Q-switched Nd-doped double-clad fiber laser
J. Swiderski, A. Zajac, M. Skorczakowski and P. Konieczny
A Q-switched operation of a 1064 nm Nd3+-doped cladding-pumped silica fiber laser using an electro-optic modulation has been presented. The laser developed worked at the repetition rate of up to 10 kHz. For a 5 m-long double-clad fiber, pulses with the energy of 0.36 mJ and the pulse duration of 84 ns have been obtained. For the same fiber of 3 m length, pulses of 154 µJ energy and 48 ns duration have been achieved.
Keywords: double-clad fiber laser, Q-switching, electro-optic modulator.
Photoelectron emission and its instrumental effect
on optogalvanic measurements in a hollow cathode discharge
D. Zhechev, N. Bundaleska, J.T. Costello, and D. Todorow
The photoelectron emission (PE) from the cathode surface of a hollow cathode discharge (HCD) with a sub-breakdown bias applied, and hence no discharge present, was measured within the framework of an optogalvanic (OG) experimental arrangement. The work function dependence on the applied sub-breakdown voltage was investigated. The PE component in a real OG measurement was found to manifest itself as an instrumental effect together with nonresonant ionization which we call here space ionization (SP). The convolution of these components was determined experimentally as an instrumental function. A deconvolution procedure to determine the actual OG signal was developed.
Keywords: hollow cathode discharge, photoelectron emission, work function, optogalvanic effect, instrumental function.
Overview of etching technologies used for HgCdTe
V. Srivastav, R. Pal and H.P. Vyas
This review is an attempt to survey all the etching techniques that have been used since the very beginning stages of HgCdTe device fabrication to the most recent ones. Recent state of the art device architectures such as high-density focal plane arrays, avalanche photodiodes, two-colour and multispectral detectors require isolation of high aspect ratio trenches with least etch induced damage at the surface and sidewalls. The most widely used dry etching techniques are electron cyclotron resonance plasma and inductively coupled plasma processing. Almost all the etching technologies have been summarized from chemistry and device perspective.
Keywords: wet and dry etching, mesa etching, ECR plasma system and etch lag.
Investigation of structural, optical and lasing
properties of YAG:Yb single crystals
M. Swirkowicz, M. Skorczakowski, J. Jabczynski, A. Bajor, E. Tymicki, B.
Kaczmarek and T. Lukasiewicz
Single crystals of yttrium aluminium garnet (YAG) doped with ytterbium ions of up to 30 at.% were grown by the Czochralski method. Using the growth rate from 1 to 3 mm/h, and the rotation rate from 15 to 30 rpm, single crystals with diameters of up to 22 mm and lengths up to 85 mm were obtained. Using the inductively coupled plasma n optical emission spectroscopy (ICP-OES) method, Yb distribution coefficient was determined to be equal to 1.10±0.02. The following methods: optical absorption spectroscopy, plane and circular polariscope, electron probe microanalysis (EPMA) to determine the radial distribution of Yb ions, X-ray diffraction methods to determine the lattice constant were used. Etch pit density distribution and lasing properties were also investigated. Samples of YAG:Yb crystals with Yb ions contents of 3, 5, 7, and 10 at.% were pumped by 940 nm laser diode for their lasing properties. The best lasing slope efficiency of 40% with respect to the absorbed pump power was achieved at 5 at.% Yb content. The lowest threshold of 2.5 W of the absorbed pump power was observed, however, for a 7 at.% Yb doped sample in quasi hemispherical resonator configuration. These investigations have been found to be in good agreement with polariscopic observations, showing a certain decrease in optical homogeneity with increase in Yb content.
Keywords: Czochralski method, YAG: Yb, growth from melt, oxides, optical and lasing properties.
