光束剖面与传播特性参数的测量

1. 光束测量功能

激光剖面成像在激光焊接、聚焦和激光在自由空间通信等应用中具有重要作用。在这些应用中，监测激光剖面可以捕捉所需数据来评价光束宽度的变化，实时确定光束形状的细节，使得用户能够评估光束中心热点的位置以及光束形状的变化。

数字波前照相机（Digital Wavefront Camera, DGC）与软件配合，可以用来测量激光在脉冲或者连续模式下的传播特性参量和波前特性。适用于可见光到远红外波长的监测，如

- 光束质量因子 M²；

- 光束束腰半径 ω₀；

- 光束发散角 θ_x θ_y；

- 束腰位置 z-z₀；

- 瑞利长度 z_Rx z_Ry；

- 椭圆率；

- 有效负荷（PSF）；

- 波前图；

- 泽尼克（Zernike）畸变模型；

还可应用以下参量测量：

- 控制激光器功率密度；

- 控制光斑大小、形状、均匀性、聚焦点大小和发散特性；

- 校准光学传播参量；

- 校准激光设备中的透镜；

- 可调谐激光放大器。

准确把握以上参量可以影响使用中的激光器性能，通过找出光束问题并纠正来使激光器达到最好的性能。 

图1  激光束及通过聚焦透镜的光束特性

2. 光束传播特性参数

M²，即光束质量因子，表示激光束与基模TEM₀₀接近程度的量。该参数与激光能够聚焦的最小点尺寸密切相关。对于在空间中传播的光束，未聚焦的基模TEM₀₀高斯光束的发散角θ₀₀可以表示为：

θ₀₀ = 4λ/πD₀₀

其中D₀₀是光束束腰直径，λ为波长。实际光束通常含有其它模式，导致更大的束腰D₀，更大的发散角θ₀，在这种情况下有：

θ₀ = M² 4λ/πD₀

θ₀ 和D₀分别为高阶模的发散角和束腰宽度，M²大于1并且依据ISO11146标准命名为“光束传播比例”。当一束纯高斯光束被聚焦后，聚焦点直径为：

d₀₀ = 4λf /πD₀₀

其中D₀₀是理想聚焦点直径，f为透镜焦距，如图1所示，聚焦点在透镜后1个焦距的长度的位置上。然而，如果是一个存在畸变的或者多模的光束聚焦后，聚焦点直径为：

d₀ = M² 4λf  / πD₀

除M ²之外，还可获得其它光束传播特性参数：

w₀ = d₀/2—在x轴（水平）和y轴（垂直）方向上的束腰半径；

z-z₀—测量平面和束腰平面之间的距离；

z_R —瑞利长度，波前曲率半径为最小值时的长度；

θ—远离束腰的远场发散角；

R—测量平面处的波前曲率半径；

3. 用数字波前照相机测量光束传播参数

3.1 原理

将一个已知焦距的透镜放在固定位置上，光束通过它聚焦进行一次高斯变换，束腰和发散角发生变化，用数字波前照相机可对该光束的传播特性进行测量。

光束传播特性参量的测量是基于高分辨率光强和波前图像的实时测量。如图2所示，在DWC中的CCD接收两个轻微散焦的光强分布图像，利用这两个图像以及他们之间的差异来计算波前。由波前特性，可以直接的获得光束的传播特征参量，但是需要繁琐的计算过程。

图2  DWC原理：在两个不同的焦平面实时获得两幅图像，取得波前并计算光束传播参数。

图3    DWC和相关软件的用户界面

3.2 系统结构

图4    用DWC测量激光传播参量的系统结构

STPV 系列一体化光束分析仪

高分辨率CCD光束剖面分析仪

实时光束传播特性和波前分析

一次聚焦测量M²

一体化DWC光束剖面分析仪结构紧凑，体积小，在一个面单点取样就可对光束传播特性进行分析。

由于它能够在极高分辨率的情况下测量瞬间强度和相位数据，因此可以在任意位置测量光束形状和光强分布，而不需要移动照相机。所有激光的关键参数，例如能量分布和光束传播参量等都可以直接测量，不需要购买额外的元器件。

