Pulsed diode lasers

In Fig. 3.5A a comparison between time-gated detection and TCSPC is shown. The time-gated detection system was based on four 2 ns wide gates. The first gate opened about 0.5 ns after the peak of the excitation pulse from a pulsed diode laser. The TCSPC trace was recorded using 1024 channels of 34.5 ps width. The specimen consisted of a piece of fluorescent plastic with a lifetime of about 3.8 ns. In order to compare the results, approximately 1700-1800 counts were recorded in both experiments. The lifetimes obtained with TG and TCSPC amounted to 3.85 0.2 ns and 3.80 0.2 ns respectively, see Fig. 3.5B. Both techniques yield comparable lifetime estimations and statistical errors. 

D. L. Farrens and Pill-Soon Song, Subnanosecond single photon timing measurements using a pulsed diode-laser, Photochem. Photobiol. 54, 313-317 (1991). 

Similar up-conversion also takes place for fluoride complexes inserted in zeolites and luminescence from Ndm occurs for [La2NdxGd2-x(AlsSAl4024)(W04)2] or La4 xNdv (A18S AI4O24X W04)21 sodahtes upon pulsed diode laser excitation at 803 nm. The optimum content of neodymium maximizing the 1.06 pm emission in the second material is 0.2 NdnI ion per unit cell (Lezhnina et al., 2006 Lezhnina and Kynast, 2005). 

For EL, the devices were driven under constant forward bias (Ca negative with respect to PEDOT PSS / ITO) and their emission was recorded using an Oriel InstaSpec IV spectrograph. The temperature was varied using a continuous-flow He cryostat (Oxford Instruments OptistatCF). For PL, the devices were optically excited through the ITO anode using a 407-nm pulsed diode laser (Pico-Quant LDH400). 

However, for light sourees of 50 to 100 MHz repetition rate, like titanium-sapphire lasers or pulsed diode lasers, the prineiple deseribed above is not applicable. The TAC must be reset eaeh 10 or 20 ns, while measuring some rare detection events between the reset pulses. Therefore, high-repetition rate systems work in the re-versed start-stop eonfiguration [267, 540]. The prineiple is shown in Fig. 2.14. 

The setup shown in Fig. 2.14 is based on the presumption that the period of the excitation pulses is constant and free of jitter down to the order of 1 ps. This is certainly correct for a titanium-sapphire laser or other mode-loeked laser systems using low-loss cavities. For pulsed diode lasers the pulse period jitter ean be eon-siderably higher. These lasers are eontrolled by quartz oseillators whieh ean have a pulse period jitter of the order of some 10 ps. The reversed start-stop eonfiguration can easily be made insensitive to pulse period jitter by introdueing a passive delay line in the referenee ehannel. The effeet of the delay is shown in Fig. 2.15. 

M. Kress, T. Meier, T.A.A. El-Tayeb, R. Kemkemer, R. Steiner, A. Riick, Short-pulsed diode lasers as an excitation source for time-resolved fluorescence applications and confocal laser scanning microscopy in PDT, Proc. SPIE 4431, 108-113 (2001)... 

A. Riick, F. Dolp, C. Happ, R. Steiner, M. Beil, Fluorescence lifetime imaging (FLIM) using ps-pulsed diode lasers in laser scanning microscopes, Proc. SPIE 4962, 160-167 (2003)... 

R. Berg, S. Andersson-Engels, and K. Rama, Medical Transillumination Imaging Using Short Pulse Diode Lasers, Appl. Opt., 32,574 (1993). 

R. Berg, O. Jarhnan, S. Svanberg Medical transillumination imaging using short pulse diode lasers. Appl. Opt. 32, 574 (1993)... 

Singlet oxygen measurements have not yet been demonstrated in patients, although this is possible in principle, subject to the limitation that the signal is weak so that it will be difficult to detect using fiber optic probes to collect the luminescence. The possibility of using a pulsed diode laser as the source, as recently proposed [25], should also make a clinical system more ergonomic. The most recent advance [26] is to scan the laser... 

