A swept light source of the present invention keeps a coherence length of an output beam long over an entire sweep wavelength range. A gain of a gain medium is changed with time in response to a wavelength sweep and the coherence length is kept maximum. The gain of the gain medium is kept close to a lasing threshold and an unsaturated gain range of the gain medium is narrowed over the entire sweep wavelength range. An SOA current waveform data acquiring method of driving while keeping the coherence length long, a novel coherence length measuring method, and an optical deflector suitable for the swept light source are also disclosed.

A laser system according to the present disclosure includes: a laser apparatus configured to emit a laser beam; a transmission optical system disposed on a path between the laser apparatus and a target supplied into an EUV chamber in which EUV light is generated; a reflection optical system configured to reflect, toward the target, the laser beam from the transmission optical system; a first sensor configured to detect the laser beam traveling from the laser apparatus toward the reflection optical system; a second sensor configured to detect return light of the laser beam reflected by the reflection optical system and traveling backward to the laser apparatus; and a control unit configured to determine that the reflection optical system is damaged when no anomaly of the laser beam is detected and a light amount of the return light exceeds a predetermined light amount value.

A low-repetition-rate (10-Hz), picosecond (ps) optical parametric generator (OPG) system produces higher energy output levels in a more robust and reliable system than previously available. A picosecond OPG stage is seeded at an idler wavelength with a high-power diode laser and its output at ˜566 nm is amplified in a pulsed dye amplifier (PDA) stage having two dye cells, resulting in signal enhancement by more than three orders of magnitude. The nearly transform-limited beam at ˜566 nm has a pulse width of ˜170 ps with an overall output of ˜2.3 mJ/pulse. A spatial filter between the OPG and PDA stages and a pinhole between the two dye cells improve high output beam quality and enhances coarse and fine wavelength tuning capability.

A method for increasing the MeV hot electron yield and secondary radiation produced by short-pulse laser-target interactions with an appropriately high or low atomic number (Z) target. Secondary radiation, such as MeV x-rays, gamma-rays, protons, ions, neutrons, positrons and electromagnetic radiation in the microwave to sub-mm region, can be used, e.g., for the flash radiography of dense objects.

A swept light source of the present invention keeps a coherence length of an output beam long over an entire sweep wavelength range. A gain of a gain medium is changed with time in response to a wavelength sweep and the coherence length is kept maximum. The gain of the gain medium is kept close to a lasing threshold and an unsaturated gain range of the gain medium is narrowed over the entire sweep wavelength range. An SOA current waveform data acquiring method of driving while keeping the coherence length long, a novel coherence length measuring method, and an optical deflector suitable for the swept light source are also disclosed.

Embodiments of an optical amplification apparatus are disclosed which include a first optical amplifier, a second optical amplifier, and a mode exchanger. The first optical amplifier is connected to an input port of the mode exchanger, and the second optical amplifier is connected to an output port of the mode exchanger. The first optical amplifier is configured to amplify optical signals carried in a plurality of transmission modes of a few-mode fiber, the plurality of transmission modes of the few-mode fiber may be grouped into N groups, each group includes two transmission modes, and N is a positive integer greater than or equal to 1. The mode exchanger is configured to exchange the two transmission modes carrying optical signals in each group. The second optical amplifier is configured to amplify the optical signals that are carried in the two transmission modes in each group and whose modes are exchanged.

A laser device is a laser device that includes an output unit that outputs seed light to a light amplifying unit. The output unit has a light source unit that outputs, as the seed light, rays of light with a plurality of wavelengths lying within a gain range of the light amplifying unit, and a seed light control unit that controls an intensity-time waveform of the seed light output from the light source unit.

A tunable laser that includes an array of parallel optical amplifiers is described. The laser may also include an intracavity N×M coupler that couples power between a cavity mirror and the array of parallel optical amplifiers. Phase adjusters in optical paths between the N×M coupler and the optical amplifiers can be used to adjust an amount of power output from M−1 ports of the N×M coupler. A tunable wavelength filter is incorporated in the laser cavity to select a lasing wavelength.

A Q switch resonator includes: an optical resonator comprising at least two mirrors, and configured to accumulate power of a continuous wave or an intermittent continuous wave incident from an outside; and a switching element provided in the optical resonator. The switching element is configured such that, when the power accumulated in the optical resonator increases to a predetermined level, the switching element outputs an optical pulse by lowering a Q factor from a first level to a second level lower than the first level.

A frequency stabilizer includes: a delay line interferometer that receives an optical signal corresponding to one frequency mode of a pulsed laser, divides and transmits the received optical signal to a reference arm and a delay arm including an optical fiber delay line, and then outputs an interference signal between signals passing through the reference arm and the delay arm; a photoelectric converter that converts the interference signal into an electrical signal; a mixer that generates a baseband signal of the electrical signal by mixing a carrier frequency signal; and a feedback controller that transmits a control signal generated based on the baseband signal to the pulsed laser. The optical signal passing through the delay arm is weighted with a delay time caused by the optical fiber delay line compared to the optical signal passing through the reference arm, and the optical signal passing through the delay arm is frequency shifted to a carrier frequency of an oscillator. A carrier-envelope offset frequency of the pulsed laser is stabilized by an offset frequency stabilizer.