照相机与测量软件，配合单次聚焦的测量方法可以获得光束传播特性参数，比如M²，发散角，斜率，任意XY平面的能量分布。

用户可以沿着Z光轴移动照相机，并用肉眼观察来进行实时调节，在调节过程中，束腰的图像和2D/3D强度剖面图都可以很容易的提取出来。

典型应用：

1. 光束和波前剖面成像

该CCD有250000个测量点，高动态范围（波前倾斜误差±1500λ@633nm），视频图像25帧，DWC是理想的光束分析工具。

多种高分辨率波前视图方式，3D图像，波前斜率，光斑边缘显示都可以实时输出。

利用固定的1M像素的CCD阵列照相机，DWC可以获得光束传播中的高分辨率的强度和波前图像。通过一次聚焦，可以获得10组位置的强度和相位测量以及光束传播参量的数值解。该仪器适用于连续和脉冲激光器（包括单脉冲），提供对光束空间特性的定量测量和M²测量，其中光束空间特性依据ISO13694标准，M²依据ISO11146标准。光斑直径测量不确定度优于2%，转化成M²因子的准确度优于4%。

2. 光束传播特性分析

DWC作为一次聚焦设备，提供了在数个瑞利长度范围内的光束传播特性的详细分析。

不需要替换仪器，也可以在DWC附近任意平面获得光束能量的数值解。光斑的能量中心、峰值位置以及峰值能量密度都能快速准确的通过纯数学计算过程获得。

在远离束腰的位置上，依然能够检测到光束质量和热点的图像。

3. 光束整形和光束检测

DWC在光强分布和相位分布的监测的优势，能够应用在光束整形和光束检测领域，比如相位空间光调制器（phase special light modulators），可变形镜（deformable mirrors）和其他光束整形、波束成形设备中。

DWC可以控制光束整形模块的调节，并利用其产生圆形和方形的焦点峰顶，提供最高分辨率、响应速度和动态范围。

主要优点：

l   集波前传感、光束传播参量和功率测量于一体

l   对光强和波前提供高空间分辨率的测量

l   一次聚焦测量M²因子，无需额外配件或移动元件

l   实时光束传播特性分析，可在任意平面测量功率

l   光强度、波前、有效负荷的实时图像显示

l   结构紧凑，可对连续和脉冲激光做剖面图

l   用常规的解决方法对紫外、近红外、远红外波长进行测量

测量能力：

l    光束的M²因子

l    传播参数

l    任意平面的能量参数

l    光束波前测量

l    适用于脉冲和连续激光器

技术参数

l   入瞳：5.9 x 3.1 mm

l   Z轴距离：17.5 mm

l   测量点：500 x 500

l   绝对精度：<0.01λ

l   灵敏度：<0.005λ

l   重复精度：<0.01λ rms

l   动态范围：500λ

l   采样频率：最大15 Hz（依据处理速度）

l   M²准确度：±5%

l   M²重复精度：<2%

l   波长范围：350 - 1100 nm (硅基CCD)  <350 & >1100 nm（其它CCD）

l   体积（mm）：25 Lx 32 W x 43 H;重量0.350kg.

软件功能：

与XP、Vista和Windows7系统兼容的GUI软件，能够快速显示强度分布和波前图像，提供光束剖面图像包括强度分布和光束传播特性参数的综合分析的功能。

1. 图像提取和显示

- 自动校准和提取图像；

- 动态显示2D和3D强度分布、波前、有效负荷、单脉冲和连续激光的提取图像

2. 光束分析

光强参数：

- 最大强度量级

- 光斑椭圆率

- 光斑长轴和短轴

- 尺寸

光束传播参数：

- X和Y方向的M²因子

- X和Y方向的束腰大小

- 传感器位置和束腰平面距离

- 瑞利长度

- 光束发散角

- 有效负荷（PSF），Strehl 比例

- 实时泽尼克显示和分析

- 波前和强度的剖面图

3. 结果输出

- 波长和泽尼克数据报告编辑，HTML语言

订货信息:

