Sapphire laser

Ti sapphire laser excitation Chem. Phys. Lett. 233 519-24... 

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. 

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.

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... 

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... 

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

Historically, the first type of laser to be tunable over an appreciable wavelength range was the dye laser, to be described in Section 9.2.10. The alexandrite laser (Section 9.2.1), a tunable solid state laser, was first demonstrated in 1978 and then, in 1982, the titanium-sapphire laser. This is also a solid state laser but tunable over a larger wavelength range, 670-1100 nm, than the alexandrite laser, which has a range of 720-800 nm. 

The lasing medium in the titanium-sapphire laser is crystalline sapphire (AI2O3) with about 0.1 per cent by weight of Ti203. The titanium is present as Ti and it is between energy levels of this ion that lasing occurs. 

A further advantage, compared with the alexandrite laser, apart from a wider tuning range, is that it can operate in the CW as well as in the pulsed mode. In the CW mode the Ti -sapphire laser may be pumped by a CW argon ion laser (see Section 9.2.6) and is capable of producing an output power of 5 W. In the pulsed mode pumping is usually achieved by a pulsed Nd YAG laser (see Section 9.2.3) and a pulse energy of 100 mJ may be achieved. 

In 1991 a remarkable discovery was made, accidentally, with a Tp -sapphire laser pumped with an Ar+ laser. Whereas we would expect this to result in CW laser action, when a sharp jolt was given to the table supporting the laser, mode locking (Section 9.1.5) occurred. This is known as self-locking of modes, and we shall not discuss further the reasons for this and how it can be controlled. One very important property of the resulting pulses is that they are very short. Pulse widths of a few tens of femtoseconds can be produced routinely and with high pulse-to-pulse stability. Further modification to the laser can... 

In Section 9.2.2 we saw that a pulsed Tp sapphire laser can produce pulses less then 10 fs in length. There are also other laser techniques which can be used to produce pulse lengths... 

AI2O3 (aluminium oxide) in ruby laser, 346 in titanium-sapphire laser, 348 3142 (cyclic) interstellar, 120 3142 (linear) interstellar, 120... 

The development of lasers has continued in the past few years and 1 have included discussions of two more in this edition. These are the alexandrite and titanium-sapphire lasers. Both are solid state and, unusually, tunable over quite wide wavelength ranges. The titanium-sapphire laser is probably the most promising for general use because of its wider range of tunability and the fact that it can be operated in a CW or pulsed mode. 

A high temperature optical fiber thermometer has beea developed (32,33). It coasists of a sputtered iridium blackbody tip oa a single crystal sapphire laser. Such a device has beea showa to be accurate to within 0.03° C at 1000°C. 

The layout of the experimental set-up is shown in Figure 8-3. The laser source was a Ti sapphire laser system with chirped pulse amplification, which provided 140 fs pulses at 780 nm and 700 pJ energy at a repetition rate of 1 kHz. The excitation pulses at 390 nm were generated by the second harmonic of the fundamental beam in a 1-nun-thick LiB305 crystal. The pump beam was focused to a spot size of 80 pm and the excitation energy density was between 0.3 and 12 ntJ/crn2 per pulse. Pump-... 

Titanium sapphire lasers typically deliver pulses with durations between 4.5 and 100 fs, and can achieve a peak power of some 0.8watts, but this is not high enough to obtain adequate signal-to-noise ratio in experiments where the number of molecules that absorb light is low. To overcome this limitation, the peak power of a femtosecond laser can be dra-... 

For near-field imaging based on nonlinear or ultrafast spectroscopy, light pulses from a femtosecond Ti sapphire laser (pulse width ca. 100 fs, repetition rate ca. 

Figure 4.6 shows an apparatus for the fluorescence depolarization measurement. The linearly polarized excitation pulse from a mode-locked Ti-Sapphire laser illuminated a polymer brush sample through a microscope objective. The fluorescence from a specimen was collected by the same objective and input to a polarizing beam splitter to detect 7 and I by photomultipliers (PMTs). The photon signal from the PMT was fed to a time-correlated single photon counting electronics to obtain the time profiles of 7 and I simultaneously. The experimental data of the fluorescence anisotropy was fitted to a double exponential function. 

In addition, combining the microscope with the use of a pulsed laser light source provides temporal information on these systems in a small domain. The dispersion of refractive index, however, strongly affects the temporal resolution in the measurements of dynamics under the microscope and typical resolution stays around 100 fs when a Ti Sapphire laser is used as an excitation source. 

Fischer A, Cremer C, StelzerEHK (1995) Fluorescence of coumarins and xanthenes after two-photon absorption with a pulsed titanium-sapphire laser. Appl Opt 34 1989-2003... 

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