Apparatus, systems, and methods of generating multi combs can be used in a variety of applications. In various embodiments, a passive resonator can be disposed in the laser cavity of a mode-locked laser to generate a nested frequency comb. The passive resonator can be a sample under investigation, where a characteristic of the sample is determined using the generated nested frequency comb. Additional apparatus, systems, and methods are disclosed.

Apparatus, systems, and methods of generating multi combs can be used in a variety of applications. In various embodiments, a passive resonator can be disposed in the laser cavity of a mode-locked laser to generate a nested frequency comb. The passive resonator can be a sample under investigation, where a characteristic of the sample is determined using the generated nested frequency comb. Additional apparatus, systems, and methods are disclosed.

Apparatus, systems, and methods of generating multi combs can be used in a variety of applications. In various embodiments, a passive resonator can be disposed in the laser cavity of a mode-locked laser to generate a nested frequency comb. The passive resonator can be a sample under investigation, where a characteristic of the sample is determined using the generated nested frequency comb. Additional apparatus, systems, and methods are disclosed.

A technique for producing a coherent beam of hard X-rays is provided. This technique is based on a short wavelength undulator that uses the fields of an electromagnetic wave to deflect a relativistic electron beam along a sinusoidal trajectory in order to cause it to emit X-rays. The undulator consists of a slow-wave structure that is energized by a second counterpropagating electron beam. Cylindrical and planar structure configurations are provided and also a mechanism for electrical and mechanical tuning to allow control over the wavelength of the emitted X-ray beam.

A technique for producing a coherent beam of hard X-rays is provided. This technique is based on a short wavelength undulator that uses the fields of an electromagnetic wave to deflect a relativistic electron beam along a sinusoidal trajectory in order to cause it to emit X-rays. The undulator consists of a slow-wave structure that is energized by a second counterpropagating electron beam. Cylindrical and planar structure configurations are provided and also a mechanism for electrical and mechanical tuning to allow control over the wavelength of the emitted X-ray beam.