Sapphire


Diamond behaves somewhat differently in that n is low in air, about 0.1. It is dependent, however, on which crystal face is involved, and rises severalfold in vacuum (after heating) [1,2,25]. The behavior of sapphire is similar [24]. Diamond surfaces, incidentally, can have an oxide layer. Naturally occurring ones may be hydrophilic or hydrophobic, depending on whether they are found in formations exposed to air and water. The relation between surface wettability and friction seems not to have been studied.  [c.440]

Ti sapphire laser excitation Chem. Phys. Lett. 233 519-24  [c.1232]

Xu Z H, Ducker W and Israelachvili J N 1996 Forces between crystalline alumina (sapphire) surfaces in aqueous sodium dodecyl sulfate surfactant solutions Langmuir 12 2263-70  [c.1749]

Horn R G, Clarke D R and Clarkson M T 1988 Direct measurement of surface forces between sapphire crystals in aqueous solutions J. Mater. Res. 3 413-6  [c.1749]

Figure B2.1.1 Femtosecond light source based on an amplified titanium-sapphire laser and an optical parametric amplifier. Symbols used P, Brewster dispersing prism X, titanium-sapphire crystal OC, output coupler B, acousto-optic pulse selector (Bragg cell) FR, Faraday rotator and polarizer assembly DG, diffraction grating BBO, p-barium borate nonlinear crystal. Figure B2.1.1 Femtosecond light source based on an amplified titanium-sapphire laser and an optical parametric amplifier. Symbols used P, Brewster dispersing prism X, titanium-sapphire crystal OC, output coupler B, acousto-optic pulse selector (Bragg cell) FR, Faraday rotator and polarizer assembly DG, diffraction grating BBO, p-barium borate nonlinear crystal.
Shortly after the development of high-energy/pulse Ti-sapphire regenerative amplifier systems, a number of investigators reported progress in using OP As in producing tunable sources of very short pulses. Wilson and co-workers [46] showed early on that an experimentally usefiil source for femtosecond spectroscopy with <50 fs pulses was obtained tluough the use of continuum seeding of a type I nonlinear OPA crystal, which was pumped by the fundamental output of an amplified Ti-sapphire laser. The main problem with the early systems was inlierent to the physics of col linearly pumped parametric amplification the signal, idler and pump frequencies have different group velocities (see below) in the nonlinear crystal, which limits the amount and frequency bandwidth of the parametric gain. In other language, the phase-matching condition for the collinearly pumped OPA works only over a small bandwidth, which tends to limit the pulse duration to fairly long (100 fs) pulses, and tuning of the OPA to different signal wavelengths requires reoptimization of the crystal s orientation. The design advanced by Wilson s group takes advantage of the smaller mismatch m group velocities m the near-IR part of the spectrum odier designs employing pumping with the second hannonic of the Ti-sapphire laser provide direct access to visible signal pulses but with significantly longer durations (150 fs) [48].  [c.1972]

Very recently, Hache and co-workers [49] found that a non-collinear pumping of an OPO crystal produces a phase-matching condition that is independent of signal wavelength over a very broad bandwidth. This discovery makes it possible to obtain very high parametric gain in an OPA with a smgle pass dirough the crystal and adjustable signal bandwidths. The result is a source of light with wide tunability and adjustable pulse durations, the ultimate femtosecond light source. The design for the OPA depicted in figure B2.T1 is an adaptation of that recently described by Riedle and co-workers [32]. 400 run light obtained by frequency doubling the output of a regenerative Ti-sapphire amplifier is overlapped at an angle of 3.7° with the femtosecond continuum light. This angle produces in BBO the wavelength-independent phase-matching condition noted by Hache and co-workers. Riedle and co-workers demonstrated that signal pulses of 15-20 fs duration could be obtained from this system, with tunability over most of the 400-800 run visible range.  [c.1972]

