Index of content:
Volume 13, Issue 4, 15 August 1968
13(1968); http://dx.doi.org/10.1063/1.1652533View Description Hide Description
A new technique for measurement of collision‐broadened homogeneous linewidths, using the nonlinear interaction between two traveling waves, is described. Measurements of homogeneous linewidth for the 6328‐Å neon line in neon and helium‐neon discharges are presented.
13(1968); http://dx.doi.org/10.1063/1.1652534View Description Hide Description
Experimental results are presented which indicate two forms of damage in CdS irradiated by either a normalmode or Q‐switched ruby laser at power densities near 108 W/cm2. The primary damage occurs as a deep crater coaxial with the incident laser beam. This crater contains many periodic transverse fractures whose spacing suggests a phonon frequency of ∼ 100 MHz, and which is attributed to stimulated Brillouin scattering. The second site is in the region where the refracted light beam exits from the crystal.
13(1968); http://dx.doi.org/10.1063/1.1652535View Description Hide Description
Data are presented showing that lightly doped or relatively pure GaAs lases basically by a band‐to‐band recombination transition at a photon energy at threshold of 1.495 eV ≈ Eg − 0.015 eV (∼77°K). The ∼0.015‐eV energy reduction from bandgap, which is greater than the exciton binding energy of 0.0034 eV (∼77°K) and unlike the exciton energy is dependent upon carrier concentration, occurs because of many‐body, electron‐hole‐lattice (EHL) interactions.
FREQUENCY‐ AND TIME‐DEPENDENT GAIN CHARACTERISTICS OF LASER‐ AND FLASHLAMP‐PUMPED DYE SOLUTION LASERS13(1968); http://dx.doi.org/10.1063/1.1652536View Description Hide Description
Dye solution lasers are observed to lase at shorter wavelengths when laser pumped than when flashlamp excited. A comparison of the computed frequency‐ and time‐dependent gains for the two pumping methods explains this behavior and the observed Q dependence of the lasing frequency. This treatment also suggests a new technique for frequency tuning dye lasers.
13(1968); http://dx.doi.org/10.1063/1.1652537View Description Hide Description
The wavelength spectrum of an organic dye laser (DTTC in ethanol) pumped by a Q‐switched ruby laser has been measured as a function of temperature (−117°C to +78°C) for several dye concentrations. Absorption and fluorescence spectra were also obtained. The results are in qualitative agreement with the model of a vibrationally broadened two‐level system, each of which is separately thermalized.
13(1968); http://dx.doi.org/10.1063/1.1652538View Description Hide Description
By combining optical strain‐birefringence with stroboscopic illumination,acoustoelectric domains in CdS have been made visible. Domain widths of 50 to 200 μ have been observed in crystals with drift field perpendicular to the C axis. In crystals with E parallel to C axis the domain travels at 30° with respect to C and forms a complex reflection pattern.
13(1968); http://dx.doi.org/10.1063/1.1652539View Description Hide Description
In conjunction with studies relating to high‐power CO2 laser windows the linear absorption coefficient α of Cr‐doped GaAs was measured by means of calorimetric techniques. It was found that α ≈ 0.02 cm−1, at room temperature. This result is shown to be consistent with theoretical considerations: At 10.6 μ, the lattice absorption of GaAs stems from the existence of a fourth‐order electric moment and does not involve the fundamental resonance.
13(1968); http://dx.doi.org/10.1063/1.1652540View Description Hide Description
A new reflective optical storage effect has been found in mixtures of certain nematic liquid crystals and cholesteric liquid crystals. When subjected to a dc field, the initially clear material becomes milky white and remains in this state when the field is removed. The material can be rapidly switched back to its clear state by an audio‐frequency signal. A preliminary model based on the principle of a field‐induced emulsion gives rough agreement with experiment.
13(1968); http://dx.doi.org/10.1063/1.1652541View Description Hide Description
The wavelength shift phenomena of a dye laser and a dye laser oscillation pumped by another dye laser were studied by introducing two dye cells in a cavity. Simultaneous laser oscillations at different wavelength ranges were obtained, and a 4‐level laser mechanism of the dye laser system is discussed.
13(1968); http://dx.doi.org/10.1063/1.1652542View Description Hide Description
Hall and photo‐Hall effects have frequently been used to distinguish between a ``numbers'' mechanism (assumed if Δn ≠ 0 and Δμ = 0), and a ``barier'' mechanism (assumed if Δn = 0 and Δμ ≠ 0) for photoconductivity in possibly inhomogeneous materials. Consideration of a simple model for an inhomogeneous material shows that a wide variety of effects can be obtained in a material with only resistivity variations and without p‐n junction barriers. In particular it may be shown that in such a model without barriers, either Δn ≠ 0 and Δμ = 0, or Δn = 0 and Δμ ≠ 0, may be obtained experimentally, depending only on the resistivity ratio between different portions of the material.
