Pulse-pumped operation of divalent transition-metal lasers

The pulse-pumped operating characteristics of liquid-nitrogen-cooled Ni:MgF2, Co:MgF2, and Ni:CaY2Mg2Ge3O12(CAMGAR) solid-state lasers have been studied. The internal quantum efficiency of the Ni:MgF2laser was found to be limited to approximately 40 percent, presumably because of excited-state absorption. The Co:MgF2laser operated with near-unity quantum efficiency, and generated 150 mJ of diffraction-limited output at repetition rates up to 50 Hz. A continuous tuning range from 1.6 to 2.3 μm was observed along withQ-switched peak output powers of 80 kW. Laser operation from the garnet-structured crystal Ni:CAMGAR was obtained at a wavelength of 1.46 μm.     

8B9--Laser emission at 1.06 µ from Nd3+-Yb3+glass

Laser emission at 1.015 μm occurs in glass singly doped and when sensitized with Nd³⁺. For double doping in a Li Mg Al Si glass, emission at 1.015 μm from Yb³⁺and 1.06 μm from Nd³⁺was reported. By monitoring the 1.35 μm fluorescent line of Nd³⁺, it can be shown that both Nd³⁺and Yb³⁺lase at 1.06 μm at room temperature in a silicate glass with 5 weight percent Nd2O3and 5 weight percent Yb2O3. Energy transfer from Nd³⁺to Yb³⁺is a linear function of the Yb³⁺concentration. The transfer increases with Nd³⁺concentration by about a factor of three in going from 1 weight percent Nd2O3to 6 weight percent Nd2O3and thereafter remains approximately constant. This indicates that the transfer from Nd³⁺to Yb³⁺is assisted by intermediate transfer steps between Nd³⁺ions. Additional transfer above 6 weight percent Nd2O3is prevented by concentration quenching.     

Determination of fluorescence quantum efficiency and laser emission cross sections of neodymium crystals: Application to KNdP4O12

The stimulated emission cross sections σLof neodymium crystals at the laser wavelengths (1.05 and 1.32 μm) are useful parameters to predict their laser performance. The determination of σLhas traditionally been a delicate experimental task. We describe here a method which relies upon the measurement of the branching ratios of the radiative transitions from the⁴F3/2doublet to the⁴I multiplets, and the calibration is provided by an absorption measurement concerning a⁴I9/2→⁴F3/2transition. The precise determination of the spectrometer system response over a broad spectral interval is not required. This method also leads to the value of the fluorescence quantum efficiency η of the⁴F3/2level. It is applied here to potassium-neodymium tetrametaphosphate, KNd P4O12.     

Continuous oscillation of a lithium neodymium tetraphosphate laser with 200-µW pump threshold

Room temperature CW oscillation of a lithium neodymium tetraphosphate (LiNdP4O12) (LNP) laser with thresholds in the fractional milliwatt range is reported. With a 5145-Å pump, observed threshold was 200 μW and the slope efficiency was 43 percent.     

Characteristics of room-temperature 2.3-µm laser emission from tm3+in YAG and YAlO3

The relaxation of low-lying excited states of Tm³⁺ions doped in YAG, YAlO3, and Y2O3due to photon and phonon emission is studied theoretically. Stimulated emission cross sections (integrated over frequency), fluorescence lifetimes, and radiative quantum efficiencies are calculated and their implications for laser operation on the 2.3-μm³F4→³H5line of Tm³⁺are discussed. The calculations, based on a few phenomenological parameters which have been determined by others, are easily generalizable to other host materials and other rare-earth (RE) ions. Room-temperature pulsed laser emission from Tm³⁺ions near 2.3 μm was observed on one line in Tm:Cr:YAG, and on four lines in Tm:Cr:YAlO3. Lower oscillation thresholds were generally obtained in the YAlO3 rods, consistent with the theory presented. A threshold of 31 J was obtained with a Tm:Cr:YAlO3rod at 2.274 μm. In the free-running pulsed mode, peak power levels up to several hundred watts and total output energies up to 12 mJ/pulse were observed. Other general, observed operating characteristics are discussed.     

Growth of Ba2NaNb5O15single crystals for optical applications

The items discussed are: developments leading to the efficient nonlinear optical materials K3Li2Nb5O15and Ba2NaNb5O15; the relation of the stability to visible radiation shown by these materials to their, respectively, "completely filled" and "filled" tetragonal tungsten-bronze-like structures; a comparison of their physical properties to those of LiNbO3; the techniques and problems of growing optically satisfactory single crystals of Ba2NaNb5O15by pulling from the melt; processing required to obtain single domain sections and eliminate microtwinning; and the effects of excess Ba, Na, or Nb in the melt and the effects of substitutions by homologous cations.     

