Ultrafast photonics, nonlinear optics and optical parametric sources.

Visible ultrafast sources

Femtosecond OPO with intracavity frequency doubling

We developed a PPLN-based femtosecond OPO synchronously pumped by a 76 MHz Ti:sapphire laser, generating infrared signal pulses that were internally frequency-doubled in BIBO.

The combination of the high nonlinear gain and broad phase-matching acceptance of PPLN and BIBO enabled continuous coverage across 665–785 nm. Output reached approximately 260 mW, with red pulses as short as 140 fs.

An important feature of the architecture was that wavelength tuning could be achieved primarily by changing the OPO cavity delay rather than repeatedly adjusting the nonlinear-crystal temperature, BIBO angle or pump wavelength.

GHz femtosecond operation

Harmonic repetition-rate optical parametric oscillators

A second direction explored a different approach to increasing the repetition rate of a SPOPO: rather than increasing the repetition rate of the pump laser itself, the OPO cavity was made longer than the fundamental synchronous cavity length.

This enabled output at successive harmonics of a 76 MHz Ti:sapphire pump. Operation reached the 13th harmonic at 988 MHz, with near-transform-limited femtosecond pulses.

With intracavity dispersion compensation using SF11 prisms, stable output was obtained up to the 14th harmonic, 1064 MHz, while retaining wavelength tunability around the 1.5 μm telecommunications region.

Multi-GHz picosecond sources

16 GHz optical parametric pulse generation

The harmonic-repetition-rate concept was extended to picosecond operation using an 81 MHz Yb-fiber laser.

The resulting OPO generated picosecond pulses at approximately 16 GHz — close to the 198th harmonic of the pump repetition rate — with about 650 mW of average power.

The source was tunable across approximately 1.45–1.75 μm, demonstrating the potential of synchronously pumped OPOs for multi-GHz wavelength-tunable ultrafast sources without requiring a multi-GHz pump laser.

High-power near- to mid-IR

Yb-fiber-laser-pumped picosecond OPO

A major part of the work focused on power scaling using a 50 mm MgO:PPLN crystal synchronously pumped by 20.8 ps pulses from an 81.1 MHz Yb-fiber laser.

The system simultaneously produced 7.1 W of signal at 1.56 μm and 4.6 W of idler at 3.33 μm, corresponding to 11.7 W of total average output power and an extraction efficiency of approximately 73%.

Broad tuning extended from approximately 1.43–1.63 μm for the signal and 3.06–4.16 μm for the idler, while maintaining single-mode spatial output and good long-term power stability.

Power optimization

Interferometric variable output coupling

Conventional optical oscillators normally use a fixed output coupler, even though the optimum coupling depends on pump power, wavelength and intracavity loss.

We introduced an antiresonant ring interferometer as a continuously variable output coupler, providing output coupling over approximately 1–60% across a broad spectral range.

In a femtosecond OPO, optimization near 30% coupling produced about twice the extracted power of a conventional low-transmission coupler without degrading pulse duration or spatial beam quality.

The concept was subsequently extended to high-power ring OPOs and to detailed optimization of Yb-fiber-pumped picosecond systems.

Nonlinear materials

BIBO and femtosecond nonlinear frequency conversion

I also contributed to a comprehensive study of bismuth triborate, BiB₃O₆ (BIBO), as a nonlinear optical material for ultrafast frequency conversion.

The work examined linear and nonlinear optical properties, phase-matching configurations, group-velocity mismatch, spectral and angular acceptance, parametric gain bandwidth, group-velocity dispersion and spatial walk-off.

These parameters are central to selecting nonlinear crystals and geometries for efficient frequency conversion while preserving short pulse duration and high spatial beam quality.