Multipass Faraday rotators and isolators.

Faraday isolators are usually limited to Faraday materials with strong Verdet constants. We present a method to reach the 45° polarization rotation angle needed for optical isolators with materials exhibiting a weak Faraday effect. The Faraday effect is enhanced by passing the incident radiation multiple times through the Faraday medium while the rotation angle accumulates after each pass.

Free-space quasi-phase matching.

We report a new, to the best of our knowledge, approach to phase matching of nonlinear materials based on the free-space multipass cells. This technique is applicable to noncentrosymmetric nonlinear crystals, including crystals that cannot be birefringent phase-matched or quasi-phase matched by periodic poling. Notably, by using this approach, the crystalline quartz is quasi-phase matched with the demonstrated increase of the second harmonic generation efficiency by a factor of 40.

Spectral broadening in convex-concave multipass cells.

Since its first demonstration in 2016, the multi-pass spectral broadening technique has covered impressive ranges of pulse energy (3 µJ - 100 mJ) and peak power (4 MW - 100 GW). Energy scaling of this technique into the joule-level is currently limited by phenomena such as optical damage, gas ionization and spatio-spectral beam inhomogeneity. These limitations can be overcome by the novel multi-pass convex-concave arrangement, which exhibits crucial properties such as large mode size and compactness.

Long-pulse 4.4-4.6 μm laser oscillations of Fe ions in a ZnMnSe (x = 0.3) crystal pumped by a 1940 nm Tm fiber laser through Cr → Fe energy transfer.

Millisecond-pulse laser operation of Fe ions at 78 K is demonstrated in the ZnMnSe:Fe,Cr (x=0.3) crystal under a Tm fiber 1940 nm laser pumping through a Cr→Fe energy transfer process for the first time, to the best of our knowledge. The laser slope efficiency was 1% with respect to absorbed pumping energy at 1940 nm.