Growth, optical properties, and CW laser action of neodymium-doped gadolinium scandium aluminum garnet

Investigation of the congruent melting rare-earth aluminum garnet Gd3Sc2Al3O12(GADSCAG) has been made. The optimum crystal growth parameters for the undoped material are a rotation rate of 20 r/min and a growth rate of 4.6 mm/hr along thelangle111rangledirection. For Nd³⁺-doped crystals the linear growth rate is 2 mm/h. The optical properties of Nd:GADSCAG which are of interest for laser operation were also determined. The stimulated emission cross section of the 1.06-μ transition in Nd³⁺at room temperature is(3.2 pm 0.3) times 10^{-19}cm², the fluorescence lifetime is256 pm 8 mus at an Nd³⁺ion density of 1 atomic percent in the crystal and the integrated peak absorption cross section in the strongest pump band (0.81 μ) is3.8 times 10^{-19}cm², A comparison of the CW laser performance of identical ND:YAG and Nd:GADSCAG rods is presented.     

Design feasibility of a single-mode optical isolator

Isolator conditions are derived by a perturbation method for optical slab isolators in which magnetooptical crystal and anisotropic dielectric crystal films are integrated for reciprocal and non-reciprocal TE-TM mode conversion functions. The general expressions show that isolator conditions can be satisfied for any combination of wavelength, normalized frequency, waveguide thickness, and gyrotropic constant of the magnetooptical crystal by appropriate choice of the magnitude of the birefringence of the top layer film and its crystal orientation angle. Design examples of single-mode isolators with waveguide thicknesses of 4, 4.5, and 5 μm are given at 1.55 μm wavelength. It is also pointed out that isolators of the above design can be fabricated with Y3Fe5O12, Y1.5Gd1.5Fe3O12, and Tm3Fe5O12crystal films as magnetooptical materials and a solid solution of LiNbO3and LiTaO3as an anisotropic film. Tolerance in the required film thickness becomes less stringent with this design. Isolation of more than 20 dB with an insertion loss of less than 0.12 dB is feasible without any parameter adjustment, even when there is as much as a ten percent deviation in the film thickness.     

8B7--Energy transfer and CW laser action in Ho3+:Er2O3

Er2O3: Ho³⁺is an unusual laser material in that the host crystal itself provides the dominant pumping mechanism by means of energy transfer. The additional pumping bands due to Er³⁺and the consequent efficient transfer of energy to the Ho³⁺laser ion lead to relatively low threshold laser operation: 5 joules pulsed and 200W CW for a 12mm long crystal at 77°K. The emission waveleng this 2.121μ, a region of good atmospheric transmission. Additional laser experiments were carried out at 145°K. Excitation and fluorescence spectra are discussed.     

Multiphonon relaxation in laser materials and applications to the design of quantum electronic devices

An account is given of the results of a recent investigation of multiphonon orbit-lattice relaxation of excited states of rare-earth ions in crystals. The use of these results in the design of quantum electronic devices is discussed, using as examples the Nd³⁺laser transition and a 10.6-μ infrared quantum counter. A discussion is presented of the infrared limit of quantum electronic devices using these materials. Extension of these concepts to transition-metal ions in crystals is considered and a measurement of¹Eto³Emultiphonon decay in Al2O3: V³⁺is presented.     

Interrelation of pyroelectric and nonlinear optical coefficients in ferroelectric crystals

An experimental relation is found between the pyroelectric and electrooptic coefficients of several ferroelectric materials. The physical basis of this relation is explained using Garrett's anharmonic oscillator model, and the pyroelectric coefficients of Sr0.25Ba0.75Nb2O6, Sr2NaNb5O15,Ba2NaNb5O15, KSr2Nb5O15, K3Li2- Nb5O15, and Ag3AsS3are predicted from the known electrooptic coefficients.     

Observations of spontaneous phase locking of LiNdP4O12lasers

Spontaneous or self-locking effects of the TEM00mode at 1.05 μm have been observed for an LiNdP4O12(LNP) laser. Pulse repetition frequency was 600 MHz, corresponding toc/2L(c: light velocity,L: cavity length). The effect of low-frequency resonance on self-locking is also discussed experimentally.     

Spiking oscillations in diode-pumped NdP5O14and NdAl3(BO3)4lasers

Using quasi-CW sinusoidally modulated excitation from a 0.8-μm-wavelength laser diode, we have obtained driven spiking oscillations in miniature, high-Nd-concentration room-temperature lasers of NdP5O14, and NdAl3(BO3)4. With modulation indices of 0.25 or less, peak-power enhancements of 11 (at 35 kHz) and 7 (at 124 kHz), respectively, have been observed for these materials. Theoretical calculations of these and other characteristics of the driven oscillations are in good agreement with experiment.     

