Lambda SRS SR475 User manual

Operation Manual
Laser Shutters
SR475 and SR476
Stanford Research Systems
Revision 1.2 •September 1, 2011
Distribution in the UK & Ireland
Lambda Photometrics Limited
Lambda House Batford Mill
Harpenden Herts AL5 5BZ
United Kingdom
E: [email protected]
W: www.lambdaphoto.co.uk
T: [phone]
F: [phone]

Certification
Stanford Research Systems certifies that this product met its published specifications at the time
of shipment.
Warranty
This Stanford Research Systems product is warranted against defects in materials and workman-
ship for a period of one (1) year from the date of shipment.
Service
For warranty service or repair, this product must be returned to a Stanford Research Systems
authorized service facility. Contact Stanford Research Systems or an authorized representative
before returning this product for repair.
Information in this document is subject to change without notice.
Copyright c Stanford Research Systems, Inc., 2011. All rights reserved.
Stanford Research Systems, Inc.
1290–D Reamwood Avenue
Sunnyvale, CA 94089 USA
Phone: [phone] •Fax: [phone]
www.thinkSRS.com •e-mail: [email protected]
Printed in U.S.A. Document number 9-01636-903
SR475 and SR476 Laser Shutters

Contents
General Information iii
Service .............................. iii
Environment ........................... iii
Laser Safety ........................... iii
Symbols ............................. iii
Notation ............................. iv
Specifications .......................... v
1 Operation 1 – 1
1.1 Introduction to the Instrument ............. 1–2
1.2 Mounting .......................... 1–6
1.3 Optical alignment ..................... 1–8
1.4 Optical power capacity .................. 1–9
1.5 Operating environment ................. 1–9
1.6 Alternate speed modes .................. 1–10
1.7 Shutter interface connector ................ 1–12
2 Remote Operation 2 – 1
2.1 Index of Commands ................... 2–2
2.2 Introduction ........................ 2–3
2.3 Commands ......................... 2–4
2.4 Command List ....................... 2–5
i

ii Contents
SR475 and SR476 Laser Shutters

General Information
The SR475 and SR476 Laser Shutters are high performance instru-
ments designed to provide fast, versatile, and reliable mechanical
blocking of a free-space laser beam while minimizing vibration and
acoustic noise.
Service
Do not install substitute parts or perform any unauthorized modi-
fications to this instrument. Contact the factory for instructions on
how to return the instrument for authorized service and adjustment.
Each SR475 and SR476 contains small parts and it is recommended
that users do not remove the covers, and in particular, the sealed inner
cover. There are no user-serviceable parts inside and reassembling
the unit to its calibrated state may be difficult or impossible.
Environment
This product is intended for use only in a clean and dry laboratory
environment. Operation in other environments may cause damage
to the product.
Laser Safety
Certain hazards are always present when working with laser radia-
tion. Visible and invisible beams of light have the potential to cause
serious bodily injury including blindness or death and to cause sig-
nificant damage to property.
While the SR475 and SR476 are designed for use with laser systems,
it is fully the users responsibility to ensure that safe operating
WARNING conditions are maintained and to provide for fail-safe operation
whenever an equipment failure could lead to a hazardous situation.
iii

iv General Information
Symbols you may Find on SRS Products
Symbol Description
Alternating current
Caution - risk of electric shock
Frame or chassis terminal
Caution - refer to accompanying documents
Earth (ground) terminal
Battery
Fuse
On (supply)
Off (supply)
SR475 and SR476 Laser Shutters

General Information v
Notation
The following notation will be used throughout this manual.
A warning means that injury or death is possible if the instructions
WARNING are not obeyed.
A caution means that damage to the instrument or other equipment
CAUTION is possible.
Typesetting conventions used in this manual are:
•Remote command names are set as A.
•Literal text other than command names is set as OFF.
Remote command examples will all be set in monospaced font. In
these examples, data sent by the host computer to the SR475 and
SR476 are set as straight teletype font, while responses received
by the host computer from the SR475 and SR476 are set as slanted
teletype font.
SR475 and SR476 Laser Shutters

