Conversion of one laser frequency to another is one of the oldest and most useful effects in nonlinear optics. In the basic process for frequency conversion, two input light fields are mixed in a nonlinear crystal to generate a third field whose frequency is the sum or difference of the input frequencies.
â€‹
In our research, we have drawn an analogy between frequency conversion and the physics of two or more coupled quantum levels. This elementary dynamical system appears in many fields of physics and particularly in optics. The analogy allows the use of a geometrical representation, known as the Bloch sphere in atomic physics or the Poincare sphere in polarization optics, in order to gain physical intuition on the dynamics of the process without having to perform numerical simulations. By adapting schemes from atomic systems, new concepts to solve fundamental problems in frequency conversion can be introduced.
â€‹
One of such fundamental problem is that in wavelength conversion devices, there is usually a tradeoff between the efficiency of the conversion and the bandwidth over which the device functions. Most often the efficiency of the process depends on maintaining small phase mismatch between the interacting beams, which leads to high conversion efficiency only for a narrow region of wavelengths. Several suggestions were made for improving the bandwidth response of frequency conversion, which is particularly important for frequency conversion of ultrashort pulses which are inherently broad. But at the cost a price of severe reduction of the conversion efficiency.
â€‹
Adiabatic frequency conversion is a novel method, which circumvents this tradeoff, making it possible to simultaneously achieve broad bandwidth and excellent conversion efficiency.
â€‹
In our first publication (2008), we have presented a geometrical representation for SFG/DFG processes , suggested the adiabatic frequency conversion scheme, and proved its validity using quasiCW lasers.
In the second publication (2009), we have introduced the theory of Landau and Zener in the realm of frequency conversion. The theory give an excellent rigorous way to design an adiabatic frequency converters. Also, we have examined the robustness of the device to other parameters of the nonlinear interaction, such as crystal length, crystal temperature, and pump intensity.
â€‹
In a third publication (2011), we have devise a way to extend the scheme to the conversion of ultrashort pulses, where we have achieved approximately 11% photon efficiency for a 80nm bandwidth in a SFG process, and ~45% photon efficiency for 20nm bandwidth for a DFG process.
In our fourth publication done with the collaboration of Prof. Kärtner and his team from MIT (2012), we have shown for the first time, nearly complete conversion of a 0.7 octave Ti:Sap oscillator into the midIRm which is the first experimental verification of the LZ formula. The fruitful collaboration allowed us to demonstrate recently also an efficient conversion of an octave spanning ultrashort pulse to the midIR.
Since our first experimental demonstration of adiabatic evolution in SFG/DFG processes, the adiabatic concept in nonlinear optics has gain popularity and several groups worldwide have further developed the concept to:

Other nonlinear parametric processes, such as adiabaticity in OPA process M. Fejer & U. Keller groups (Stanford & ETH).

Other adiabatic processes, such as performed by G. Porat & A. Arie at TAU, and by A. Rangelov and N. Vitanov from Sofia university.

Adiabaticity in the full nonlinear dynamical interaction, developed by G. Porat & A. Arie at TAU and Phillips & M. Fejer (Stanford).
For further reading on adiabatic processes in frequency conversion, one can read our recent article in Laser & Photonics Review. Also, we have published a more popular article in Optics and Photonics News, discussing the adiabatic scheme, along with with other broadband frequency conversion devices.
â€‹â€‹
Relevant Publication:

H. Suchowski, D. Oron, A. Arie, Y. Silberberg, "Geometrical representation of sum frequency generation and adiabatic frequency conversion", Phys. Rev. A 78, 063821 (2008). Read Article >>

H. Suchowski, V. Prabhudesai, D. Oron, A. Arie, Y. Silberberg, "Robust efficient sum frequency conversion", Opt. Exp. 17, 12732 (2009). Read Article >>

H. Suchowski, B. D. Bruner, A. Arie, Y. Silberberg, "Broadband frequency conversion", Optics and Photonics News, 21, 10, 3641 (2010). PDF

H. Suchowski, B. D. Bruner, A. GannanyPadowicz, I. Juwiler, A. Arie, Y. Silberberg, "Efficient upconversion of ultrafast pulses", App. Phys. B. 105, 697 (2011). PDF

J. Moses , H. Suchowski, F. X. Kärtner, "Fully efficient adiabatic frequency conversion of broadband Ti:sapphire oscillator pulses”, Opt. Lett., 37, 1589 (2012). PDF

H. Suchowski, P. R. Krogen, S. W. Huang, F. X. Kärtner, J. Moses, “Octavespanning coherent midIR pulses via adiabatic difference frequency generation”, Opt. Exp. 21, 28892 (2013). PDF

H. Cankaya, A. L. Calendron, H. Suchowski, F. X. Kärtner, “Highly efficient broadband sumfrequency generation in visible wavelength range”, Opt. Lett. 39, 2912 (2014). PDF

H. Suchowski*, G. Porat*, A. Arie, “Adiabatic processes in frequency conversion”, Laser and Phot. Rev. 8, 333 (2014). PDF
â€‹
Patent:

H. Suchowski, Y. Silberberg, "Efficient Broadband Optical Wavelength Conversion", WO2009118738, EP2265992 (2009). PDF