Acoustic phonon generation and detection inGaAs∕Al0.3Ga0.7Asquantum wells with picosecond laser pulses

Abstract

Picosecond acoustic-phonon pulse generation and detection is investigated in a sample containing three GaAs/ Al 0.3 Ga 0.7 As quantum wells of different thickness with an interferometric optical pump and probe technique. The pump photon energy is tuned through the hh1-e1 transitions of each well and the probe photon energy is chosen to allow the detection of the phonon pulses at the sample surface. The phonon pulse shapes are explained with a model that relates the carrier wave functions to the acoustic strain, and the acoustic strain to the detected optical reflectance and phase changes.

Investigation of coherent acoustic phonons in terahertz quantum cascade laser structures using femtosecond pump-probe spectroscopy

“…This gradual transition from real to virtual excitation has strong consequences regarding the selectivity of the optically generated coherent phonons. 13,[23][24][25] This conceptually explains the abrupt sign change of the electronic contribution to DR=R observed between 150 K and 100 K [see Fig. 3(a)], and the change in the acoustic components in Fig.…”

Picosecond Acoustics in Single Quantum Wells of Cubic GaN/(Al,Ga)N

“…For the shortest probe wavelength of λ ¼ 370 nm [see the lowest curves in Figs. 3(a) and 3(b)], SðtÞ has a simple shape, which is typical for a picosecond strain pulse detected in a thin layer near the surface [3,4]. We attribute this signal to the response of the c-GaN QW to the picosecond strain pulse.…”

“…They can be observed at the surface of bulk materials by optical transitions covering a broad spectral range from the ultraviolet (UV) to the near infrared [2]. If also in-depth information is required, an established technique is based on exploiting buried semiconductor quantum wells (QWs) [3][4][5]. Nitride semiconductor QWs [e.g., GaN=ðInGaÞN] are highly efficient nanostructures for the generation and detection of coherent phonons with frequencies of up to 2 THz [6].…”

Coherent acoustic phonons in nanostructures investigated by asynchronous optical sampling

“…Inherent difficulties of mostly technical nature have often limited the performance of femtosecond pump-probe techniques for practical applications such as electro-optic sampling of high speed circuits [13,14], laser based ultrasonics [10,[15][16][17][18], for spintronics [19][20][21] or time-domain THz spectroscopy [22][23][24]. In addition, imaging applications in biology or materials research call for a minimization of the time required for the acquisition of a pump-probe trace in order to reduce the pixel dwell time.…”