An optic-microwave frequency discriminator includes: a fiber coupler receives and combines a first laser and a second laser, than the fiber coupler respectively generates and outputs a first light signal and a second light signal; a photodiode module respectively receives the first light signal and the second light signal, and converts the first light signal into a first microwave signal and converts the second light signal into a second microwave signal; a microwave phase shifter generates a shifted microwave signal by introducing a phase shift to the second microwave signal; a 90° microwave bridge combines the first microwave signal and the shifted microwave signal for generating a first bridge signal and a second bridge signal; a normalized balanced detection module generates an error signal; and a control module generates a controlling voltage signal according to the error signal for tuning a frequency of the second laser.

A laser apparatus including an optical element made of a CaF.sub.2 crystal and configured to transmit an ultraviolet laser beam obliquely incident on one surface of the optical element, the electric field axis of the P-polarized component of the laser beam propagating through the optical element coinciding with one axis contained in <111> of the CaF.sub.2 crystal, with the P-polarized component defined with respect to the one surface. A method for manufacturing an optical element, the method including causing a seed CaF.sub.2 crystal to undergo crystal growth along one axis contained in <111> to form an ingot, setting a cutting axis to be an axis inclining by an angle within 14.18±5° with respect to the crystal growth direction toward the direction of another axis contained in <111>, which differs from the crystal growth direction, and cutting the ingot along a plane perpendicular to the cutting axis.

Generator for wholly optical tunable broadband linearly chirped signal comprising a mode-locked laser, a first optical coupler, a first optical filter, a first dispersion module, a second optical filter, a second dispersion module, a tunable time delay module, a second optical coupler, an optical amplifier, and a photodetector. The generator of the present invention employs just one mode-locked laser as a light source, thus preventing instability of the generated signal resulting from independent unrelated lasers. By making use of the principle of wavelength-time mapping and by means of adjusting the center wavelength and the filter bandwidth of the first optical filter and the second optical filter, easy and flexible tuning of the center frequency and sweep bandwidth of the generated linearly chirped signal is realized. The present invention possesses a big advantage on the aspect of generating a broadband linearly chirped signal over other solutions.

Disclosed is a method of performing a measurement in an inspection apparatus, and an associated inspection apparatus and HHG source. The method comprises configuring one or more controllable characteristics of at least one driving laser pulse of a high harmonic generation radiation source to control the output emission spectrum of illumination radiation provided by the high harmonic generation radiation source; and illuminating a target structure with said illuminating radiation. The method may comprise configuring the driving laser pulse so that the output emission spectrum comprises a plurality of discrete harmonic peaks. Alternatively the method may comprise using a plurality of driving laser pulses of different wavelengths such that the output emission spectrum is substantially monochromatic.

Devices and methods are described herein to measure optical power in scanning laser projectors. In general, the devices and methods utilize a filter component and photodiode to measure optical power being generated by at least one laser light source, with the filter component configured to at least partially compensate for the non-uniform electric current response of the photodiode. Such a configuration facilitates accurate optical power measurement using only one photodiode, and thus can facilitate accurate optical power measurement in a relatively compact device and with relatively low cost.

The laser system may include first and second laser apparatuses and a beam delivery device. The first laser apparatus may be provided so as to emit a first laser beam to the beam delivery device in a first direction. The second laser apparatus may be provided so as to emit a second laser beam to the beam delivery device in a direction substantially parallel to the first direction. The beam delivery device may be configured to bundle the first and second laser beams and to emit the first and second laser beams from the beam delivery device to a beam delivery direction different from the first direction.

A stabilized laser source includes a fiber-ring Brillouin laser that incorporates a circulator for non-reciprocal operation and for launching of a pump optical signal. Most of the pump optical signal is launched in a forward direction and drives Brillouin laser oscillation in the backward direction, a portion of which exits via an optical coupler as the optical output of the laser source. A small fraction of the pump optical signal is launched in the backward direction via the optical coupler, and a fraction of that backward-propagating pump optical signal exits via the optical coupler as an optical feedback signal. A frequency-locking mechanism receives the optical feedback signal and controls the pump optical frequency to maintain resonant propagation of the backward-propagating pump optical signal. A second pump optical signal can be launched in the forward direction to generate a second Brillouin laser oscillation.

An optical device may include a laser emitter to generate a first laser beam and a second laser beam with orthogonal polarization states. The optical device may include first and second photodetectors to generate respective first currents based on optical powers of the first and second laser beams. The optical device may include a polarization-based beam splitter to combine the first and second laser beams. The optical device may include a wavelength filter to filter the first and second laser beams based on respective wavelengths of the first and second laser beams. The optical device may include a third photodetector and a fourth photodetector to generate respective second currents based on optical powers of the first and second laser beams after filtration. The wavelengths of the first and second laser beams may be controlled based on the first currents and the second currents.

A narrow linewidth laser in which an all-optical feedback line-up is used to improve the linewidth from a conventional laser source, such as a laser diode. The feedback line-up comprises an optical device having a controllable unbalanced optical coupler arranged on a cavity input path to couple a source signal from the laser source into the optical cavity, and to couple a seed signal received back from the optical cavity into the laser source. The seed signal has a lower power than the source signal. The unbalanced optical coupler may be an optical isolator arranged to couple the seed signal into the laser source at a power level selected to promote preferential stimulated emission within a narrower linewidth. By controlling the power of seed signal such that only a small portion thereof influences the lasing cavity, the narrowing effect of the preferential stimulated emission can be enhanced.

A device may include a first photodetector to generate a first current based on an optical power of an optical beam. The device may include a beam splitter to split a portion of the optical beam into a first beam and a second beam. The device may include a wavelength filter to filter the first beam and the second beam. The wavelength filter may filter the second beam differently than the first beam based on a difference between an optical path length of the first beam and an optical path length of the second beam through the wavelength filter. The device may include second and third photodetectors to respectively receive, after the wavelength filter, the first beam and the second beam and to generate respective second currents.