If the blue head to head cable (or either one of the black triax cables for systems that do not have a blue triax cable) was removed during operation of the PEM, there is a good chance that your PEM will need to be returned for repair. Follow the test procedure that is on page…
faqs
My PEM is not providing stable retardation and/or there is noise if I look at my signal on an oscilloscope. What could be wrong?
There are several possibilities. A list of questions to begin troubleshooting is: What is your optical and electronic setup? What is the light source you are using and the wavelength or wavelengths (in particular, are you using a laser)? What detector are you using? When the PEM is operating, is the limit light off, on…
What is the difference between photoconductive and photovoltaic detectors?
The difference between these two classifications is that photoconductive detectors use the increase in electrical conductivity resulting from increases in the number of free carriers generated when photons are absorbed (generation of current), whereas photovoltaic current is generated as a result of the absorption of photons of a voltage difference across a p-n junction (generation…
Can my optical head be close to an electric field?
Yes. The optical head itself contains no electronic components and is safe to use in an electronic field. However, depending on the strength of the field, it may be advisable for you to have longer head to head cables so that the electronic head can be sufficiently removed from the electrical field so that performance…
Can I use standard cables in place of the cables that you provide?
The cables that we provide are standard cables. However, the cables are part of the entire PEM resonant circuit. The length of any replacement cables must be precisely matched to the length of Hinds cables in order for the resonant circuit to be maintained. Hinds can provide you with replacement cables that have been designed…
Are my dual coax cables interchangeable?
Yes. If your PEM has 2 dual coax cables instead of one blue triax head to head cable, the 2 cables are interchangeable….
Can I use my electronic head in a vacuum?
The electronics are not meant to be operated in a vacuum. The optical head itself contains no electronics and is safe to use in a vacuum. We can provide you with longer head to head cables so that the electronic head is not in the vacuum. Please click here to look at Hinds PEM vacuum…
Can I use my electronic head with a different optical head?
No. The PEM is a resonant device, with the resonant frequency being determined by the size of the optical assembly. In spite of very tight manufacturing tolerances, each optical head is slightly different in size and this results in a slightly different frequency. The controller, electronic head, and optical head are all calibrated to work…
How close can my electronic head be to a magnetic field?
Based on our testing, we recommend that the magnetic field strength at the electronic head and controller be no more than 100 gauss field. We provide an MFC option for PEMs that includes an 8 ft (244 cm) head to head cable which allows removing the electronic head and controller from a magnetic field….
Can a PEM be used to provide a steady retardation level (can they be used as static waveplates)?
As the name would suggest, a PEM provides polarization modulation, that is, a changing retardation that follows a sinusoidal pattern. As such, applications that need a steady retardation level are not well suited for PEMs….
Can I use my optical head with a different controller than it came with?
Yes, but it will require recalibration. The PEM is a resonant device, with the resonant frequency being determined by the size of the optical assembly. In spite of very tight manufacturing tolerances, each optical assembly is slightly different in size and this results in a slightly different frequency. The controller, electronic head, and optical head…
What is the maximum laser power I can use with my PEM?
The maximum laser power is determined by the PEM optical material required for your application. If the laser is powerful enough to damage the material from which the optical assembly is made, then it cannot be used with a PEM. This is seldom a problem, however if you have a question about your particular laser,…
What are my options for minimizing modulated interference effects (using my PEM with a laser)?
When PEMs are used with lasers as light sources, modulated interference effects may occur. These manifest themselves in the form of spurious signals at the fundamental and harmonic frequencies of the PEM. Modulated interference is not a problem with any light source other than lasers. This effect is caused by multiple reflections of the light…
I ONLY want right and left circular light. Can you help me?
All PEMs are capable of generating left and right circularly polarized light. In the case of the Hinds I/FS50 PEM, you would be able modulate light in a continuously varying fashion between left-circular and right-circular at a frequency of 50 kHz. The PEM modulates polarization as the function: f(t) = A*cos(wt), where w = 2π *50kHz….
What spectral range do Hinds’ PEMs cover?
Hinds manufactures over a dozen standard PEM models. Collectively, they cover the range from 130 nm – 57µm….
How long is the stationary acoustic wave in the optical element?
Photoelastic modulators are resonant devices which produce oscillating birefringence. The optical bar shaped element vibrates along its long dimension at a frequency determined by the length of the bar and the speed of a longitudinal sound wave in the optical element material. In other words, a free standing acoustic vibration mode is used, of acoustic…
Are PEMs thermally stable?
PEMs have a feedback circuit to help control thermal stability. In addition, we recommend a 15 minute warm up time for the PEM to reach resonance equilibrium and stabilize before measurements are taken. However, if there is a rapid or large change in ambient temperature, it is possible there will be a slight drift associated…
What are the advantages of PEMs over other forms of polarization modulation?
PEMs have several unique features such as wide spectral range, large aperture, wide acceptance angle, and high precision of phase modulation. The PEM is typically used for fast, high sensitivity measurements. Fused silica PEM optical elements are isotropic when no stress is applied (as contrasted with Pockels cells and electro-optic modulators). This gives the PEM a…
How Does My Optical Head Work?
The basic principle of operation of the PEM is the photoelastic effect. A mechanically stressed sample exhibits birefringence proportional to the strain caused by the induced stress. As such, the PEM can be described as a birefringence modulator. Light moves along one axis faster than another because, as a result of resonating the optic, birefringence…
How does the PEM work?
The PEM is a resonant device whose precise oscillating frequency is determined by the physical properties of the optical element/transducer assembly. The electronic head, optical head and the cables that connect them make up a circuit that operates like a crystal-controlled oscillator circuit. The PEM controller controls the amplitude of the PEM oscillations and generates…