Nuclear & Electronics contains other products and information you need, so please check it out.
The acousto-optical Q-switch often used in the laser marking makes use of mutual interaction between an ultrasonic wave and a light beam in a scattering medium. The light beam that enters in a direction forming a Bragg angle to the wave surface of the acoustic wave in the scattering medium is diffracted in accordance with periodic changes in the diffraction rate produced by the acoustic wave.
The situation is briefly explained. First of all, an RF signal is impressed to the transducer adhered to the molten quartz and thickness extensional vibration is produced. Ultrasonic shear waves are caused to advance in the molten quartz by this vibration, and phase grating formed by acoustic waves is produced. The laser beam is diffracted when it satisfies the Bragg angle with respect to this phase grating, and is separated in space from the incident light.
If the laser optical resonator is constructed against 0-dimensional diffracted light (undiffracted light), the diffracted light deviates from the laser optical resonator axis when a RF signal is impressed. As a result, loss occurs in the laser optical resonator and laser oscillation is suppressed. To make use of this phenomenon, an RF signal is impressed for a certain length of time only (status of low Q-value) to suspend laser oscillation. In the meantime, the population inversion of the Nd:YAG rod is accumulated by continuous pumping. When the RF signal is reduced to zero (status of high Q-value) and the loss to the laser optical resonator is removed, the accumulated energy is activated as laser oscillation in a pulse form within an extremely short length of time. They are Q-switch pulses.
This situation is briefly explained. When an RF signal is subjected to pulse modulation, it is possible to periodically take out a Q-switch pulse. When the period of Q-switch pulses becomes shorter than the life (about 200 ms) of the higher order of the Nd:YAG rod, however, the population inversion decreases and the peak value of Q-switch pulses decreases.
1. QS Series Q-switches at nm
A water-cooled acousto-optic Q-Switch for use in high-power Nd:YAG laser systems. Combining top grade fused silica with high quality optical finishing and in-house anti-reflection coatings, this Q-Switch exhibits very low insertion loss and high damage threshold. Through an innovative design and manufacturing process, RF powers up to 100W may be applied.
Standard options include a choice of frequencies (24 to 68MHz), active apertures (1 to 8mm), acoustic modes (compressional for linear polarisation, shear for unpolarised) and water connectors. Customised housings are available for OEM�s.
Specifications:
Model No: See "Options" below
Interaction Medium: Fused Silica
Operational Wavelength: nm
Anti Reflection Coating: Hard multi-layer dielectric
- Reflectivity: <0�2% / surface (< 0�1% typical)
- Damage Threshold: > 500MW cm-2
Insertion Loss: <10% (< 5% typical)
Active Aperture: See "Options" below
VSWR: 1�2:1
Maximum CW Drive Power: 100W
Thermal Interlock: +50�C
Water Cooling
Flow rate: 190cc / min (minimum) Acousto-Optic Q-Switch Selection Guide
Recommended water operating: <32�C
Recommended water maximum: 40�C
Water Connectors: See "Options" below
Options
QS
27
-4
S
-B
-X X n
DEVICE
FREQUENCY
ACTIVE
APERTURE
ACOUSTIC
MODE
WATER
CONNECTOR
SPECIAL
DESIGNATION
Device : QS - Q-Switch
Frequency : 24, 27, 41 - Value in MHz
Aperture : 1.6, 2, 3, 4, 5, 6�5, 8 - Value in mm (In general, the aperture of Q-switch is equal to or larger than the diameter of laser beam or YAG rod.
Acoustic Mode : C - Compressional, S - Shear
Water Connector : S - Screw-on (Swagelok etc.), B - Barbed Push-on
Special Designation : - For non-standard Q-switch models identification characters which define the configuration may be allocated.
Driver Selection Acousto-Optic Q-Switch Selection Guide
QSD series or R series drivers
2. QS Series Q-switches at -nm
Model No.
QS027-4H-xxx
Interaction material
Infrasil (water-free fused silica)
Wavelength
-nm
AR coating reflectivity
< 0.2% per surface
Damage threshold
> 100MWcm-2
Polarisation
Linear (vertical to base)
Interaction length
46.0mm
RF frequency
27.12MHz
VSWR
< 1.2 1 at 50.
