In some implementations, an optical assembly comprises an optical cavity; one or more detectors; and an optical component having an input face and an output face configured to receive an input beam to the input face and to produce one or more primary output beams, and a plurality of secondary output beams from the output face, the secondary output beams resulting from multiple internal reflections within the optical component. At least one of the input face is not perpendicular to the input beam or the output face is not perpendicular to the one or more primary output beams. Each primary output beam is transmitted through the optical cavity perpendicular to at least one surface of the optical cavity, and directed to a respective one of the one or more detectors. Each detector is arranged to exclude at least a portion of each secondary output beam.

In some implementations, an optical assembly comprises an optical cavity; one or more detectors; and an optical component having an input face and an output face configured to receive an input beam to the input face and to produce one or more primary output beams, and a plurality of secondary output beams from the output face, the secondary output beams resulting from multiple internal reflections within the optical component. At least one of the input face is not perpendicular to the input beam or the output face is not perpendicular to the one or more primary output beams. Each primary output beam is transmitted through the optical cavity perpendicular to at least one surface of the optical cavity, and directed to a respective one of the one or more detectors. Each detector is arranged to exclude at least a portion of each secondary output beam.

According to the present disclosure, there is provided a device (2) and a method for measuring a wavelength for a laser device. The device (2) for measuring a wavelength for a laser device includes: a first optical path assembly and a second optical path assembly. The first optical path assembly and the second optical path assembly constitute a laser wavelength measurement optical path. The second optical path assembly includes: an FP etalon assembly (11) and an optical classifier (13). The homogenized laser beam passes through the FP etalon assembly (11) to generate an interference fringe. The optical classifier (13) is arranged after the FP etalon assembly (11) in the laser wavelength measurement optical path, and configured to deflect the laser beam passing through the FP etalon assembly (11). The FP etalon assembly (11) allows two FP etalons (FP1, FP2) to share the same optical path for an interference imaging, and therefore a compact structure having a small volume, a simple design, and a high stability are achieved. In cooperation with the optical classifier (13), a precise measurement for a laser wavelength may be achieved, and at the same time a wavelength measurement range is large. It is suitable for an online measurement for a laser wavelength and a corresponding closed-loop control feedback.

A narrow band laser apparatus may include: a laser resonator; a pair of discharge electrodes; a power supply; a first wavelength measurement device configured to output a first measurement result; a second wavelength measurement device configured to output a second measurement result; and a control unit. The control unit calibrates the first measurement result, based on a difference between the second measurement result derived when the control unit controls the power supply to apply a pulsed voltage to the pair of discharge electrodes with a first repetition frequency and the second measurement result derived when the control unit controls the power supply to apply the pulsed voltage to the pair of discharge electrodes with a second repetition frequency, the second repetition frequency being higher than the first repetition frequency.

A laser source may include a laser diode, a modulation device, and a feedback device. The modulation device may include an electric power source and may be suitable for modifying a current intensity applied to the laser diode, which may modify an emission frequency of the laser diode. The feedback device may be suitable for modifying a current intensity applied to the laser diode by the electric power source as a function of the electromagnetic radiation emitted by the laser diode.

An optical locker may include an assembly. The assembly may include a beam splitter, configured to split an input beam into at least three beams; an etalon having at least three regions, positioned so that each beam passes through a different region; a detector configured to measure output intensities, Tn, of the etalon for the beam; and a controller configured to determine a ratio, Ta/Tb, of the output intensities, wherein that ratio has a slope at the output intensities which is above a threshold, obtain a target frequency of the input beam, and determine an actual frequency of the input beam based on the target frequency and the ratio of the output intensities.

An optical locker may include an assembly. The assembly may include a beam splitter, configured to split an input beam into at least three beams; an etalon having at least three regions, positioned so that each beam passes through a different region; a detector configured to measure output intensities, Tn, of the etalon for the beam; and a controller configured to determine a ratio, Ta/Tb, of the output intensities, wherein that ratio has a slope at the output intensities which is above a threshold, obtain a target frequency of the input beam, and determine an actual frequency of the input beam based on the target frequency and the ratio of the output intensities.

In a general aspect, a wavelength of light is measured. In some aspects, a wavelength measurement system includes an interferometer, a camera system, a sensor and a control system. The interferometer includes two reflective surfaces and a transmission medium between the two reflective surfaces. The interferometer is configured to receive an optical signal from a laser and produce an interferogram in response. The camera system is configured to receive the interferogram from the interferometer and generate interferogram data in response. The interferogram data represents the interferogram received from the interferometer. The sensor is configured to sense an environmental parameter of the transmission medium and generate sensor data in response. The control system is configured to perform operations including, receiving the interferogram data from the camera system and the sensor data from the sensor; and computing a wavelength of the laser based on the interferogram data and the sensor data.

A wavelength measuring device configured to detect a wavelength of ultraviolet laser light outputted from a laser resonator with at least one etalon, the wavelength measuring device includes: a first housing having an interior space being sealed and accommodating the etalon, an input window through which the ultraviolet laser light enters to the first housing, the input window being provided at a first opening of the first housing, a first sealing member configured to seal a gap between a rim part of the input window and a circumferential portion of the first opening, a shielding film provided between the rim part of the input window and the first sealing member and configured to shield the first sealing member from the ultraviolet laser light coming from the input window, and a diffusing element provided outside of the first housing and configured to diffuse the ultraviolet laser light before being incident on the input window.

A process for characterizing an optical source including a fixed cavity having a free spectral range, the process including: generating a first radiation; receiving at least a portion of this first radiation by at least one sensor; measuring a signal by each sensor and for each scanned state of the source; on the basis of the signals measured, and for each scanned state of the source, calculating a first data item which represents the wavelength of the first radiation, the calculation including, for each scanned state of the source, a selection of a selected value of the first data item from a plurality of possible values, the selection including the elimination of the values of the first data item which do not correspond to a modulo constant of the free spectral range of the fixed cavity expressed according to the units of the first data item.