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Group velocity mismatch-absent nonlinear frequency conversions for mid-infrared femtosecond pulses generation.

Zhong H, Zhang L, Li Y, Fan D - Sci Rep (2015)

Bottom Line: The system employs MgO-doped periodically poled LiNbO3 as the nonlinear medium.Desired group-velocity dispersion would be obtained via appropriately temperature regulation.Compared with the conventional scheme of type-0 QPM, the quantum-efficiency can be more than doubled with nearly unlimited bandwidth.

View Article: PubMed Central - PubMed

Affiliation: SZU-NUS Collaborative Innovation Center for Optoelectronic Science &Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.

ABSTRACT
A novel group velocity mismatch (GVM) absent scheme for nonlinear optical parametric procedure in mid-infrared was developed with type-I quasi phase matching by use of an off-digital nonlinear optical coefficient d31. This was achieved by matching of the group velocities of the pump and the signal waves, while the phase velocities were quasi phase matched. The system employs MgO-doped periodically poled LiNbO3 as the nonlinear medium. Desired group-velocity dispersion would be obtained via appropriately temperature regulation. To demonstrate its potential applications in ultrafast mid-infrared pulses generation, aiming at a typical mid-infrared wavelength of ~3.2 μm, design examples of two basic nonlinear frequency conversion procedures are studied for both the narrow-band seeding mid-IR optical parametric amplification (OPA) and the synchronously pumped femtosecond optical parametric oscillation (SPOPO). Compared with the conventional scheme of type-0 QPM, the quantum-efficiency can be more than doubled with nearly unlimited bandwidth. The proposed GVM- absent phase matching design may provide a promising route to efficient and broadband sub-100 fs mid-infrared ultrafast pulses generation without group-velocity walk-off.

No MeSH data available.


Related in: MedlinePlus

Group velocities for 800 nm (e-polarization) and a series of mid-IR wavelengths at 1.8–3.4 μm (both e-polarization(a) and o-polarization (b)) in 5-mol % MgO-doped LiNbO3 as a function of crystal temperature. All the data were calculated through temperature-dependent Sellmeier equations provided by the HCP Company19.
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f2: Group velocities for 800 nm (e-polarization) and a series of mid-IR wavelengths at 1.8–3.4 μm (both e-polarization(a) and o-polarization (b)) in 5-mol % MgO-doped LiNbO3 as a function of crystal temperature. All the data were calculated through temperature-dependent Sellmeier equations provided by the HCP Company19.

Mentions: For conventional nonlinear crystals based on angle-tuning PM, when group velocities are matched, the phase velocity matching condition usually cannot be satisfied simultaneously, resulting in poor conversion efficiency. In the QPM structure, the sign of the nonlinear coefficient is reversed just at the depth where the generated waves would start to oscillate out of phase. It ensures that any frequency conversion can be noncritically phase matched within the transparent wavelength range only if an appropriate poling period is chosen22. The key idea of the proposed GVM-absent PM is modifying the group-velocities of the interacting waves through temperature regulation. On this basis, phase velocities matching can be achieved simultaneously via QPM with a proper grating period. As we all know, refractive index is temperature-dependent, the group velocity should be temperature-relative as well. In Fig. 2 we plot the group velocity of νg for certain typical wavelengths versus the crystal temperature in both o and e polarization. The given νg was calculated based on the temperature-dependent Sellmeier equations of 5% doped MgO:PPLN, provided by the HCP company23. As shown by the calculated results, for the typical near-IR wavelength of 800 nm and mid-IR wavelengths of 1.8–3.4 μm, there is definitely remarkable difference between their group velocities when they are both in e-polarization, which seems to be indelible just via simply regulating the crystal temperature (Fig. 2(a)). In other words, even adding the degree of freedom of temperature-tuning, it is still impossible to set up a GVM-absent frequency conversion system under the conventional type-0 QPM condition. Whereas, when these waves transmit in the MgO:PPLN with orthogonal polarizations, i.e., 800 nm is e-polarized while 1.8–3.4 μm is o-polarized, their group velocities may be matched at certain temperatures, e.g., T = ~175 oC for 800 nm and 3.2 μm (Fig. 2(b)). As a reference, the GVM between these waves is expected to be ~200 fs/mm for conventional type-0 interaction in the same MgO:PPLN. It should be noted that, to suppress the photorefractive damage, in general, MgO:PPLN should be heated and operate at temperatures above 100 °C. As shown in Fig. 2(b), supposing a typical 800 nm Ti:sapphire femtosecond laser serve as the pump source, the proposed GVM-absent scheme can be applied to generate ultrashort pulses at ~1.8 to 3.4 μm in a temperature range of 20–220 oC. In principle, this scheme can be adopted in much broader spectral region based on other pump sources, e.g., the familiar wavelength between 950 nm to 1050 nm.