Figure B2.1.3 Output of a self-mode-locked titanium-sapphire oscillator (a) non-collinear intensity autocorrelation signal, obtained with a 100 pm p-barium borate nonlinear crystal (b) intensity spectrum. Figure B2.1.3 Output of a self-mode-locked titanium-sapphire oscillator (a) non-collinear intensity autocorrelation signal, obtained with a 100 pm p-barium borate nonlinear crystal (b) intensity spectrum.
Norris T B 1992 Femtosecond pulse amplification at 250 kHz with a Ti sapphire regenerative amplifier and application to continuum generation Opt. Lett. 17 1009-11  [c.1992]

Reed M K, Steiner-Shepard M K and Negus D K 1994 Widely tunable femtosecond optical parametric amplifier at 250 kHz with a Ti sapphire regenerative amplifier Opt. Lett. 19 1855-7  [c.1993]

Figure C2.16.2 shows tire gap-lattice constant plots for tire III-V nitrides. These compounds can have eitlier tire WTirtzite or zincblende stmctures, witli tire wurtzite polytype having tire most interesting device applications. The large gaps of tliese materials make tliem particularly useful in tire preparation of LEDs and diode lasers emitting in tire blue part of tire visible spectmm. Unlike tire smaller-gap III-V compounds illustrated in figure C2.16.3 single crystals of tire nitride binaries of AIN, GaN and InN can be prepared only in very small sizes, too small for epitaxial growtli of device stmctures. Substrate materials such as sapphire and SiC are used instead. Figure C2.16.2 shows tire gap-lattice constant plots for tire III-V nitrides. These compounds can have eitlier tire WTirtzite or zincblende stmctures, witli tire wurtzite polytype having tire most interesting device applications. The large gaps of tliese materials make tliem particularly useful in tire preparation of LEDs and diode lasers emitting in tire blue part of tire visible spectmm. Unlike tire smaller-gap III-V compounds illustrated in figure C2.16.3 single crystals of tire nitride binaries of AIN, GaN and InN can be prepared only in very small sizes, too small for epitaxial growtli of device stmctures. Substrate materials such as sapphire and SiC are used instead.
Infrared pulses of 200 fs duration with 150 of bandwidth centred at 2000 were used in this study. They were generated in a two-step procedure [46]. First, a p-BaB204 (BBO) OPO was used to convert the 800 mn photons from the Ti sapphire amplifier system into signal and idler beams at 1379 and 1905 mn, respectively. These two pulses were sent tlirough a difference frequency crystal (AgGaS2) to yield pulses  [c.1173]

The great sensitivity and bandwidth of electro-optic approaches to optical-THz conversion also enable a variety of new experiments in condensed matter physics and chemistry to be conducted, as is outlined in figure Bl.4.6. The left-hand side of this figure outlines the experimental approach used to generate ultrafast optical and THz pulses with variable time delays between them [M]. A mode-locked Ti sapphire laser is amplified to provide approximately 1 W of 100 fs near-IR pulses at a repetition rate of 1 kHz. The 850 mn light is divided into tliree beams, two of which are used to generate and detect the THz pulses, and the third of which is used to optically excite the sample with a suitable temporal delay. The right-hand panel presents the measured relaxation of an optically excited TBNC molecule in liquid toluene. In such molecules, the charge distribution changes markedly in the ground and electronically excited states. In TBNC, for example, the excess negative charge on the central porphyrin ring becomes more delocalized in the excited state. The altered charge distribution must be acconnnodated by changes in the surrounding solvent. This so-called solvent reorganization could only be indirectly probed by Stokes shifts in previous optical-optical pump-probe experiments, but the optical-THz approach enables the solvent response to be directly investigated. In this case, at least tln-ee distinct temporal response patterns of the toluene solvent can be seen that span several temporal decades [M]. For solid-state spectroscopy, ultrafast THz studies have enabled the investigation of coherent oscillation dynamics in the collective (phonon) modes of a wide variety of materials for the first time [49].  [c.1249]

