C. K. Subramanian

Laser induced damage in zinc tris(thiourea) sulfate and bis(thiourea) cadmium chloride

Laser induced damage threshold values are reported for two metal‐organic complex crystals, zinc tris(thiourea) sulfate, and bis(thiourea) cadmium chloride. These crystals have single shot and multiple shot damage thresholds which are the highest among the solution grown crystals. The damage morphology, obtained by irradiating with fluences close to the threshold, reflects the symmetry of the face of the test site. At higher fluences the damage leads to stress‐induced fracture or thermo‐chemical degradation.

Lasing in active, sub-mean-free path-sized systems with dense, random, weak scatterers.

We report enhanced emission and gain narrowing in Rhodamine 590 perchlorate dye in an aqueous suspension of polystyrene microspheres. A systematic experimental study of the threshold condition for and the gain narrowing of the stimulated emission over a wide range of dye concentrations and scatterer number densities showed several interesting features, even though the transport mean free path far exceeded the system size. The conventional diffusive-reactive approximation to radiative transfer in an inhomogeneously illuminated random amplifying medium, which is valid for a transport mean-free path much smaller than the system size, is clearly inapplicable here. We propose a new probabilistic approach for the present case of dense, random, weak scatterers involving the otherwise rare and ignorable sub-mean-free-path scatterings, now made effective by the high gain in the medium, which is consistent with experimentally observed features.

Optical phase conjugation in methylene blue films.

Optical phase conjugation in methylene blue sensitized gelatin film has been obtained with 514.5-nm radiation from an argon-ion laser with power levels as low as 50 mW/cm(2) for the pump beam in a degenerate four-wavemixing configuration. The film with a thickness of 110-120 microm prepared from a solution of a 1.8-mmol concentration of methylene blue sensitized gelatin shows a good phase-conjugate reflectivity of 0.5% for this power level at 514.5 nm, which is well away from its absorption peak at ~ 650 nm.

Transient phase conjugation in dye-doped polymer saturable absorbers

Abstract Dye-doped polymer saturable absorbers are an important class of nonlinear optical materials where nonlinear interactions like four-wave mixing and two-wave mixing can be observed even at low laser intensities. The modulation of the nonlinear absorption coefficient of the dye medium by an appropriate interaction of laser radiation can be utilized to generate a large phase conjugate (PC) signal in degenerate four-wave mixing geometries. By probing this population grating at time scales less than the dye relaxation times very high transient PC signals can be observed. Here we report on the generation of transient PC signals using azo dye-doped polymer films, by delaying the arrival time of the backward propagating pump beam with respect to the grating writing beams. A theoretical analysis of this delayed four-wave interaction is given to explain the large transient gain in the phase conjugate intensity. Experimental observations on the magnitude of the transient gain along with its dependence on various parameters like the intensity of the interacting beams, the number density of the saturable absorbers, the read beam time delay, etc. are also presented.

Laser damage threshold studies in L-arginine phosphate monohydrate

The semiorganic L-arginine phosphate monohydrate crystals were grown from aqueous solutions by slow cooling. Single shot damage threshold of LAP was measured and compared with other nonlinear materials. Annealing of these crystals further improves their damage resistance. The nature of damage in LAP is discussed in terms of its thermal and mechanical properties

Optical phase conjugation by two-wave mixing in iron-doped lithium niobate

A novel technique to generate forward phase conjugate wave by two-wave mixing (TWM) in photorefractive iron-doped lithium niobate crystal has been demonstrated. An optical beam from a positive transparency was forward phase conjugated by TWM technique. The experimental scheme was then extended to a specific interferometric application.

Two beam coupling in linbo3:Fe

Abstract Some interesting new features of temporal fluctuations in the intensities of optical beams (λ=488nm) interfering to form a volume grating in an iron doped Lithium Niobate crystal have been studied. These intensity fluctuations have hitherto not been studied in detail and may help in identifying the carrier transport mechanism during the formation of the volume grating in photorefractive crystals.

Non-linear optical response of rutile-related oxides, LiM(V)M(VI)O(6), and their derivatives obtained by ion-exchange and intercalation

Polycrystalline samples of oxides of the general formula LiM(V)M(VI)O(6) (M(V) = Nb, Ta; M(VI) = Mo, W), crystallizing in a non-centrosymmetric (space group P (4) over bar 2(1)m) trirutile structure, exhibit second harmonic generation (SHG) of 1064 nm radiation with efficiencies 15-45 times that of alpha-quartz; interestingly, the SHG response is retained by the protonated derivatives HM(V)M(VI)O(6) . xH(2)O, and their n-alkylamine intercalates as well.

Experimental observations of transient phase conjugate waves in photorefractive bismuth silicon oxide crystals

The formation of transmission or reflection gratings is experimentally identified in the

Interferometric schemes using forward phase conjugation in a ferroelectric photorefractive crystal

Bi_{12}SiO_{20}