency and provide a frequency comb with carrier frequency .sub.o and comb modes in frequency space. The intra-cavity dispersion is selected such that round trip phases have a dependency on frequency according to

[00001]$\left(\right)=.Math..Math.m\left(\sqrt{1+4.Math..Math.\frac{-{}_0}{m.Math..Math.{}_r}}-1\right)+\frac{L}{c}.Math.{}_0$

wherein m is an integer providing effective repetition rate (m.sub.r) in combination with mode spacing .sub.r at optical carrier frequency (.sub.o), and the mode-locking mechanism provides a coupling of the resonator modes whereby frequency difference (n=.sub.n+1.sub.n) between neighboring mode frequencies (.sub.n, .sub.n+1) is a linear function of mode frequency number n. Furthermore, a spectroscopy method for investigating a sample, a laser pulse source apparatus and a spectroscopy apparatus are described.

Methods and apparatuses of generating and processing a real-time time-domain cavity ringdown spectroscopy (CRDS) signal from absorbing species in an optical detection system having an optical ringdown cavity using off-axis paths are provided. At least one modulated light signal is generated using one or more light sources, each modulated at specified modulation frequency. Each modulated signal has harmonic frequency components and is input off-axis relative to the cavity's optical axis. The cavity contains mirrors arranged in a predetermined configuration. The optical axis is defined by a path passing through centers of mirrors. The modulated light signal is resonated off axis without astigmatic optical elements to produce CRDS signal and passes at least twice through cavity and across the mirrors without interfering with itself. An overall path length through cavity is greater than path length of optical axis. A photodetector detects the CRDS signal, which is demodulated dependent upon selected harmonics.

Various embodiments are directed to methods, apparatuses, and systems for sensing one or more gases and particulate matter. In various embodiments, a method of detecting a gas and particulate matter within a sensing region comprises emitting, from a beam component, an optical beam along a beam path defined within a sensing region; detecting particulate matter within the sensing region based on particulate data generated by one or more photodetector, the particulate data being defined by a detection of a scattered portion of the optical beam reflected from a particulate positioned along the beam path; and detecting a first gas based on gas data generated by the beam component, wherein the gas data is generated by the beam component via an optical gas sensing means, and wherein the gas data is defined by a detected absorption of the optical beam at a first wavelength corresponding to the first gas.

An optofluidic laser with an ultrasmall Fabry-Perot (FB) micro-cavity, This optofluidic laser consists of two highly reflective cavity mirrors and a micro capillary. The two reflective minors are arranged in parallel to form a resonant cavity with an output mirror on the top and a total reflective mirror on the bottom of the cavity. The cavity length L is 30-50 m, the reflectance of the total reflective mirror is higher than 99.9% and the transmittance of the output mirror is 2%-10%. The capillary, serving as the pathway for the micro fluid, is placed between the two Bragg reflectors. The two ends of the capillary arc connected to Teflon soft tubes. The solution containing either gain medium or biological samples is transported to the FB micro-cavity through the soft tubes. The biological samples pass through the water-soluble or organic liquid gain medium in the micro fluid chamber with a certain speed and, under irradiation of a pumping light, produce high intensity, narrow-band output laser signals. The current invention replaces the traditional fluorescent signals with laser signals as the sensing and imaging medium, to achieve biological sensing with ultra-sensitivity and biological imaging with ultra-resolution.

Systems and methods for detecting trace gases utilize a resonance optical cavity and a coherent light source coupled to the cavity through a cavity coupling mirror. The cavity is constructed of a material having the same or a similar coefficient of thermal expansion as the mirror elements defining the cavity. The main (bulk) cavity material may be the same as the main (bulk) material that forms the mirror elements, or it may be different. Such resonant cavity configurations provide improved accuracy and stability as compared to existing cavity configurations based upon similar principles.