In order to achieve a reasonable signal strength from the nonlinear response of approximately one atomic monolayer at an interface, a laser source with high peak power is generally required. Conuuon sources include Q-switched ( 10 ns pulsewidth) and mode-locked ( 100 ps) Nd YAG lasers, and mode-locked ( 10 fs-1 ps) Ti sapphire lasers. Broadly tunable sources have traditionally been based on dye lasers. More recently, optical parametric oscillator/amplifier (OPO/OPA) systems are coming into widespread use for tunable sources of both visible and infrared radiation.  [c.1281]

Other frequently used resonators are dielectric cavities and loop-gap resonators (also called split-ring resonators) [12]. A dielectric cavity contains a diamagnetic material that serves as a dielectric to raise the effective filling factor by concentratmg the B field over the volume of the sample. Hollow cylinders machmed from Ilised quartz or sapphire that host the sample along the cylindrical axis are conunonly used.  [c.1560]

These limitations have recently been eliminated using solid-state sources of femtosecond pulses. Most of the femtosecond dye laser teclmology that was in wide use in the late 1980s [11] has been rendered obsolete by tliree teclmical developments the self-mode-locked Ti-sapphire oscillator [23, 24, 25, 26 and 27], the chirped-pulse, solid-state amplifier (CPA) [28, 29, 30 and 31], and the non-collinearly pumped optical parametric amplifier (OPA) [32, 33 and 34]- Moreover, although a number of investigators still construct home-built systems with narrowly chosen capabilities, it is now possible to obtain versatile, nearly state-of-the-art apparatus of the type described below Ifom commercial sources. Just as home-built NMR spectrometers capable of multidimensional or solid-state spectroscopies were still being home built in the late 1970s and now are almost exclusively based on commercially prepared apparatus, it is reasonable to expect that ultrafast spectroscopy in the next decade will be conducted almost exclusively with apparatus ifom conmiercial sources based around entirely solid-state systems.  [c.1969]

Figure B2.T1 depicts an instrument that takes advantage of many of the most recent teclmical developments. The best strategy for generating wavelength-tunable ultrashort laser pulses for time-resolved spectroscopy involves use of an OPA as the only wavelength-tunable element. This approach is organized around the principle that extremely stable, fixed wavelength, high-energy pulse trains can now be generated using an amplified Ti-sapphire-based system. The chief advantage of instruments like the one shown in figure B2.T1 is that experimental demands for specific operatmg wavelengths are met by adjustment of the last device in the pulse-fonning cham, the OPA. One can expect such a design to be considerably more robust and user-Ifiendly than systems based on wavelength tunable oscillators, which demand manipulation of every device in the instrument in response to tuning to a new wavelength. Figure B2.T1 depicts an instrument that takes advantage of many of the most recent teclmical developments. The best strategy for generating wavelength-tunable ultrashort laser pulses for time-resolved spectroscopy involves use of an OPA as the only wavelength-tunable element. This approach is organized around the principle that extremely stable, fixed wavelength, high-energy pulse trains can now be generated using an amplified Ti-sapphire-based system. The chief advantage of instruments like the one shown in figure B2.T1 is that experimental demands for specific operatmg wavelengths are met by adjustment of the last device in the pulse-fonning cham, the OPA. One can expect such a design to be considerably more robust and user-Ifiendly than systems based on wavelength tunable oscillators, which demand manipulation of every device in the instrument in response to tuning to a new wavelength.
The most connnonly used femtosecond oscillator at this point is the self-mode-locked Ti-sapphire laser [23, 24. 25. 26 and 27], shown in figure B2.1.1 which can routinely produce pulses of light with durations adjustable over the 10-150 fs range. The wavelength of the Ti-sapphire oscillator can be timed over the 700-1100 mn range using an intracavity slit or birefringent filter, providing pulse durations that are essentially limited by the bandwidth of the filtering element. (It should be emphasized, however, that timing an oscillator of this type is not as routinely done as is timing an OP A.) The pulse energy that can be directly obtained from the oscillator is typically limited to the 2 nJ/piilse regime, but the oscillator emits pulses at a high repetition rate, typically 75-100 MFIz, depending on the cavity dimensions.  [c.1970]

