Pulse Train Energy Research Articles

Amplification of flat laser pulse train.

We present modeling and measurements of flattop amplification of a laser pulse train in a diode pumped Nd:YLF system. We establish a theoretical model, accounting for the transverse Gaussian shape of an amplified laser beam, in order to explain remaining slopes in the pulse train energy. The influence of the transverse Gaussian shape on the train's flatness has been experimentally verified. Based on the model we are able to increase the total amplification of a long train of infrared seed beam in the drive laser system at the Fermilab Accelerator Science and Technology facility. The single-pass amplifier improvements resulted in a gain of ∼7 with flat output pulse train for up to 1000 seed pulses.

Development of beluga calf calls (Delphinapterus leucas) in the first six months of life

As part of an ongoing effort to understand beluga mother-calf communication and impacts of anthropogenic noise on neonate calls, we investigated a male beluga calf’s vocal development at Oceanogràfic, using a calibrated digital hydrophone with a sampling rate of 256 kHz. His initial vocalizations were broadband pulse-trains with upper frequency limits reaching ≥128 kHz on his first day of life, higher than reported by earlier studies limited by lower sampling rates. Over the calf’s first six months, pulsed trains were the predominant call type, increasing significantly in peak and first quartile frequencies and pulse repetition rate during this period. First and third quartile frequencies also increased significantly over the calf’s first month, indicating an early and continuous shift in pulse train energy distribution towards higher frequencies. While mixed and tonal calls appeared sporadically in the calf’s first month of life, they were not common until his third month, when they comprised 13% of his vocalizations. Additionally, estimated source levels of the calf’s calls increased throughout his first month, but were lower than those for adult belugas. This, coupled with the progressive shift in energy distribution, has important implications regarding a neonate’s ability to compensate for noise.

The passive Q-switching regime in a solid state laser with a multiloop cavity

A compact, pulsed-periodic YAG: Nd3+ laser with self-pumped phase-conjugate multiloop cavity and passive Q-switching by YAG: Cr4+ and GSGG: Cr4+ crystals has been studied. It is established that the energy and temporal parameters of radiation in separate pulses of a periodic train can be controlled almost without changing the pulse train energy. A regime of generating modulated radiation pulses with a peak power of up to 30 MW and a spatial brightness of 1.7 × 1015 W/(cm2 sr) at a radiation beam quality parameter of M2 < 1.2 has been realized in experiment.

Raman laser with intracavity conversion of laser radiation in a crystal

Intracavity Raman conversion of radiation of a Nd : YAG laser by a crystal into the first-Stokes component is studied in different operation regimes. In the case of passive -switching of the Nd : YAG laser, the SRS radiation has an average power of with a pulse train energy up to , an individual pulse duration of , and a pump pulse repetition rate of . In the case of active -switching, the average SRS power is at a pulse energy up to , a pulse duration of , and a pump pulse repetition rate of .

Small autonomous passively Q-switched Nd3+:YAG laser with a Cr4+:YAG Q switch emitting pulse trains

The energy and time characteristics of a passively Q-switched Nd3+:YAG laser with a Cr4+:YAG Q switch emitting pulse trains are studied and analysed theoretically. The description and technical parameters of a small autonomous laser with intracavity second-harmonic generation (ICSHG) in the pulse-train regime are presented. The laser provides a high total pulse-train energy for a relatively low peak power of a single pulse, stable operation in a wide temperature range, and has a small weight and size, which is convenient in operation. The enhanced reliability and stability of the laser operation are provided by its original technical design: the ICSHG scheme for type II phase matching without polarisers, the use of temperature-noncritical phase matching in KTP crystals, dust- and moisture-proof casing, and battery-operated pulsed power supply for the pump flashlamp.

Localization of the femtosecond pulse train energy in a one-dimensional nonlinear photonic crystal

Computer simulation demonstrates the feasibility of pumping a one-dimensional nonlinear photonic crystal (layered one-dimensional periodic structure) by optical energy localizing in the crystal when it is irradiated by a femtosecond pulse train. Simulation is based of the recently suggested approach to similar problems. It is shown that the pumping effect can be employed in 3D optical storages.