Investigations of a laser radiation energy meter
with a photoacoustic converter
Z. Bielecki, K. Jach and M. Nowakowski
The paper presents a measuring method of laser radiation energy using a photoacoustic converter. Mathematical-physical model of the converter and its numerical analysis are described. Influence of the selected design factors and operation conditions on a level of a voltage signal produced at a converter output was analysed. The results of theoretical investigations have been confirmed by the experimental ones. Development of a meter of laser radiation energy with a photoacoustic converter was a final results.
Keywords: photoacoustic converters, meters of laser radiation energy.
Optical waveguides produced in ion exchange process
from the solutions of AgNO3-NaNO3 for planar chemical amplitude sensors
R. Rogozinski and P. Karasinski
The paper presents the results of studies on the production of planar optical waveguides to be applied in amplitude chemical sensors, using ion exchange technique Ag+<=>Na+ from the solutions of AgNO3-NaNO3. Substrates from BK-7 glass and from soda-lime glass were applied. The influence of the parameters of the applied technologies on the shape of refractive index profiles of the produced planar waveguides was presented. For the produced waveguides the dependence was determined between modal attenuation coefficients as the function of mode order as well as the uniformity parameters of modes reaction with absorption sensor layer.
Keywords: optical waveguides, chemical sensors, refractive index.
Growth and properties of MOCVD HgCdTe epilayers on
GaAs substrates
P. Madejczyk, A. Piotrowski, W. Gawron, K. Klos, J. Pawluczyk, J. Rutkowski,
J. Piotrowski and A. Rogalski
Growth of MOCVD Hg1-xCdxTe (HgCdTe) epilayers on GaAs substrates is described. The paper focuses on the interdiffused
multilayer process (IMP). In this process, the CdTe/HgTe growth times are comparable with transition times between the
phases. The non-optimum flow velocities and partial pressures that may induce poor morphology and reduce growth rate
characterize the growth during transition stages. The optimum conditions for the growth of single layers and complex
multilayer heterostructures have been established. One of the crucial stages of HgCdTe epitaxy is CdTe nucleation on GaAs substrate. Successful composite substrates have
been obtained with suitable substrate preparation, liner and susceptor treatment, proper control of background fluxes and appropriate
nucleation conditions. Due to the large mismatch between GaAs and CdTe, both (100) and (111) growth may occur.
It mostly depends on substrate disorientation and preparation, nucleation conditions and growth temperature. Cd or Te substrate
treatment just before growth results in (100) and (111) orientation, respectively. Generally, layers with orientation
(100) show superior morphology compared to (111) but they are also characterized by hillocks.
The benefits of the precursors ethyl iodine (EI) and arsine (AsH3) for controlled iodine donor doping and arsenic acceptor
doping are summarized. Suitable growth conditions and post growth anneal is essential for stable and reproducible doping.
In-situ anneal seems to be sufficient for iodine doping at any required level. In contrast, efficient As doping with near 100%
activation requires ex-situ anneal at near saturated mercury vapours. The transport properties of HgCdTe epilayers indicate on achieving device quality material. Reproducible n- and p-type
doping at the low, intermediate and high level (1015-1018
cm-3) has been achieved with stable iodine and arsenic dopants. The mobilities and carrier lifetimes achieved for extrinsically doped n-type and p-type layers follow essentially the same
trends observed in state-of-the-art liquid phase epitaxy grown HgCdTe.
Keywords: MOCVD growth, HgCdTe ternary alloy, carrier lifetime, transport properties.
Influence of sun radiation on results of non-contact
temperature measurements in far infrared range
H. Madura and M. Kolodziejczyk
Non-contact measurements of an object temperature in IR range carried out in outdoor conditions can suffer from significant errors. An error of temperature measurement can be very high when sun radiation after reflection from an object propagates along optical axis of a measuring device (thermovision camera, pyrometer). Radiation beams reflected from an object and objectís radiation itself are added and a final value of temperature is higher. The paper presents results of theoretical estimations of errors of temperature measurement and their comparison with experimental results. Calculations and measurements were made for objects of various emissivities in a spectral range of 8n9 µm.
Keywords: pyrometry, thermography, sun radiation.