Charge centroid in MIOS nonvolatile memory structures

The experimental charge-centroid relations in MNOS, MAOS (A = Al2O3), and MANOS nonvolatile memory structures were analyzed and compared. New data on trap density, trapping length, and capture cross section for Al2O3and Si3N4were derived from these measurements. The trapping length in Al2O3is about 5 times larger than in Si3N4. The charge-detrapping rate in Al2O3is smaller than in Si3N4. The experimental charge-centroid relation during charge trapping and charge detrapping is described by two expressions which include the capture cross section as the only physical parameter. The calculated capture cross section is constant for MNOS and also during charge trapping in MAOS, but decreases linearly with propagating centroid position after onset of charge detrapping within Al2O3. Trap-assisted tunneling over multiple deep trap levels in Al2O3is proposed to interpret the results for MAOS. Oxygen annealing of Al2O3enhances storage capability of injected negative charge within the lower bandgap Si3N4region of the MANOS structure. This behavior is related to blocking of detrapped nitride charge at the oxygen densified energy barrier created at the Si3N4- Al2O3boundary.     

Absorption coefficients and the temperature variation of the refractive index difference of nonlinear optical crystals

Data on two parameters important for judging the deleterious effects of heating on the efficiency of nonlinear optical processes are presented. These parameters are absorption coefficients at 10.6 μm and the temperature variation of the refractive index difference for second harmonic generation of 5.3 μm. The crystals examined are GaSe, Tl3AsSe3, AgGaSe2, CdGeAs2, and Ag3AsS3.     

Analysis of the threshold voltage and its temperature dependence in electrolyte-insulator-semiconductor field-effect transistors (EISFET's)

A first-order theoretical model is developed that allows the temperature dependence of the threshold voltage of an electrolyte-insulator-semiconductor field-effect transistor (EISFET) to be determined. Specifically, a detailed analysis is presented for a representative cell consisting of a Ag/AgCI reference electrode, a simple 1:1 electrolyte, and an ISFET. In addition, an insulator is assumed for which the site-binding model is applicable. All temperature-dependent parameters are identified and quantitatively described. Results are computed for SiO2and Al2O3insulators over a pH range from 1 to 12, and a temperature range from 20 to 80°C. Graphs of the surface-site occupancies versus the pH are shown to provide useful physical insight in interpreting the results. The threshold-voltage temperature coefficient is shown to be highly dependent on the pH; however, for Al2O3, over a 20-80°C range, the variation is roughly linear.     

Atomic Sn, Sb, and Ge photodissociation lasers

Stimulated emission has been observed on the 380.1 nm line of atomic tin, the 326.7 nm line of atomic antimony, and the 326.9 nm line of atomic germanium following photodissociation of SnI2, SbI3, and GeI4molecular vapors. A 193 nm ArF laser was used as the excitation source. Bond energies for the dissociation of monoiodides were estimated. Output energies of 200, 80, and 75 μJ were obtained for 380.1, 326.7, and 326.9 nm transitions, respectively.     

Lateral mode stabilization of diode lasers by means of apertured facet reflectors

We report the design, fabrication, and testing of an apertured facet reflector for a GaAs/GaAlAs room temperature CW diode laser. The reflector, composed of Al2O3, Si, Te, and Al2O3layers with the Te ablated by the laser beam itself at the mode center, has a higher reflectivity at its center compared to the unablated surrounding region. This nonuniform reflectivity acts to stabilize laterally the fundamental mode and substantially increase the "kink" level. Specifically, the "kink" level of a large optical cavity (LOC) heterostructure laser with an 8 μm wide stripe was increased from ≈ 10 mW before coating to above 30 mW by the addition of the apertured reflector.     

Characteristics of MOSFET prepared on Si/MgO.Al2O3/SiO2/Si structure

A new silicon on insulator (SOI) wafer with epitaxial-Si/ epitaxial-MgO.Al2O3(0.1 µm)/SiO2(0.5 µm)/     

Choice of dielectrics for TFEL displays

The commonly used dielectrics, Y2O3, Al2O3, Si3N4, and Ta2O5, were evaluated for use in ac thin-film electroluminescent displays, along with a composite dielectric SiAlON. Adhesion, stress cracking, charge storage capacity, and display brightness and efficiency were studied for devices with ZnS: Mn layers fabricated under identical conditions. A combination of SiAlON and Ta2O5appears to be optimum as a double-layer dielectric system for ACTFEL displays.