STPV 一体化光束分析仪，包括硬件和软件。

1. 硬件

  l   CCD光束剖面成像仪：CCD2/3”, 1392x1040, 6.45μm²像素点，动态范围66dB，帧率15帧，位宽12位；

  l   波长350 – 1100 nm；

  l   500 x 500个测量点，实时和同步获得光束强度和相位分布

  l   最大光束尺寸3.2mm x 3.2mm；

  l   USB2.0接口，2m长缆线；

  l   C-安装光学界面

2. 软件

兼容XP/Vista/Windows7，提供：

l  沿传播轴的一次聚焦M ²因子测量和任意光强度剖面图像

l  单脉冲和连续光测量：获得图像、处理以及显示；

l  自动触发脉冲和连续激光测量模式

l  2D和3D强度分布和波前的图像显示

l  距离束腰一定范围内的平面的完整光束传播特性分析

光强分布参数

l  所获得图像最大光强度量级

l  在接收平面处长轴处光斑尺寸

l  在接收平面处短轴光斑尺寸

l  光斑的椭圆率

l  利用三角法获得椭圆长轴方向

光束传播特性参数

l  X和Y轴的M²因子

l  X和Y轴的4σ束腰尺寸

l  测量平面和束腰平面之间的距离

l  瑞利长度

l  光束发散角

l  光束波前曲率半径

光束波前参数：

l  泽尼克图像显示：系数值

输出数据：

l  强度分布剖面图

STPV2光束分析仪

最便宜的光束分析仪

实时光束和波前分析

STPV2是一款体积小、性价比高的波前传感器，适用于动态分析波前形状和激光源的强度分布，以及由于光学元件导致的波前变形。主要特征如下：

l         USB接口

l         500×500个数据点测量波前

l         无需透镜，实现动态测量的同时满足图像高分辨率

实时光束监测

同步测量相位和强度

高分辨率波前显示

实时柱状图对泽尼克分析

进行光束分析无需位移

瞬间光束传播特性分析，特别是对任意平面的强度分布

光束监测和分析软件

STPV2应用与XP、Vista、Windows 7 兼容的GUI软件。用户图形界面提供了全面的监测和分析信息，包括波前和强度分布的图像提取、显示、测量和分析。

应用

高精度光束剖面成像

使用空间光调制器的光束监测和整形

复杂光学系统的波前分析

LOAs和HOAs测量

光束质量

自适应光学

硬件特性

STPV与STPV2之间的区别:

STPV基于12位动态响应范围的CCD，软件包括强度分布，波前分析（泽尼克分析）和光束传播特性分析。

STPV2基于8位动态响应范围的CMOS，软件包括强度分布、波前分析但是不包括光束传播特性的分析。

VIS/NIR Beam Profiler: STCam CCD

Our CCD is developed to provide excellent sensitivity from the VIS to NIR spectral range. Thanks to its high resolution and its small pixel size, the STCam is a high performance tool for laser beam analysis of continuous wave (CW) and pulsed laser modes. Due to its high dynamic range the STCam captures even higher laser modes with outstanding detail.

The passive cooled sensor of the STCam is constructed without cover glass to avoid interference patterns. For sensor protection a low distortion neutral density filter is integrated. The STCam supports the ultra-fast FireWire IEEE 1394b interface with data transfer rates up to 800 Mbit/s. The plug and play

design facilitates easy and flexible integration and operation.

The portable STCam is designed to be used in a variety of applications in industry, science, research and development, including:

l         Laser beam analysis of CW and pulsed lasers,

l         Quick control of laser modes and adjustment errors,

l         Test equipment for scientific research,

l         Near-Field and Far-Field analyses of lasers, LED devices and other light sources.

The enhancement of product quality, process reliability and efficiency are just a few of the many benefits of our unique beam profiler cameras. The STCam includes the specifically designed analysis software, STRayCi, which supports Windows XP/Vista operating systems. Its sophisticated software architecture opens up new opportunities in laser beam analysis according to ISO standards.

The concept of the STCam enables easy adaption to standard optical imaging systems, attenuators and opto-mechanical components ensuring highest flexibility. This includes:

l         Microscope lens and beam expander,

l         UV-Converter and IR-Converter,

l         Fixed and variable attenuators, etc.

