Anne-Lise Viotti

Counter-propagating parametric interaction with phonon-polaritons in periodically poled KTiOPO 4

Strongly enhanced backward stimulated polariton scattering (BSPS) is demonstrated in periodically-poled KTiOPO4 (KTP) crystals with a high power-conversion efficiency up to 70%. We study the physical mechanism of such counter-propagating parametric interaction with phonon-polaritons in χ(2) modulated structures. BSPS is a three-wave mixing that is distinguished from backward stimulated Raman scattering (BSRS), while a strong absorption at large polariton wave-vectors can still make BSPS display certain characteristics of BSRS such as self-compression of the Stokes pulse. We also compare BSPS with counter-propagating parametric oscillation in the near- and mid-infrared range, providing an estimation of the fabrication error margin to expect the outcome of their competition in the same device.

Cascaded counter-propagating nonlinear interactions in highly-efficient sub-mu m periodically poled crystals

Mirrorless optical parametric oscillators (MOPOs) are very attractive parametric devices that rely on the nonlinear interaction of counter-propagating photons to inherently establish distributed feedback, without the use of external mirrors or surface coatings. These devices offer unique spectral and coherence properties that will benefit a large variety of applications ranging from spectroscopy to quantum communications. The major obstacle in exploiting their full potential is ascribed to the difficulty in engineering a nonlinear material in which the generation of counter-propagating waves can be phase matched. Here we present a reliable and consistent technique for fabrication of highly-efficient sub-micrometer periodically poled Rb-doped KTiOPO4. We experimentally demonstrate the first cascaded counter-propagating interactions in which the generated forward signal serves as a pump for a secondary MOPO process, reaching pump depletion larger than 60%. The cascaded process exemplifies the high efficiency of our nonlinear photonic structures. Our domain-engineering technique paves the way to realize counter-propagating schemes and devices that have been deemed unfeasible until now.

Supercontinuum generation and soliton self-compression in chi((2))-structured KTiOPO4

Ultrafast sources in the mid-IR are indispensable research tools for spectroscopic and medical applications and can also potentially be used to generate attosecond pulses. We investigated a route t ...

Highly efficient periodically poled KTP-isomorphs with large apertures and extreme domain aspect-ratios

Since the early 1990’s, a substantial effort has been devoted to the development of quasi-phased-matched (QPM) nonlinear devices, not only in ferroelectric oxides like LiNbO3, LiTaO3 and KTiOPO4 (KTP), but also in semiconductors as GaAs, and GaP. The technology to implement QPM structures in ferroelectric oxides has by now matured enough to satisfy the most basic frequency-conversion schemes without substantial modification of the poling procedures. Here, we present a qualitative leap in periodic poling techniques that allows us to demonstrate devices and frequency conversion schemes that were deemed unfeasible just a few years ago. Thanks to our short-pulse poling and coercive-field engineering techniques, we are able to demonstrate large aperture (5 mm) periodically poled Rb-doped KTP devices with a highly-uniform conversion efficiency over the whole aperture. These devices allow parametric conversion with energies larger than 60 mJ. Moreover, by employing our coercive-field engineering technique we fabricate highlyefficient sub-µm periodically poled devices, with periodicities as short as 500 nm, uniform over 1 mm-thick crystals, which allow us to realize mirrorless optical parametric oscillators with counter-propagating signal and idler waves. These novel devices present unique spectral and tuning properties, superior to those of conventional OPOs. Furthermore, our techniques are compatible with KTA, a KTP isomorph with extended transparency in the mid-IR range. We demonstrate that our highly-efficient PPKTA is superior both for mid-IR and for green light generation – as a result of improved transmission properties in the visible range. Our KTP-isomorph poling techniques leading to highly-efficient QPM devices will be presented. Their optical performance and attractive damage thresholds will be discussed.

Periodically Poled KTP with Sub-wavelength Periodicity: Nonlinear Optical Interactions with Counter Propagating Waves

We present the recent development on periodically poled nonlinear crystals with subwavelength periodicities as short as 500 nm. These devices show conversion efficiencies larger than 45%. Their uni ...

Generation of widely-tunable narrowband infrared radiation by PPRKTP mirrorless OPO and broadband chirped-pulse OPA

Self-established optical parametric oscillation (OPO), or mirrorless OPO (MOPO), owing to the feedback provided by counter-propagating second-order interaction, is characterized by spectral properties drastically different from those observed in co-propagating OPOs [1]. One of the most striking among those is the large asymmetry in the signal and idler spectral widths, where the bandwidth of counter-propagating idler wave is inherently narrow and comprises less than 2% of the bandwidth of the pump. The signal wave then inherits the phase modulation information from the pump [2]. Although the narrow bandwidth of the idler in the near- and mid-infrared region would be a useful feature for many spectroscopic applications, the insensitivity of the idler wavelength to the wavelength of the pump makes MOPO idler rather difficult to tune by tuning the pump wavelength. For instance, tuning the idler by 1 THz would require pump tuning over 100 THz which is comparable to the Ti:Sapphire gain bandwidth. Angular and temperature tuning ranges are also essentially limited to a hundred GHz [3].