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Experimental investigation was carried out to study the transient regimes during the buildup and decay of the active mode-locked state in a laser diode. The mode locking was achieved through a sinusoidal modulation of the diode current with the laser in an external cavity. The pulse shape evolution and the time constants for the buildup and decay were determined.
Recent work with laser diodes has indicated their potential usefulness in optically pumping atomic frequency standards. Various optical pumping schemes for (87)Rb incorporating such light sources at two D1 frequencies for experimental situations of either evacuated wall-coated cells or atomic beams are considered. Numerical integration of rate equations governing the level populations with arbitrary pumping light choices of intensity, D1 hyperfine transition(s), and polarization and subsequent calculation of scattered light provide a simplified 0-0 hyperfine signal analysis. By frequency modulating one laser diode, two optical transitions were excited in an evacuated wall-coated cell and a large delta m(F) = 1 hf signal was observed.
Infrared heterodyne spectroscopy is a passive technique employing coherent optical detection for the study of spectral features in remote sources. It employs optical components such as mirrors and lenses normally associated with incoherent optics, but because of it's coherent nature, it offers the advantages of ultrahigh spectral resolving power, high frequency precision, and diffraction limited field-of-view. Attention is given to the development of an ultrahigh resolution diode laser heterodyne spectrometer for observational and laboratory use. The instrument is designed for operation in the spectral range from 7.5 to 8.5 microns. A PbSe tuneable diode laser (TDL) is employed as local oscillator. A closed-cycle cooler is employed to keep the oscillator at operating temperatures in the range from 12 to 60 K. Attention is given to factors determining the TDL heterodyne sensitivity, the spectrometer design, and a survey of 8 micron observations, SiO could be detected in the sunspot spectrum.
An instrument has been designed for the measurement of stratospheric trace species which utilizes tunable infrared diode lasers as sources for sensitive in situ absorption spectroscopy in selected wavelength regions. This instrument, the Balloon-Borne Laser In Situ Sensor (BLISS), is a high-resolution absorption spectrometer designed to provide measurements of the concentrations of stratospheric species and their diurnal variations. The instrument employs second-harmonic detection of the absorption of tunable diode laser (TDL) radiation (3-30 microns) in a 1 km path length defined by a retroreflector lowered 0.5 km below the BLISS gondola. Retroreflector tracking under microprocessor control is obtained using a He-Ne laser and coaligned TV camera with CID imaging. Simultaneous measurements of molecular species in the 20-40 km altitude range will be performed using four TDLs, with the predicted minimum-detectable mixing ratio at 30 km being typically less than or equal to 0.1 ppbv.
The dual-beam diode laser spectrometer described by Jennings (1980) is adapted to use a 50-cm confocal etalon for frequency calibration. The collimated radiation from the laser is split at a wedged ZnSe window, and the reference beam is then focused at the midpoint of the etalon length. After the etalon, the reference beam is recollimated and continues its regular path to the monochromator and detectors. An aperture is placed before the etalon in order to limit the entrance beam diameter to approximately 5 mm. Both ends of the etalon are furnished with two-axis adjustments. Initial alignment is achieved using an He-Ne laser, and final optimization involves adjustment of the cavity length as well as the etalon pitch and yaw. The 50-cm confocal etalon produces fringes separated by 150 MHz (0.005/cm). With the aid of a CO2 laser, it is found to have fringe widths (FWHM) of 2 MHz. The confocal etalon makes it possible to improve the accuracy of relative frequency measurements in diode laser spectra and to check the spectral purity and stability of the laser during the recording of spectra.
Quantum phase noise limited Lorentzian power spectral densities were achieved with tunable lead-salt diode lasers. Linewidths as narrow as 22 kHz were observed. A truly programmable infrared synthesizer was produced by frequency-offset-locking the tunable diode lasers to the combination of a stable CO2 (or CO) reference laser and a programmable microwave frequency synthesizer. Absolute frequency accuracy and reproducibility of about + or - 30 kHz (0.000001 kaysers) relative to the primary Cs frequency standard may now be obtained with this technique.
New family of fast-recovery high-voltage power diodes compatible with D60T and D7ST transistors developed. Have wide range of applications in spacecraft and aircraft electrical distribution equipment, dc/dc inverters, and ac motor controllers for high-horsepower electric motors operating from 480-volt ac lines. Fast-Recovery 1,200-V Power Diodes use chip of hexagonal geometry to maximize effective silicon area.
Power is extracted from plasmons, photons, or other guided electromagnetic waves at infrared to midultraviolet frequencies by inelastic tunneling in metal-insulator-semiconductor-metal diodes. Inelastic tunneling produces power by absorbing plasmons to pump electrons to higher potential. Specifically, an electron from a semiconductor layer absorbs a plasmon and simultaneously tunnels across an insulator into metal layer which is at higher potential. The diode voltage determines the fraction of energy extracted from the plasmons; any excess is lost to heat.
An arrangement for damping the resonance in a laser diode is described. This arrangement includes an additional layer which together with the conventional laser diode form a structure (35) of a bipolar transistor. Therein, the additional layer serves as the collector, the cladding layer next to it as the base, and the active region and the other cladding layer as the emitter. A capacitor is connected across the base and the collector. It is chosen so that at any frequency above a certain selected frequency which is far below the resonance frequency the capacitor impedance is very low, effectively shorting the base to the collector.