ACCESSORIES

Neutral Density Filter: To expand the power range of the STCam several absorptive and metallic-coated neutral density filters are available, which are specified by optical densities ranging from OD 1.0 to OD 4.0.

FireWire Component: We offer different FireWire PCI / PCI Express cards for installation direct into the PC. Standard FireWire cables are suitable for industrial applications and are available in various lengths.

Trigger Device: To synchronize the STCam with pulsed laser systems, our trigger device is perfectly suited. This frequency and delay generator is software controllable and enables the synchronization of up to four beam profilers with different delay times simultaneously.

* without condensation

.

Neutral Density Filter

Our neutral density filters allow broadband attenuation for a spectral range from VIS to NIR. Due to their excellent surface quality the absorptive and reflective filters enable precise beam attenuation for low power applications. The level of attenuation is specified by the optical density. Filters with different optical densities can be combined. A filter adapter is available to mount the filters on the STCam aperture.

CO2 Laser Beam Profiler

The high performance STCL system is based on industry’s unique imaging technique. It is designed for monitoring high-power CO2 lasers in best performance. Thanks to its high resolution and its incomparable real-time capabilities, this highly efficient beam profiler is optimized for laser beam analysis of continuous wave (CW) and pulsed laser systems. The STCL system ensures beam profiling:

l         By high frame rates and high resolution,

l         Without optical components in the beam path,

l         Without scanning techniques, fluorescent materials or toxic fumes through acrylic mode burns.

The STCL supports the ultra-fast FireWire IEEE 1394a/b interface with data transfer rates up to 800 Mbit/s. The plug and play design facilitates easy and flexible integration and operation.

The compact and portable STCL is designed to be used in a variety of applications in industry, science, research and development, including:

l         Laser beam analysis of CW and pulsed lasers,

l         Quick control of laser modes and adjustment errors,

l         Test equipment for scientific research,

l         Near-Field and Far-Field analyses of lasers.

The enhancement of product quality, process reliability and efficiency are just a few of the many benefits of our unique beam profiling system.

The STCL system includes the specifically designed analysis software, STRayCi, which supports Windows XP/Vista operating systems. Its sophisticated software architecture opens up new opportunities in laser beam analysis according to ISO standards.

ACCESSORIES:

Attenuation Units: The water-cooled attenuation units are based on zinc selenide (ZnSe) and are designed for a 10° / 45° angle of incidence. Due to its excellent performance the unit can be used up to laser powers of 3kW and intensities of 5kW/cm2.

FireWire Components: We offer different FireWire PCI/PCI Express cards for installation direct into the PC. Standard FireWire cables are suitable for industrial applications and are available in various lengths.

Trigger Device: To synchronize the STCL system with pulsed laser systems, our trigger device is perfectly suited. This frequency and delay generator is software controllable and enables the synchronization of up to four beam profilers with different delay times simultaneously. 

Technical Specifications:

* different parameters on request

** without condensation

Laser Beam Profiling Software STRayCi

Our sophisticated beam profilers are available with the specifically designed analysis software, STRayCi, which supports Windows XP/Vista operating systems. It is available as 32 Bit / 64 Bit version and can control up to eight beam profiler cameras on a single computer.

Due to its clearly designed menu structure, STRayCi shows self-explanatory functions, which help the user to access quickly standard settings. Incomparable visualization modes, extensive analytical capabilities as well as new developed correction algorithms ensure the highest accuracy in laser beam analysis.

A wide range of beam width techniques e.g. 2nd Moment, Knife Edge, Moving Slit, Plateau, Gauss-Fit can be applied to determine quick and reliable standard beam parameters. The unique measurement tool enables the continuous monitoring of beam parameters, beam position and power density distribution. Helpful features like AOI Tracking, AOI Optimization, Zoom Functions, Look-Up Tables, etc.

simplify the laser beam analysis.

The extraordinary graphical and analytical tool of STRayCi can be used for live data (LiveMode) and stored data (SaveMode) simultaneously, while each mode has its own individual functions. This makes STRayCi the most advanced analysis software on the market.

STRayCi is equipped with flexible data and image output capabilities. This permits the user to store data and images in the format that is compatible with their needs.