vi General Information
Specifications
Operation
General
Primary function Block/unblock laser beam
Controller/Driver type SR470 Series
Clear aperture 0.120” (3 mm) min. (SR475)
0.040” (1 mm) min. (SR476)
Lifetime 107cycles min.
Shutter blade
Blade material BeCu alloy, black oxide finish
Optical power Low-power laser beams;
no absolute specification is established
Bearing type Sapphire jewel bearing
Blade position Servo controlled; neither open
nor closed is preferred
Power-offstate Blade position is indeterminate
Hold time Indefinite in either open or closed state.
Mounting
Orientation Any
Mounting holes 8-32 (3), 1/4-20 (1)
Housing material Anodized aluminum
Performance
Open/close time 5 ms full-stop to full-stop, in full-speed mode;
User selectable to 10 ms, 20 ms, or 40 ms (SR475)
4 ms full-stop to full-stop, in full-speed mode;
User selectable to 8 ms, 16 ms, or 32 ms (SR476)
Maximum rate 100 Hz (SR475)
125 Hz (SR476)
(Limited by open/close time).
Laser beam Determined by beam size/quality and shutter mode.
rise/fall time 500 μs typ., in full-speed mode (SR475)
750 μs typ., in full-speed mode (SR476)
Insertion delay jitter 10 μsrms typ.
(Measured at 10 Hz rep rate in full-speed mode.)
Bounce None allowed, at opening or closing
SR475 and SR476 Laser Shutters

General Information vii
Electrical and Mechanical
General
Interface SRS Shutter interface connector
Weight 0.28 lbs
Dimensions 2.25 W×1.6 H×1.0 D
Operating temperature 0 ◦Cto35◦C, non-condensing
Maximum temperature 90 ◦C
Shutter interface
Voltage inputs +12 VDC, +4.5 VDC
Current draw 1.20 A max. continuous (12 VDC)
0.25 A max. continuous (4.5 VDC)
Signal lines Serial TX, Serial RX, logic-level control
Connector type Mechanically compatible
with 6-pin IEEE-1394 cables.
Cable length 10 ft (3 m) max.
Cable shield Internally connected to housing
SR475 and SR476 Laser Shutters

viii General Information
SR475 and SR476 Laser Shutters

1 Getting Started
This chapter gives you the necessary information to begin using the
SR475 and SR476 Laser Shutters.
In This Chapter
1.1 Introduction to the Instrument ............. 1–2
1.1.1 Overview ..................... 1–2
1.1.2 Design and theory of operation ......... 1–2
1.1.3 Mechanical performance ............. 1–3
1.1.4 Power-offand standby states .......... 1–4
1.1.5 Power-on state .................. 1–6
1.1.6 Resetting the shutter head ............ 1–6
1.2 Mounting ......................... 1–6
1.2.1 Vibration considerations ............. 1–6
1.2.2 Thermal considerations ............. 1–7
1.2.3 Grounding considerations ............ 1–8
1.3 Optical alignment .................... 1–8
1.4 Optical power capacity ................. 1–9
1.5 Operating environment ................. 1–9
1.5.1 Dust ........................ 1–9
1.5.2 Magnetic field ................... 1–10
1.5.3 Temperature .................... 1–10
1.5.4 Vacuum ...................... 1–10
1.5.5 Oxygen-rich environments ........... 1–10
1.6 Alternate speed modes .................. 1–10
1.7 Shutter interface connector ............... 1–12
1.7.1 Direct interfacing ................. 1–12
1–1

1–2 Operation
1.1 Introduction to the Instrument
The SR475 and SR476 Laser Shutters are high performance instru-
ments designed to provide fast, versatile, and reliable mechanical
blocking of a free-space laser beam while minimizing vibration and
acoustic noise.
The shutters are suitable for low-power beam switching and pulse
selection applications. They are also particularly suited to provide
additional extinction to optical systems incorporating fast optoelec-
tronic shutters.
1.1.1 Overview
The basic function of the laser shutter, or “shutter head” is to block
or unblock a laser beam when commanded to do so.
The shutter head is normally operated in conjunction with a shutter
driver or controller that provides power, a serial communications
interface, and a control input. Details about this interface are given
in §1.7.
1.1.2 Design and theory of operation
Mechanical laser shutters have traditionally been electronic descen-
dants of camera shutters, consisting of a solenoid-driven blade (or
set of blades) with a return spring. The shutter’s open and closed
positions are then determined by physical stops that limit the blade
travel.
By contrast, the SR475 and SR476 Laser Shutters do not use physical
stops to control the blade position. Instead, the blade position is
precisely measured in real time and a digital servo loop is used to
hold the blade in the desired location. During a transition between
the open and closed states, the shutter blade is guided along a pre-
determined trajectory such that it arrives at its final position with
zero velocity, without encountering a physical stop.
This design reduces or eliminates many of the less desirable char-
acteristics of conventional solenoid-based mechanical laser shutters.
Most importantly, it removes the high impulse that is encountered
when a solenoid or a return spring drives a shutter blade into a hard
stop. This high impulse is responsible for the bulk of vibration and
mechanical noise associated with shutters, but is also a contributing
factor in the limited lifetime of such devices.
A typical shutter with a solenoid and return spring necessarily has
a defined normal state—either open or closed—and expends energy
not only to reach but also to hold in the normal state. By using an
SR475 and SR476 Laser Shutters