The influence of temporal pulse train modulation during laser percussion drilling

The temporal pulse train modulation during laser percussion drilling was found to effect significant changes to the material ejection processes. In particular, distinct differences in the material ejection processes have been observed between a temporal pulse train shaping technique termed as sequential pulse delivery pattern control (SPDPC) and the normal delivery pattern (NDP), wherein the parameters of successive laser pulses were constant. Due to the reduced upward material removal fractions in SPDPC drilling, the spatter deposition area was reduced from approximately 6.7 to 2.7 mm 2 . In addition, the melt layer thicknesses at the hole bottom were significantly increased from 11–61 to 18– 369 μm . Such changes were identified as being due to the low laser pulse intensities before beam breakthrough associated with the SPDPC method. It was observed that the use of the linearly increasing SPDPC method increased the downward material removal fractions, from 20% to 28% observed in NDP drilling, to 34%–39%. Such an increase in the downward material ejection mechanism in SPDPC drilling was identified as being primarily due to the pointed blind-hole profile generated before the onset of beam breakthrough. The work has shown that modulating the entire pulse train in laser percussion drilling could control the material ejection processes. Furthermore, the fundamental elements of the SPDPC technique are given in terms of the rate of energy deposition and total pulse train energy.

Dynamic-cavity passive Q-switch Nd-glass laser

Lasing regimes in a passive Q-switch Nd-glass laser with self-phase-conjugation in the active medium and LiF: F 2 − crystal were studied. We demonstrate the possibility of single-mode lasing with a pulse train energy above 2 J, peak power up to 0.5 MW, spatial brightness above 1×1011 W/(cm2 sr), and a coherence length of 0.95 m.

High energy negative feedback controlled passively mode-locked Nd: YAG laser

High energy picosecond pulse trains from a passively mode-locked Nd: YAG laser are obtained. The negative feedback controlled oscillator delivers 10–30 μs trains with energies of up to 30 mJ and single pulse duration of less than 25 ps. The laser is operated with a repetition rate of 10 Hz. An active Q-control of the cavity generates a short pulse train with duration of 30–40 ns. The long pulse train energy reproducibility is better than ± 1.5%.

Passively Q-switched transverse-diode-pumped Nd^3+:YLF laser oscillator

The design and performance of a diode-pumped Nd3+:YLF laser oscillator is described. A simple transverse-pump geometry in which a lensing duct efficiently couples the two-dimensional diode-pump array radiation to the YLF rod is employed. Using a color-center LiF crystal as a passive Q switch, we have produced burst-mode pulse trains that have a total energy of 115 mJ at a 30-Hz pulse-repetition frequency. The Q-switched pulse-train energy is 71% of the optimized free-lasing pulse energy, which is 163 mJ. Using an unstable cavity with a graded-reflectivity output coupler, we have generated Q-switched pulses that have 12-ns duration and near-diffraction-limited spatial profiles.

Passive mode-locking of an Alexandrite laser for picosecond pulse generation

The Alexandrite laser belongs to the class of vibronical lasers. The broad spectral laser gain of Alexandrite laser gain of Alexandrite suggests the possibility to generate femto-second laser pulses with passive mode locking. Experiments showed, however, that a limit of pulsewidth shortening is reached near 10 ps. This effect is caused by the limited mode-locking capability of the passive absorber. The results of eight different passive absorbers used to generate mode locking are presented. The effect of bandwidth narrowing of the laser emission spectrum of Alexandrite on pulsewidth and pulse-train energy was measured for these absorbers. The dependence of laser output energy with the temperature on the active medium was also investigated.