Acoustic Mode
Compressional
Active aperture
5.0mm
Loss modulation
> 80% at 50W RF power
Housing
Standard QS24/27 range (Aluminium)
Water connectors
Barbed
3. QS Series Super Q-switches at nm
Model: QS2x-xD-x-xxx
High efficiency
For unpolarised, high power, high gain lasers
2 x 50W RF power handling
A new compressional mode, water-cooled, AO Q-Switch designed for use in high power unpolarised lasers giving faster switching, better pulse-to-pulse stability and higher power densities. Enhance your systems performance with greater punch and increased power, specifically for laser processing applications.
Before the Super Q-Switch, some customers were using 2 x Compressional mode Q-Switches (like the QS27-4C-S) in the same cavity. One of the Q-Switches is rotated 90degrees to the other. Because the Compressional mode Q-Switch is more efficient for polarised light, the first Q-Switch would block one polarisation & the second Q-Switch blocks the other. This is a good solution, but takes a large space in the cavity. The Super Q-Switch gives the same performance as using 2 x Compressional Q-Switch, but they are incorporated into 1 device.
This Q-switch uses a dual channel driver to operate two orthogonal compressional mode transducers bonded to a single monolithic optical cell and mounted in one convenient housing. Our proprietary bonding techniques and power handling technology allows this device to operate up to 50W per channel giving an efficient, compact, single device for the next generation of high power, high gain, solid state lasers.
Interaction Material
Fused Silica
Wavelength
to nm
Anti-Reflection Coating
< 0.2% per surface
Damage Threshold
> 500MWcm-2 (1GWcm-2 typical)
Transmission (single pass)
> 99.6%
Frequency
24.00 or 27.12MHz
VSWR
< 1.2:1 (50. input impedance)
Active Aperture
1.6, 2, 3, 4, 5 or 6.5mm2
Clear Aperture
9 x 9mm
Acoustic Mode
Compressional (Orthogonal)
Rise-Time / Fall-Time
109ns/mm
RF Power Rating
2 x 50W cw
Water Flow Rate
190cc / minute, minimum
Maximum Water Temperature
+40�C (recommended, 22�C to 32�C)
Water Connectors
Screw-fit or Barbed (push-on)
Thermal Switch Cut-Off
+55�C � 5�C
Housing / Flow Chamber Material
Aluminium HE30TF
Driver Selection:
Aperture size 1.6D, 2D or 3D, use 25W dual channel driver (R390xx25DMzz-2CH, or R390xx-25DSzzz-2CH)
Aperture size 4D, 5D or 6.5D, use 50W dual channel driver (R390xx25DMzz-2CH, or R390xx-25DSzzz-2CH)
Options and Model
4. Stallion Series AO Q-Switches at nm Wavelength
A �Stallion� version of our industry standard water cooled Acousto-optic Q-Switch, for use in high power lamp or diode pumped Nd:YAG lasers.
The patent pending �Stallion� manufacturing technique provides superior corrosion resistance whilst maintaining optimum performance and RF power handling capabilities up to 100W.
Combining top grade fused silica with high quality optical finishing and in-house anti-reflection coatings, this Q-Switch exhibits very low insertion loss and high damage threshold.
In addition to the standard product shown, custom configurations are available for specialized applications. These include alternative housing options, wavelengths and RF frequencies.
Key Features:
Industry standard for Nd:YAG lasers
Superior corrosion resistance
Stainless steel cooling channels
High damage threshold
Push fit water-connectors
Up to 100W RF power handling
Custom configurations available
Applications:
Material processing:
Laser marking
Laser engraving
Laser cutting
Laser drilling
Medical (surgery)
Lithography
Technical Specifications:
Interaction material:
Fused silicon
Wavelength:
nm
AR coating reflectivity:
< 0.2% per surface
Damage threshold:
> 1GWcm-2
Transmission (single pass):
> 99.6%
Static insertion loss:
' 6% at 50W laser power
VSWR:
< 1.2:1 (<1.4:1 at 50W RF power)
RF power rating:
100W cw (max)
Water flow rate:
> 190cc / minute
Water-cooling channel material:
Stainless steel 316
Recommended water temperature:
+22oC to +32oC
Thermal switch cut-off:
+55oC +/- 5oC
Ordering Codes
Example: I-QS027-4S4G-N5-ST1 (Q-Switch, 27.12MHz, 4mm active aperture, shear mode, fused silica, nm, 4mm OD straight push fit water-connectors, BNC, Stallion housing with M3 mounting holes).
