Laser system and method for generating laser pulses
A laser system generates laser pulses having a determined carrier-envelope-offset, CEO. The laser system includes a Cr-doped II-VI based laser oscillator system having a resonator cavity, which emits laser pulses having a peak power of at least 0.75 MW. The laser system further includes a nonlinear optical element for spectrally broadening at least a part of the emitted laser pulses irradiated onto the nonlinear optical element to provide the laser pulses with octave-spanning spectral components, and a frequency-doubling element for generating second harmonic spectral components of at least a part of the octave-spanning spectral components. In addition, the laser system includes an f-2f-interferometry device for generating a beating signal of at least a part of the overlapping spectral components exiting the frequency-doubling element and interfering with each other at the f-2f-interferomtry device and for determining and/or controlling the CEO of the emitted laser pulses based on the beating signal.
1 . A laser system for generating laser pulses having a determined carrier-envelope-offset, CEO, the laser system comprising:
a Cr-doped II-VI based laser oscillator system having a resonator cavity, wherein the laser oscillator system is configured to emit laser pulses from the resonator cavity having a peak power of at least 0.75 MW;
a nonlinear optical element for spectrally broadening at least a part of the emitted laser pulses irradiated onto the nonlinear optical element to provide the laser pulses with octave-spanning spectral components;
a frequency-doubling element for generating second harmonic spectral components of at least a part of the octave-spanning spectral components of the spectrally broadened laser pulses when irradiating the spectrally broadened laser pulses onto the frequency-doubling element, such that a part of the second harmonic spectral components spectrally overlap with a part of the remaining octave-spanning spectral components of the laser pulses, wherein the nonlinear optical element for spectrally broadening and the frequency-doubling element are separate elements; and
an f-2f-interferometry device for generating a beating signal of at least a part of the overlapping spectral components exiting the frequency-doubling element and interfering with each other at the f-2f-interferomtry device and for determining and/or controlling the CEO of the emitted laser pulses based on the beating signal.
2 . The laser system according to claim 1 , wherein overlapping second harmonic spectral components exiting the frequency-doubling element propagate collinearly and temporally overlapping with residual fundamental spectral components along a common optical path.
3 . The laser system according to claim 1 , wherein the beating signal is generated only by the interfering overlapping spectral components of the second harmonic spectral components and the octave-spanning spectral components of the laser pulses remaining after the frequency-doubling element.
4 . The laser system according to claim 1 , further comprising a spectral filter element for spectrally filtering the overlapping spectral components prior to generating the beating signal.
5 . The laser system according to claim 1 , wherein controlling the CEO of the emitted laser pulses comprises adjusting the laser oscillator system such as to emit laser pulses having a predetermined CEO.
6 . The laser system according to claim 5 , wherein adjusting the laser oscillator system comprises adjusting an internal dispersion of the resonator cavity and/or adjusting a pumping power for pumping the gain medium of the laser oscillator system and/or adjusting an internal optical loss of the resonator cavity.
7 . The laser system according to claim 1 , wherein controlling the CEO comprises stabilizing the CEO to a predetermined CEO.
8 . The laser system according to claim 1 , wherein the nonlinear optical element for spectrally broadening has a thickness of 1 mm or less.
9 . The laser system according to claim 1 , wherein the nonlinear optical element for spectrally broadening comprises or consists of rutile TiO 2 .
10 . The laser system according to claim 1 , wherein the Cr-doped II-VI based laser oscillator system comprises a gain medium comprising or consisting of Cr-doped ZnS and/or Cr-doped ZnSe.
11 . The laser system according to claim 1 , wherein the Cr-doped II-VI based laser oscillator system comprises an imaging unit forming part of the resonator cavity, wherein the imaging unit is adapted to decouple a spot size of an intra-cavity laser beam at a gain medium from an intra-cavity length of the resonator cavity, and wherein the resonator cavity and the imaging unit are configured such that the laser oscillator system emits laser pulses at a repetition rate of 50 MHz or less.
12 . The laser system according to claim 11 , wherein the imaging unit includes an end mirror of the resonator cavity.
13 . The laser system according to claim 12 , wherein the imaging unit is configured to image the end mirror of the resonator cavity included in the imaging unit to an image plane, and wherein the imaging unit is adapted to maintain a distance of the image plane from another end mirror of the resonator cavity unchanged when adapting a length of the resonator cavity by the imaging unit.
14 . The laser system according to claim 1 , wherein the laser oscillator system is configured to emit laser pulses having a pulse duration of 40 fs FWHM or less.
15 . The laser system according to claim 1 , wherein the laser system is configured such that the beating signal has a signal-to-noise ratio of 40 dB or more measured at a radio-frequency resolution bandwidth of 100 kHz.
16 . The laser system according to claim 1 , further comprising a diode-based pump source for optically pumping a gain medium of the Cr-doped II-VI based laser oscillator system.
17 . The laser system according to claim 16 , wherein the diode-based pump source comprises one or more light-emitting diodes and/or one or more laser diodes.
18 . A method for generating laser pulses having a determined carrier-envelope-offset, CEO, the method comprising:
providing laser pulses having a peak power of at least 0.75 MW and spectral components in a range from 1.8 μm to 2.4 μm emitted from a resonator cavity of a Cr-doped II-VI based laser oscillator system;
spectrally broadening the laser pulses in a nonlinear optical element for spectrally broadening to provide the laser pulses with octave-spanning spectral components;
generating second harmonic spectral components of at least a part of the octave-spanning spectral components of the spectrally broadened laser pulses in a frequency-doubling element, such that a part of the second harmonic spectral components spectrally overlap with a part of the remaining octave-spanning spectral components of the laser pulses, wherein the nonlinear optical element for spectrally broadening and the frequency-doubling element are separate elements;
generating a beating signal of at least a part of the overlapping spectral components exiting the frequency-doubling element and interfering with each other at an f-2f-interferometry device; and
determining and/or controlling the CEO of the emitted laser pulses based on the beating signal.
19 . The method according to claim 18 , wherein controlling the CEO of the emitted laser pulses comprises adjusting the laser oscillator system such as to emit laser pulses having a predetermined CEO.