13(1968); http://dx.doi.org/10.1063/1.1652543View Description Hide Description
P–N junctions have been formed in GaP using the liquid‐phase epitaxy process. In addition to the shallow donors and acceptors, nitrogen has been added to the grown layer to increase η, the room‐temperature external quantum efficiency of the electroluminescence of the green emitting A line and its phonon replicas. The measured value of η was as high as 0.1% dc and 0.2% pulsed. The nonradiative processes are reduced by using sulfur rather than other shallow donors to fabricate the n side of the junction.
13(1968); http://dx.doi.org/10.1063/1.1652545View Description Hide Description
High‐resolution spectroscopy was performed on the C 3Π u → B 3Π g (0, 0) band of N2 using a crossed‐grating Echelle spectrograph. The large incremental gain of these transitions produces significant line narrowing which permits wavelength measurements to a relative accuracy of one part in 107. Observed lines have been identified as 27 P branch and 2 R branch transitions distributed among the Π0, Π1, and Π2 spin multiplet sets, and extending from lower level J = 4 to J = 15. Each transition in the Π0 set is observed to originate from the lower Λ component level. A calculation of the relative gain which treats the electron excitation in the optical limit indicates the dominance of these transitions.
13(1968); http://dx.doi.org/10.1063/1.1652546View Description Hide Description
Laboratory measurements have been made of the evaporation rate of fog when subjected to an intensity of 5 to 50 W/cm2 of 10.6‐μ radiation. The measurements agree with calculations and show that most of the absorbed laser energy goes into heating the air by conduction from the dropletsurface. This heated air induces a motion which prevents the laser from completely clearing the fog. A correlation is found which describes the visibility improvement as the fog and power density are varied.
13(1968); http://dx.doi.org/10.1063/1.1652547View Description Hide Description
It has been found that ferroelectric Sr1−x Ba x Nb2O6 has a very large pyroelectric coefficient at room temperature for 0.25 < x < 0.5. This suggested that the material may be useful as a detector of infrared radiation. A detector, constructed with a value of x=0.33 was successfully used at 300°K to detect single pulses of 10.6‐μ radiation from a Q‐switched CO2 laser with a rise time of less than 30 nsec. Detectors with a low frequency responsivity of better than 104 V/W and a minimum detectable power of 4 × 10−9 W‐cm−1‐cps−1/2 are easily constructed. Methods of improving on these results are discussed.
13(1968); http://dx.doi.org/10.1063/1.1652548View Description Hide Description
Irondiffusion in gold has been measured using the Mössbauer effect. Similar to earlier results on irondiffusion in copper, we find that the broadening of the Mössbauer line is approximately equal to ℏ/τ instead of 2ℏ/τ as predicted by the jump model of diffusion, where τ is the mean life for sitting in a specified lattice site. Since the broadening for both irondiffusion in gold and irondiffusion in copper is approximately a factor of two smaller than predicted theoretically, the results appear to be somewhat general. This lends support to the view that the relaxation of a specified ion out of a lattice site is not a simple exponential in time, as assumed in the theory, but is altered when the vacancy mechanism is responsible for diffusion.
13(1968); http://dx.doi.org/10.1063/1.1652550View Description Hide Description
Prolonged application of large uniform electric fields at low (150°C) temperatures to crystals of KBr with silverelectrodes causes the silver to decorate dislocations and subgrain boundaries. Charge transport at these temperatures is a highly inhomogeneous process, presumably dominated by dislocation and boundary conduction.
ALPHA‐IODIC ACID: A SOLUTION‐GROWN CRYSTAL WITH A HIGH FIGURE OF MERIT FOR ACOUSTO‐OPTIC DEVICE APPLICATIONS13(1968); http://dx.doi.org/10.1063/1.1652551View Description Hide Description
The photoelastic properties of α‐HIO3 have been measured and the applicability of the material for acousto‐opticdevice applications determined. In the blue and green portions of the visible the material has the highest figure of merit, n 6 p 2/ρv 3, of any known crystal, approximately twelve times that of LiNbO3 and fifty times that of fused silica. Other desirable properties for these applications include (a) the availability of large solution‐grown single crystals of high optical quality, (b) low acoustic and optic losses, and (c) the absence of ``optical damage.''
A simple acoustically driver beam deflector was also constructed to demonstrate the potential of this material. It was found that 70% of a 0.63‐μ laser beam could be deflected, over a bandwidth of 55 MHz, with an electrical drive power of 265 mW, while 70% of a 0.488‐μ laser beam could be deflected over the same bandwidth with 94 mW of electrical power.