5. Other Q-Switches
The Q-Switches are for use in both industrial and laboratory applications. Q-Switching is used principally on high peak power solid state Nd:YAG lasers at 1.06 micrometer wavelength. The Q-Switches are divided into three categories: for use with multi-mode, un-polarized lasers, with beam sizes 5mm and larger; for use with miniature, polarized or un-polarized, solid state diode pumped lasers; and single mode, polarized, low divergence solid state lasers, with beam size of 1 to 2 mm.
Wavelength(nm)
Q-Switch Model
Driver Power
Loss
Modulation (%@Watts) @nm
Polarization
Active Aperture
(mm)
Center Frequency
(MHz)
Rise Time
(ns / mm beam dia.)
Optical Power Density /(cm2)
Ave./Pk
Interaction Material
Outlook
drawing
10.6um
-3
30
85
3
27.12
120
500
Ge
53B
10.6um
-5
30
75
5
27.12
120
500
Ge
53B
If you are looking for more details, kindly visit acousto-optic q-switch driver.
-50-4
50
55
4x13
24
175
50K/500M
Fused Silica
53B
-50-4
50
55
4x13
27.12
175
50K/500M
Fused Silica
53B
-50-5-I-HGM-W
50
70
5x10
24
115
50K/500M
Crystal Quartz
53B
-50-5-I-HGM-CMS
50
70
5x10
24
115
50K/500M
Crystal Quartz
53B
-50-5-I-HGM-W
50
85
70
5x10
27.12
115
50W/500M
Crystal Quartz
53B
-50-5-I-HGM
50
70
5x10
27.12
115
50W/500M
Crystal Quartz
53B
-50-5-I-HGM-CMS
50
70
5x10
27.12
115
50W/500M
Crystal Quartz
53B
-50-5-I-M3
50
85
70
5x10
27.12
115
Crystal Quartz
53C
-70-7
70
55
7x13
24
175
50K500M
Fused Silica
53B
-70-7
70
55
7x13
27.12
175
50K/500M
Fused Silica
53B
-70-7-I-HGM-W
70
85
7x10
24
115
50K/500M
Crystal Quartz
53B
-70-7-I-HGM-CMS
70
85
7x10
24
115
50K/500M
Crystal Quartz
53B
-70-7-I-HGM-W
70
85
7x10
27.12
115
50K/500M
Crystal Quartz
53B
-70-7-I-HGM-CMS
70
85
7x10
27.12
115
50K/500M
Crystal Quartz
53B
-100-4-HGM-W
100
90
4x13
24
175
50K/500M
Fused Silica
53B
-100-4-HGM-W
100
90
4x13
27.12
175
50K/500M
Fused Silica
53B
-100-4-HGM-CMS
100
90
4x13
27.12
175
50K/500M
Fused Silica
53B
Remark: EO Q-switches operating at 10.6um (CO2 lasers) available.
6. STBR series free space Q-switch
STBR series Acousto-Optic Q-switching systems for industrial and laboratory applications. The STBR free space Q-switches are designed for the highest conversion efficiency of RF energy into acoustic energy by attaching the transducer to the crystal with an advanced vacuum metallized process. Q-switches are special modulators designed for use inside laser cavities. They are fabricated from high optical quality Fused Quartz, Flint Glass, and Tellurium Dioxide, or other acousto-optic materials with Brewster cut optical faces or durable hard oxide AR coatings for high optical power applications.
