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KTiOPO 4 , KTiOAsO 4 , andKNbO 3 crystals for mid-infrared femtosecond optical parametric amplifiers : analysis and comparison
| Content Provider | Semantic Scholar |
|---|---|
| Author | Cussat-Blanc, Sandrine Ivanov, A. A. Lupinski, Dominique Freysz, Eric |
| Copyright Year | 2000 |
| Abstract | We have designed a simple mid-IR femtosecond OPA seeded by a white-light continuum and delivering very stable, largely tunable and energetic output pulses. This OPA requires fewer than 200μJof 120-fs Ti:sapphire pump pulses as energy. This system allowed us to experimentally compare the performances of potassium crystals (KTP, KTA, and KNbO3) for the generation of up to 100-fs Fourier-transformlimited pulses tunable in1–4.6μm mid-IR wavelengths. PACS: 42.65.Yj; 45.65.Re; 42.70.Mp The development ofs sources working in the spectral domain around3μm is important since it makes it possible to study time-resolved infrared vibrational spectroscopy of C-H, N-H, O-H,... fundamental stretching modes which are involved in many physical and chemical as well as biological processes. In recent years, the development of powerful and reliablefs lasers has made optical parametric sources a reality: optical parametric amplifiers (OPA) routinely generating sub-100-fs pulses largely tunable in the near infrared with sup-1-μJ energy pulses now available. Data on the performance of infrared OPA sources have been published [1–3] but to our knowledge, only one attempt in comparing the performances of KTP family crystals has been made [4]. In that study the authors used a fs OPA seeded by a Q-switched NdYLF laser and pumped by the tunable output of a Ti:sapphire regenerative amplifier. Such a device has two drawbacks: first the frequency tuning of such an OPA is not convenient since besides the oscillator, it involves re-adjusting many elements in the Ti:sapphire regenerative amplifier. Second, such tuning affects the comparison between the different crystals since it may alter many pump pulse parameters. In the present paper, we propose a theoretical and experimental study of three crystals containing potassium: KTiOPO4 (KTP), KTiOAsO4 (KTA), and KNbO3 using a double-pass f OPA pumped by the fixed output of a Ti:sapphire regenerative amplifier. This OPA is seeded by a white-light continuum and the frequency tuning is achieved through a rotation of the crystal. The paper is organized in the following way. First, we discuss important crystal parameters such as the phase-matching curves, group velocities mismatch, and second-order nonlinear effective susceptibility which partly control the amplitude and the temporal and spectral structure of parametrically generated IRfs pulses. Second, we present our very simple experimental OPA setup and the techniques we used to characterize the generated IR pulses. Finally, we discuss our results. For spectroscopic purposes, the important parameters of IR pulses generated by the OPAs are their high peak power, great stability, and their Fourier-transform-limited (FTL) nature. All are influenced by the characteristics of the crystal used in the OPA. Manyfs OPO or OPA systems working in the mid-IR domain ( 2–5μm) have been built around one of the three crystals KTP, KTA, and KNbO3, which contain potassium. All these biaxial crystals belong to the mm2 point group of symmetry. For fs nonlinear applications, the KTP crystal is well known and has often been used for generating FTL mid-IR pulses in both OPA and OPO [1– 3, 5, 6]. It has a very high damage threshold, a good transparency range ( 0.35–4.5μm) and high nonlinear coefficient (d32≈ 2.65 pm/V). Compared to KTP, the KTA crystal has a higher transparency range ( 0.35–5.3μm) and a larger d32≈ 4.5 pm/V nonlinear coefficient. Therefore it should make it possible to extend the IR spectral range covered by KTP crystal and improve the overall conversion efficiency. The KNbO3 crystal is known for its large nonlinear effective susceptibility (d32≈−13.7 pm/V) and for its large transparency range (0.4−4μm). Therefore, it could be used to generate more powerful IR fs pulse energy than KTP and KTA crystals but in a smaller IR spectral range if the conclusions drawn in the well-known crystal handbook hold [7]. However, in a real OPA system, we shall see that a simple and direct comparison of the performances of the crystals in our OPA lead us to slightly different conclusions. 1 Theoretical background To build our OPA system, we first theoretically studied the signal, idler, and pump pulse configuration polarization for mid-IR generation. To compute the cut angles, the optimum thickness, and to determine the spectral tuning range of each |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.newlightphotonics.com/v1/KTA-OPA-pump800nm-MIR-2000.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
