Vescent Photonics D2-110 User manual

Spectroscopy
Module
Vescent Photonics, Inc.
www.vescentphotonics.com
4865 E. 41st Ave
Denver, CO 80216
Phone [phone]
Fax [phone]

General Warnings and Cautions
The following general warnings and cautions are applicable to this instrument.
WARNING
This instrument is intended for use by qualified personnel who
recognize shock hazards or laser hazards and are familiar with
safety precautions required to avoid possible injury. Read the
instruction manual thoroughly before using to become familiar
with the instrument’s operations and capabilities.
CAUTION
There are no serviceable parts inside the instrument. Work
performed by persons not authorized by escent Photonics may
void the warranty.
CAUTION
Although ESD protection is designed into the instrument,
operation in a static-fee work area is recommended.
WARNING
To avoid electrical shock hazard, connect the instrument to
properly earth-grounded, 3-prong receptacles only. Failure to
observe this precaution can result in severe injury or death.
WARNING
Do not clean outside surfaces of any escent Photonics products
with solvents such as acetone. Front panels on electronics
modules may be cleaned with a mild soap and water solution.
Do not clean optics modules.

Limited Warranty
escent Photonics warrants this product to be free from defects in materials and workmanship for a period of one year
from the date of shipment. If this product proves defective during the applicable warranty period, escent Photonics, at
its option, either will repair the defective product without charge or will provide a replacement in exchange for the
defective product. The customer must notify escent of the defective product within the warranty period and prior to
product return. The customer will be responsible for packaging and shipping the defective product back to escent
Photonics, with shipping charges prepaid.
escent Photonics shall not be obligated to furnish service under this warranty from damage caused by service or repair
attempts made without authorization by escent Photonics; from damage caused by operation of equipment outside of
its specified range as stated in either the product specification or operators manual; from damage due to improper
connection to other equipment or power supplies.
This warranty is in lieu of all other warranties including any implied warranty concerning the suitability or fitness of
the product for a particular use. escent Photonics shall only be liable for cost of repairs or replacement of the
defective product within the warranty period. escent Photonics shall not be liable for any damages to persons or
property resulting from the use of the product or caused by the defect or failure of this product. escent Photonics'
liability is expressly limited to the warranty set out above. By accepting delivery of this product, the purchaser
expressly agrees to the terms of this limited warranty.
escent Photonics
Printed Jun 10, 2008

Absolute Maximum Ratings
Note: All modules designed to be operated in laboratory environment
Parameter Rating
Environmental Temperature >15°C and <30°C
Environmental Humidity <60%
Environmental Dew Point <15°C

Vescent Photonics D2 Series Product Manual
1. Spectroscopy Module
Model No. D2-110
1.1. Description
The spectroscopy module provides saturated absorption spectroscopy to atomic rubidium. It contains a
rubidium absorption cell, TEC, balanced photodetector, and associated mirrors and beamsplitting optics.
Nominally, it takes two 1% samples from the input beam. Temperature control stabilizes the number
density of atoms in the cell, and a balanced photodetection circuit compensates for intensity drifts giving
stable control over the lock point for side locking applications. Two beamsteering adjustments are
provided for optimizing overlap of the counter-propagating beams, and positioning on the signal
photodiode. The photodiode output is shot-noise limited out to ~12 MHz for photocurrents of 50 µA and
above. The high bandwidth of the feedback enables tight solid locking that is immune to vibrations and
shock.
Note The spectroscopy module should not be placed closer than 3” from the DBR laser module because
the magnetic fields from the isolator can interfere with the hyperfine transitions causing lock instability
and dc shifts.
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Vescent Photonics D2 Series Product Manual
Figure 1: Spectroscopy Module with cover removed.
1.2. Specifications
Value Units
Photodiode Amplifier
Transimpedance
(signal)
20,000 Ω
Bandwidth (signal) 12 MHz
Noise @ 10 MHz
(shot level)
80 n /√Hz
Set Temperature ~35 °C
Temperature Stability ~0.01 °C
Beam Height 0.95 inches
Total package Size
(L x W x H)
4.25 x 4 x 2 inches
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Output
Input
Ref. PD
Signal
PD
Fine steering adj.
Focusing lens
Rb Cell
Signal SMA
Course adj.
x
y
Cable
connector
Input beamsplitter
Telescope
Output
Input
Ref. PD
Signal
PD
Fine steering adj.
Focusing lens
Rb Cell
Signal SMA
Course adj.
x
y
Cable
connector
Input beamsplitter
Telescope

