M. H. Sher

Bio: M. H. Sher is an academic researcher from Stanford University. The author has contributed to research in topics: Laser & Laser pumping. The author has an hindex of 4, co-authored 5 publications receiving 113 citations.

Saturation of the Xe III 109-nm laser using traveling-wave laser-produced-plasma excitation

Abstract: We describe the construction and operation of a 109-nm, photoionization-pumped, single-pass laser in Xe iii. The laser is pumped by soft x rays emitted from a laser-produced plasma in a traveling-wave geometry. Using a 3.5-J, 300-psec, 1064-nm laser pump pulse, we measure a small-signal gain coefficient of 4.4 cm−1 and a total small-signal gain of exp(40). The laser is fully saturated and produces an output energy of 20 μJ in a beam with 10-mrad divergence.

2-Hz 109-nm mirrorless laser

Abstract: We report 2-Hz operation of a single-pass 109-nm laser with a small-signal gain of exp 33 and a saturated output energy of 1 μJ. The laser is based on an oblique-incidence, laser-produced-plasma pumping geometry and requires only 500 mJ of 1064-nm energy in a 0.5-nsec pump pulse. We use the laser to produce a two-slit interference pattern and demonstrate a focusable intensity of greater than 109 W/cm2.

Prepulsing of laser-produced plasmas for more efficient pumping of extreme-ultraviolet lasers

Abstract: We have used a low-energy prepulse to enhance the soft-x-ray emission of laser-produced plasmas in a parameter range that has been used to pump photoionization lasers. We have prepulsed a laser-produced-plasma-pumped Xe iii 109-nm laser, which was pumped with an 80-ps 1064-nm pulse, and we observed a greater than tenfold increase in output.

Soft x-ray pumping of inner-shell excited levels for extreme ultraviolet lasers

Abstract: When a 1.06-μm laser beam is focused onto a high-Z target at intensities of 1012–1014 W cm−2, a plasma is formed from which a burst of soft x rays is emitted with a conversion efficiency in excess of 10%. This burst of x rays can be used as an x-ray flashlamp to pump potential extreme UV laser systems.1,2

Table-top soft x-ray lasers

Abstract: This article reviews the progress in the development of practical table-top sources of soft x-ray laser radiation. The field is rapidly approaching the stage at which soft x-ray lasers sufficiently compact to fit onto a normal optical table will be routinely utilized in science and technology. This is the result of recent advances in the amplification of soft x-ray radiation in both compact laser-pumped and discharge-pumped devices. The use of excitation mechanisms that take full advantage of new ultrafast high power optical laser drivers and multiple pulse excitation schemes has resulted in the demonstration of saturated soft x-ray amplification at wavelengths as short as 14 nm using several Joule of laser-pump energy. Moreover, several schemes have demonstrated significant gain with only a fraction of a Joule of laser-pump energy. In addition, the demonstration of saturated table-top soft x-ray lasers pumped by very compact capillary discharges has shattered the notion that discharge-created plasmas are insufficiently uniform to allow for soft x-ray amplification, opening a route for the development of efficient, high average power soft x-ray lasers. Recently, a table-top capillary discharge laser operating at 46.9 nm has produced millijoule-level laser pulses at a repetition rate of several Hz, with a corresponding spatially coherent average power per unit bandwidth comparable to that of a beam line at a third generation synchrotron facility. This review summarizes fundamental and technical aspects of table-top soft x-ray lasers based on the generation of population inversions in plasmas, and discusses the present status of development of specific laser systems.

Development and applications of compact high‐intensity lasers

Abstract: The development of compact high‐intensity lasers, made possible by the technique of chirped pulse amplification, is reviewed. This includes the complexities of high‐power laser implementation, such as the generation of short pulses, pulse cleaning, wide‐bandwidth amplification, temporal stretching and compression, and the requirements for high‐average powers. Details of specific solid‐state laser systems are given. Some applications of these lasers to short‐pulse coherent short‐wavelength [x‐ray ultraviolet (XUV)] sources are also reviewed. This includes several nonlinear effects observed by focusing a subpicosecond laser into a gas; namely, an anomalous scaling of harmonic generation in atomic media, an upper limit on the conversion efficiency of relativistic harmonics in a plasma, and the observation of short‐pulse self‐focusing and multifoci formation. Finally, the effects of large ponderomotive pressures (100 Mbars) in short‐pulse high‐intensity laser–plasma interactions are discussed, with relevance both to recombination x‐ray lasers and a novel method of igniting thermonuclear fusion.

Proposal for soft-x-ray and XUV lasers in capillary discharges.

Abstract: Capillary plasmas with large length-to-diameter ratios (1/d > 100) are proposed as amplification media for soft-x-ray and XUV radiation by direct discharge excitation. The capillary geometry provides a small volume and an adequate resistance for ohmic heating. Heat conduction to the capillary walls provides rapid cooling of the plasma during the decay of the excitation pulse, resulting in a large recombination rate and a population inversion. A time-dependent collisional–radiative model of the capillary plasma predicts gains of the order of 5 cm−1 in the 18.2-nm line of C vi.

Photoionization-pumped x-ray lasers using ultrashort-pulse excitation

Abstract: Recent advances in the production of ultrashort x-ray pulses by using femtosecond laser-produced plasmas coupled with the development of terawatt ultrashort-pulse lasers may make possible ultrashortpulse photoexcited x-ray lasers. I examine the creation of a population inversion on the K-alpha transition of neon at 1.5 nm by using the photoionization scheme first suggested by Duguay and Rentzepis in 1967. It is shown that this laser can be produced by using a pump laser of ~ 10 J in 50 fs, provided that a sufficiently bright laser-produced plasma x-ray source can be created. Recent experimental and theoretical results are discussed that verify the potential feasibility of this scheme.