Group velocity mismatch-absent nonlinear frequency conversions for mid-infrared femtosecond pulses generation.

Zhong H, Zhang L, Li Y, Fan D - Sci Rep (2015)

Group velocities for 800 nm (e-polarization) and a series of mid-IR wavelengths at 1.8–3.4 μm (both e-polarization(a) and o-polarization (b)) in 5-mol % MgO-doped LiNbO3 as a function of crystal temperature. All the data were calculated through temperature-dependent Sellmeier equations provided by the HCP Company19.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477408&req=5

f2: Group velocities for 800 nm (e-polarization) and a series of mid-IR wavelengths at 1.8–3.4 μm (both e-polarization(a) and o-polarization (b)) in 5-mol % MgO-doped LiNbO3 as a function of crystal temperature. All the data were calculated through temperature-dependent Sellmeier equations provided by the HCP Company19.
Mentions: For conventional nonlinear crystals based on angle-tuning PM, when group velocities are matched, the phase velocity matching condition usually cannot be satisfied simultaneously, resulting in poor conversion efficiency. In the QPM structure, the sign of the nonlinear coefficient is reversed just at the depth where the generated waves would start to oscillate out of phase. It ensures that any frequency conversion can be noncritically phase matched within the transparent wavelength range only if an appropriate poling period is chosen22. The key idea of the proposed GVM-absent PM is modifying the group-velocities of the interacting waves through temperature regulation. On this basis, phase velocities matching can be achieved simultaneously via QPM with a proper grating period. As we all know, refractive index is temperature-dependent, the group velocity should be temperature-relative as well. In Fig. 2 we plot the group velocity of νg for certain typical wavelengths versus the crystal temperature in both o and e polarization. The given νg was calculated based on the temperature-dependent Sellmeier equations of 5% doped MgO:PPLN, provided by the HCP company23. As shown by the calculated results, for the typical near-IR wavelength of 800 nm and mid-IR wavelengths of 1.8–3.4 μm, there is definitely remarkable difference between their group velocities when they are both in e-polarization, which seems to be indelible just via simply regulating the crystal temperature (Fig. 2(a)). In other words, even adding the degree of freedom of temperature-tuning, it is still impossible to set up a GVM-absent frequency conversion system under the conventional type-0 QPM condition. Whereas, when these waves transmit in the MgO:PPLN with orthogonal polarizations, i.e., 800 nm is e-polarized while 1.8–3.4 μm is o-polarized, their group velocities may be matched at certain temperatures, e.g., T = ~175 oC for 800 nm and 3.2 μm (Fig. 2(b)). As a reference, the GVM between these waves is expected to be ~200 fs/mm for conventional type-0 interaction in the same MgO:PPLN. It should be noted that, to suppress the photorefractive damage, in general, MgO:PPLN should be heated and operate at temperatures above 100 °C. As shown in Fig. 2(b), supposing a typical 800 nm Ti:sapphire femtosecond laser serve as the pump source, the proposed GVM-absent scheme can be applied to generate ultrashort pulses at ~1.8 to 3.4 μm in a temperature range of 20–220 oC. In principle, this scheme can be adopted in much broader spectral region based on other pump sources, e.g., the familiar wavelength between 950 nm to 1050 nm.

Bottom Line: The system employs MgO-doped periodically poled LiNbO3 as the nonlinear medium.Desired group-velocity dispersion would be obtained via appropriately temperature regulation.Compared with the conventional scheme of type-0 QPM, the quantum-efficiency can be more than doubled with nearly unlimited bandwidth.

View Article: PubMed Central - PubMed

Affiliation: SZU-NUS Collaborative Innovation Center for Optoelectronic Science &Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.

ABSTRACT
A novel group velocity mismatch (GVM) absent scheme for nonlinear optical parametric procedure in mid-infrared was developed with type-I quasi phase matching by use of an off-digital nonlinear optical coefficient d31. This was achieved by matching of the group velocities of the pump and the signal waves, while the phase velocities were quasi phase matched. The system employs MgO-doped periodically poled LiNbO3 as the nonlinear medium. Desired group-velocity dispersion would be obtained via appropriately temperature regulation. To demonstrate its potential applications in ultrafast mid-infrared pulses generation, aiming at a typical mid-infrared wavelength of ~3.2 μm, design examples of two basic nonlinear frequency conversion procedures are studied for both the narrow-band seeding mid-IR optical parametric amplification (OPA) and the synchronously pumped femtosecond optical parametric oscillation (SPOPO). Compared with the conventional scheme of type-0 QPM, the quantum-efficiency can be more than doubled with nearly unlimited bandwidth. The proposed GVM- absent phase matching design may provide a promising route to efficient and broadband sub-100 fs mid-infrared ultrafast pulses generation without group-velocity walk-off.

No MeSH data available.


Related in: MedlinePlus