1.1 Introduction to the Instrument 1–3
active servo system instead of a solenoid and return spring, the SR475
and SR476 do not have a preferred state, and can stay indefinitely in
either state without significant power dissipation. Significant power
is only used when opening or closing, and each shutter head is rated
for continuous duty without duty cycle restrictions.
The shutter blade in an SR475 or SR476 is mounted in a sapphire
jewel bearing to minimize friction, and is driven as a part of a tightly
integrated rotary motor. The motor design, along with the impulse
reduction from eliminating physical stops, results in a head lifetime
that is orders of magnitude more than is typically found in other
laser shutter systems.
The on-board electronics in the shutter head detect the blade position,
servo control the blade position, and provide control, communica-
tion, and error detection functions. Electrical, over-temperature, and
mechanical faults are detected and can be reported over the shutter
head’s serial interface.
1.1.3 Mechanical performance
Figure 1.1: Mechanical action of the SR475 and SR476 shutter heads.
Part (a) illustrates the shutter head in the closed position, where the
shutter blade blocks the aperture. Part (b) shows the shutter head in
the open position, where the shutter blade is clear of the aperture.
The location of the shutter blade in its open and closed positions is
illustrated in Fig. 1.1. In the open position the shutter blade is clear of
SR475 and SR476 Laser Shutters

1–4 Operation
the laser aperture, and in the closed position the shutter blade fully
covers the aperture.
The process of opening or closing the shutter consists of guiding the
blade along a smooth, pre-determined trajectory between the closed
and open positions. In what follows we will describe this in more
detail. For clarity we will discuss only the case of opening, but the
sequence of events applies equally to closing the shutter.
When the shutter is initially closed and it receives a signal to open,
it begins moving the shutter blade under servo-loop control along
the preprogrammed “opening” trajectory. Once this has begun, the
shutter will guide the blade along the entire trajectory—bringing
the blade to a full stop at the open position—before carrying out
any subsequent instruction to close. In other words, a transition
in progress cannot be reversed or aborted (except by disabling the
motor).
Sample trajectories for opening and closing are illustrated in Fig. 1.2.
For the SR475, each pre-programmed trajectory takes 5 ms to com-
plete when running at full speed. This means that the minimum time
to complete a closed-open-closed full cycle is 10 ms, which gives the
shutter’s maximum rate of 100 Hz. The minimum exposure time be-
tween the midpoint of opening and the midpoint of closing is 5 ms.
For the SR476, each full-speed pre-programmed trajectory takes 4 ms,
and a full cycle takes a minimum of 8 ms. This gives a maximum
rate of 125 Hz and a minimum exposure time of 4 ms. For both mod-
els, when full speed is not needed, there are alternate speed modes
available that use less power and create less vibration; see §1.6.
1.1.4 Power-off and standby states
The SR475 and SR476 Laser Shutters do not incorporate return
springs. The shutter blade is in an indeterminate position when-
ever the shutter is powered offor in the Standby mode.
The shutter is in the Standby mode whenever its +4.5 VDC “logic”
power supply is available but the motor is not enabled. In this mode,
the logic power supply provides power for serial communications,
but the motor is turned offand the shutter blade position is therefore
indeterminate.
The shutter head can be placed into Standby with a remote com-
mand. It also enters Standby mode automatically when certain fault
conditions are detected. These conditions include mechanical failure,
over temperature, and undervoltage on the +12 VDC power supply
for the motor. The shutter head may also be put into Standby by
intentionally turning offthe +12 VDC power supply. To ensure that
SR475 and SR476 Laser Shutters

