A method of performing spectroscopic measurements provides an optical frequency comb, and directs the comb through or at a sample. The optical frequency comb is generated by gain switching a laser diode constructed from Gallium Nitride and related materials. Various techniques are described for manipulating the comb source to achieve desired benefits for spectroscopy.

We present here systems and methods for generating a heterodyne signal using the naturally occurring chirp of a pulsed single-mode laser. The electrical square-wave pulse used to drive the laser heats the laser cavity, causing the laser frequency to change or chirp during the emission of the optical pulse. This chirped optical pulse can be split into a chirped signal pulse that interacts with a sample and a chirped reference pulse that interferes with the chirped signal pulse on a detector to produce a heterodyne modulation whose instantaneous phase and amplitude depend on the sample's dispersion and absorption, respectively. The chirp is reproducible, so the heterodyne modulation, instantaneous phase, and/or instantaneous amplitude can be average over many measurements, either with multiple pulses from the same laser or multiple pulses from different lasers, each emitting at a different wavelength.

A sensitivity boosted laser dispersion spectroscopy system for sensing a sample in a sample cell or in an open path crossing the sample. The system includes a local oscillator arm and a sample arm containing the sample cell or the open path crossing the sample. A laser source is configured to generate a first light beam directed along the sample arm and a second light beam, the second light beam being frequency shifted and directed along the local oscillator arm. An intensity modulator/phase modulator/frequency shifter is disposed in the sample arm configured to generate a multi-frequency beam having known frequency spacing which is then passed through the sample cell to generate a sample arm output. A beam combiner is configured to combine the sample arm output and the second light beam from the local oscillator arm and generate a combined beam. A photodetector is configured to detect the combined beam for sensing the sample in the sample cell.

There are provided a light source device, which is more compact and inexpensive than a known light source device, and an endoscope system having a compact and inexpensive light source device. In a light source device, a light source unit includes a first light source that emits blue light, a second light source that emits broadband green light including not only a green component but also a red component, and an optical filter that adjusts the amount of broadband green light for each wavelength. The optical filter has a characteristic in which the reflectance of the green component is smaller than the reflectance of the red component in the case of reflecting the broadband green light or a characteristic in which the transmittance of the green component is smaller than the transmittance of the red component in the case of transmitting the broadband green light.

A photo-thermal interferometer for measuring the light absorption of an aerosol or gas comprises a first laser source emitting a laser beam and a beam splitter adapted to divide the laser beam into a probe beam and a reference beam. The interferometer further comprises first optical elements which are adapted to direct the probe beam such that it passes through the aerosol and interferes with the reference beam thereafter thereby causing interference patterns. A detector detects the interference patterns. The interferometer further comprises a second laser source configured to emit a pump beam for transferring energy to the aerosol. Second optical elements are adapted to direct the pump beam such that it overlaps with the probe beam at least partially in the aerosol or gas. At least one of the second optical elements modifying the pump beam is an axicon.

An interferometric fluid sensing system includes: a laser; a plurality of first fibre portions arranged to receive laser light from the laser; a second fibre portion configured to provide a reference arm for the interferometric fluid sensing system; and a detector arranged to receive light from the first and second fibre portions, wherein the laser light that passes through a void of each first fibre portion is caused to interfere with light passing through the second fibre portion at or before reaching the detector, wherein each of the first fibre portions is arranged such that that light passing through the void of each first fibre portion travels from the laser to the detector over a different path length from the light passing through the voids of the other first fibre portions.

A method for studying cell viability and protein aggregation involves establishing a Fabry Perot etalon signal within an optical spectroscopic feature, e.g., in the near infrared region. Protein aggregation and cell viability can be reflected by changes observed in the magnitude of the Fourier Transform peaks observed in the frequency or space domain associated with the contrast of the etalon. In short, the presence of viable cells and protein aggregates can degrade the etalon contrast of an etalon window. In some cases, the concentration of cells and monomeric protein can be measured as well.

A fluid analyzer includes a substrate, a quantum cascade laser formed on a surface of the substrate and including a first light-emitting surface and a second light-emitting surface facing each other in a predetermined direction parallel to the surface, a quantum cascade detector formed on the surface and including the same layer structure as the quantum cascade laser and a light incident surface facing the second light-emitting surface in the predetermined direction, and an optical element disposed on an optical path of light emitted from the first light-emitting surface across an inspection region in which a fluid to be analyzed is to be disposed and reflecting the light to feed the light back to the first light-emitting surface.

We present here systems and methods for generating a heterodyne signal using the naturally occurring chirp of a pulsed single-mode laser. The electrical square-wave pulse used to drive the laser heats the laser cavity, causing the laser frequency to change or chirp during the emission of the optical pulse. This chirped optical pulse can be split into a chirped signal pulse that interacts with a sample and a chirped reference pulse that interferes with the chirped signal pulse on a detector to produce a heterodyne modulation whose instantaneous phase and amplitude depend on the sample's dispersion and absorption, respectively. The chirp is reproducible, so the heterodyne modulation, instantaneous phase, and/or instantaneous amplitude can be average over many measurements, either with multiple pulses from the same laser or multiple pulses from different lasers, each emitting at a different wavelength.

A method of performing spectroscopic measurements provides an optical frequency comb, and directs the comb through or at a sample. The optical frequency comb is generated by gain switching a laser diode constructed from Gallium Nitride and related materials. Various techniques are described for manipulating the comb source to achieve desired benefits for spectroscopy.