The Ti-sapphire oscillator is extremely iisefiil as a stand-alone source of femtosecond pulses in the near-IR region of the spectrum. Some iiltrafast experiments, especially of the pump-probe variety (see below), can be conducted with pulses obtained directly from the oscillator or after pulse selection at a lower repetition rate. Far-IR (terahertz) radiation is usually generated using a semiconductor (usually GaAs) substrate and focused Ti-sapphire oscillator pulses [7]. If somewhat higher-energy pulses are required for an experiment, the Ti-sapphire oscillator can be cavity dumped by an mtracavity acousto-optical device known as a Bragg cell.  [c.1970]

Although many usefiil femtosecond spectroscopic experiments on condensed-phase targets can be easily performed with low-energy pulses, in the 100 pj to 1 nJ regime, higher-energy pulses are required if wavelength tunability is desired. A femtosecond continuum [39] can be generated in water or sapphire if the pulse energy is higher than 200 nJ OPA sources require even higher energies, in excess of 1 pJ/pulse. Amplification of Ti-sapphire oscillators is at this point routinely perfonned, with excellent connnercial systems readily available of the regenerative amplifier type [28, 30, 31, 40, 4T], and there are simple multipass amplifier designs [42, 43] that are easily constmcted in the laboratory.  [c.1971]

Pulses are selected for amplification from the oscillator s 75-100 MHz pulse train at a much lower repetition rate, ranging in published designs from 10 Hz to 250 kHz, either by a Pockels cell or a Bragg cell (as shown in figure B2.T1. The selected pulse train is amplified in Ti-sapphire gam media using a method known as chirped-pulse amplification [28, 29, 30 and 31]. In this scheme, oscillator pulses are stretched temporally well into the picosecond regime prior to amplification so that the damage tlireshold for the gain crystal is not exceeded [44]. If the amplifier is designed to operate in the >10kHz regime, like the one depicted in figure B2.T1 a stretcher may not be required. A grating-pair pulse compressor [45] is used to compress the pulse back nearly to its original duration after it emerges from the amplifier. Regenerative amplifiers capable of producing 75-150 fs pulses are die most common systems in use [30, 40], but recently a multipass ring amplifier has been described that produces 20 fs pulses [43]. The multipass amplifier depicted in figure B2.T1 is a non-ring design that pennits a more facile input and extraction of the amplified pulse.  [c.1971]

The most connnon commercially prepared amplifier systems are pumped by frequency-doubled Nd-YAG or Nd-YLF lasers at a 1-5 kHz repetition rate a continuously pumped amplifier that operates typically in the 250 kHz regime has been described and implemented connnercially [40]. The average power of all of the connnonly used types of Ti-sapphire amplifier systems approaches 1 W, so the energy per pulse required for an experiment effectively detennines the repetition rate.  [c.1971]

The OPA should not be confiised with an optical parametric oscillator (OPO), a resonant-cavity parametric device that is syncln-onously pumped by a femtosecond, mode-locked oscillator. 14 fs pulses, tunable over much of the visible regime, have been obtained by Hache and co-workers [49, with a BBO OPO pumped by a self-mode-locked Ti-sapphire oscillator.  [c.1972]

