Single Giant Pulse Research Articles

Generation of orange pulse laser in waterproof fluoride glass fibre with graphene thin film

Orange laser pulses were successfully generated in a Pr-doped waterproof fluoride glass fibre (Pr:WPFGF) using a graphene thin film as a saturable absorber (SA). Two pulse generation modes were observed: a continuous mode with 0.47 μs pulse duration with a 2.61 μs repetition period and a single giant pulse mode with 9.7 ns pulse duration. The peak wavelength was 603 nm. This result shows that a graphene thin film can be effective as an SA in the visible region, and in the future a visible ultra-short pulse laser with a modelocking technique may be demonstrated.

Multifrequency Study of Giant Radio Pulses from the Crab Pulsar with the K5 VLBI Recording Terminal

Abstract Simultaneous multifrequency observations of Crab pulsar giant pulses (GPs) were performed with the 64-m Kalyazin radio telescope at four frequency ($\nu$$=$ 0.6, 1.4, 2.2, and 8.3 GHz) using the K5 VLBI recording terminal. The K5 terminal provided continuous recording in 16 $\times$ 4-MHz wide frequency channels distributed over 4 frequency bands. Several thousand GPs were detected during about 6 hours of observations on two successive days in 2005 July. The radio spectra of single GPs were analyzed at separate frequencies and over the whole frequency range. These spectra manifest notable modulation over the frequency ranges, $\Delta\nu$, both on large ($\Delta\nu/\nu$$\approx$ 0.5) and small ($\Delta\nu/$$\nu$$\approx$ 0.01) frequency scales. A cross-correlation analysis of GPs at 2.2 GHz showed that their pulse shapes can be interpreted as being an ensemble of unresolved bursts grouped together on time scales of $\approx$1$ \mu$s, being well-correlated over a 60-MHz band. The corresponding GP cross-correlation functions do not obey the predictions of the amplitude-modulated noise model of Rickett (1975), thus indicating that unresolved components represent a small number of elementary emitters.

Probing cosmic plasma with giant radio pulses

VLBI observations of the Crab pulsar with the 64-m radio telescope at Kalyazin (Russia) and the 46-m radio telescope of the Algonquin Radio Observatory (Canada) at 2.2 GHz and single-dish observations of the millisecond pulsar B1937+21 with the GBT (USA) at 2.1 GHz were conducted to probe the interstellar medium and study the properties of giant pulses. The VLBI data were processed with a dedicated software correlator, which allowed us to obtain the visibility of single giant pulses. Two frequency scales of 50 and 450 kHz were found in the diffraction spectra of giant pulses from the Crab pulsar. The location of the scattering region was estimated to be close to the outer edge of the nebula. No correlation was found between the power spectra of giant pulses at left- and right-hand circular polarization. We explain this lack of correlation through the influence of the strong magnetic field on circularly polarized emission in the region close to the Crab pulsar. Combining the measurement of the decorrelation bandwidth with that of the scattering time of giant pulses for B1937+21, we found three frequency scales of 1.7, 3.8, and 16.5 MHz. The scattering time of giant pulses of B1937+21 at 2.1 GHz was found to be 40+-4 ns. We obtained an upper limit of the intrinsic width of giant pulses from B1937+21 of less than 8 ns. The frequency dependences of the scattering times for the Crab pulsar and PSR B1937+21 were found to be different. They are characterized by exponents of -3.5 and -4.2, respectively. We attribute the difference to the large influence of scattering in the Crab nebula.

Giant pulses—The main component of the radio emission of the crab pulsar

The paper presents an analysis of dual-polarization observations of the Crab pulsar obtained on the 64-m Kalyazin radio telescope at 600 MHz with a time resolution of 250 ns. A lower limit for the intensities of giant pulses is estimated by assuming that the pulsar radio emission in the main pulse and interpulse consists entirely of giant radio pulses; this yields estimates of 100 Jy and 35 Jy for the peak flux densities of giant pulses arising in the main pulse and interpulse, respectively. This assumes that the normal radio emission of the pulse occurs in the precursor pulse. In this case, the longitudes of the giant radio pulses relative to the profile of the normal radio emission turn out to be the same for the Crab pulsar and the millisecond pulsar B1937+21, namely, the giant pulses arise at the trailing edge of the profile of the normal radio emission. Analysis of the distribution of the degree of circular polarization for the giant pulses suggests that they can consist of a random mixture of nanopulses with 100% circular polarization of either sign, with, on average, hundreds of such nanopulses within a single giant pulse.

