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Laser sources have been well adopted in spectrophotometry and optical materials measurements with excellent advantage of high spectral output power and hence large signal-to-noise ratio compared with traditional lamp sources. However, continuous wave lasers normally have very small tuning spectral range, due to either the limited bandwidth of the gain profile or low conversion efficiency due to the limited amount of pump power. Pulsed laser sources can be generated via nonlinear processes such as optical parametric oscillation or amplification and so on to cover a wide spectral range. For instance, supercontinuum laser sources have been developed with above 1 W/nm collimated spectral power over the visible to mid-infrared range. The output of the supercontinuum laser sources can be extended to cover UV range via second harmonic generation. Normally the spectral bandwidth of the output can be from tens to thousands nm and a monochromator or its equivalents can be used to select or tune the desired working wavelengths. The repetition rate of the laser sources can be from a few Hz to more than 1 GHz, with reduced pulse interval and efficiency due to more distributed pulse energy and hence peak power. A pulsed laser source with an original pulse width of ~ 130 fs, a repetition rate of ~ 80 MHz, and the spectral range from 280 to 2000 nm is applied for spectrophotometry calibration and research works have been devoted to converting the pulsed laser into continuous wave in order to improve the measurement linearity. Optical fiber bundles were used to divide each laser pulse into hundreds of small pulses via different optical path length and then recombine them for a temporally further distributed pattern. Two different types of optical fibers were adopted for the bundle, one for 280 nm ~ 700 nm wavelength range, and the other for 700 nm ~ 2000 nm. The numerical aperture of the optical fiber is 0.22 and the core diameter is ~ 200 μm. Each bundle has 100 pairs of optical fibers with different lengths. The refractive indices were extrapolated over the wide spectral range and used to calculate the optical fiber lengths for uniform time interval after recombination. The optical losses of the optical fibers over the wide spectral range were evaluated. After taking the spectral optical losses, fiber lengths, and input beam spatial power distribution into account, the arrangement of the optical fibers with different lengths at the input terminal was optimized for overall high performance over the two desired working spectral range. The time interval, relative power, spatial distribution of the distributed pulses throughout the designed optical fiber bundles were validated using a highspeed photodetector and oscilloscope. The optical fiber bundles can be useful for a variety of spectrophotometry calibration and optical materials measurement works using pulsed laser sources.

In this work, the degradation of GaN-based packaged white light-emitting diodes (LEDs) caused by accelerated humidity testing will be investigated using non-destructive failure analysis tools, namely the mixed statistical distribution, spectrum analysis and parameters extraction. Physical failure analysis techniques are then used to verify and conclude the deduced failure mechanisms obtained by the non-destructive failure analysis tools.

An automatic multi-wavelength filter radiometer (MWFR) was developed at the National Metrology Centre (NMC) of Singapore to realize the spectral irradiance scale in the wavelength range from 250 nm to 1600 nm. The UV–VIS range (250 nm to 900 nm) is covered by a silicon trap detector with 17 filters, while the near IR range (900 nm to 1600 nm) is covered by an InGaAs photodiode with 7 filters. A complete run of measurements at all 24 wavelength points takes only 12 min. The spectral irradiance scales of NMC and MIKES/TKK (Finland) in the spectral range from 280 nm to 900 nm were compared successfully using this instrument. Measurement results of three standard lamps calculated using MIKES/TKK's algorithm showed excellent repeatability and very good agreement with their assigned values. It is concluded that, compared with the conventional monochromator based spectroradiometers, a properly designed MWFR with sufficient spectral coverage is a good alternative instrument for spectral irradiance comparison owing to its faster speed and better short-term reproducibility.

The time-of-flight method was used to calibrate an optical fiber length standard and its uncertainty of measurement was evaluated theoretically and experimentally according to the Evaluation of measurement data - Guide to the expression of uncertainty in measurement (GUM), JCGM 100:2008. The major uncertainty components in the measurement of transit time difference were identified and analyzed. The uncertainty due to temperature instability was investigated experimentally in the temperature range from 20 °C to 25 °C using a temperature chamber with precise temperature control. The temperature coefficient of the fiber length standard was derived by linear regression of the measurement data. The experimental results showed that the temperature control is critical for the calibration of optical fiber length standard. When the temperature instability was improved from ± 2 °C to ± 0.1 °C, the expanded measurement uncertainties for the optical fiber length standard (optical length : ~11780 m) were significantly reduced from 0.16 m to 0.014 m at wavelength of 1310 nm and from 0.19 m to 0.015 m at wavelength of 1550 nm.