Figure B2.T6 depicts a standard type of apparatus used for the hole-buming type of time-resolved absorption experiment [112. 113. 123]. A pulse train from an amplified laser is split into two portions. The minor portion is used directly as a source of pump photons the major portion is used to generate a broad-band probe source derived from a femtosecond contimiiun. In this application, the contimiiun is typically generated by focusing a > 1 pJ pulse of light into flowing water or ethylene glycol in a cuvette [39] a contimiiun with particularly good optical properties can be generated in a thin sapphire crystal [47]. After the pump and probe pulses are overlapped in the sample, the transmitted probe light is dispersed in a monochromator and then detected either by a photodiode or by a multichannel detector, such as a charge-coupled device (CCD). The most conunon detection scheme involves using a mechanical chopper to modulate the intensity of the pump beam the pump-induced changes in the transmission of the probe beam are then detected by using a lock-in amplifier. Figure B2.T6 depicts a standard type of apparatus used for the hole-buming type of time-resolved absorption experiment [112. 113. 123]. A pulse train from an amplified laser is split into two portions. The minor portion is used directly as a source of pump photons the major portion is used to generate a broad-band probe source derived from a femtosecond contimiiun. In this application, the contimiiun is typically generated by focusing a > 1 pJ pulse of light into flowing water or ethylene glycol in a cuvette [39] a contimiiun with particularly good optical properties can be generated in a thin sapphire crystal [47]. After the pump and probe pulses are overlapped in the sample, the transmitted probe light is dispersed in a monochromator and then detected either by a photodiode or by a multichannel detector, such as a charge-coupled device (CCD). The most conunon detection scheme involves using a mechanical chopper to modulate the intensity of the pump beam the pump-induced changes in the transmission of the probe beam are then detected by using a lock-in amplifier.
Figure B2.1.6 Femtosecond spectrometer for transient hole-burning spectroscopy with a continuum probe. Symbols used bs, 10% reflecting beamsplitter p, polarizer. The continuum generator consists of a focusing lens, a cell containing flowing water or ethylene glycol or, alternatively, a sapphire crystal and a recollimating lens. Figure B2.1.6 Femtosecond spectrometer for transient hole-burning spectroscopy with a continuum probe. Symbols used bs, 10% reflecting beamsplitter p, polarizer. The continuum generator consists of a focusing lens, a cell containing flowing water or ethylene glycol or, alternatively, a sapphire crystal and a recollimating lens.
Spence D E, Kean P N and Sibbett W 1991 60 fs pulse generation from a self-mode-locked Ti sapphire laser Qpt. Lett. 16 42—4  [c.1991]

Pshenichnikov M S, de Boeij W P and Wiersma D A 1994 Generation of 13 fs, 5 MW pulses from a cavity-dumped Ti sapphire laser Opt. Lett. 19 572-4  [c.1992]

Joo T, Jia Y and Fleming G R 1995 Ti sapphire regenerative amplifier for ultrashort high-power multikilohertz pulses without an external stretcher Opt. Lett. 20 389-91  [c.1992]

Tilsch M and Tschudi T 1997 Self-starting 6.5-fs pulses from a Ti sapphire laser Opt. Lett. 22 1009-11  [c.2149]

Brakenhoff G J, Squier J, Norris T, Bliton A C, Wade M FI and Athey B 1996 Real-time two-photon confocal microscopy using a femtosecond, amplified Ti sapphire system J. Microscopy 181 253-9  [c.2506]

Rothberg L, Higashi G S, Allara D L and Garoff S 1987 Thermal disordering of Langmuir-Blodgett-films of cadmium stearate on sapphire Chem. Phys. Lett. 133 67-72  [c.2631]

The most powerful teclmique for studying VER in polyatomic molecules is the IR-Raman method. Initial IR-Raman studies of a few systems appeared more than 20 years ago [16], but recently the teclmique has taken on new life with newer ultrafast lasers such as Ti sapphire [39]. With more sensitive IR-Raman systems based on these lasers, it has become possible to monitor VER by probing virtually every vibration of a polyatomic molecule, as illustrated by recent studies of chlorofonn [40], acetonitrile [41, 42] (see example C3.5.6.6 below) and nitromethane [39, 43].  [c.3035]


See pages that mention the term Sapphire : [c.26]    [c.113]    [c.188]    [c.352]    [c.1248]    [c.1282]    [c.1968]    [c.1971]    [c.1971]    [c.1973]    [c.1974]    [c.1976]    [c.1982]    [c.1991]    [c.1992]    [c.1993]    [c.2003]    [c.2492]    [c.2965]   
Modern inorganic chemistry (1975) -- [ c.150 ]

Solids under high-pressure shock compression - mechanics, physics, and chemistry (1992) -- [ c.21 , c.31 , c.86 , c.87 , c.107 , c.108 ]