Blue Diode Lasers: New Opportunities in Chemical Education

Whitten, James E.

doi:10.1021/ed078p1096

Cited by 7 publications

(8 citation statements)

References 6 publications

(11 reference statements)

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“…The results from this demo are consistent with those observed for an actual vacuum phototube in that no current (or voltage) is observed for source wavelengths longer than that corresponding to the response of the detector. 1,6 In the case of the phototube, the incident energy must be greater than the work function of the photocathode to produce current. For the LED detector, no current or voltage is to be expected unless the source radiation can provide sufficient energy to allow electrons to surmount the band gap of the semiconductor material in the LED.…”

Section: ■ Discussionmentioning

confidence: 99%

Demonstrations of Frequency/Energy Relationships Using LEDs

Cheek

2015

J. Chem. Educ.

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The use of LEDs (light-emitting diodes) to demonstrate the relationship between frequency (or wavelength) and semiconductor energy level differences is described. LEDs can function as light detectors, and this ability is exploited to show the minimum light frequency needed to produce a voltage response in the LED. Light having higher energy (lower wavelength) than the detector LED bandgap energy produces a significant voltage response, whereas lower-energy light results in minimal response. The light sources can be other LEDs or a flashlight with colored filters. Alternatively, the voltage measured across an LED as it emits light under power can also be related to the LED bandgap energy, providing a somewhat more accurate estimate of the bandgap energy than that obtained from the LED detector mode. Although these demonstrations using LEDs are not technically the same as the classic photoelectric effect as presented in most freshman chemistry courses, they nevertheless illustrate the same relationships between frequency, wavelength, and energy level differences.

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Section: ■ Discussionmentioning

confidence: 99%

Demonstrations of Frequency/Energy Relationships Using LEDs

Cheek

2015

J. Chem. Educ.

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“…The reference signal must be similar to the source signal to "lock" the signal to the frequency of interest. The LIA has been used in many applications such as measurement of signal to noise ratio of photothermal signals [1], chemistry experiments using diode laser [2], in a ring laser gyroscope [3] and nanoelectromechanical systems [4].…”

Section: Introductionmentioning

confidence: 99%

Lock-in Amplifier as a Sensitive Instrument for Biomedical Measurement : Analysis and Implementation

Djawad¹,

Kiely²,

Wraith³

et al. 2014

TELKOMNIKA

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A measuring instrument plays important role in the biomedical measurement since the biological process in living organism generates very weak signal. Therefore, a reliable and sensitive measuring instrument is needed. In this study, a lock-in amplifier was analysed and tested. This paper presents an experiment to investigate the lock-in amplifier for biomedical measurement. An experiment using RC (resistor capacitor) tissue model to measure the voltage change related to impedance change was performed using a lock-in amplifier to evaluate the accuracy of the lock-in amplifier. Three different values of the capacitor in the RC tissue model were applied regarding to simulate small impedance changes. The measurement results were compared with the theoretical calculation and an impedance measurement system. An error analysis was conducted to investigate the accuracy of the measurement. The comparison result showed that impedance measurement using lock-in amplifier is an effective technique, which could able to measure very small voltage regarding impedance change in the RC tissue model.

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“…They are expected to eventually replace their red counterparts as light sources for the next generation of DVD players. As part of our efforts to modernize physical chemistry teaching laboratories, we recently discussed several experiments using blue diode lasers in this Journal (12). In this article, we demonstrate for the first time the simultaneous use of violet and red diode lasers to study the kinetics of colloidal sulfur particle growth from the decomposition of sodium thiosulfate by hydrochloric acid.…”

mentioning

confidence: 99%

Monitoring Particle Growth: Light Scattering Using Red and Violet Diode Lasers

Ahn

Whitten

2005

J. Chem. Educ.

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A physical chemistry laboratory light scattering experiment using 407-nm violet and 670-nm red diode lasers is described. The use of two wavelengths at the extremes of the visible spectrum to monitor the growth of colloidal sulfur particles provides a dramatic demonstration of the preferential scattering of violet light by small particles and intense scattering of red light as particle size increases. By simultaneously monitoring the intensities of the scattered 407- and 670-nm light with two photodiode detectors, the kinetics of the reaction of sodium thiosulfate with hydrochloric acid to form sulfur particles can be studied. This reaction is found to obey approximately first-order kinetics with respect to sodium thiosulfate when its concentration is varied in the presence of excess acid.

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Blue Diode Lasers: New Opportunities in Chemical Education

Cited by 7 publications

References 6 publications

Demonstrations of Frequency/Energy Relationships Using LEDs

Demonstrations of Frequency/Energy Relationships Using LEDs

Lock-in Amplifier as a Sensitive Instrument for Biomedical Measurement : Analysis and Implementation

Monitoring Particle Growth: Light Scattering Using Red and Violet Diode Lasers

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