There is recently an increasing interest in holographic techniques and holographic optical elements (HOEs) related to virtual reality and augmented reality applications which demand new laser technologies capable of delivering new wavelengths, higher output powers and in some cases improved control of these parameters. The choice of light sources for optical recording of holograms or production of HOEs for image displays is typically made between fixed RGB wavelengths from individual lasers (457 nm, 473 nm, 491 nm, 515 nm, 532 nm, 561 nm, 640 nm, 660 nm) or tunable laser systems covering broad wavelength ranges with a single source (450 nm – 650 nm, 510 nm – 750 nm) or a combination. Lasers for holographic applications need to have long coherence length (>10 m), excellent wavelength stability and accuracy as well as very good power stability. As new applications for holographic techniques and HOEs often require high volume manufacturing in industrial environments there is additionally a growing demand for laser sources with excellent long-term stability, reliability and long operational lifetimes. We discuss what performance specifications should be considered when looking at using high average power, single frequency (SF) or single longitudinal mode (SLM) lasers to produce holograms and HOEs, as well as describe some of the laser technologies that are capable of delivering these performance specifications.
We have studied interband optical transitions, electronic structure and structural quality of p-type (Be) and n-type (Si) &dgr;-
doped GaAs/AlAs MQWs designed for selective THz sensing applying differential surface photovoltage (DSPV)
spectroscopy. Sharp derivative-like features associated with excitonic optical transitions in GaAs/AlAs MQWs have
been observed in the spectra at 300 K and 90 K temperature. The energies and line broadening parameters for a large
number of QW related excitonic transitions were determined from the line-shape analysis of the DSPV spectra. The
spectroscopic data of transition energies were found to be in a good agreement with calculations within the envelope
function approximation which took into account the nonparabolicity of energy bands. Analysis of the dependence of the
exciton linewidth broadening on the quantum subband number allowed evaluate line-broadening mechanisms and
interface roughness in the MQW structures. It was determined that doping with Si broadens more effectively the optical
spectra lines in comparison with the structures of the same design doped with Be.
We present comprehensive experimental study of p-type (Be) and n-type (Si) &dgr;-doped GaAs/AlAs multiple quantum
wells (QWs) intended to be used as selective sensors/emitters in terahertz (THz) range. The structures of various designs
and doping levels were studied via different optical-photoreflectance-, surface photovoltage- and differential surface
photovoltage. spectroscopies and a THz photocurrent technique using as THz emission source either free electron- or
optically-pumped molecular THz laser within 4.300 K range of temperatures. Analysis of Franz-Keldysh oscillations in
photoreflectance spectra and line shapes of the differential surface photovoltage spectra enabled to estimate built-in
electric fields and excitonic parameters for a large number of QW subbands. The experimental interband transition
energies were compared with calculations performed within the envelope function approximation taking into account
non-parabolicity of the energy bands. The dominant exciton line broadening mechanisms were revealed, and the
interface roughness was evaluated from analysis of the dependence of exciton linewidth broadening on the QW width.
Terahertz spectroscopic measurements in p-type structures have indicated strong absorption around 55 &mgr;m wavelength
due to intraband absorption of the bound holes, while increase in photocurrent in the structures below 80 &mgr;m wavelength
is caused by photothermal ionization of Be acceptors.