Direct observation of bulk second-harmonic generation inside a glass slide with tightly focused optical fields

Bulk second-harmonic generation (SHG) inside glass slides is directly detected unambiguously without interference from surface contributions. This is enabled by tightly focused and highly localized ultrashort laser pulses. The theoretical calculations based on vector diffraction theory and the phenomenological model of SHG inside centrosymmetric materials agree well with the measured far-field SHG radiation patterns for different polarization states of the fundamental beam. The results indicate that the observed bulk SHG is predominantly related to the bulk parameter ${\delta }^{\prime }$ and originates from the three-dimensional field gradient in the focal region.

Figure 1

Spectra of the fundamental (red dashed line) and bulk generated SH (black solid line) beams, recorded by the spectrometer.

Figure 2

Measured intensities of SHG (solid squares) and THG (open circles) as the function of focal position inside a borosilicate glass slide.

Figure 3

Power conversion efficiency of bulk SHG from borosilicate, BK7, Pyrex, and soda lime glass samples.

Figure 4

SH radiation patterns for different φ values. Values used for φ and their corresponding polarization states of the incident PW (first row), the experimentally measured patterns (second row), theoretical calculations for ${\delta }^{\prime }=1$ and $\gamma =0$ (third row), ${\delta }^{\prime }=0$ and $\gamma =1$ (fourth row), and ${\delta }^{\prime }=1$ and $\gamma =-0.5$ (fifth row).