A clearly arranged and printable protocol view displays the chosen measurement parameters as well as the most important laser beam analysis results.

STRayCi is compatible with guidelines of the international standard organization for laser beam measurements:

l         ISO 11145: Vocabularies and symbols

l         ISO 11146: Beam width, propagation ratio,…

l         ISO 11670: Beam positional stability,…

l         ISO 13694: Beam power density distribution,…

STRayCi works only with a USB software protection lock. It is a hardware based security solutions to protect and encrypt the software against piracy.

MINIMUM SYSTEM REQUIREMENTS:

l         Windows XP / Vista

l         Pentium IV / AMD Processor

l         128 MB graphic card, Open GL V1.4 compatible

l         100 MB free memory

l         PCI / PCIe slot for FireWire card

l         USB port for dongle connection

l         CD / DVD-ROM drive for software installation

l         Internet access for update request

STRayCi Special Features

REAL-TIME BEAM PROFILING

2D / 3D intensity plots / Cross sections / Histogram

Pointing stability (x-y fluctuation, COG- position analysis, ect.)

Parameter stability (intensity, power, center x-y, beam size)

Parameter results (beam statistics, beam width, beam parameter)

CAMERA CONTROL

Multiple camera support

Different measure types

User-selectable exposure time and gain factor, auto-exposure time

Floating average and variable brightness

ANALYSIS FUNCTIONS

Beam statistics (power, max intensity, COG, etc.)

Beam width (2nd Moment, Gauss / Super-Gauss-Fits, Plateau, Knife Edge, Moving Slit, ect.)

Beam parameter (beam width, ellipticity, uniformity, etc.)

CALIBRATION AND CORRECTION TOOL

Background subtraction, auto-background

Pixel correction technology (offset correction, linearity, etc.)

Power calibration

OTHER FEATURES

User-defined Area of Interest (AOI)

AOI tracking and optimization

Color palettes incl. auto-contrast function

Zoom functions

2D profile arithmetic operations, filters, transformations, etc.

E-mail support

FLEXIBLE OUTPUT

Data: txt, tiff

Image: jpeg, png, bmp, gif, tiff

Protocol: pdf

  STBQM-10 Beam Profile Analysis

The STBQM10 laser beam profiler is a high precision, CCD based beam profiler for use with lasers with wavelengths between 190 and 1100 nm. Allied with our powerful but intuitive software package, the BQM10 makes quick and accurate characterization of your lasers a reality.

The high quality 12-bit CCD array gives excellent resolution. Features include USB2.0 interface means portability and ease of use, RJ45 GPI/O connector for control of synchronization of lighting and 32MB onboard memory for frame buffering. Thus, the STBQM10 can be easily transferred to different laptop or desktop computers. The user interface is simple and intuitive but with many useful features.

Specifications:

• Parameters of ISO 11146 series of standards

• ½” format CCD 1392x1040 array with 4.65um square pixels

• 12-bit digitization – 60dB dynamic range

• No frame grabber required (32MB RAM on-board memory)

• USB2.0 direct connection with no external power supply required

• Compact (45x45x56mm) and lightweight (130grams)

• 15 fps at 1392x1040, 30 fps at 640x480

• Measures both CW and pulsed beams

• Second-moment and Gaussian fit

• ~3% beam diameter accuracy

The STBQM10 laser beam profiler comes with the following

·   Optical head

·   User software on CD

·   Cables

·   User manual

Options -

Wavelength range - 350nm to 1100nm

Accessories -

STBQM - 100      Variable attenuator

STBQM - 110      Set of 6 ND filters, screw mount

STBQM - 120      Beam pick off

STBQM-30 Beam Quality Monitor (M²)

The STBQM-30 is designed to allow single shot measurement of laser beam propagation characteristics. The real-time measurement capability and easy set-up make it an ideal tool for monitoring changes in beam parameters of CW and pulsed lasers.

The STBQM-30 utilizes the patented distorted diffraction grating known as IMPTM (Image MultiPlex) grating developed by QinetiQ plc in the UK, to acquire intensity data from nine image planes along the axis of the beam simultaneously. This enables beam propagation parameters to be calculated from a single frame of data from the 12-bit CCD array giving a true one-shot measurement capability. The camera operates at 0.15 mW per sq cm for CW operation, 1.0 mJ per sq cm for pulsed operation.  Would need the filters if power/energy density is higher.

