H. J. Caulfield

Line narrowing in the dye solution with scattering centers

Abstract As was shown by Markushev et al. [1], laser-like emission without cavity can be obtained from a scattering gain medium, such as powder of Nd doped laser crystals. In the recent work by Lawandy et al. [2] a close phenomenon was observed in a concentrated rhodamine 640 dye solution in the presence of scatterers. The work in Ref. [2] is the first where gain and scattering are separate. In this case lasing evidently is not initiated within the particles, in contrast to the Markushev et al. case, where the gain is in the particles, which supports morphology-dependent resonances. The work by Sha et al. [3] showed similar results in concentrated dye, but it also showed that introduction of a low density of scatterers raises the threshold required for the laser-like effects in the low-concentrated dye. We carried out our own experiments in rhodamine 6G laser dye and observed the laser-like effects both in dilute and concentrated dye with and without scatterers. In our experiment the wavelength of stimulated emission was strongly dependent on the scatterers concentration. Our observations and some results of Refs. [2,3] are explained with a simple ASE (amplified spontaneous emission) model.

Short-pulsed stimulated emission in the powders of NdAl 3 (BO 3 ) 4 , NdSc 3 (BO 3 ) 4 , and Nd:Sr 5 (PO 4 ) 3 F laser crystals

Short (>300-ps) pulses of stimulated emission were found from powders of NdAl3(BO3)4, NdSc3(BO3)4, and Nd:Sr5(PO4)3F laser crystals during 532- and 805-nm excitation. Study of stimulated emission in the mixture of two powders has shown that the different components influence each other. That implies a collective behavior of emitting particles. The main features of experimentally observed stimulated emission are described with a simple model accounting for 4F3/2 excited-state concentration and emission energy density. The threshold of stimulated emission in powders is shown to be inversely proportional to the small-signal amplification along the photon path in the pumped volume.

Optical characterization of Mn:YAlO 3 : material for holographic recording and data storage

Photoinduced coloration and the holographic grating recording associated with it are experimentally studied in Mn-doped yttrium orthoaluminate (Mn:YAlO3). High diffraction efficiency is demonstrated in visible and in infrared light. The diffraction efficiency at 514.5 nm exceeds 50%. The strong energy exchange between the writing beams observed in a two-wave mixing experiment suggests that diffraction in Mn:YAlO3 is due to mainly nonlocal holographic effect and an electro-optical effect. Mn:YAlO3 is shown to be a promising material for holographic recording and optical storage.

Diffusion and pseudo-phase-conjugation effects in coherent backscattering from Nd0.5La0.5Al3(BO3)4 ceramic

Abstract We study coherent backscattering in Nd 0.5 La 0.5 Al 3 (BO 3 ) 4 ceramic and demonstrate what we call the effect of pseudo phase conjugation from scattering medium. We show that coherent backscattering can correct for large-scale distortions of the light wave front. The imperfections in the backscattering imaging as well the impossibility of correcting for small-scale wave front distortions are discussed. An `optical equivalent circuit of known components which give the same behavior as a scattering medium is offered.

Holographic current study in laser and photorefractive crystals

Summary form only given. We generalized the theory behind the light-induced grating (LIG) electro-motive force (EMF) technique for material characterization and interferometry, first introduced by Petrov et al. In particular, we have accounted for the screening length, that allowed us to describe adequately the dependence of the amplitude, and the decay-time.

Propagation of ultrashort pulses through lenses

Ordinary optical components may behave in extraordinary ways when illuminated with ultrashort optical pulses. In the cases of lenses, only the flat lenses such as Fresnel lenses, Fresnel zone plates, and holographic lenses display such anomalies. For them, the pulse may be both elongated temporally and spread spatially unless very high focal number lenses are used.

Study of photoconductivity and holographic current in rare-earth-doped Y 3 Sc 2 Ga 3 O 12 laser crystals

The photoconductivity and holographic current have been studied in Er-, Tm-, and Ho-doped Y3Sc2Ga3O12 laser crystals under visible and infrared excitation. Kinetics and spectroscopic studies have shown that photoconductivity is linearly proportional to the concentration of excited 4f states. The holographic current was described with a model accounting for the energy transfer between the rare-earth and ligand electronic shells, ionization, recombination, and the diffusion and drift currents in the conduction band. The dependence of the holographic current on the modulation frequency, grating vector, etc. were used to determine the carriers’ diffusion length and the screening length in Er-doped crystals.

Study of migration in Cr:Er:YSGG using an upconversion light induced grating technique

Abstract An excitation migration over the level 4 I 1 1 2 was studied in Cr:Er:YSGG laser crystal using an upconversion nonholographic light induced grating (LIG) technique A long distance of migration (≃ μm) was found. The diffusion coefficient was determined to be equal to 7 × 10−7 cm2/s. This value was compared to that calculated in dipole-dipole approximation from the emission and absorption spectra overlap. The analysis shows, that excitation migration in Er:Cr:YSGG cannot be described in terms of dipole-dipole energy transfer, other possibilities are discussed.

Optical communication at the source bandwidth limit

The possible limiting components on optical communication bandwidth are the source, the modulator, the propagation medium, and the detector. It is easy to show that the source bandwidth is the fundamental limit. The possibility of source bandwidth limited communication is demonstrated theoretically and experimentally. The basic principles involved are readily extendable to more practical partial approaches to this limit.

Second Harmonic Generation in Powder Laser

Periodically poled KTP (PP-KTP) crystals offer a number of fraturer. biicli i ih phnar-marching w t h the highest nodmeat cocfficienf lo* temperature ~enritiviry and relatirriy high opllcal damage Lhreshold, which make them anmove tor extracavily and insacwiry frequency doubling (FD) of the Nd doped iarer hosts. Recently, we ihave demonstrated 66 % cxtracnvit) FD cfticiensy O t the Qswitched NdYAG laser by using penndically puled flux-grown K1 P I I] Our iiiYeErigationS show that the 1.0 eftisisncy in PP-KTP i s about WO times higher than ~n convenrianel type-I1 phase-matched KTP Moreover, the measured optical damage threshold for the IPKTP WRE more than 1.5 tlmel higher than m conventional KTP.