1.1 Introduction to the Instrument 1–5
Figure 1.2: Blade trajectory for the SR475 Laser Shutter (top) and
SR476 Laser Shutter (bottom). Curve (a) illustrates the position of
the SR475 blade as it moves from the closed to the open position, and
curve (b) illustrates the closing trajectory. Curve (c) illustrates the
position of the SR476 blade as it moves from the closed to the open
position, and curve (d) illustrates the closing trajectory.
SR475 and SR476 Laser Shutters

1–6 Operation
the shutter head enters standby mode, the +12 VDC power should
be kept low for at least three seconds. Once in Standby mode, the
shutter head will remain so until reset.
Note: The +4.5 VDC “logic” power supply is always provided to a
shutter while it is connected to a powered-on SRS shutter controller
such as the SR470 Shutter Controller or the SR474 Four-Channel
Shutter Driver. Placing a shutter drive channel on one of these in-
struments into the “off” or “sleep” states will put a SR475 or SR476
attached to that channel into the Standby mode.
1.1.5 Power-on state
At turn-on, the SR475 or SR476 executes a brief mechanical initial-
ization to verify motor function and perform the initial servo-lock
of the shutter blade position. This can potentially last several sec-
onds and/or involve minor mechanical bumps in excess of normal
operation.
All settings and modes of the SR475 and SR476 are in volatile mem-
ory, and at power-on the instrument always returns to its default
state.
1.1.6 Resetting the shutter head
The SR475 and SR476 can be reset by turning offand restoring the
+4.5 VDC power supply, through a remote command to reset the
shutter head, or by restoring the +12 VDC power supply after it has
been turned off.
1.2 Mounting
SR475 and SR476 Laser Shutters can be mounted and operated in
any orientation. 8-32 mounting holes are provided on three sides of
the shutter head, and a single 1/4−20 mounting hole is provided on
the bottom side, as shown in Fig. 1.3.
Orientation may be chosen for convenient routing of the shutter
cable, for aligning to the appropriate beam height above an optical
table, or for pulsing one of two closely separated laser beams.
1.2.1 Vibration considerations
SR475 and SR476 Laser Shutters should be firmly mounted to a solid
surface. Using long and/or narrow mounting posts will increase the
apparent vibration induced by the shutter.
SR475 and SR476 Laser Shutters

1.2 Mounting 1–7
Figure 1.3: Physical dimensions and mounting of the SR475 and
SR476 . The clear aperture is 0.120” (3 mm) for the SR475 and 0.040”
(1 mm) for the SR476.
For optimal results, use short, large-diameter mounting posts or
other sturdy optomechanical hardware to mount SR475 and SR476
Laser Shutters to appropriate surfaces. Attaching the shutter head
rigidly to a heavy, damped optical table will minimize its vibrational
effects.
1.2.2 Thermal considerations
Like most other mechanical shutters, the performance of the SR475
and SR476 Laser Shutters are fundamentally limited by their ability
to dissipate heat. The motor can get hot when run continuously (or
nearly so), particularly in full-speed mode.
The outer case of the shutter head may get warm but should not
become too hot to touch under normal operating conditions. Solidly
mounting shutter heads to metal surfaces can assist heat sinking
SR475 and SR476 Laser Shutters

1–8 Operation
and help them to run at a comfortable temperature, particularly in a
warm laboratory environment.
An internal thermal sensor will trip offif the shutter head overheats.
In this case, the head will declare a fault and go to the Standby state.
1.2.3 Grounding considerations
For reliable operation of a SR475 or SR476, it is essential that the
shield of the shutter cable is properly grounded.
Inside the shutter head, there is an electrical connection between its
chassis (case) and the shield of the cable. If the chassis of the shutter
head is electrically connected to earth ground, for example by way
of attachment to a grounded optical table, then the shield will be
grounded as well.
SRS shutter controllers, such as the SR470 Shutter Controller and
the SR474 Four-Channel Shutter Driver, provide optional internal
grounding of the shutter cable shield. If a shutter case is prop-
erly grounded and thereby providing a suitable ground to the cable
shield, it may be desirable to disconnect the shield-ground connec-
tion within the controller; consult that instrument’s operation man-
ual for details.
Apart from the cable shield, the shutter cable uses a separate “signal
ground” as one of the power supply lines. This ground is normally
isolated from the shutter case and cable shield. Under certain cir-
cumstances it may be desirable (for the control of ground loops,
for example) to establish an electrical connection between the signal
ground and the cable shield. To do so, unplug the shutter head and
solder a jumper wire across location J11 on the circuit board. To ac-
cess the circuit board, you will need to temporarily remove the outer
case, which is held on by four screws.
1.3 Optical alignment
The SR475 and SR476 Laser Shutters are designed for easy alignment.
The clear aperture of the SR475 is aperture of 0.120” (3 mm), and the
clear aperture of the SR476 is 0.040” (1 mm). The laser beam may
enter the shutter head from either side, but there is less potential for
leakage of indirect scattered light if the beam enters from the side
marked “Front” in Fig. 1.3.
SRS shutter controllers incorporate an “Align” mode that chops the
shutter open and closed at a rate of 1 Hz to assist with manual
alignment. A similar chopping function is also directly built into the
shutter head firmware, and can be enabled over the remote interface.
SR475 and SR476 Laser Shutters