Model # FSQ-24-2-BC FSQ-27-5-BC FSQ-80-5-BC TEQ-27-4-BC TEQ-80-20-BC Substrate SiO2 SiO2 SiO2 TeO2 TeO2 Brewster cut yes yes ye yes yes Laser Wavelength (nm) 800 Active Aperture (mm) 2 2 1 1.5 3 Center Frequency (MHz) 2 27 80 27 80 Digital Modulation Bandwidth (MHz) 2 5 6.5 4 (3dB Bandwidth) 20 (3dB Bandwidth) Optical Transmission (%) 99.8 99.8 >99.5 >99.5 >99.5 Maximum Diffraction Efficiency (%) 30 30 25 >50 >65 Rise Time (nsec) 100 100 85 150/630Wave Front Distortion
λ/10
λ/10
λ/10
λ/10
λ/10
Separation Angle
5 mrad @ nm
5 mrad @ nm
5 mrad @ nm
1 deg @ nm
0.9 deg @ 800nm
Input Impedance
50 ohms
50 ohms
50 ohms
50 ohms
50 ohms
Optical Polarization
Linear (perpendicular to acoustic wave)
Linear
Perpendicular to acoustic wave
VSWR
2.1:1
For the associated RF drivers, please refer to �RF Drivers for STBR series�
Air-cooled Q-switch Q-switch drivers Fiber Q
Basics of Acousto-Optic Q-switch Frequently Asked Questions
The acousto-optical Q-switch often used in the laser marking makes use of mutual interaction between an ultrasonic wave and a light beam in a scattering medium. The light beam that enters in a direction forming a Bragg angle to the wave surface of the acoustic wave in the scattering medium is diffracted in accordance with periodic changes in the diffraction rate produced by the acoustic wave.
The situation is briefly explained in Figure 1. First of all, an RF signal is impressed to the transducer adhered to the molten quartz and thickness extensional vibration is produced. Ultrasonic shear waves are caused to advance in the molten quartz by this vibration, and phase grating formed by acoustic waves is produced. The laser beam is diffracted when it satisfies the Bragg angle with respect to this phase grating, and is separated in space from the incident light.
Figure 1: Principle of A-O Q-switch
If the laser optical resonator is constructed against 0-dimensional diffracted light (undiffracted light), the diffracted light deviates from the laser optical resonator axis when a RF signal is impressed. As a result, loss occurs in the laser optical resonator and laser oscillation is suppressed. To make use of this phenomenon, an RF signal is impressed for a certain length of time only (status of low Q-value) to suspend laser oscillation. In the meantime, the population inversion of the Nd:YAG rod is accumulated by continuous pumping. When the RF signal is reduced to zero (status of high Q-value) and the loss to the laser optical resonator is removed, the accumulated energy is activated as laser oscillation in a pulse form within an extremely short length of time. They are Q-switch pulses.
This situation is briefly explained in Figure 2. When an RF signal is subjected to pulse modulation, it is possible to periodically take out a Q-switch pulse. When the period of Q-switch pulses becomes shorter than the life (about 200 's) of the higher order of the Nd:YAG rod, however, the population inversion decreases and the peak value of Q-switch pulses decreases.
Figure 2: Laser oscillation output of a Q-switch laser
The following pictures show the relations among the main laser parameters such as average power, peak power, pulse width, pulse energy and diode current (proportional to diode laser's power). The data comes from a diode end pumped Q-switched laser.
1. Which parameters do I need to specify if I want to order a Q-Switch?
You will need to specify the frequency, aperture, acoustic mode and the type of water connector.
2. Which frequency should I use?
The answer depends on your location. There are various regulatory bodies (for example the ITU) that stipulate the maximum levels of RF radiation that can be emitted in certain frequency bands. The Q-Switch drive frequency is usually chosen to be within one of the permitted bands for the country in which it will operate. Historically, 24.0MHz has been the chosen frequency in the USA and Japan and 27.12MHz in Europe and elsewhere. However, this has been less rigidly observed in recent years and 27.12MHz is now used widely in the USA.
3. What is the difference between clear aperture and active aperture? ,
The clear aperture of a Q-Switch is defined by the size of the block of silica in which the light and sound interact. For the QS24/27 Series the minimum clear aperture is 9mm.
The active aperture is defined by the height of the acoustic beam inside the silica block. This is the dimension that matters when specifying a Q-Switch.
