Pulse stretcher

Pulse stretcher Fast linear pulse Conventional shaped linear pulse of amplitude equal to input pulse... 

Figure 6 Block diagram of the two-color optical parametric amplifier (OPA) and IR-Raman apparatus. CPA = Chirped pulse amplification system Fs OSC = femtosecond Ti sapphire oscillator Stretch = pulse stretcher Regen = regenerative pulse amplifier SHGYAG = intracavity frequency-doubled Q-switched Nd YAG laser YAG = diode-pumped, single longitudinal mode, Q-switched Nd YAG laser KTA = potassium titanyl arsenate crystals BBO = /J-barium borate crystal PMT = photomultiplier tube HNF = holographic notch filter IF = narrow-band interference filter CCD = charge-coupled device optical array detector. (From Ref. 96.)...

Fig. 20 Schematic of the electronics module controlling the CWBP. DA -darlington amplifiers, DAC -digital to analog converter, ADC - analog to digital converter, Amp-disc -amplifier discriminator for the photomultiplier (PMT), PS -pulse stretcher, OSC -oscillator, Zero pos - zero position sensor, Top pos -dip probe position sensor, RM - carousel rotary stepper motor, UPM - linear actuator for the dip probe of the carousel, RT - resistance thermistor, TEC -thermoelectric heat exchanger, Tset - set temperature. (Reprinted from Dhadwal et al. [2], with permission of Elsevier)...

Figure 2 Schematic representation of a grating based pulse stretcher. The incident pulse enters at the top left, is dispersed by the left grating, collimated by the left lens, focused by the right lens, subtractively dispersed by the right grating (gratings are anti-parallel), and reflected back through the system by the mirror. In our application, a portion of the red end of the spectrum is sharply cut off in the spectrally-collimated region between the second grating and the mirror.

Fig. 6.56 Experimental setup for parametric amplification of ultrashoit pulses, including a pulse stretcher before and a pulse compressor after amphfication [739]...

Fig. 11.36. (a) Schematic diagram of chirped pulse amplification (CPA) (b) P sign of pulse stretcher with a grating pair [11.95]... 

We will now discuss the different components of this process in more detail. The oscillator consists of one of the femtosecond devices discussed previously. The pulse stretcher uses a grating pair, where the two gratings, however, are not parallel as for pulse compression, but are tilted against each other (Fig. 11.36b). This increases the path difference between the blue and the red components in the pulse and stretches the pulse length. An aberration-free pulse stretcher with two curved mirrors and a grating is described in [11.96] and is depicted in Fig. 11.37. 

Fig. 11.37. Aberration-free pulse stretcher. C is the center of curvature of both mirrors, ROC is the radius of curvature [ 11.96]...

Pulse stretcher Pulse shaper that produces an output pulse whose duration is greater than that of the input pulse and whose amplitude is proportional to that of the peak ampKtude of the input pulse. Pulse repetition frequency (PRF) The frequency at which a pulsing signal recurs equal to the fundamental frequency of the pulse train. 

The amplifier system is composed of three logic subunits, a femtosecond pulse stretcher (Fig. 2.27), the titanium sapphire regenerative amplifier (Fig. 2.28) and a femtosecond pulse compressor (Fig. 2.29). To exploit the storage capability of titanium sapphire the system uses chirped-pulse amplification [264-266]. For this a seed pulse (80 fs, 5nJ) of the titanium sapphire oscillator is stretched to about 500 ps and then amplified. The stretched pulse can be safely amplified because the peak power has been significantly lowered, thereby avoiding any nonlinear effects that could result in damage to the... 

Fig. 2.27. Top view of the femtosecond pulse stretcher (Quantronix model 4822) and laser beam tracing. The pulse from the seed laser is stretched about 5000 times with the use of a diffractive grating mounted at Littrow incidence to reduce aberrations. To prevent optical feedback to the seed laser a Faraday rotator (FR) is used for optical isolation. A aperture TFP thin-film polarizer (by courtesy of Quantronix)...

Fig. 8.54. Operational principle of a pulse stretcher (a) and a pulse compressor (b) [8.161]...

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... 

Figure 6.12 Experimental two-color setup featuring an IR beamline, to generate intense shaped IR pump pulses, and a VIS probe beamline, to provide time-delayed probe pulses of a different color. Both beams are focused collinearly into a supersonic beam to interact with isolated K atoms and molecules. Photoelectrons released during the interaction are measured by an energy-calibrated TOE spectrometer. The following abbreviations are used SLM, spatial light modulator DL, delay line ND, continuous neutral density filter L, lens S, stretcher T, telescope DM, dichroic mirror MCP, multichannel plate detector.

In a CPA, because a large secondary dispersion is added to the stretcher, the spectrum is mapped to the temporal waveform in the amplifier. For that reason, the phase change added to the pulse shaper cannot cause a large change in the pulse shape in the CPA. Self-phase modulation depends on the temporal amplitude transition. Therefore, the phase perturbation can be regarded as almost linear in the amplifier. Thus, the inverse of the spectrum phase difference between the acquired and the target phase is added to the pulse shaper. 

Personnel in the appropriate protective clothing (usually Level A or B) should find those persons who are alive but not ambulatory. The rescuers should remove them from the scene using a long backboard or other improvised stretcher. Only lifesaving medical treatment (airway management, bleeding control, and use of NAAK) is performed at this time. Victims who are unresponsive with no pulse should be left on-scene at this time. 

Coherent Chemistry. Short-pulse laser radiation normally leads to broad and rather unspecific excitation of vibrational modes (See also Sect. 10.4). By tailoring the pulses, which typically would have a pulse length of 100 fe, by sending them into a pulse shaper, certain modes can be enhanced and others be suppressed. In particular, discrimination between chiral molecules (right- or left-handed) otherwise performing in an identical way could be considered, A pulse shaper is a stretcher-like arrangement (Sect. 8.7.2) with... 

Figure 1. Schematic of coincidence/noncoincidence y-ray pulse height analyzer. Key to symbols Dl, D2, Harsnaw 16MB16/5A detector FA, Ortec 113 preamplifier LA, Ortec 485 linear amplifier TSCA, Ortec 551 timing single channel analyzer FC, Ortec 414A fast coincidence DA, Ortec 489 delay amplifier LGS, Ortec 442 linear gate and stretcher PHA/RTC, nuclear data pulse hei t analyzer with segmented memory and real time clock.

Gaussian pulses (Fig. 9.9) from amplifiers keep their maximum value only for a short moment. Therefore, for any precise determination, which is time consuming, their amplitude should be stored. This is done by using the special unit STRETCHER. The form of the obtained pulse is given in Fig. 9.9. Such operation can be realized by using the circuit given in Fig. 9.10. However, its properties are not adequate. The real stretcher has incorporated more than 20 20 transistors and a few Integrated circuits. 

To check the STRETCHER operation, for example, the STRET OFF signal must be low when the input pulse appears. If it is not low, we can simply push it down by grounding the STRET OFF line for a short moment. However, such an approach is not possible in many cases. The output of a TTL circuit cannot be connected to the +5 V without causing permanent damage. 

---