Pulsed fiber laser using micro-electro-mechanical mirrors

Two different types of micromirrors are integrated with a fiber laser to modulate the cavity Q-factor. Both systems operate at frequencies up to 60 kHz and generate a pulse peak power 100 times higher than the continuous emission. We simulate the emitted pulses and find a good agreement with the measured value for the period of relaxation oscillations. The simulations also show the necessity of a shorter rise time of the Q-factor modulation to achieve one single giant and narrow Q-switched pulse.

New nanosecond polymer passive switch for neodymium lasers

A new nanosecond passive switch for neodymium lasers was developed on the basis of a highly elastic polyurethane matrix with an optical strength of 1200 MW cm-2, containing a photostable organic dye NOK. The switch was investigated under various Q-switching conditions in YAG, GSGG : Cr : Nd, and yttrium aluminate crystal lasers. Nanosecond single giant pulses and bursts of pulses were generated. The service life was 2×106 pulses at a single point of the switch. The energy of giant single pulses was 0.9 J. Repetition of single pulses at 50 Hz was possible.

Wide-bandwidth adjustable Q switch based on rubidium dimers

A new type of Q switching for a flash-lamp-pumped Nd:YAG laser based on the saturable absorption of rudibium dimers is demonstrated. The variation of laser parameters such as output energy, pulse length, and repetition rate by means of temperature-controlled vapor pressure is shown. For a temperature of 320°C, a train of 40-ns pulses separated by 6-µs intervals is generated. When the temperature is 360°C, a single giant pulse with energy of 100 mJ and a pulse length of 10-15 ns is observed. Comparison with a solid-state passive Q switch based on LiF is provided. The new cell construction, consisting of a sealed-off sapphire cell containing rubidium vapor, is proposed for reliable, efficient, adjustable Q switchingthat is applicable to all types of solid-state lasers. The advantages of this mechanism of Q switching, such as thermal insensitivity, frequency locking and line narrowing, and wide spectral bandwidth, covering 0.6-1.3 µm, are discussed.

Active and passive Q-switching of a 2.79 μm Er: Cr: YSGG laser

Active and passive Q-switched operation of the Er: Cr: YSGG laser at a wavelenght of λ = 2.79 μm has been achieved using three different shutters. Passive switching was obtained using InAs-layers as saturable absorbers, active switching was performed electrooptically and with the FTIR (frustrated total internal reflection) technique. Single giant pulses with output energies up to 34 mJ and pulse widths of 35 ns at fwhm were achieved. InAs-layers were also used as output mirrors for passive Q-switching. In this way bursts of multiple giant pulses were generated (27 mJ in 9 pulses with pulse widths from 89 to 130 ns at fwhm). The different Q-switches were compared with regard to their applicability to medical surgery.

Nd:YAG laser which generates a train of giant pulses for applications in ophthalmology

An Nd:YAG laser which generates a train of giant pulses in one laser-application event is described. The cumulative effect of the pulses of the train produces the necessary clinical effect, while the unwanted side effects characteristic of a single giant pulse are substantially reduced.

Use of an intracavity cell containing Cs2forQswitching and stabilizing the frequency of a laser utilizing concentrated neodymium phosphate glass

It was demonstrated experimentally that when a cell containing molecular cesium was placed inside the resonator of a laser utilizing concentrated phosphate glass, passive Q switching resulted in the generation of either a single giant pulse, having a minimum duration of 3?5 ns, or a train of 3?7 pulses, having a minimum pulse duration of 1.5?3 ns. In the case of the single giant pulse, the spectral width of the laser pulses did not exceed 7???103 cm?1, whereas in the case of the train of giant pulses it was less than (1?1.5)???10?2 cm?1, i.e., the laser pulse durations were close to being bandwidth-limited. Frequency stabilization of the laser pulses was observed. Quasicontinuous tuning of the laser pulse frequency was realised in the range of 1.05?1.06 ?m.