Vescent Photonics D2 Series Product Manual
1.3. Inputs, Outputs, and Controls
Input Conne tor (8-pin ir ular)
Power and temperature control signals from the Laser Servo are made through an 8-pin circular
connector. The pin definitions (pin numbers are marked on the connectors) are listed below,
where Rth and Rth_Rtn are the two ends of the thermistor.
Pin Signal
1 TEC+
2 TEC-
3 +15
4 Rth_Rtn
5 Rth
6 -15
7 NC
8 GND
Signal Output (SMA)
To minimize electro-magnetic interference, the photodiode signal to the Laser Servo is output
through an SMA connector.
Course verti al and horizontal beam positioning
The spectroscopy module contains a 3x Galilean beam expander. The output lens is mounted on
a spring-loaded mount with 2-56 screws that serve as a course adjustment for the beam
positioning onto the signal photodiode and also to control the retro reflection of the reflecting
mirror (Figure 1, inset).
Fine verti al and horizontal beam positioning
The spectroscopy module contains a focusing lens for the signal photodiode on a spring-loaded
mount with 2-56 screws for fine adjustment of the beam onto the photodiode (Figure 1).
1.4. Aligning the Spectroscopy Module
The spectroscopy module is shipped factory aligned and should need only minor adjustment. However, it
is not uncommon that alignment is required after initial set up. To realign, follow this procedure:
1. Loosen the three locking screws on the back of the DBR module ½ turn past the crack point.
2. Fashion two small 1 cm x 3 cm cards from an index card for use as viewing screens.
3. Remove the cover on the Spectroscopy Module.
4. Use the card and the vertical and horizontal positioning controls on the DBR module to center the
beam onto the 6 mm diverging lens. This is the most critical alignment.
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Vescent Photonics D2 Series Product Manual
5. At this point the beam should be going through the center of the input and output apertures on the
module, the center of the 6 mm lens, and the second pick off should be impinging on the
reference photodiode (see Figure 1). Make adjustments as necessary.
6. Retighten the locking screws on the DBR module.
7. Use the card to ascertain the position of the returned beam on the first corner mirror.
8. Use the course positioning controls to place the retro-reflected beam as close as possible to the
incoming beam.
9. Use the card to probe the opposite corner mirror (along short side) to see if the retro beam is now
passing back through the input beamsplitter.
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Vescent Photonics D2 Series Product Manual
10. If the beam is visible on the card, center it with the course positioning controls. If not, repeat
from Step 8.
11. Check to see that the beam is relatively well centered on the retro reflecting mirror at the end of
the Rb cell. If not, the beam is not centered well enough on the 6 mm divergent lens. Start again
from Step 4.
12. Fold the second card lengthwise (light goes through a single layer) and block the reference
photodiode while monitoring the SMA OUTPUT on an oscilloscope or voltmeter.
13. Use the Course and fine steering controls to maximize the signal (actual signal is negative) on the
voltmeter. Generally, the fine steering controls have little effect. You might find them useful if
you wish to use the course controls to center the beam on the retro mirror and find this moves the
beam off center from the signal diode.
The fine steering controls and signal PD
14. Remove the card from the reference photodiode.
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Vescent Photonics D2 Series Product Manual
15. Adjust the trimpot until a desired lockpoint for sidelocking crosses zero volts (with oscilloscope
connected to the ERROR INPUT monitor, or until an eyeball average of the hyperfine transitions
lies near zero volts. This step determines how well the balancing circuit cancels intensity drifts.
(Note: for peak locking applications this is not important since dc drifts have no affect on the
lockpoint.)
16. The spectroscopy module is now ready for use. Replace the cover.
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