Product highlights:

· Parameters of ISO 11146 series of standards

· Real time measurement

· Easy to set up - speeds up analysis

· USB2.0 direct connection with no external power supply required

· Small form factor (45mm H x 45mm W x 170mm L)

· Second-moment and Gaussian fit

· 5% M2 accuracy

Typical applications:

· Laser, LD, LED and VCSEL monitoring

· Measuring pulsed lasers

· Laser beam process control e.g. during warm-up

The STBQM30 range of laser beam quality monitor comes with the following

·  Optical head

·  User software on CD

·  Cables

·  User manual

STBQM30 gratings are optimised for a particular wavelength so please specify the wavelength you want fitted as standard. The following gratings are available.

G1064        - 1064nm

G532           - 532nm

Others available on request .

Accessories -

STBQM-100: Variable attenuator

STBQM-110: Set of 6 ND filters, screw mount

STBQM-120: Beam pick off

STBP Laser Beam Profiler

The Laser Beam Profiler provides high resolution real-time monitoring and quantitative characterization of spatial beam intensity distributions. Primarily designed for excimer lasers, it may be utilized for all pulsed or CW lasers as well as for incoherent sources, covering an extremely wide spectral range from NIR to soft X-rays. The UV/EUV sensitivity is achieved by a quantum conversion coating on the CCD chip. 

A variety of different sensor types (large/small area, highest spatial resolution, sensitivity and dynamic range) are available and can be adapted to specific applications. The software supports also periphery devices like adaptive mirrors, stepper motors, attenuators, shutters or power monitors. Automated or remote-controlled measurements are facilitated by the help of a powerful macro language.

The applications comprise:

-          Determination of beam parameters according to ISO 11146

-          Diagnosis of pointing stability (ISO 11670)

-          Pulse-to-pulse fluctuations

-          Beam propagation analysis (caustic measurement)

-          Characterization of beam shape (uniformity, steepness) according to ISO 13694 (especially for homogenized beams)

-          On-line laser beam inspection (e.g. recognition of “hot spots”)

-          Optimizing of laser operational parameters

-          Alignment of optical components

Special Features:

-          Wide spectral range: 1064 … 13nm

-          Small and large area CCD sensors

-          USB 2.0 interface (ideal for laptop)

-          High dynamic range (12/14 bit)

Applications:

-          Beam diagnostics (NIR, Vis, UV, EUV)

-          ISO beam parameters

-          Beam propagation/focusability

-          M²  (caustic measurement)

STBC Laser Beam Characterization

Beam Parameters

Quantitative determination of all relevant laser beam parameters from the acquired profiles is achieved with the help of the comprehensive beam characterization software “MrBeam”, which makes use of standard ISO evaluation procedures.

Beam parameters according to ISO standards:

• Beam width 2^nd moment (ISO 11146)

• Divergence, M² (with caustic setup; ISO 11146)

• Pointing stability (ISO 11670)

• Beam shape/uniformity (ISO 13694)

Software:

• Various acquisition modes: ‘grab’, ‘averaging’, ‘floating average’

• Evaluation of beam parameters: beam width (2^nd moment, centroid, ellipticity, uniformity, relative pulse energy, pointing stability etc.

• 2D profile arithmetics (ADD, SUB, MULT, DIV etc.)

• Selection of area-of-interest for analytic beam evaluations

• Real-time display and evaluation of cross-sections, 3D graphics

• Profile-fit (Gaussian, super-Gaussian, top-hat etc.)

• Colour palettes incl. Analytic functions (e.g. ‘intensity threshold’)

• Easy-to-use ‘zoom’-functions

• Comprehensive user-programmable macro language

• Export of all data and profiles

The system includes:

-          Digital camera (USB 2.0 interface for note-book or PC)

-          Beam analysis software

Optional extensions:

-          Translation stage (e.g. for caustic measurement)

-          Hartmann-Shack wavefront sensor

-          Adaptive mirror for closed-loop beam stabilization

Trigger/delay generator