4. How do I select the appropriate aperture for my application?
As a rule of thumb, the active aperture of the Q-Switch should be the same as the beam diameter of the laser at the point where the Q-Switch will be located. If the gain of the laser is modest it may be possible to use a Q-Switch with an active aperture one size smaller than the actual beam diameter (e.g. a 3mm active aperture Q-Switch in a laser with a 4mm diameter rod). This has the advantage of requiring lower RF drive power (drive power scales linearly with active aperture), which means less heat input and consequently greater efficiency and improved beam quality. It may even mean a lower cost driver can be used. On the downside, alignment of the Q-Switch in the cavity may be more critical.
5. Which acoustic mode would suit me best?
The choice is between shear (S) mode and compressional (C) mode (also known as longitudinal mode). If your laser is unpolarised you should choose shear mode. For polarised systems better results (less RF power = lower cost driver, less heat = better beam quality) will be obtained by using a compressional mode Q-Switch.
6. Which water connector should I choose?
The choice is between screw-on (S) connectors with a nut and olives which grip the outside of the flexible tubing, and barbed (B) push-on connectors, which grip the inside of the flexible tubing. There is little to choose between the two and it usually depends what type of pipe fitting is used as standard in the laser system. Overall the push-on fittings are probably best because there is no danger of them restricting the water flow. (The olives in the screw-on type can constrict the soft-wall tubing usually used in laser systems.)
7. How do I know that the Q-Switch is not over-heating?
The Q-Switch is fitted with a thermal interlock. If, for example, the cooling water fails it will shut down the driver when the temperature reaches 50 degrees C, preventing damage to the Q-Switch.
8. What is the optimum operating temperature of the Q-Switch?
The temperature should be set slightly above ambient to prevent the possibility of condensation forming on the optical surfaces of the Q-Switch. Around 32 degrees C is typical. For optimum performance and lifetime we do not recommend operating the Q-Switch at temperatures above 40 degrees C.
9. How do I know that the QS24/27 Series Q-Switch is the best choice for my application?
Please call one of our engineers if you are in any doubt about which Q-Switch to use. The QS24/27 Series Q-Switches are 'industry standard' devices that have been developed and refined over many years. As a result they are very reliable and because they are manufactured in large quantities they are lower cost than some of the more specialised products we can offer. Basically, if you have a lamp-pumped industrial or medical Nd:YAG laser this is probably the Q-Switch for you. It is also suitable for the latest generation of high-power industrial diode-pumped lasers.
10. I am designing a compact laser and the QS24/27 Series Q-Switch is too large. What should I do?
G&H manufacture a range of standard compact Q-Switches that may be suitable for your application. If not, we have considerable experience of designing application-specific Q-Switches. We supply Q-switches to many of the leading diode-pumped laser manufacturers and it is likely that we will have a design that can easily be adapted to suit your requirements.
11. I have a single-mode polarised laser. Will the QS24/27 Series Q-Switch be suitable? ,
Yes. You can use a compressional mode version with a small active aperture (3mm or less). However, you may find that the integrated Q-switch, with its integral RF driver is a more cost effective solution that also offers performance advantages in terms of higher average Q-Switched output power.
12. How much laser power can I hold off? ,
It depends on the design of your laser cavity, where the Q-Switch is placed in it and so on. Hold-off is not a parameter of the Q-Switch alone, but of the Q-Switch/laser combination. We can however determine the extra-cavity loss modulation of the Q-Switch, which is a direct measure of its effectiveness at blocking the laser beam.
13. I have a high gain laser and need the maximum possible loss modulation. How do I achieve this? ,
There are two ways; by using two compressional mode Q-Switches in series and orientated such that the acoustic beams are orthogonal to each other you can obtain a high, polarisation insensitive, loss modulation with minimum RF drive power. Also available is a newly developed Q-Switch incorporating two orthogonal compressional mode transducers in a single monolithic cell and mounted in one convenient housing. A dual channel RF driver is available for both applications.
14. Can I trust the damage threshold quoted in the data sheet?
Yes. We periodically send a sample Q-Switch to a NIST certified test house to have the optical damage threshold verified. G&H take the utmost care in the polishing of the optical surfaces and in their preparation and coating. All these operations are carried out in-house in order to have total control of the process.
For more information on Q-switches, please go there.
Want more information on introduction to radiation detectors? Feel free to contact us.