Mechanism of laserQswitching by intracavity stimulated scattering

An experimental investigation was made of Q switching of a laser resonator by intracavity stimulated Brillouin scattering. It was found that reduction in the high initial Q factor of the resonator by distortion of the transverse structure of the radiation (for example, by the use of an active element of low optical quality) resulted in effective modulation of the Q factor because of wavefront reversal in the scattering. When the active medium was YAG:Nd3+, single giant pulses of 25?30 nsec duration, peak power 0.3?0.5 MW, and repetition frequency up to 100 Hz were obtained without circulation of the scattering substance in the Q switch.

Influence of self-focusing on the operation of a neodymium glass laser

An acetone-filled cell was placed inside the resonator of a neodymium laser. A slight inclination of the nontransmitting laser mirror made it possible to emit single giant pulses of 0.3 MW power and 50 nsec duration. This was attributed to self-focusing and splitting of the beam into separate filaments.

Laser with a polyhedral active element emitting long nanosecond pulses

The results are given of anexperimentalinvestigationof a laser with a polyhedral neodymium-glass element operating under Q-switching conditions. The Q switching was performed by a passive switch. The dependence of the duration of a single giant pulse on the initial transmission coefficient of the switch was determined. Pulses of ~700 nsec duration and ~400 kW output power were obtained. The width of the emission spectrum was determined and found to be less than 0.01 cm–1 for a pumping intensity exceeding the threshold by not more than 10%. The angular divergence of the output radiation did not exceed 10–3 rad. The experimental and calculated results were compared.

A pulsed ruby laser with individually Q-switched multiple cavities

Four individually Q -switched laser cavities have been established sharing a common ruby laser rod. Single giant pulses have been emitted with a time duration of ≈ 30 ns (half-width) and energies of 0.16 J from each cavity apertured by a 2.54-mm-diameter hole. The spacing of the pulses was continuously variable in time from 0 to 1.25 ms plus or minus a jitter time of approximately 13 ns. This multiple-cavity laser light source can be used as a stroboscopic illuminator for photographic or holographic recording of fast events.

VARIABLY SPACED GIANT PULSES FROM MULTIPLE LASER CAVITIES IN A SINGLE LASING MEDIUM

Multiple laser cavities have been established in a single lasing medium. Single giant pulses with a time duration of 40 nsec have been emitted from each cavity and spaced less than 80 nsec to 4 μsec apart. The 0.4-mm spatial separation between the cavities indicates that many cavities could be established in a single lasing medium. Sequentially switching large numbers of cavities, repumping depleted regions, and reswitching could result in a high-repetition-rate giant-pulse laser system for use in photography and holography.

Self-Q-switched Nd3+: YAG and ruby lasers

Self-Q-switched operation of Nd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> : YAG lasers at 77°K and ruby lasers at 300 and 77°K pumped by the 5145-Å output of a pulsed argon ion laser is described. Self-Q-switched operation was obtained 1) by static mirror misalignment and 2) by static misalignment of the filament of the pumped laser material with respect to the mirror resonator axis. An output that consisted of a single giant pulse could be obtained for ruby by either method; for Nd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> : YAG, the output always consisted of one or more giant pulses and characteristic relaxation oscillations.

SELF-Q-SWITCHING IN RUBY LASERS

A laser consisting solely of a pumped ruby rod and rear reflector has been operated so as to produce single giant pulses.

Faraday Rotators for High Power Laser Cavities

The large values of Faraday rotation obtained with the use of pulsed high field magnets are shown to be applicable to the control of laser cavities. Experiments are described in which high-field magnets are operated up to 400 kOe in order to introduce large rotations in short, highly transparent optical media. With a ruby laser, interesting pulse enhancement and periodic equispaced output is observed and related to the switching rate of the field, typically 20 kOe/micro sec. Used with a cryptocyanine shutter, it is found that either a single giant pulse or a well-spaced series of pulses can be obtained. These are synchronized with respect to the varying magnetic field with fractional microsecond accuracy.

Spectrum of Laser Light Scattered from a Single Giant Pulse in a Laboratory Plasma

IN a previous communication1 we reported the forward scattering of a laser beam in a θ-pinch plasma in which co-operative effects dominated the scattered spectrum.

ION ENERGIES PRODUCED BY LASER GIANT PULSE

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