The objective of this program is to develop 60 GHz GaAs IMPATT Diodes suitable for communications applications. The performance goal of the 60 GHz IMPATT is 1W CW output power with a conversion efficiency of 15 percent and 10 year life time. During the course of the program, double drift (DD) GaAs IMPATT Diodes have been developed resulting in the state of the art performance at V band frequencies. A CW output power of 1.12 W was demonstrated at 51.9 GHz with 9.7 percent efficiency. The best conversion efficiency achieved was 15.3 percent. V band DD GaAs IMPATTs were developed using both small signal and large signal analyses. GaAs wafers of DD flat, DD hybrid, and DD Read profiles using molecular beam epitaxy (MBE) were developed with excellent doping profile control. Wafer evaluation was routinely made by the capacitance versus voltage (C-V) measurement. Ion mass spectrometry (SIMS) analysis was also used for more detailed profile evaluation.
One of the main goals of the study was to demonstrate a low-power efficient Nd:YAG laser oscillator for applications in remote coherent Doppler anemometry. An electrical-to-optical slope efficiency of 6.5 percent has been achieved by using commercially available CW laser diodes of up to 100 mW to pump monolithic Nd:YAG rod lasers. The observed Nd:YAG oscillation threshold is at 2.3 mW of laser-diode output power, i.e., a small fraction of the rated output power. The highest Nd:YAG CW output power reached is 4.4 mW at an overall electrical-to-optical efficiency of 1.5 percent. The frequency jitter is less than 10 kHz in 0.3 s.
Infrared tunable diode lasers were developed in the 1960s and have been a valuable radiation source for high resolution laboratory and in situ spectroscopy. Use of Pb-salt Tunable Diode Lasers (TDL) in heterodyne applications impose stringent requirements on the TDL not normally required for laboratory spectroscopy. A review will be made of progress associated with TDLs in such heterodyne applications. Areas addressed will include such items as lifetime, operating temperature, and factors affecting excess noise. The review will emphasize the experience at Langley Research Center, but will include material from other users. The Langley information will include a description and current status of the Laser Heterodyne Spectrometer experiment and atmospheric solar absorption data obtained from a groundbased heterodyne system.
Spectra taken for a pulsed variable spacing phase-locked laser diode array (VSA) were recorded and processed to determine the magnitude of wavelength fluctuations present in the diode's output field. Analysis revealed that a pulsed VSA emits primarily into a single longitudinal mode.
Air-broadened and N2-broadened halfwidths at room temperature for twenty-five transitions in the nu-4 fundamental band of (C-12)H4 have been determined from IR absorption spectra recorded with a tunable diode laser spectrometer. Two tunable diode lasers operating in the 1250-1380-kayser region were used to obtain these data. Air-broadened halfwidths for twenty of these lines were also determined from additional spectra recorded at 0.01-kayser resolution with the Fourier transform spectrometer in the McMath solar telescope complex on Kitt Peak. The air-broadened halfwidths obtained from these two techniques are very consistent with agreement better than 3 percent in most cases.
The efficiency with which microscope objectives and custom lenses collimate laser diode emission was measured. Four microscope objectives of 10, 21, 45, and 60 power and two custom lenses of 1 and 0.8 power were used. An autocollimator system was used to measure throughput. It consisted of 1 m focal length lens, a 10 power microscope objective, and a 128-element G series Reticon linear array. Collimating throughput efficiency was defined as the ratio of measured collimated power to total laser output power. Two throughput efficiencies were obtained: one for the didoe operation below lasing and the other for the diode operation above lasing. The custom lenses had higher throughput efficiencies than the microscope objectives. The f/0.8 system provided better throughput efficiencies than the f/1.0 system.
The stability upon thermal cycling and handling of ten small, epoxy-encapsulated silicon diode thermometers at six temperatures in the range from liquid nitrogen temperatures to about 60 C. The nominal temperatures of measurement were -196, -78, 0, 20, 40, and 60 C, as measured on the International Practical Temperature Scale of 1968. Diodes were to be thermally cycled 15 to 20 times. Since NASA anticipates that the uncertainty in their temperature measurements will be + or - 50 mK, uncertainties as large as + or - 10 mK in the measurements of the evaluaton can be accommodated without deleteriously affecting the value of the results of the investigation.
Diode-laser-pumped Nd:YLF lasers are demonstrated at 1.047 microns with less than 1-mW thresholds and internal quantum efficiencies approaching 70 percent. Operation at 1.053 microns has also been achieved. Intracavity second-harmonic generation using MgO:LiNbO3 has generated up to 145-micro-W output at 523.6 nm for 30.1 mW of diode-laser pump power.
Different sensors and installation techniques for surface temperature measurement of cryogenic wind tunnel models were investigated. Silicon diodes were selected for further consideration because of their good inherent accuracy. Their average absolute temperature deviation in comparison tests with standard platinum resistance thermometers was found to be 0.2 K in the range from 125 to 273 K. Subsurface temperature measurement was selected as the installation technique in order to minimize aerodynamic interference. Temperature distortion caused by an embedded silicon diode was studied numerically.