A wavelength tunable laser includes a filter region having a wavelength selection function on light from a gain region, wherein the filter region is a Sagnac interferometer and includes two ring resonators. The ring resonator has two optical couplers, and first and second curved waveguides that connect the two optical couplers and lengths of which equal to each other, each of the two optical couplers is configured to receive input of the light from the gain region through the input-output port, to couple light of a resonant peak to a bar port of the input-output port, and to couple light except light at a resonant peak wavelength to a cross port of the input-output port, and the first curved waveguide connects the bar ports of the input-output ports of the two optical couplers, and the second curved waveguide connects the cross ports of ports, of the two optical couplers, that the first curved waveguide is connected to.

A line narrowing module includes a prism including an entrance side surface that light enters, an exit side surface from which the light is emitted, and a bottom surface, and configured to wavelength-disperse the light having entered the entrance side surface and to emit the light from the exit side surface; a holder portion having a stationary surface on which the bottom surface of the prism is secured; a rotary mechanism portion including a rotary stage on which the holder portion is secured, the rotary stage being configured to rotate the prism around an axis perpendicular to a dispersion plane of the light emitted from the prism; a drive unit configured to rotate the rotary stage; and a grating configured to reflect the light emitted from the prism, centroids of the prism, the holder portion, and the rotary stage being located on the axis.

A line narrowing module includes a prism including an entrance side surface that light enters, an exit side surface from which the light is emitted, and a bottom surface, and configured to wavelength-disperse the light having entered the entrance side surface and to emit the light from the exit side surface; a holder portion having a stationary surface on which the bottom surface of the prism is secured; a rotary mechanism portion including a rotary stage on which the holder portion is secured, the rotary stage being configured to rotate the prism around an axis perpendicular to a dispersion plane of the light emitted from the prism; a drive unit configured to rotate the rotary stage; and a grating configured to reflect the light emitted from the prism, centroids of the prism, the holder portion, and the rotary stage being located on the axis.

A system for producing single-frequency or near-single-frequency operation of a laser beam includes a laser for emitting a laser beam at each one of a plurality of cavity lengths, A detector is configured to receive at least a portion of the laser beam emitted, and generate a signal. A computer system is configured to identify at least one beat note in the signal for each of at least one of the plurality of cavity lengths, the at least one beat note indicating the presence of one or more higher-order transverse modes, longitudinal modes, or both, in the received at least the portion of the laser beam emitted at the at least one of the plurality of cavity lengths. The cavity is adjusted to one of the plurality of cavity lengths for eliminating or minimizing the at least one beat note.

A system for producing single-frequency or near-single-frequency operation of a laser beam includes a laser for emitting a laser beam at each one of a plurality of cavity lengths, A detector is configured to receive at least a portion of the laser beam emitted, and generate a signal. A computer system is configured to identify at least one beat note in the signal for each of at least one of the plurality of cavity lengths, the at least one beat note indicating the presence of one or more higher-order transverse modes, longitudinal modes, or both, in the received at least the portion of the laser beam emitted at the at least one of the plurality of cavity lengths. The cavity is adjusted to one of the plurality of cavity lengths for eliminating or minimizing the at least one beat note.

A wavelength control method of a laser apparatus includes sequentially obtaining target wavelength data of a pulse laser beam, sequentially saving the target wavelength data, sequentially measuring a wavelength of the pulse laser beam to obtain a measured wavelength, calculating a wavelength deviation using the measured wavelength and the target wavelength data at a time before a time when the measured wavelength is obtained, and feedback-controlling the wavelength of the pulse laser beam using the wavelength deviation.

Online calibration of laser performance as a function of the repetition rate at which the laser is operated is disclosed. The calibration can be periodic and carried out during a scheduled during a non-exposure period. Various criteria can be used to automatically select the repetition rates that result in reliable in-spec performance. The reliable values of repetition rates are then made available to the scanner as allowed values and the laser/scanner system is then permitted to use those allowed repetition rates.

Online calibration of laser performance as a function of the repetition rate at which the laser is operated is disclosed. The calibration can be periodic and carried out during a scheduled during a non-exposure period. Various criteria can be used to automatically select the repetition rates that result in reliable in-spec performance. The reliable values of repetition rates are then made available to the scanner as allowed values and the laser/scanner system is then permitted to use those allowed repetition rates.

A laser light source includes: a resonance unit with a light emitter; and an optical negative feedback unit. The resonance unit includes: a first waveguide; a first reflector to input the reflected light to the first waveguide; a second waveguide; a second reflector connected to the second waveguide; and a ring resonator between the first waveguide and the second waveguide. The light from the first reflector is blocked from the ring resonator and partially transmitted to a first end of the first waveguide opposite to a second end connected to the light emitter and the first reflector. The optical negative feedback unit includes: a third waveguide to which the light transmitted to the first end of the first waveguide is inputted; and a third reflector connected to the third waveguide. The light from the third reflector is inputted to the first waveguide via the third waveguide.

A laser light source includes: a resonance unit with a light emitter; and an optical negative feedback unit. The resonance unit includes: a first waveguide; a first reflector to input the reflected light to the first waveguide; a second waveguide; a second reflector connected to the second waveguide; and a ring resonator between the first waveguide and the second waveguide. The light from the first reflector is blocked from the ring resonator and partially transmitted to a first end of the first waveguide opposite to a second end connected to the light emitter and the first reflector. The optical negative feedback unit includes: a third waveguide to which the light transmitted to the first end of the first waveguide is inputted; and a third reflector connected to the third waveguide. The light from the third reflector is inputted to the first waveguide via the third waveguide.