We have constructed a laser measurement system for automatic calibration of height setting micrometer. This automation is accomplished by an interactive software tool which performs essential calibration functions. The instrument incorporates a double frequency stabilized laser based on the heterodyne measurement technique. Positioning of height setting micrometer is undertaken by a X-Y stage driven by the servo motors and calibration is performed by combining laser and electronic probe readings. Abbe offset tilting error is eliminated by using the double-path interferometer scheme. The instrument has a capability of measurement range 0 - 350 mm, resolution 40 nm, expanded uncertainty of height measurement better than 0.5 micrometer at the 95% confidence level over the full range. The whole calibration procedure can be completed in two hours making it much more efficient than the conventional method of gauge block comparison. The instrument can also be applied to various linear measurements with high accuracy to reduce the measuring time and to simplify the measurement setup.

A method is described for the calibration of vertical piezoelectric transducer (PZT) stages using a large range metrological atomic force microscope (LRM-AFM). A vertical PZT stage is mounted onto the system andanoptical-flat sampleisattachedonthetopofthePZTstage.TheAFM probe is operated in contact mode and used as a null indicator to measure the movement of the optical-flat as it is driven by the PZT stage. As the PZT stageisscannedvertically,theAFMprobeisincontactwiththetestsurface without lateral scanning. The displacement of the vertical stage of the LRM-AFM is measured by the integrated laser interferometer, and the corresponding laser interferometer readings and the nominal position of the PZT stage are recorded. This body of data is then used to establish the relationship between the laser interferometer reading and the nominal displacement of the PZT stage. Our results show that this method can be used to calibrate PZT stages up to a range of 250 μm with an expanded uncertainty of less than 5 nm. © 2012 Society of Photo-Optical Instrumentation Engi

APMP.PR-S1, a supplementary comparison of irradiance responsivity of UVA detectors, was carried out among seven national metrology institutes piloted by SPRING Singapore from 2003 to 2005. Two quantities, the narrow band UV (365 nm ± 5 nm) irradiance responsivity and the broad band UVA (315 nm–400 nm) irradiance responsivity of the transfer detectors, have been compared. Commercial UV source (medium pressure mercury short arc lamp) and UVA detectors were used as transfer standards in the comparison. Measurement results from participants were reported and their uncertainties associated with the comparison were analysed in this report. The method of weighted mean with cut-off was used to calculate the comparison reference values. The results from most participating labs lie within ±5% against the comparison reference values with a few exceptions. The degree of agreement of the comparison depends not only on the base scales of spectral responsivity and spectral irradiance of a laboratory, but also equally importantly on the method used for the measurement. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

The observation of self-induced transparency on the magnetic dipole 2P1/2 F = 3 5 2P3/2 F′ = 4, j MF = 0 transition of atomic iodine has been extended to cover pulse areas up to 4 ~. Laser pulses of various areas have been shown to be reshaped considerably by the coherent field-matter interaction. Pulses have been found to narrow by two-thirds for a 3 ~ -pulse. The lower limit of the homogeneous relaxation time T′2 of atomic iodine vapour is determined from pulse broadening and transmission measurements.

Self-induced transparency (SIT) has been observed on a Q(J)-branch transition (J=2) for the first time. Coherent field-matter interaction was studied using a photodissociation atomic iodine laser system operating on the 2P1/2 F=2 →2P3/2 F′=2 magnetic dipole hyperfine transition and a self-resonant iodine vapour. With linearly polarized radiation the propagation phenomena are characterized by high transparency and large time delay at pulse areas θ > π and small-pulse splitting at θ ≃ π. With circularly polarized radiation, non-degenerate SIT is observed. The results can be explained by the dynamic effects of the different dipole moments involved in the process.

A multi-functional differential spectral responsivity (DSR) measurement system for primary calibration of the shortcircuit current (SCC) of reference solar cells with WPVS (World Photovoltaic Scale) design [1] is reported in this paper. Based on the dual beam principle, the system is able to measure DSR at different bias levels, spatial uniformity, linearity, temperature coefficient of the spectral responsivity of reference cells in the spectral range from 280 nm to 1200 nm. The measurement principle, system design and construction as well as the performance of the system are described in this work. An uncertainty ≤ 1% for SCC measurement is confirmed by experimental results.