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Water-window high harmonic generation with 0.8-µm and 2.2-µm OPCPAs at 100 kHz
Optics Express
|November 23, 2021
Summary
Generating water-window harmonics using 0.8-µm and 2.2-µm lasers shows comparable efficiency. While longer wavelengths offer higher flux, shorter wavelengths provide a viable alternative for water-window harmonic generation.
Area of Science:
- Attosecond science
- High-intensity laser-matter interactions
- Quantum optics
Background:
- High-order harmonic generation (HHG) is crucial for producing extreme ultraviolet (XUV) and soft X-ray radiation.
- The water window (283-543 eV) is a key spectral region for biological imaging due to the high contrast of carbon-based samples.
- Laser wavelength significantly impacts HHG efficiency and spectral characteristics.
Purpose of the Study:
- To compare the generation of high-order harmonics in the water window using 0.8-µm and 2.2-µm few-cycle laser systems.
- To investigate the underlying generation mechanisms, particularly for the 0.8-µm driver.
- To evaluate the flux and efficiency of water-window harmonic generation at different driving wavelengths.
Main Methods:
- Comparison of HHG spectra from helium and neon.
- Utilizing a 100 kHz pulse repetition rate laser system with few-cycle pulses.
- Employing the same beamline and pump laser for both 0.8-µm and 2.2-µm drivers for direct flux comparison.
- Analysis of phase-matching conditions (conventional vs. non-adiabatic self-phase-matching).
Main Results:
- Photons up to 0.6 keV (2 nm) were generated with both laser systems.
- A 10-100 times higher flux for water-window harmonics was observed with the 2.2-µm laser compared to the 0.8-µm laser at photon energies around 280 eV.
- The crossover energy, where the 2.2-µm driver yields higher flux, was found to be as high as 0.2 keV.
- The 0.8-µm laser system demonstrated an efficiency close to the 2.2-µm source for water-window harmonic generation.
Conclusions:
- Long-wavelength lasers in a phase-matched regime are effective for efficient water-window harmonic generation.
- The 0.8-µm laser wavelength, despite being more common, can achieve competitive efficiency for generating water-window harmonics.
- This study provides valuable insights for selecting optimal laser parameters for specific water-window harmonic generation applications.
