Laser peak power

Figure 3.70. Photosensitivity of AZ1450J resist measured at different laser peak powers. Reproduced with permission from reference 222.)...

The brute-force solution of time-domain analog recording is to use a low signal repetition rate and a correspondingly higher laser peak power. The light intensity... 

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. 

The so-called peak power delivered by a pulsed laser is often far greater than that for a continuous one. Whereas many substances absorb radiation in the ultraviolet and infrared regions of the electromagnetic spectrum, relatively few substances are colored. Therefore, a laser that emits only visible light will not be as generally useful as one that emits in the ultraviolet or infrared ends of the spectrum. Further, witli a visible-band laser, colored substances absorb more or less energy depending on the color. Thus two identical polymer samples, one dyed red and one blue, would desorb and ionize with very different efficiencies. 

The excimer laser radiation is pulsed with a typical maximum rate of about 200 FIz. Peak power of up to 5 MW is high compared with that of a nitrogen laser. 

CW dye lasers are usually pumped wifh an argon ion laser, up to abouf f W of continuous dye laser power being produced, compared wifh abouf f MW peak power which may be produced in a pulsed dye laser. 

The extremely high peak power densities available ia particle beams and lasers can heat the small amounts of matter ia the fuel capsules to the temperatures required for fusion. In order to attain such temperatures, however, the mass of the fuel capsules must be kept quite low. As a result, the capsules are quite small. Typical dimensions are less than 1 mm. Fuel capsules ia reactors could be larger (up to 1 cm) because of the iacreased driver energies available. 

The transversely excited atmospheric-pressure (TEA) laser, inherently a pulsed device rather than a continuous laser, is another common variety of carbon dioxide laser (33,34). Carbon dioxide—TEA lasers are an important class of high-power pulsed lasers. Pulse durations are in the submicrosecond regime peak powers exceed 10 MW. 

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-... 

To determine optical damage in bulk benzil crystals a Q-switched Nd YAG laser with 1KW peak power, pulse width of 0.1 ps and pulse repetition rate of 500Hz was used. The laser power was attenuated using a set of neutral density filters and focussed onto a bulk benzil crystal using a x10 microscope objective. No optical damage was observed with optical intensities of upto 100MW/cm - Also, no optical damage was observed in benzil cored fibres with similar optical intensities. 

The probability of two-photon absorption depends on both spatial and temporal overlap of the incident photons (the photons must arrive within 10 18 s). The cross-sections for two-photon absorption are small, typically 10 so cm4 s photon-1 molecule 1 for rhodamine B. Consequently, only fluorophores located in a region of very large photon flux can be excited. Mode-locked, high-peak power lasers like titanium-sapphire lasers can provide enough intensity for two-photon excitation in microscopy. 

Dye lasers have been one of the most widely used types of tunable laser. In pulsed conditions, typical peak powers are in the range of 10 -10 W. In the cw regime, reported powers are in the order of watts, with linewidths of around 1 MHz. Due to their flexibility in design and performance, dye lasers have been commonly used in a great variety of spectroscopic techniques, including high-resolution spectroscopy. 

Semiconductor lasers can operate in the cw regime (with output powers ranging from /xwatts to tens of watts) or in the pulsed regime, with typical peak powers of tens of watts. 

Figure 13. (a) Relative blue pulse peak powers from bulk appKTP and bulk KNb03 crystals, (b) Dependence of SHG efficiency on fundamental spectral bandwidth of femtosecond Cr LiSAF laser. 

The fact that several lasers can generate very short light pulses (down to 10 sec duration) with high peak powers (up to 10 watts) which can be used to investigate short term transitions (e. g. lifetime measurements, flash photolysis, etc.). 

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