7B3 - Characteristics of a traveling-wave ruby single-mode laser as a laser radar transmitter
TL;DR: In this article, a single-mode ruby laser transmitter has been developed having the following properties: master oscillator: power output ≈ 20 kW; pulse width = 1μs; repetition rate = 1 pps.
Abstract: As part of a laser radar program, a single-mode ruby laser transmitter has been developed having the following properties: Master Oscillator: power output ≈ 20 kW; pulse width =1μs; repetition rate = 1 pps. Power Amplifier: (measured gain 24 dB). This paper describes results obtained with this laser transmitter. The techniques to determine the key properties of this laser transmitter are described along with the actual results that have been obtained. The particular characteristics of interest are 1) coherence of the laser, 2) frequency shift of "chirp" during the pulse, and 3) method of achieving the single mode.
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Patent•
03 Dec 1992
TL;DR: In this paper, a method and apparatus for utilizing a single frequency, self seeding laser pulse signal transmitted to create a target beam to be projected toward an atmospheric target whereby a portion will be reflected back upon itself, and a local oscillator beam constructed to a shape approximating a low level elongated square wave pulse to be heterodyned with the returning target beam.
Abstract: The invention presents a method and apparatus for utilizing a single frequency, self seeding laser pulse signal transmitted to create a target beam to be projected toward an atmospheric target whereby a portion will be reflected back upon itself, and a local oscillator beam constructed to a shape approximating a low level elongated square wave pulse to be heterodyned with the returning target beam. A radio frequency voltage drives an acousto-optic modulator and amplitude modulates the local oscillator beam to form an optical output that is a flat top pulse resembling a square wave function. The local oscillator beam and returning target beam are polarization adjusted to match and are then combined and focused onto detector. The system is effective for use as an aircraft velocimeter.
41 citations
TL;DR: In this paper, the authors present the generation of 12.1 ns frequency chirped pulses from a distributed feedback laser diode via injection current modulation and demonstrate its application to absorption-based methane sensing at 1650.9 nm.
Abstract: We present the generation of 12.1 ns frequency chirped pulses from a distributed feedback laser diode via injection current modulation and demonstrate its application to absorption-based methane sensing at 1650.9 nm. The chirp spectral distribution is found to be significantly impacted by the transient dynamics of these short pulses. A simplified, two-part model is used to evaluate the chirp property, suggesting spectral mixing and oscillation. The chirp enables intra-pulse self-calibrated gas sensing by taking the amplitude ratio between the absorption peak and a reference, which is demonstrated for methane concentrations from 0 to 22.6% with a detection limit of 25 ppm. It also provides resistance to power fluctuation from various sources. These short pulses offer high spatial and temporal resolution and can potentially enable reflection-based, highly multiplexed gas sensing systems.
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TL;DR: In this article, it was shown that the spatial variation in the field intensity of the various modes produces non-uniform distributions in the inverted population and one can show that there is little tendency for these distributions to smooth out due to spatial cross relaxation.
Abstract: Experiments show that conventional solid‐state lasers can go into oscillation simultaneously in many modes. This is somewhat surprising since it appears impossible to ``eat holes'' in temperature‐broadened lines and thus only one or, at most, a few modes should be able to oscillate. However, the spatial variation in the field intensity of the various modes produces nonuniform distributions in the inverted population and one can show that there is little tendency for these distributions to smooth out due to spatial cross relaxation. Such nonuniform distributions could lead to simultaneous oscillation in many modes. Formulas which relate the number of unstable modes to the pump power and various other maser parameters are obtained. The results show that it is exceedingly difficult to obtain single mode operation in conventional masers at high pumping levels. Ways to avoid a nonuniform distribution density and methods to achieve high‐power single‐mode operation in practice are discussed. It is also possible to show the effect of slow spatial cross relaxation on the spiking behavior.
346 citations
TL;DR: In this paper, the conditions under which spiking in the laser output can be completely suppressed were investigated theoretically and experimentally with a single-mode traveling-wave laser, and it was found that the time delay between the build-up of the electromagnetic energy in the cavity and the corrective action of the Kerr cell is a rather important parameter.
Abstract: We have investigated theoretically and experimentally the conditions under which spiking in the laser output can be completely suppressed. It is predicted that a nonlinear absorber in the cavity producing greater loss at the higher power levels, and vice versa, should be highly effective. Experimental work was carried out with a single‐mode traveling‐wave laser, since in this case the predictions can be most easily checked. Instead of using a nonlinear absorber, a Kerr cell controlled by a feedback circuit was used. It was found, in agreement with theory, that the time delay between the build‐up of the electromagnetic energy in the cavity and the corrective action of the Kerr cell is a rather important parameter. Spike suppression can only be obtained when this time delay is short as compared to the duration of one oscillation pulse.
61 citations
TL;DR: In this paper, the macroscopic maser rate equations are derived systematically from the Boltzmann equation for the density matrix of the atomic systems and Maxwell's equations for the radiation fields.
Abstract: Masers exhibit interesting transient behavior that cannot be completely understood on the basis of the rate equations. The use of the rate equations in most transient analyses is usually justified on a more or less intuitive basis and the implied assumptions are not always clear. In this paper, the macroscopic maser rate equations are derived systematically from the Boltzmann equation for the density matrix of the atomic systems and Maxwell's equations for the radiation fields. When the coherence linewidth (T2−1) of the atomic systems is much larger than the cavity linewidth and the natural linewidth (T1−1) of the atomic emission, and with a WKB approximation, in the lowest order of approximation one obtains the two widely used, coupled first‐order nonlinear rate equations of Statz and deMars. On the other hand, if the cavity linewidth is much larger than the atomic linewidths (T1−1 and T2−1), one can use the so‐called ``reaction‐field principle'' of Anderson and obtain, again, two coupled first‐order rat...
54 citations
TL;DR: In this article, the effects of slow spatial cross relaxation is extended in two directions: off-axis modes are included in the calculations, and thus it becomes possible to calculate the number of oscillating offaxis modes as a function of the various laser parameters.
Abstract: Previous work by the authors on the effects of slow spatial cross relaxation is extended in two directions. First, off‐axis modes are included in the calculations, and thus it becomes possible to calculate the number of oscillating off‐axis modes as a function of the various laser parameters. In this way the expected beam angle of a laser can be predicted. Second, a more detailed analysis of the spiking behavior is given; both regular and irregular spiking trains may be obtained depending upon the laser parameters and the pump power.
52 citations