Generation and characterization of coherent beams of tunable spectral and spatial properties using optical parametric oscillators

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dc.contributor.advisor Singh, R. P. Aadhi, A. 2016-03-30T12:24:47Z 2016-03-30T12:24:47Z 2015
dc.identifier.citation Aadhi, A. (2015). Generation and characterization of coherent beams of tunable spectral and spatial properties using optical parametric oscillators (PhD. Dissertation). Indian Institute of Technology, Gandhinagar, pp. 126 (Acc No: T00101) en_US
dc.description.abstract Optical parametric oscillators (OPOs) have become standard source of coherent radiation inaccessible to ordinary lasers. Based on nonlinear optical effect, the OPOs convert a ffxed pump laser wavelength to a wide band of coherent radiations ranging from visible to far-IR. Additionally, development of new nonlinear crystals with improved crystal parameters including high nonlinearity, high damage threshold and wide wavelength transparency demands advancement in OPOs with extended wavelength coverage in all the time scales. While OPO based sources produce high output power in Gaussian spatial beam profle, optical beam in diferent spatial profles such as optical vortex and Airy beams are of paramount interest for diferent scientifc and technological applications. Therefore, the focus of this thesis is the development and characterization of OPO based sources of coherent optical radiation in continuous-wave (cw) and picosecond time scales with spectral and spatial tunability. The development of OPOs in singly-resonant confguration (SRO), the focus of the current thesis, is challenging due to high threshold. Additionally, photorefractive efect in visible pumping, thermal damage, and thermal efects are some of the important issues to overcome. Therefore, it is important to have proper cavity design while maintaining the overall cavity losses to a minimum. A proper selection of the nonlinear crystals and appropriate design of the difractive optical element is required for spatial modifcation of the intra-cavity OPO beam into structured beams. A high power, single-frequency, tunable radiation source in the ultraviolet (UV) region have been developed using intra-cavity frequency-doubling of the resonant signal of a MgO:sPPLT crystal based SRO pumped in the green. Two diferent nonlinear crystals, BIBO and PPKTP have been used for frequency doubling. The BIBO based source produces UV radiation with output power as much as 770 mW at 398.24 nm, while pumping at 8W of green power. The UV source can be tuned across 355.2-418 nm with a continuous wavelength tunability of 62.8 nm in single frequency radiation with an instantaneous line-width of 14.5 MHz. On the other hand, the PPKTP based UV source generates maximum UV power of 336 mW at 398.28 nm and wavelength tunability of 18.1 nm in a TEMoo spatial mode for 5W of green pump power. The BIBO and PPKTP based UV sources have Gaussian spatial profle with ellipticity of 0.66 and 0.93, respectively. The line-width of the UV radiation is measured to be 18.5 MHZ. We have also demonstrated tunable UV radiation in ultrafast pulses at high repetition rate using a SRO based on MgO:sPPLT crystal synchronously pumped at green. The source produces high-repetition-rate picosecond UV pulses at 240 MHz with internal frequency doubling of the visible signal pulses of the SRO into the UV in BIBO. The device is tunable across 317-340.5 nm with a single set of mirrors, with the tuning range currently limited by the available grating periods in the MgO:sPPLT crystal and cut angle of the BIBO crystal. In addition to UV generation, the OPO provides tunable signal pulses across 634-681 nm in the visible with a maximum average power of 800 mW at 642 nm, and corresponding mid-IR idler radiation over 2429-3298 nm with up to 147 mW of output power. In OPOs, the signal and idler radiations are constrained by energy conservation. Therefore, it is not possible to tune the wavelength of the signal and idler beams independently. We have developed a novel approach based on two nonlinear crystals inside a single SRO cavity for the generation of two signal-idler wavelength pairs with truly independent and arbitrary tuning, which are unbound by energy conservation and phase-matching, using a simple design based on two nonlinear crystals in a compact four-mirror ring-cavity OPO. We have studiedsuch novel SRO architecture theoretically and experimentally to understand various parameters in uencing the performance of a such scheme. The intra-cavity parametric amplifcation of the resonant signal of one crystal in the other crystal shows the possibility of using diferent combinations of crystals and pump radiation. We verifed the coherent energy coupling between the intra-cavity resonant signal felds resulting in Raman spectral emission. While we have demonstrated optical radiation in the wavelength range from UV to near-IR in cw and picosecond time scales, in all cases, the output beams have Gaussian spatial structure. To verify the possibility of generating output beam with a diferent spatial distribution other than Gaussian from a SRO, we have demonstrated a compact source of widely tunable, high-power, single frequency output beam in Airy intensity profle. Based on cubic phase modulation of the intra-cavity beam of a MgO:PPLN crystal based SRO pumped at 1.064 nm, the source provides Airy beam tunable across 1.5 to 2 m wavelength range with output power of 8.1 W at 42 W of pump power in the wavelength of 1.571 m. In addition, it generates Gaussian beam across 2.3-3.6 m wavelength range in the mid-IR with a maximum power of 10.1Wat 2.35 m. We also examined all the peculiar properties of Airy beam such as self-acceleration, self-healing, nondi fraction for diferent wavelengths. This generic approach can be used for the generation of diferent structured beams on demand through proper modulation of the intra-cavity beam of the SRO. en_US
dc.description.statementofresponsibility by Aadhi A.
dc.format.extent 126 p.; col.; ill; 31 cm. + 1 CD-ROM
dc.language.iso en_US en_US
dc.publisher Indian Institute of Technology Gandhinagar en_US
dc.subject Nonlinear optics en_US
dc.subject Optical parametric oscillator en_US
dc.subject Parametric ampli cation en_US
dc.subject Phase matching en_US
dc.subject Second harmonic generation en_US
dc.subject Ultraviolet radiation en_US
dc.subject Laser beam shaping en_US
dc.subject Airy beam en_US
dc.title Generation and characterization of coherent beams of tunable spectral and spatial properties using optical parametric oscillators en_US
dc.type Thesis en_US
dc.contributor.department Physics Ph.D.

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