1.4 Optical power capacity 1–9
The rise and fall time of a laser beam chopped by the shutter are ap-
plication dependent, determined by the size and profile of the laser
beam. A narrower beam will blink on and offquickly compared to
a broader beam, since the blade edge will take less time to transit a
smaller beam. Similarly, the insertion delay, i.e., the time between
initiating an open-closed transition and when the laser beam is ac-
tually switched, depends upon the beam profile and its location in
the clear aperture. In general, the insertion delay will be different for
opening and closing.
While it may be desirable to gently focus a laser beam through the
shutter aperture to reduce the apparent open/close time, it should
be noted that this speed increase comes as a tradeoffwith increased
sensitivity to insertion delay jitter.
1.4 Optical power capacity
The SR475 and SR476 use a thin BeCu alloy shutter blade with a
black oxide finish and are intended for use in “low-power” laser
beam applications.
The maximum power handling capability of a laser shutter depends
on wavelength, duty cycle, and many other environmental factors.
SRS does not establish optical power ratings for laser shutters; please
contact SRS if you would like to request sample shutter blades to
evaluate for your application.
1.5 Operating environment
The SR475 and SR476 Laser Shutters are designed for operation in a
clean and dry laboratory environment.
1.5.1 Dust
Both the bearing and the position detection system within the shutter
head are susceptible to impairment in a dusty environment. This can
potentially result in a fault condition, when either the blade is unable
to move to the commanded position, or when the readout system is
unable to verify that the blade is in the correct position.
Always operate the laser shutter with its outer cover in place to
minimize the potential for dust to collect inside the shutter head.
If dust contamination inside the shutter is suspected, the outer cover
can be unscrewed and dust can be gently blown out. Use only low-
velocity air to remove dust from the shutter head, for example a
handheld hair dryer with the heat turned off.
SR475 and SR476 Laser Shutters

1–10 Operation
Never expose the SR475 and SR476 Laser Shutters to compressed
CAUTION air or other compressed gas dusters, since they could potentially
damage the shutter mechanism.
Never touch or attempt to clean the shutter blade.
CAUTION
1.5.2 Magnetic field
The SR475 and SR476 Laser Shutters use a magnetic mechanism
and may not operate properly in the presence of a strong external
magnetic field.
1.5.3 Temperature
The SR475 and SR476 Laser Shutters are designed for operation in a
0◦Cto35◦C laboratory environment.
The internal thermal sensor will trip if the shutter head exceeds
a temperature of approximately 60 ◦C, as measured on the circuit
board. In this case, the head will declare a fault and go to the Standby
state. See also §1.2.2.
The absolute maximum storage temperature of the shutter head is
90 ◦C. Above this temperature permanent damage can result.
1.5.4 Vacuum
The SR475 and SR476 Laser Shutters are not designed for use in a
vacuum environment. The shutter mechanism relies on convection
cooling and would overheat quickly unless active external cooling
were applied.
Also note that adhesives used in construction of the SR475 and SR476
Laser Shutters are not rated for vacuum compatibility.
1.5.5 Oxygen-rich environments
Because of the adhesives used in construction, the SR475 and SR476
Laser Shutters are not suitable for use in oxygen-enriched, pure
oxygen, or other similar environments.
1.6 Alternate speed modes
The SR475 and SR476 Laser Shutters are by default configured to
operate in full-speed mode, where the opening/closing time is fixed
at its minimum possible value. During the transition from one state
to the other, the shutter blade is guided along a pre-determined
trajectory between the two states, as discussed in §1.1.3.
SR475 and SR476 Laser Shutters