Experimental Equipment

This page provides details focused on the pieces of equipment: how they're assembled, efficiencies, general purposes.

Contents

Visible-Light Filter Assembly

Pump Laser Steering

This sub-section of the experimental setup pertains to the spontaneous parametric down conversion of the 85mW blue (405nm) diode laser.

• the pump laser

• two mirrors

• beam block

• irises

Blue Diode Laser

Power Technology, Inc. (PTI) IQ1C50(405-60B)G26

This is commonly referred to as the pump laser. Serves as the source of the down-converted light.

• • Power Output: 85.4mW

• Wavelength: 403nm (Approx.)

• Collimation: focal length of 175ft

Mirrors

ThorLabs BB1-E02

Reflects strongly in the visible region. See picture.

Beam Block

ThorLabs LB1

Essentially a brick-walled Russian with single scar over his right eye.

Irises

ThorLabs ID12 / ID15

There are two types of irises: 1.2" diameter (4x) and 1.5" diameter (2x). The smaller irises are easier to place in the A/B detector arms. Use the larger ones for the more optically-open areas.

When used correctly, irises will be your best friend for aligning. A small, well collimated beam makes aligning components much easier than a wide full strength beam.

Down-Conversion

• 405nm half-wave plate

• BBO crystal

• 810nm narrowband filters

• colliamted detectors

• Continuous ND Filter

405nm Half-Wave Plate

CVI Melles-Griot QWPO-400-05-2-R10

The 405nm half-wave plate allows for control over the blue pump laser's plane of polarization. This is necessary as after reflecting off the two walking mirrors prior to its contact with the BBO down-converting crystal, the polarization is unpredictable, and needs to be altered in order to down-convert as maximum intensity. The half-wave plate is contained within a continuous rotational mount.

Beta-Barium Borate (BBO) Crystal

Newlight Photonics

This is the down-converting crystal. It is specifically designed to cut a single photon exactly in half when supplied with a 405nm pump laser. The crystal has an arrow on its edge. When mounting, always have this arrow pointing in the direction of down conversion, ie towards the detectors. Note that this process isn't perfect, and not only 810nm photon beams will emit from the BBO crystal. Therefore, narrowband filters are required.

810nm Filters (Narrowband)

ThorLabs FB810-10

These allow 810nm light, with some inefficiency (see chart). Maximum of ~35% light transmitted at 810nm. The one seen in the picture is on a flip-mount. This is required in the B-detector arm, as a 810nm bandpass filter will entirely block the red (635nm) polarized HeNe laser. This is sometimes referred to as 10nm bandpass filter. 810nm is the center, and 10nm is the width.

Collimators

ThorLabs FC220FC-B

Each detector serves as a housing for a fibre-coupling lens. These lenses have a fibre-channel and a collimated input/output (depending on use).* Just for clarification, these are not the actual detectors which count photons. These are collimators that collect the light and focus it into a fibre optic channel. The real detectors are the Single Photon Counting Modules.

Continuous Neutral Density (ND) Filter

ThorLabs NDL-10C-4

Continuous neutral density (ND) filters are convenient when a dynamic range of attenuation is required. In this experiment, it can be used, if needed, to attenuate the blue beam in order to reduce overall counts.

Visible Light Filtering Unit / SPCMs

• Cage assembly

• Longpass filters

• Optical Fibers

• SPCMs

Cage assembly

Link to Cage assembly

Optical Fibers

ThorLabs M31L01

PerkinElmer SPCM-QC9

There are two type of optical fibers. The orange ThorLabs fibers (8x) are for general use on the optical table; connecting detectors and whatnot. The black-jacketed

Single Photon Counting Modules

We were able to do a calibration each of the Single Photon Counting Modules (SPCM's) to determine the dark counts. This was done by disconnecting the fiber-optic cable from the input and putting the rubber cover over the input that was originally shipped with the SPCM's. Then, all lights in the room were put out, the computer monitor was turned off and the door to the room was made to be mostly light tight. Then we used the computer to run 19 cycles for 30 seconds each which averaged the photon counts in Hz. This data for the four SPCM's is shown in the table to the right.

Polarized Statistics

• Polarized HeNe

• Pickoff Mirror

• Polarized Beamsplitting Cube

• 810nm HWP

Polarized HeNe Laser

CVI Melles-Griot circa 1989

This laser serves as both an alignment and experimental tool. After the irises are inserted into the B-detector arm, the top of the pickoff mirror is placed in front of the BBO crystal, and adjusted such that this laser is directed into the B-detector. Then the polarizing beam splitter is inserted. For more information, see

Alignment of Polarized HeNe

Pickoff Turning Mirror

ThorLabs NX1F with mounted ThorLabs BB1-E02

These mirrors are used whenever an optical beam has to cross paths with another device. In this case, the device in the way can simply be removed, but the pickoff base remains, keeping the place of the device. This experiment should always use the 'A' position for simplicity. When removing the pickoff mirror, always grip where there's no chance of a bumped knob. Note the picture on the right.

Neutral Density Filter

Thorlabs NE50B, NE40B, NE30B)

These filters have Optical Densities of 5, 4, and 3 (respectively). Using these is filters is a must if measurements with HeNe laser are ever made.

Polarized Beamsplitting Cube

CVI Melles-Griot PBSH-670-980-050

The polarizing beamsplitter is composed of two prisms cut at 45 degrees. In between the prisms is a dielectric coating which reflects vertically polarized light and transmits horizontally polarized light. This allows us to "select" which path a photon will follow based on its polarization. The prisms are arranged in a cube configuration such that horizontally polarized light will pass through and the vertically polarized light will be reflected at a 90 degree angle.

810nm HWP

CVI Melles-Griot QWPO-810-05-2-R10

There are two of these HWPs. In the Hardy's Test experiment, it is these two HWPs that create the 4 combinations of Alice and Bob angles that are used.

Quarter Wave Plate

ThorLabs Zero-Order Mounted Quarter Wave Plate WPQ10M-405

The Quarter Wave Plate is used to convert linearly polarized light into circularly/elliptically polarized light and vice versa. This is accomplished by delaying one axis of polarization by 90 degrees, relative to the other axis of polarization.

Quartz Plate

The quartz plate is essentially a wave plate. While the QWP and HWP are specifically cut for certain wavelengths, the quartz plate can be used for a much broader range of wavelengths. For the Hardy's Test experiment, the quartz plate is used as a more cost effective replacement for the QWP. Data for the Hardy's Test experiment using the QWP and the quartz plate are given here.

Rotational Stage

This stage allows the optical component( in this case the QWP or quartz plate) to be tilted in the direction which the laser propagates. For course adjustment, loosen the center screw and use your hand to turn the stage. For fine adjustment, tighten the center screw and then loosen the big screw to finely adjust the stage. The big screw can cover a range of about 10 degrees before it needs to be reset. To reset the big screw, loosen the center screw and then tighten the big screw.

The Black Box

Beware this behemoth of single photon counting. Some say that contained within its horrible walls lies four cables, each of which having 100% internal reflection. No light (or kindness) escapes those cables, so ye better think twice about opening it. I heard that Kurt Wick once opened it only so find his own personal worst nightmare, and it didn't even move him.

• NEXUS 3

NEXUS 3

See details on this in the Computer Interface page

Interferometer

Coming Soon