Laser illumination of electrodes as a thermoelectrochemical method dates back to 1975 [50], when Barker and Gardner applied pulsed diode laser light to implement thermal modulation as a new method. That time, many authors experimented with different modulation techniques in order to separate useful signal from noise. A scheme of the instrument of Barker and Gardner is given in Fig. 4.7. When periodic heat pulses in the form of a square wave function are imposed at the electrode interface, thermal changes of the electrode processes result in periodic... 

Muller R et al 1996 Time-resolved identification of single molecules in solution with a pulsed semiconductor diode laser Chem. Phys. Lett. 262 716-22... 

Figure C3.3.4 shows a schematic diagram of an apparatus tliat can be used to study collisions of tlie type described above [5, 9,12,16]. Donor molecules in a 3 m long collision cell (a cylindrical tube) are excited along tlie axis of tlie cell by a short-pulse excimer laser (typically 25 ns pulse widtli operating at 248 mil), and batli molecules are probed along tliis same axis by an infrared diode laser (wavelengtli in tlie mid-infrared witli continuous light-output...

The light source for excitation of Nd YAG lasers may be a pulsed flashlamp for pulsed operation, a continuous-arc lamp for continuous operation, or a semiconductor laser diode, for either pulsed or continuous operation. The use of semiconductor laser diodes as the pump source for sohd-state lasers became common in the early 1990s. A variety of commercial diode-pumped lasers are available. One possible configuration is shown in Figure 8. The output of the diode is adjusted by composition and temperature to be near 810 nm, ie, near the peak of the neodymium absorption. The diode lasers are themselves relatively efficient and the output is absorbed better by the Nd YAG than the light from flashlamps or arc lamps. Thus diode-pumped sohd-state lasers have much higher efficiency than conventionally pumped devices. Correspondingly, there is less heat to remove. Thus diode-pumped sohd-state lasers represent a laser class that is much more compact and efficient than eadier devices. 

Sum-frequency mixing of two solid-state YAG lasers in a nonlinear crystal (see Ch. 20) to generate 589 nm in CW, CW mode-locked and macromicro pulse formats. The Nd YAG lasers can be pumped by flashlamps, but higher efficiency is obtained using diode lasers. 

Linearly polarized, near-diffraction-hmited, mode-locked 1319 and 1064 nm pulse trains are generated in separate dual-head, diode-pumped resonators. Each 2-rod resonator incorporates fiber-coupled diode lasers to end-pump the rods, and features intracavity birefringence compensation. The pulses are stabilized to a 1 GHz bandwidth. Timing jitter is actively controlled to < 150 ps. Models indicate that for the mode-locked pulses, relative timing jitter of 200 ps between the lasers causes <5% reduction in SFG conversion efficiency. 

Although nanosecond flashlamps operated in the near-IR possess much less intensity and repetition rate, as well as giving much broader pulses when compared to diode lasers, the recent development of flashlamp operation in the near-IR has... 

Argon ion lasers, mode-locked to produce pulses in the picosecond domain, are in widespread use, producing power levels generally higher than diode lasers up to ca. 

Photodiodes are based on a pn junction operated at a reverse bias voltage (i.e., the opposite bias to the LED and diode laser). The reverse rather than forward bias voltage has the effect of increasing the voltage across the depletion region such that any photoinduced electron-hole pairs are rapidly swept across the junction, generating a current pulse in the external circuitry (Figure 12.24). 

Lasers and LEDs. Dye lasers pumped by Ar ion, Cu ion and frequency doubled Nd YAG solid state lasers. LEDs operating at 635-652, diode lasers at 635 (AlGalnP), 652 (InGaAlP) and 730 mn (AlGaAs). Solid state pulsed lasers, (e.g. Nd YAG, Nd YLF) operating at second, third and fourth harmonic generation. 

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