Diode lasers peak power

The high optical quality of fluoride crystals make them attractive for laser applications. Because of low nonlinear index, they can sustain high peak powers without causing beam distortion. LiYF4 Nd (A = 1.053 /xm) is used as amplifiers in high power lasers. It also has significant advantage over YAG Nd3+ for diode-pumped systems [14]. 

Picosecond diode laser heads offer an interesting alternative to mode-locked lasers. They are much less expensive. They can produce light pulses as short as 50-90 ps with repetition rates from single shot to 40-80 MHz. Peak powers up to 500 mW can be obtained. However, the main disadvantage is the absence of tunability, and the number of wavelengths is limited 375, 400, 440, 635 to 1550 nm. No wavelength below 375 nm is presently available. 

Two-photon laser scanning microscopes and microscopes for two-photon single molecule experiments use femtosecond lasers. Two-photon fluorescence excitation with a picosecond diode laser cannot be expected to work with the same efficiency. The average intensity is only a few mW. Moreover, the pulse duration is of the order of 100 ps, so that the peak power is many orders of magnitude lower than for a fs Ti Sapphire laser. The relative excitation efficiency of different lasers can be estimated as follows ... 

The maximum peak power of the diode laser pulses is of the order of a few 10 mW to about 1 W. Higher peak power results in substantial pulse broadening or reduced diode lifetime. Therefore, the maximum average (CW equivalent) power depends almost linearly on the repetition rate. The average power that can... 

Fig. 9.35 Output performance of the main amplifier with image relay optics at a repetition rate of 10 Hz output energy as a function of the laser diode peak power for different pump duration. Reproduced with permission from [261]. Copyright 2009, Elsevier...

The tunable Ti Sapp and the fixed frequency diode laser outputs are combined, chopped at 400 Hz, and focused by an aspherical lens onto the photomixer in vacuum. A maximum power of 1 pW of THz radiation is obtained from 0.06 THz to 3 THz, with the THz output power decreasing as co " beyond the peak value at 0.6 THz. The focused THz beam passes through the cryogenically cooled sample at 4.2 K and is detected by a liquid-helium-cooled silicon-composite bolometer. Power detection sensitivity of the bolometer is <1 nW up to 3 THz in a 400 Hz bandpass (NEP of the bolometer is 1 pW/Hz ). 

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