Generation of controlled-duration ultrashort pulses in a passively mode-locked YAG:Nd3+laser

The results are given of an investigation of a simple method for generating controlled-duration ultrashort pulses in a YAG:Nd3+ laser, passively mode-locked by a nonlinear filter with saturable absorption. The physical basis of the duration control is a variable initial transmission of the filter and the predominance of the action of temporal pulse compression by the nonlinear filter over the pulse broadening factor during the linear amplification stage in the active medium and corresponding spectral narrowing. The technical realization of the method of controlling the duration of ultrashort pulses is based on the use of a polymer switch utilizing dye No. 4363, an analog of No. 3274, and made in the form of a wedge. A service life was achieved in which ~104 pulses were generated at a single point in the switch when the pulsetrain energy was ~2 mJ. The range in which the duration of ultrashort pulses from the YAG:Nd3+ laser could be controlled was 15–100 psec, with practically 100% reproducibility of lasing of a single pulse per axial period. The 100% probability of isolating a single ultrashort pulse per period was due to the mode self-locking in the free-lasing regime.

Characterization of pulsed Nd:YAG active/passive mode-locked laser

The influence of the distance of an active modulator to one of the resonator's end mirrors is investigated both theoretically and experimentally and is found not to be critical for high-gain lasers. The effect of the active modulator on the pulse length of an active/passive mode-locked Nd:YAG laser is discussed qualitatively. Threshold, stability, pulse length, and output energy are investigated experimentally with respect to their dependence on modulation power of the active modulator, dye concentration of the passive modulator, and resonator length mismatch. At a repetition rate of 10 Hz the best achievable stability for the pulse-train energy was ± 1 percent with a single pulse length of 25 ps. The resonator length has to be maintained with an accuracy of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 100 \mu</tex> m.

Picosecond photodissociation and subsequent recombination processes in carbon monoxide hemoglobin.

Excitation of HbCO by a single 6-psec 530-nm pulse results in photodissociation with a first-order constant of 0.89 X 10(11) sec-1. The kinetics of photodissociation, monitored by following absorbance changes in the Soret band at 440 nm, are interpreted as corresponding to predissociation followed by a corssing into a dissociative state. Subsequent recombination of CO with the porphyrin system and protein structural transformations were monitored by use of a continuous He-Cd laser beam spatially coincident with the photolysis and Soret interrogation beams at the sample. We find that the latter events take place in three distinct time regions, depending on exciation pulse energy and repetition rate. Exictation of HbCO with a single pulse (0.8--5 mJ) results in a relaxation to the ground state with an associative first-order constant of 5 X 10(3) sec-1. With a 100-pulse train (approximately 7.5 mJ), a new decay grows with a rate constant of 63 sec-1. For a pulse-train energy of 12 mJ or higher, a delay occurs at the onset of the second (slower) recombination.

Interference Blanker for Dissimilar Modified Huffman Sequences

There are many pulse-coded sequence solutions for a pulse compression design that are available from D. A. Huffman's polynomial approach. If a sequence of length 13 is considered then there are 122 independent sequence solutions for the autocorrelation function of design. Out of this diversity of possible solutions some will be usable because pulse train energy utilization is high. The components of any chosen sequence possess different amplitude and phase excitation values which could be implemented by today's technology. In this paper an "interference blanker" is defined as a device that permits simultaneous operation of two or more pulse compression equipments so that there is no suppression of range resolution accuracy. The pulse compression decoder for the modified D. A. Huffman impulse-equivalent pulse trains is shown to be an " interference blanker" because the cross-correlation function between any two usable sequence solutions shows great variation from the autocorrelation function of design. Because in a practical implementation, there is a limit to the time sidelobe reduction that can be accomplished, D. A. Huffman's zero time sidelobe condition is modified. As an example, the ten most favorable sequence solutions for the time sidelobe level of 32.3 dB and a sequence length 13 are studied.

Modified Barker Code Approximating Huffman's Impulse-Equivalent Sequence

It is shown by use of D.A. Huffman's polynomial representation for a finite sequence of contiguous pulses in a pulse train that Barker's binary-coded sequences can be modified, by a weighting of pulse amplitudes, to a condition where time sidelobes in the pulse compressed signal are substantially reduced. In such a pulse amplitude modification there is a sacrifice in pulse train energy since each pulse does not have maximum energy. Results here are provided for Barker's sequence of length 13 only.