Optical Amplification Properties And Devices Of Micro-and Nano-Structured Organic Semiconductors

There is a large variety of organic semiconductor materials and a number of them exhibit high optical-gain performance,enabling their applications as gain medium for laser oscillators and amplifiers.The simple processability and mechanical flexibility of organic semiconductor materials make them good candidates for extensive scientific research and applications in micro-or nano-scale organic laser and optical amplifiers.This thesis is centered on organic thin-film laser amplifiers using microcavities and their photophysical performance and includes the following research work:(1)Femtosecond injection-locked amplifiers based on organic distributed feedback(DFB)microcavities The injection-locked amplification technique is combined with the organic thin-film DFB lasers,where the DFB microcavity was constructed by coating the nanograting with a thin film of polymeric semiconductor materials.Selective amplification was achieved for the normal injection of the seed light beam with a matching between the amplified wavelength and the resonance of the DFB microcavity.By measuring the amplification dynamics for different polarizations of the pump and injection laser pulses,we investigated the polarization dependence of the injection-locked amplification process.The results indicate that only the injection polarized along the grating lines can be amplified efficiently and the amplification is stronger influenced by the pump polarization.Additionally,the amplified spectrum can be tuned by changing the injection angle slightly.The injection-locked amplification not only keeps the characteristics of excellent collimation,excellent directionality,and the spectral bandwidth of the injection beam,but also enables far-field application and flexible control of the output from DFB microcavities.(2)Femtosecond injection-locked laser amplifier based on organic thin film and chirped-grating DFB microcavities The resonant wavelength of the DFB microcavities is related to the effective refractive index and the period of the gratings.Using period-chirped grating,we achieved DFB microcavities that support continuously tunable resonant wavelengths.Thus,by changing the injection position of the seed laser beam on the chirped grating,largerange tunability of the injection-locked amplification was achieved.The two-beam interference lithography scheme can be easily constructed by using a cylindrical lens focused beam and a collimated laser beam.Adjusting the distance between the cylindrical lens and the recording plane,or changing the focal length of the cylindrical lens,can be utilized to change the density of grating lines and the variation rate of the grating period with spatial positions,which enables controlling the tuning rate of the amplification wavelength.(3)Femtosecond organic amplifiers based on injection into DFB microcavities of slant gratings The slant-grating DFB microcavities with larger tuning bandwidth were constructed by coating organic semiconductor thin films onto the photoresist gratings with slanting grating lines,which is on the basis of the Finite-Difference Time-Domain simulation results.Then,the injection-locked amplification processes were studied systematically.By changing the injection angle,the amplified spectrum can be tuned within a large range using such slant-grating DFB microcavities.The basic principles lie in that the asymmetric structures reduce slightly the resonance selectivity of the microcavities,resulting in a lower Q factor,and consequently a largely broadened tuning range of the amplification wavelength.Meanwhile,due to the limitation by the gain bandwidth of the active medium,the amplification factor differs largely for different wavelength.By changing the fluence of the pump and the injection laser beams,the broad-band amplification factors can be balanced to some extent between different wavelengths for such slant-grating microcavities.(4)Organic laser amplifiers integrated onto fiber ends Making use of the flexible transfer technique,the DFB microcavities fabricated on planar substrates were transferred successfully to the fiber end facets,which enables realization of ultrathin DFB microcavity laser amplifiers integrated onto the fiber tips.Thus,at the achievement of the injection-locked laser amplification,we have also realized long-range transmission and remote application of the amplified signals.Additionally,after being transferred to the end facets of optical fibers,the fiber-end integrated DFB microcavities consisting of slant gratings may be utilized to achieve tuning of the output wavelengths amplifiers by changing the angle of injection.